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Astronomy/Questions Answered by Expert Courtney Seligman
| Subject | Date Asked |
| NGC pics | 1/12/2012 |
| Q: Following up on my last question. The software I'm writing is for use on my personal laptop. The ... A: Here is the page with information about accessing the Sloan Digital Sky Survey database: ... | |
| black holes | 12/5/2011 |
| Q: What happens to the objects that are swallowed by black holes A: They fall into the singularity (the point of infinite density, temperature, and gravity) at the ... | |
| big bang/void | 11/29/2011 |
| Q: When the big bang occurred, with all the universe and space/time in it, what was outside the big ... A: Presuming the origin of the Big Bang is as generally thought -- a single point of space-time in some ... | |
| can meteors change direction? | 10/30/2011 |
| Q: I am having an argument with people who think a particular video shows a UFO, when I think that it ... A: Meteors (or more accurately, the meteoroids that produce meteors) can change their path, usually as ... | |
| A thought experiment | 10/20/2011 |
| Q: I wonder if you could attempt an answer to this thought experiment I am presently struggling with. ... A: I'm afraid the answer is no, we can't look into our past. When we say that we can look "into the ... | |
| the whole shabang | 10/18/2011 |
| Q: As an amateur cosmologist I come across much talk of multiverse, dimensions etc. It seems to me that ... A: If by the xth dimension you are referring to a quantity encompassing the "space" occupied by all the ... | |
| the whole shabang | 10/18/2011 |
| Q: As an amateur cosmologist I come across much talk of multiverse, dimensions etc. It seems to me that ... A: Yes, I would agree that if something can affect part of our Universe, then it should be considered ... | |
| the whole shabang | 10/17/2011 |
| Q: As an amateur cosmologist I come across much talk of multiverse, dimensions etc. It seems to me that ... A: (Note added partway through answering yourThe start of this answer is about a definition of hidden ... | |
| Lunation through the ages? | 9/20/2011 |
| Q: Greetings! Basically my question is if a real month (the time between let's say 2 consecutive full ... A: The tidal interaction between the Earth and Moon is gradually slowing the rotation of the Earth (by ... | |
| titans | 9/10/2011 |
| Q: Titan, one of Saturn's many moons, has an atmosphere, but our own Moon does not. What is the ... A: One reason is that Titan is ten times further from the Sun, and as a result, far colder. This allows ... | |
| Energy and the expansion of the universe | 8/29/2011 |
| Q: Okay, so I have had a question that has been bugging me about all energy in the universe being ... A: As it happens, the solution to Olbers' Paradox isn't that the Universe is expanding, but simply that ... | |
| Relationship of distance and time | 8/27/2011 |
| Q: I have read and understand your answer of 8/13/2011 to the question about the age of the universe ... A: (Sorry for the delay in replying. I wrote an answer several hours ago, but when I tried to 'send' ... | |
| BIG BANG | 8/20/2011 |
| Q: i was watching this documentary on BIG BANG on discovery channel and there i heard a couple of ... A: "hello sir,i was watching this documentary on BIG BANG on discovery channel and there i heard a ... | |
| Universe | 8/17/2011 |
| Q: From what I know (which is probably wrong), the way we have discovered that the universe is 13 ... A: In its simplest form, the age of the Universe is determined from the rate of its expansion, compared ... | |
| Relationship of distance and time | 8/13/2011 |
| Q: How is it possible that the light from the cosmic horizon is older than the age of our universe? ... A: The 42 billion light years refers to the present distance of objects that we see near the cosmic ... | |
| age of universe | 8/13/2011 |
| Q: How is it possible that the light from the cosmic horizon is older than the age of our universe? A: It isn't possible. Wherever you heard that has to be wrong. The cosmic horizon represents the time ... | |
| mars and earth | 7/28/2011 |
| Q: Sir, If there is any orbital changes between earth and mars and mars comes close to earth. Is any ... A: It would depend upon how close it came. At the moment, the closest it can get is about 35 million ... | |
| astronomy | 7/25/2011 |
| Q: sir, I wont to know what is the difference between astronomy,astrophysics and cosmology? and ... A: Astronomy is the entire field of astronomy. It involves anything that has to do with the sky and its ... | |
| Elliptical Orbits | 7/21/2011 |
| Q: Why all the planets and stars revolve around everything in an elliptical orbit rather circular? If ... A: The expansion of the Universe that started with the Big Bang is not related to the orbits of planets ... | |
| Habitable planets | 7/15/2011 |
| Q: I have been using the build your own solar system gimmick on this website:- ... A: The numbers are "off", as are those for a 4-planet system more or less identical to Mercury, Venus, ... | |
| orbits | 6/3/2011 |
| Q: You recently posted a question to Patrick Weiler in category Astronomy:hello..in his first law, j. ... A: I haven't heard back from you, concerning exactly what sort of answer you are looking for. I realize ... | |
| orbits | 5/17/2011 |
| Q: You recently posted a question to Patrick Weiler in category Astronomy:hello..in his first law, j. ... A: Just wanted to let you know that I have not forgotten you, and am working on a page about orbital ... | |
| The earth | 5/17/2011 |
| Q: We would like to ask a question. If there is no air in space, how come there is air on earth? ... A: When the planets formed, there was a lot of gas moving around the Sun, in what is called the Solar ... | |
| Venus | 5/13/2011 |
| Q: I've been trying to get information about Venus' gross atmospheric loss rate. Specifically, how ... A: The rate of loss of low mass atoms, such as hydrogen, is accelerated by the effects of the solar ... | |
| View of Earth from Moon | 4/25/2011 |
| Q: I enjoy doing little brain exercises, but I cannot find enough info on the web to satisfy my ... A: To a first approximation, the Moon moves north and south during one orbital period (27.3 days) the ... | |
| Coriolis and the Foucault Pendulum? | 4/21/2011 |
| Q: Almost every reference explains the apparent rotation of the Foulcault Pendulum on the coriolis ... A: From my earlier followup (slightly modified): I took a quick look at the first of the three sites ... | |
| Satellite tracking | 4/18/2011 |
| Q: Just saw 2 satellites pass overhead (both visible with naked eye simultaneoulsy) at approx 22.55 ... A: Try Heavens Above, at http://www.heavens-above.com/ You just have to enter your position to ... | |
| Astronomy | 4/16/2011 |
| Q: Do scientists know yet what started the planetary straight line movement and do scientists know what ... A: We know how gravity works (in a simple way, as described by Newton, and an equally simple but ... | |
| universe | 4/15/2011 |
| Q: I just wanted to know what is the biggest things right away? I thought that would a universe. ... A: As I explained above, it isn't possible to tell if the so-called multiverse even exists. So whether ... | |
| universe | 4/15/2011 |
| Q: I just wanted to know what is the biggest things right away? I thought that would a universe. ... A: Ah. I see your point now. In that case, most cosmologists would probably agree with you. The only ... | |
| universe | 4/15/2011 |
| Q: I just wanted to know what is the biggest things right away? I thought that would a universe. A: It depends upon what you mean by "thing". The Universe isn't an actual object, in the normal sense ... | |
| Coriolis and the Foucault Pendulum? | 4/15/2011 |
| Q: Almost every reference explains the apparent rotation of the Foulcault Pendulum on the coriolis ... A: I take it from the way you phrased your question that you understand the situation at the Poles -- ... | |
| astronomy | 4/13/2011 |
| Q: Why orbits of all planets are elliptical? A: Your question doesn't make it clear whether you want the physics behind the answer, or just why they ... | |
| keyholes | 4/4/2011 |
| Q: I have a question regarding magnetic keyholes. This will sound crazy at first but please read all of ... A: I believe you mean gravitational keyholes, not magnetic; but either way, the only thing that affects ... | |
| Planetary possibilities in a binary star system | 3/28/2011 |
| Q: I had asked this question of another expert, but he mentioned his knowledge of orbital mechanics ... A: Depending upon the relative and total masses of the stars (remember, the situation is less stable if ... | |
| Planetary possibilities in a binary star system | 3/28/2011 |
| Q: I had asked this question of another expert, but he mentioned his knowledge of orbital mechanics ... A: I see. You're wondering whether the planet could remain stationary at the so-called center of mass ... | |
| Planetary possibilities in a binary star system | 3/27/2011 |
| Q: I had asked this question of another expert, but he mentioned his knowledge of orbital mechanics ... A: You're basically asking if you could have a planet orbit between two binary stars at the same rate ... | |
| Gas Giants | 3/26/2011 |
| Q: I was curious, what exactally is a Gamma Ray Burst? I saw them on a television documentary once, but ... A: A gamma-ray burst is a short-lived emission (hence a "burst") of extremely high energy photons (or ... | |
| super moon | 3/25/2011 |
| Q: Mr. Seligman: I was hoping you could speak to me about the relationship between the moon and tides. ... A: The super full moon (or for that matter, any full moon which takes place near perigee) is only about ... | |
| More Questions | 3/25/2011 |
| Q: Its me again, the one who asked all those questions about astronomy before ... A: If the two stars are close together, you could have planets far away from them, which orbit them ... | |
| Filament Universe, Millennium Simulation | 3/15/2011 |
| Q: Seligman, What does your expert mind conjure when viewing the Millennium Simulation produced by the ... A: I haven't seen the simulation you refer to, but will look it up, as it sounds very interesting. ... | |
| Computation of Planetary longitudes | 3/13/2011 |
| Q: , Read a lot of information on the recent earthquakes and shift of earths axis etc. I wonder if ... A: It will have no effect on planetary longitudes. The orbital motions are calculated in comparison ... | |
| Questions | 3/10/2011 |
| Q: I love the universe, and think that it is the most interesting subject out there. Out of curiosity, ... A: (Added answers to last two questions, at the end) Iron is the most stable element. When atoms ... | |
| Earth's spin and Sun | 2/26/2011 |
| Q: The Earth has a sidereal rotation t=86164.09 seconds and when Earth makes 360° around its axis, it ... A: The Sun does create a torque like the Moon does, but the cause of the torque is the action of the ... | |
| Earth's spin and Sun | 2/26/2011 |
| Q: The Earth has a sidereal rotation t=86164.09 seconds and when Earth makes 360° around its axis, it ... A: "The Earth has a sidereal rotation t=86164.09 seconds and when Earth makes 360° around its axis, it ... | |
| rotating universe follow-up | 2/25/2011 |
| Q: I completely understand your last 2 paragraphs. It is virtually impossible to have access to ... A: I've been ill recently, and haven't had a chance to take a look at any of your recent posts (I ... | |
| Apparant Magnitude | 2/24/2011 |
| Q: I need some help on a question in my astronomy class, I've tried to understand this and figure it ... A: Somewhere in the textbook discussion of magnitudes it should point out that each magnitude ... | |
| A balloon pops, a gun fires -- Our Universe more similar to | 2/19/2011 |
| Q: Weiler, Why is the structure of the Universe like a cone. Why is it not in 360. Why isn't ... A: Apparently Mr. Weiler put this in the Question Pool, which is where I just noticed it. Answering ... | |
| Expansion vs closure | 2/16/2011 |
| Q: In your 10/27/2009 answer about expansion of the universe you used terms like 'the center' and 'the ... A: Reviewing the answer I think you are referring to, I don't see any reference to a center or an edge, ... | |
| Electromagnetic radiation and heat | 2/14/2011 |
| Q: I picked up a NASA brochure on electromagnetic radiation at the recent AAS conference in Seattle. It ... A: Individual photons of light do have more energy, the shorter the wavelength of the light. But the ... | |
| galaxy and planet rotation | 2/13/2011 |
| Q: like our northern and southern hemisperes in relation to tornados and cyclone rotation.do planets ... A: No, they don't. The Coriolis effect which leads to the phenomena you mention on Earth is due to the ... | |
| Cosmic inflation | 2/9/2011 |
| Q: Courtney, My understanding is that the inflation theory related to the big bang was devised ... A: First, a summary of how the Inflation theory was developed: The original theory of the Cosmic ... | |
| hydrogen fusion on the sun | 2/7/2011 |
| Q: The sun fuses hydrogen to make helium on the sun. Does the helium fuse with other helium or hydrogen ... A: Lithium is produced in the Sun (and other stars and, for that matter, in the Big Bang); but it has a ... | |
| the universe | 2/6/2011 |
| Q: We know that our universe is expanding. Into what kind of infinity (rhetorical)? What do you think ... A: The most commonly used example of how the Universe works is to imagine the surface of a balloon as ... | |
| Earth-Moon-Sun alignement | 2/6/2011 |
| Q: since Earth's and Moon's orbital inclination compared to ecliptic oscillates with time, what's the ... A: To have a lunar or solar eclipse, all three objects have to be in line. At such times, it doesn't ... | |
| Time | 1/29/2011 |
| Q: I have a young child that keeps asking me when time began and when it will stop. As I'm not a ... A: You are correct in assuming that (according to current scientific theory) time began with the Big ... | |
| Weight at pole and equator | 1/27/2011 |
| Q: Does our technology enable one to measure in a decent way the difference of weight (that's provoked ... A: The difference is about a third of a percent of the weight of the object, so you just need something ... | |
| origen of water | 1/26/2011 |
| Q: Courtney, I very much appreciated a previous answer from you. My question today is related to water ... A: If there were water molecules in space, they would be blown away from our orbit by the solar wind, ... | |
| Sunrise-sunset changes | 1/21/2011 |
| Q: Beginning at the winter solstice. Why do the change in sunrise and sunset differ. In Seattle, after ... A: Added note, in response to feedback: I'm sorry that my answer wasn't as clear as it could have been. ... | |
| Moon sidereal period | 1/19/2011 |
| Q: An mere observer can know how long the Moon takes to do 1 synodic period by looking its phases,but ... A: To measure the sidereal period, note exactly where the Moon is relative to the background stars on ... | |
| Astronomy | 1/14/2011 |
| Q: So many societies have used astronomy to establish time and calendar. I have read, that circa ... A: The quote you have read about 12/21/2012 is a hoax. The planets will not be lined up with anything, ... | |
| Eccentric Orbits on Earth-like Planets | 12/17/2010 |
| Q: In the old 60s TV show "Lost in Space" the Robinsons landed on a planet with some pretty extreme ... A: That's correct. Our distance from the Sun is relatively constant (varying by only 3.4%), and the ... | |
| Eccentric Orbits on Earth-like Planets | 12/17/2010 |
| Q: In the old 60s TV show "Lost in Space" the Robinsons landed on a planet with some pretty extreme ... A: No, there's no way that orbital effects could cause such changes. You could have very high ... | |
| Hypothetical Earth-Moon Planet | 12/14/2010 |
| Q: Mr Seligman I enjoy your answers so much I wish I could have you as a teacher. Your classes must be ... A: As for your question, I'm afraid you're going at things backward, starting with a combined radius. ... | |
| Asteroids and Magnitudes | 12/12/2010 |
| Q: again. I've just finished reading about 'zodiac lights', and I was wondering... I know that ... A: The key to seeing the zodiacal light (and the counterglow, or gegenschein, which is opposite the ... | |
| Jupiter's influence | 12/12/2010 |
| Q: Mr Seligman. My question has two parts. First, it concerns Jupiter. I understand that the ... A: The eccentricity of an orbit is due to a planet's current motion. If outside influences (anything ... | |
| follow-on to question entitled 'cosmology!' | 12/3/2010 |
| Q: some further points,if i may. You gave me a run-through of quantum mechanics,which i understand ... A: (Sorry about the delay in answering you. I've been swamped with work for a project that was due ... | |
| why does the night sky (universe) look black | 11/29/2010 |
| Q: it seems to me that since black is the result of all light wavelengths being absorbed, and since ... A: The basic problem with your statement is that black is not the result of all light wavelengths being ... | |
| Question about a certain cluster of stars/constellation. | 11/27/2010 |
| Q: I've been outside in the past few weeks and I've seen this same cluster of stars in the sky, and I ... A: That sounds like Orion, which is rising nearly due east in the early evening. If so, there would be ... | |
| Morning sky observation | 11/23/2010 |
| Q: I live in Southern CA; this morning I got my scope out to look at what I thought was Venus in the SE ... A: Venus goes through phases, just like the Moon. A few weeks ago it was more or less in between us and ... | |
| Moon orbit VS Earth angular velocity | 11/22/2010 |
| Q: If a tiny ball is stuck thanks to a glue on the border of a spinning disk, the quicker the disk ... A: I haven't seen the forces involved expressed as actual forces, but as accelerations (that way, you ... | |
| Sun influence on Moon | 11/19/2010 |
| Q: So since Sun's acceleration on Earth is equal to Sun's acceleration on Moon, does this ensure that, ... A: That's correct. Whether the Sun exerted a force on the Moon or not, the Moon's basic orbit would be ... | |
| galaxy | 11/15/2010 |
| Q: I have been reading a lot on the origin of the universe and often come across the reference to the ... A: The redshift is caused by the expansion of the space the light is passing through, on its way here. ... | |
| cosmology! | 11/10/2010 |
| Q: I have a number of points that i would like your comments on please. Dark matter has invoked various ... A: (Finally have time to finish the answer. See the additional material below the dashed line.) As far ... | |
| Influence of velocities | 11/8/2010 |
| Q: Let's suppose a motionless planet called A and its satellite B. B revolves around A at the velocity ... A: You are correct that the non-linear motion of the Earth would produce a (small) non-inertial ... | |
| Influence of velocities | 11/7/2010 |
| Q: Let's suppose a motionless planet called A and its satellite B. B revolves around A at the velocity ... A: The orbital speed of the planet does not affect the orbital speed of a satellite. This is a ... | |
| big bang | 11/4/2010 |
| Q: When scientists talk of the big bang they say expansion started from a size 'smaller than a spec of ... A: You are correct in saying that we only know the size of the observable Universe, not its absolute ... | |
| irregularities in space logic | 11/3/2010 |
| Q: How is it that meteor craters are perfectly formed with regular sides . It stands to reason ... A: (Note added afterward, in response to a followup comment about the effects of a lack of atmosphere: ... | |
| Doppler effect and light | 10/29/2010 |
| Q: I am a lawyer with a healthy interest in science. I read the popular science books and magazines. ... A: The expansion of the Universe is caused by the expansion of the empty space within it. On the ... | |
| northern latitude visibility for alpha/beta Kentarus | 10/18/2010 |
| Q: I am doing a research project that involves ancient Egypt and Greece. In my Starry Night program ... A: The stars are not visible from Athens at this time. Athens is nearly 38 degrees north of the ... | |
| Big Bang | 10/4/2010 |
| Q: I hope I'm right in thinking that when an explosion takes place, there is an inwards force as well ... A: With a "bomb" of finite size, the central portion could be compressed by the force of the outer ... | |
| asteroids | 10/1/2010 |
| Q: Courtney, I often hear of asteroids as being pebbles and rocks and boulders that never became a ... A: In the early solar system, any rocky body more than a couple of hundred miles across would have ... | |
| Galaxies Speeds etc | 9/25/2010 |
| Q: So say Alpha Centuri is 4.5 light years away and if i was to travel there at light speed its a case ... A: You are correct in that when you travel at the speed of light, time "seems" to stand still for you, ... | |
| black holes | 9/20/2010 |
| Q: Has a star been observed falling into a black hole and disappearing? A: No. We have seen ordinary black holes emitting high energy jets of material, which must be the ... | |
| Planetary Science | 9/12/2010 |
| Q: Assume there are two planets at equal distance from their sun. Planet #1 is markedly hotter than ... A: The main factor would be what kind of difference there is in their atmospheres. If they had the same ... | |
| Effect of atmospheric friction on low Earth orbits | 9/6/2010 |
| Q: Why does atmospheric friction increase the speed of a satellite in low Earth orbit? A: The direct effect of the friction is to slow down the satellite. But this makes the orbit "decay", ... | |
| The gravitational relationship between the Earth and the moon | 9/5/2010 |
| Q: I am currently watching the program 'Universe' on the Tv and i am always interested in working out ... A: It's been more than a decade since anyone asked me to do such a calculation, and with a 70% ... | |
| The gravitational relationship between the Earth and the moon | 9/4/2010 |
| Q: I am currently watching the program 'Universe' on the Tv and i am always interested in working out ... A: First, I agree that my discussion would have been much easier to follow with diagrams. When I gave ... | |
| The gravitational relationship between the Earth and the moon | 9/3/2010 |
| Q: I am currently watching the program 'Universe' on the Tv and i am always interested in working out ... A: The Moon's pull does have an effect on the Earth -- it makes the Earth move around the center of ... | |
| Matter and antimatter | 8/13/2010 |
| Q: After big bang , both matter and antimatter created in same ratio, than why we see only matter ... A: They were created in almost, but not exactly the same ratio. Estimates are that the ratio was off by ... | |
| Light | 8/13/2010 |
| Q: You told in previous question that speed of every colour in vaccum is same but we know that ... A: All light waves (or if light is thought of as particles, all photons) move through empty space at ... | |
| Light | 8/12/2010 |
| Q: Why light didn't disperse into seven colour in vaccum or air ? Why it also didn't disperse from ... A: Dispersion is caused by a difference in the speed of different colors of light, as the light passes ... | |
| Light | 8/8/2010 |
| Q: Sir as you told previous that light bends due to the difference of refractive index but i think that ... A: As noted in my previous answer, the refractive index (the ratio of the speed of light in a vacuum to ... | |
| Light | 8/6/2010 |
| Q: Sir, i read somewhere that bending of light is created due to difference in eletic and magnetic ... A: (In the last sentence of paragraph two of my original answer, I mis-stated the way that the light ... | |
| Universe and its beginning | 8/5/2010 |
| Q: I can't manage to grasp something in what many cosmologists state: according to them, the Universe ... A: As far as our own space time is concerned, there is a beginning -- a time when there was only a ... | |
| Space and big bang | 8/5/2010 |
| Q: Which of the following first created , big bang or space time? A: As noted in my previous answer, our Universe presumably formed as the result of a quantum ... | |
| Before big bang | 8/5/2010 |
| Q: What was before big bang and how it created? A: According to quantum mechanics, any point in space can undergo random fluctuations in energy, as ... | |
| black holes | 7/30/2010 |
| Q: Depictions of black holes are usually funnel-shaped, "down-the-drain" illustrations of warped ... A: Yes, it would be more spherical than not. There are a couple of complications that would affect the ... | |
| gravity | 7/30/2010 |
| Q: It's generally understood that people weigh less in the morning than at night. I've read this is due ... A: I'm afraid that if it did, you couldn't tell, because the effect is so small; and it actually works ... | |
| 21 Aug 2017 | 7/24/2010 |
| Q: Seeing a total solar eclipse is in the top ten of my "bucket list," a list of things I'd love to do ... A: I presume that astronomy magazines (physical and online) will be full of weather predictions in the ... | |
| solar/galactic plane | 7/21/2010 |
| Q: Courtney, Is there any relationship between solar ecliptics in galaxies (particularly in the Milky ... A: (Sorry about the delay. I thought I already answered this question (yesterday?), and presume I had a ... | |
| Type 1a Supernovae | 7/20/2010 |
| Q: I have a couple of questions about the role of angular momentum in type 1a supernovae. First, does ... A: Type 1a supernovae result from the ignition of nuclear reactions in a white dwarf companion to a ... | |
| Einstein's Cosmological Constant | 7/14/2010 |
| Q: I am reading Brian Greene's The Fabric of the Cosmos & managed to get confused about his description ... A: Einstein's original equations predict that if the mass-density of the Universe is greater than a ... | |
| star/planet id | 7/8/2010 |
| Q: I was looking west from Wailea in Maui at 8:30 last night ( July 7, 2010) and there was an extremely ... A: That was Venus. It will be gradually getting lower and setting earlier over the summer, but will ... | |
| Universe is eternal? | 7/7/2010 |
| Q: could the Universe have been beginless, or eternal (thus having actually INFINITE PAST)? some ... A: Standard cosmology (the study of the origin and evolution of the Universe) treats the Universe as ... | |
| the primordial atom | 7/4/2010 |
| Q: I time, space and the primordial atom are frequent topics but I am unable to answer a specific ... A: I understand what you mean, but you are assuming that the Universe existed as a specific point-mass ... | |
| Speed of Light | 7/1/2010 |
| Q: I usually hear that the speed of light is 186,000 miles per second vs the exact 186,282 miles per ... A: Whether the more exact measurement is used depends upon the accuracy needed. The rounded off value ... | |
| seen from space | 6/28/2010 |
| Q: what type of lights or man made structures or for that matter any type of structures can be seen ... A: I presume you mean without optical aid... From low or near Earth orbit, city lights can be easily ... | |
| Nostradamus | 6/19/2010 |
| Q: As a follow up question, a massive object ould pull the surface of the Earth like the moon does with ... A: I presume you mean, "could it also pull the atmosphere away from the planet". The answer to that ... | |
| Black holes | 6/12/2010 |
| Q: If light has no rest mass, why is it attracted and captured by black holes? A: Light isn't "attracted" by black holes (or gravity). But according to Einstein's theory of general ... | |
| Hubble Constant | 6/10/2010 |
| Q: Hey Courtney, I'm doing a culminating activity for my astronomy class and I'm having a little ... A: I'm not supposed to answer homework questions, but I can give you a couple of brief comments, and a ... | |
| Galaxies | 6/7/2010 |
| Q: How long does it take for a galaxy to be formed? also, what are the steps to forming a solar system? ... A: For solar systems, refer to http://cseligman.com/text/ssevolve/ssorigin.htm (The Origin of the Solar ... | |
| Ref question | 6/3/2010 |
| Q: Good day What cause the earth to spin? I am aware that the earth spins at a certain speed. How was ... A: The rotation rate of the Earth (approximately 23 hours 56 minutes 4 seconds) is determined by seeing ... | |
| start escaping galasies | 5/24/2010 |
| Q: I just saw a show on astronomy, specializing in black holes. It stated that for a star to escape a ... A: To answer part B of your question first, yes, in a sufficiently crowded environment, single stars ... | |
| designing a scarf with contellations | 5/19/2010 |
| Q: I am designing a scarf for a small charity called "Afghan Hands" to benefit tribal woman in ... A: I think that what you want can be found at http://www.astroviewer.com/ The site allows you to ... | |
| big bang | 5/4/2010 |
| Q: What caused the big bang? I understand it to be a singularity that through gravity eventually ... A: In normal physics, empty space would be considered to have nothing in it -- neither mass, nor ... | |
| Black Hole Singularity Formation | 4/1/2010 |
| Q: How exactly do black hole singularities form, when considering the effects of the zero gravity core ... A: (Sorry for the delay in answering. I had an appointment this morning, and just picked this up.) ... | |
| Expanding universe | 4/1/2010 |
| Q: We see distant galaxies receeding away from us, doesn't this indicate that the universe is ... A: You have to make a distinction between what we can see, which is called the Observable Universe, and ... | |
| Massive stars, supernovae, black holes. | 3/29/2010 |
| Q: Courtney, I hope you can help me understand a couple of empty area in my knowledge, about the death ... A: Actually, I'm a he, but the mistake is understandable. When I was born (in the middle of the last ... | |
| Massive stars, supernovae, black holes. | 3/29/2010 |
| Q: Courtney, I hope you can help me understand a couple of empty area in my knowledge, about the death ... A: (1) Iron-core collapse: The maximum density of a star (or a region in a star) is usually determined ... | |
| Follow up on asteroids and comets. | 3/16/2010 |
| Q: Christ!!! That wave from the asteroid that took out the dinosaurs to sweep over all the carribean ... A: I find almost all of astronomy interesting. I'm not as interested in the nuts and bolts -- how ... | |
| Follow up on asteroids and comets. | 3/13/2010 |
| Q: Christ!!! That wave from the asteroid that took out the dinosaurs to sweep over all the carribean ... A: (Note added March 16) I reread your question, and realized I forgot to answer the last part of it ... | |
| Is there really a planet X? | 3/12/2010 |
| Q: I've been reading recently about theories for the end of the world in 2012, and apparently there is ... A: The Earth does move around 65 thousand miles per hour. A comet could move through our part of the ... | |
| Is there really a planet X? | 3/11/2010 |
| Q: I've been reading recently about theories for the end of the world in 2012, and apparently there is ... A: There is nothing currently known (which, among other things, means large enough to notice) to have ... | |
| Is there really a planet X? | 3/10/2010 |
| Q: I've been reading recently about theories for the end of the world in 2012, and apparently there is ... A: There is no planet X, in the sense discussed by those who believe in Nibiru. That is a fairy tale ... | |
| Mt. Krakatoa | 3/8/2010 |
| Q: How many deaths/injuries happen during the 1883 MT. Krakatoa eruption in Indonesia? A: My internet connection failed as I was sending my reply, so I don't know if you received it. The ... | |
| Hoag's Object | 3/5/2010 |
| Q: When you look at a picture of Hoag's Object you can clearly see the blue stars in the ring, but in ... A: The yellow object in the middle is the nucleus of the galaxy, and consists not of a single star, but ... | |
| which way is up? | 3/2/2010 |
| Q: i have always wondered. is there an up down left and right when you reach outer space? let me ... A: You have pretty much answered your own question, but perhaps the following will help clarify things, ... | |
| Moon | 2/27/2010 |
| Q: Why doesn't our 'Moon' spin on its axis ( rotates ) like the moon's of Jupiter and Saturn? A: Our Moon does rotate. It just rotates synchronously -- that is, it rotates once, each time it goes ... | |
| absolute zero | 2/27/2010 |
| Q: since it has been proven that motion is relative to time and movement no mater how little actually ... A: The movements and physical state of a blob of air can be exploited in various ways. Depending upon ... | |
| absolute zero | 2/27/2010 |
| Q: since it has been proven that motion is relative to time and movement no mater how little actually ... A: For the simplest case related to your discussion, that of a gas (such as the air in a room), the ... | |
| space-time | 2/26/2010 |
| Q: since it has been proven that motion is relative to time and movement no mater how little actually ... A: Motion does not cause you to travel into the future. It simply changes how you age, as you do so. If ... | |
| moons of Mars | 2/17/2010 |
| Q: /bows thank you for your time. I never see rover pics from Mars at night, but I love the sunrise ... A: I think they power down the rovers at night, to save on battery power, and because it gets so cold ... | |
| The stars we see | 2/15/2010 |
| Q: How much closer to earth were the stars that we see at the time that the pyramids were being built! A: For all practical purposes, the stars were at the same distance then, as they are now. For one ... | |
| Influence of Sun on sattelites | 2/12/2010 |
| Q: i'm 17 and curious about astronomy. I'm wondering: does the Sun an influence on planets' satellites ... A: Basically, the answer is no, for three reasons: (1) The Earth's gravity is the main cause of the ... | |
| stars | 2/5/2010 |
| Q: Why each planet differs from each other in their content? Both are formed due to dust clouds. ... A: What different planets are like depends upon the temperature in the region where they formed. The ... | |
| near light speed | 1/29/2010 |
| Q: How much mass would a photon effectively have at 99.995% the speed of light. How about an electon. ... A: Photons have energy, corresponding to their wavelength -- the longer the wavelength, the less the ... | |
| near light speed | 1/29/2010 |
| Q: How much mass would a photon effectively have at 99.995% the speed of light. How about an electon. ... A: Photons have no mass, and only move at the speed of light; so the first part of your question has no ... | |
| universe age | 1/28/2010 |
| Q: As far as i am aware we have dated the universe to be approximately 14 billion years old,depending ... A: The "age" is the time it took the light from the furthest reaches of the Universe to reach us, ... | |
| universe age | 1/28/2010 |
| Q: As far as i am aware we have dated the universe to be approximately 14 billion years old,depending ... A: Until the last decade, the age was estimated by assuming a rate of expansion equal to the current ... | |
| Planet orbital intersections | 1/24/2010 |
| Q: I can visualize how the planets corkscrew through space relative to the sun's moving path. My ... A: The Sun's motion through space is much faster than any of the planetary motions, and is at an angle ... | |
| the sun | 1/14/2010 |
| Q: is it possible that the sun could have been a planet? A: it was considered a planet, when the term planet meant an object that moved around in the sky, ... | |
| Sun & Moon Eclipses | 1/13/2010 |
| Q: Moslems are praying during Sun %26 Moon Eclipses! do you think there is a resone for their afraid? ... A: The gravitational effects of the Sun and Moon on the Earth are the same at every new moon, whether ... | |
| White Dwarf stars | 1/13/2010 |
| Q: I was wondering if a white dwarf star was theoretically capable of supporting a living planet such ... A: The density of the star wouldn't make any difference -- just the size of the planet's orbit, and the ... | |
| the iron | 1/6/2010 |
| Q: some people are saying the iron is not originally from earth! is it true?? A: I've never heard of such a thing, so I don't know why they would say that. But there is no doubt ... | |
| Light Years | 1/6/2010 |
| Q: I am a biology major but I've always been fascinated with astronomy, too. I've been following the ... A: For distances such as 13.2 billion light years, we use the assumption that the rate of expansion of ... | |
| Sun Chasing speed | 1/3/2010 |
| Q: I am a sculptor and I have this idea for a kinetic sculpture that the top needs to be under the sun ... A: If I understand your idea, the lower part of your sculpture will rotate to the "east" as the Earth ... | |
| black holes | 12/25/2009 |
| Q: We have 'calculated' expansion rates of the universe. We have observed black holes and learn so ... A: The idea that the Universe is or could become a black hole corresponds to the Closed Universe ... | |
| Universe | 12/12/2009 |
| Q: Is the universe finite or infinite? If it is finite, how big is it? A: It is half-infinite, meaning that it presumably has some finite size now, but will be infinitely ... | |
| Mayan Calendar | 12/3/2009 |
| Q: How is it possible that the Mayans could have accurately predicted the aligning of plants? What ... A: The planets will not be aligned at all in late 2012, but will be scattered all along the Ecliptic ... | |
| Lunar rilles | 11/3/2009 |
| Q: i saw your answer about Lunar rilles but the other expert said "The surface of the moon is replete ... A: If such a thing had ever occurred, we should see immense cracks where things were put back together, ... | |
| Lunar rilles | 11/2/2009 |
| Q: i saw your answer about Lunar rilles but the other expert said "The surface of the moon is replete ... A: I read the answer I believe you're referring to, and the page you linked to. The latter makes a ... | |
| expansion of the universe | 10/27/2009 |
| Q: !! Here is myGiven that the expansion rate of the universe is 74.2 ±3.6 ... A: It is correct that the objects we now see as they were 13.7 billion years ago are now much farther ... | |
| expansion of the universe | 10/26/2009 |
| Q: !! Here is myGiven that the expansion rate of the universe is 74.2 ±3.6 ... A: The problem is your units (and a probable decimal place error). The "observable" Universe is 13.7 ... | |
| Big Bang Theory | 10/12/2009 |
| Q: Was there at least one inward secondary shock-wave during the initial expansion from the big bang, a ... A: There wouldn't be any reflected wave, because that requires a surface to reflect off of, and no such ... | |
| any scenario of seeing Neptune or maybe Jupiter's moons with the naked eye? | 10/5/2009 |
| Q: I know all about how Saturn is generally considered the last of the "naked eye" visible Planets but ... A: I've heard apocryphal statements about some people being able to see exceptionally faint objects in ... | |
| THE SHAPE OF THE UNIVERSE | 9/24/2009 |
| Q: Where is cosmology now on the overall shape of the universe? Is it a big sphere, with the galaxies ... A: It is probably a blob of no particular shape, which is growing in all directions at an effectively ... | |
| Moon Behavior. | 8/29/2009 |
| Q: For the sake of photography my question is what is the behavior of the moon relative to the sun? ... A: The position of the Moon changes relative to the Sun over the course of a lunation, or cycle of ... | |
| orion's belt | 8/28/2009 |
| Q: Is orion's belt visible Aug. sky in Central Ontario Canada? A: Yes, but only late at night. In the early evening in mid-summer, the stars that are up are "summer ... | |
| time and space | 8/24/2009 |
| Q: I saw a special on tv that theorized that time travel was possible either through the use of a ... A: You are correct in presuming that given our current understanding of the laws of physics, none of ... | |
| astronomy question--correction | 8/21/2009 |
| Q: I first heard Carl Sagan discuss a little known theory that the universe might be surrounded by ... A: I've read about theories of displacement of the crust and mantle relative to the liquid core, which ... | |
| astronomy question | 8/21/2009 |
| Q: I first heard Carl Sagan discuss a little known theory that the universe might be surrounded by ... A: I see what you mean. You're referring not to an allegory, but a supposedly actual presence of water ... | |
| astronomy question | 8/21/2009 |
| Q: I first heard Carl Sagan discuss a little known theory that the universe might be surrounded by ... A: I believe that the discussions you're referring to are a way of visualizing the multiple-universe ... | |
| Supernova | 8/18/2009 |
| Q: Hai, I am Steffi Michael, When there is a supernova the energy given out by the star is more than it ... A: Supernovae can be several hundred billion times brighter than the Sun, but only for a short period ... | |
| Appearance of Charon | 8/12/2009 |
| Q: How large would Charon appear in the sky of Pluto, or vice versa? Degrees of arc would be a clear ... A: Charon would appear to be a little over 3 degrees in diameter, as seen from the surface of Pluto. ... | |
| orbit | 8/11/2009 |
| Q: Why everything revolves around everything in an elliptical pattern? And how it revolves with only ... A: It just has to do with how the force of gravity acts on the objects orbiting the Sun. As a planet ... | |
| Dark Matter | 8/11/2009 |
| Q: What is dark matter and what it is doing in space? If there is no light in a room, will the dark ... A: We don't know what dark matter is. As far as dark matter in galaxies is concerned, it could be ... | |
| Stellar Parallax | 8/10/2009 |
| Q: I am looking for a simple explanation of calculating the distance of a star using stellar parallax. ... A: For a simple diagram, you might use http://abyss.uoregon.edu/~js/glossary/parallax.html If you're ... | |
| tools | 8/8/2009 |
| Q: If I were living during the days of Johannes Kepler (1571-1630) What tools and theorys would I have ... A: The mass of the Earth is determined by measuring the constant of gravity, G, and comparing its value ... | |
| flares | 8/2/2009 |
| Q: Please forgive me if my questions sound arogant, I have little scientific knowledge, but I would ... A: A solar flare represents a phenomenon in which energy trapped in the Sun's magnetic field is ... | |
| Big bang | 7/29/2009 |
| Q: is it true that before the Big Bang all matter was joined together as 1 unit. so the entire universe ... A: First, I apologize for the delay in answering your question. The electric company was working on our ... | |
| Expansion of space/redshift | 7/9/2009 |
| Q: I was wandering what distance from our present position the present edge of the observable universe ... A: To answer the second part of your question first, I seriously doubt that you have any doppelgangers ... | |
| Astronomy | 7/6/2009 |
| Q: This is a problem from my astronomy homework and I have been trying to figure it out but I keep ... A: You'll need to look up Io's mass in kilograms (it should be in your textbook, but if not, you can ... | |
| moon going away | 6/28/2009 |
| Q: It's well known that the Moon is going away from the Earth at few centimers per years; but will it ... A: The Moon's retreat is caused by the tidal interaction of the Earth and Moon. This interaction ... | |
| merging galaxies | 6/26/2009 |
| Q: seen one of those photographs from the hubble telescope of two galaxies on a collision course and ... A: I don't know about at the beginning of our evolution, but if it were to happen now, the odds are ... | |
| merging galaxies | 6/26/2009 |
| Q: seen one of those photographs from the hubble telescope of two galaxies on a collision course and ... A: The stars attract each other, but by and large, not as individual objects. Each star in each galaxy ... | |
| ASTRONOMY | 6/24/2009 |
| Q: On March 21 is the length of daylight (sunrise to sunset) longer, shorter or the same on the Equator ... A: Ignoring its size, the Sun would be up exactly the same amount of time (half its 24-hour day-to-day ... | |
| Lunar eclipse Saros series numbering | 6/21/2009 |
| Q: As far as I know, Saros series are numbered according to when the eclipse that has the least gamma ... A: The answer is simpler than I thought, so I was able to figure it out within a few spare minutes. ... | |
| Astronomy | 6/20/2009 |
| Q: this is a question from my astronomy homework and I can't seem to figure out how to go about ... A: This is about Kepler's Third Law of Planetary Motion, which says that the mass of the bodies ... | |
| Astronomy: Solstice and Equinox | 6/18/2009 |
| Q: I have a question about the ecliptic. What are the times or dates during the year when a place on ... A: At the Equator, there are 12 hours of sunlight and 12 hours of night every day, throughout the year. ... | |
| planets | 6/16/2009 |
| Q: on bbc's the sky at night, they were looking at possible planet formations around other stars,they ... A: Although looking for exoplanets is interesting in its own right, and might greatly increase our ... | |
| planets | 6/15/2009 |
| Q: on bbc's the sky at night, they were looking at possible planet formations around other stars,they ... A: I don't know what the limiting size would be, but there are two factors which argue against very ... | |
| Space | 6/15/2009 |
| Q: How are the weights and sizes of planets like uranus, mercury and earth and asteroids determined? A: Size Estimates: (1) TYPICALLY BEST -- observations of how large the object appears (in a telescope ... | |
| black holes | 6/11/2009 |
| Q: the creation of black holes is formed in the aftermath of supernova so does this happen ... A: Any light / gases /etc inside the event horizon (a more or less spherical surface which defines the ... | |
| black holes | 6/11/2009 |
| Q: the creation of black holes is formed in the aftermath of supernova so does this happen ... A: The formation of the black hole takes only a fraction of a second, but it wouldn't be 'visible' for ... | |
| milky way | 6/9/2009 |
| Q: hypothetical question what if the only galaxy created from the big bang was our own, would life ... A: There are theories which propose that 'local' conditions can be affected by the nature of the ... | |
| comets,astroids etc | 6/8/2009 |
| Q: often when mentioning these objects on tv,films etc the narrator will talk about the impact of a ... A: The only equivalence involved is the total amount of energy. If, say, an impact has a total energy ... | |
| eclipses | 6/6/2009 |
| Q: solar eclipses are slightly more common than lunar eclipses. Why then is it more likely that your ... A: Lunar eclipses can be seen anywhere on the night side of the Earth, but solar eclipses can only be ... | |
| black holes | 5/29/2009 |
| Q: what happens to all the matter that goes into black holes? A: It falls to the center, and becomes part of the singularity at the center. As it nears the ... | |
| solar system | 5/26/2009 |
| Q: I agree the moon orbits the earth at aprox. 62,000 miles an hour,but Idon't agree that we orbit the ... A: The Moon only orbits the Earth at about 2,000 miles per hour. The Earth orbits the Sun at about ... | |
| Solar & Planets | 5/24/2009 |
| Q: Has anyone ever done an estimate of the Mass of the Trojans- & why are they spaced at approx 60 ... A: I don't know if there is a specific estimate of their total mass, but there are only a few hundred ... | |
| tidal locking | 5/23/2009 |
| Q: Can planets become tidally locked to stars in the same way that moons are tidally locked to their ... A: Yes, they can. In fact, until the 1960's, it was thought that Mercury was tidally locked to the Sun. ... | |
| gravity & speed | 5/21/2009 |
| Q: mars has a gravity 38% that of earth...if earths gravity was the same how fast will a man be able to ... A: The difference in gravity wouldn't affect how fast things could go -- only how fast they fell. For ... | |
| How close does something have to be to see it? | 5/19/2009 |
| Q: I'd like to know how far away I can see objects in the daytime sky, such as balloons. Assuming an ... A: There are two possible answers to this question, depending upon what you mean by 'seeing' it. One, ... | |
| cat's eye nebula | 5/10/2009 |
| Q: could you tell me what the TRUE color of Cat's eye Nebula is? Is it that: ... A: I presume you mean, if you were looking at the nebula directly, without any optical aid or ... | |
| GETTING UP CLOSE | 5/10/2009 |
| Q: I was wondering would you please tell me: why do we have daylight savings? Thanks A: The basic idea is that since most people are up in the evening and abed in the morning, they can do ... | |
| particles | 5/5/2009 |
| Q: i saw a show on the science channel hosted by micho kaku and he was on top of a mountain talking ... A: He was probably talking about mu mesons produced by cosmic rays bombarding atoms in our upper ... | |
| my grandma has a question for you | 5/3/2009 |
| Q: why do the planets orbit the earth on a parallel line like they all go across if you where to draw a ... A: This is explained by the Solar Nebula theory of the origin of the Solar System. The planets formed ... | |
| Observing Our Early Universe | 4/30/2009 |
| Q: I just finished reading this article at ... A: When it is said that we see something 13 billion light years away, what it really means is that the ... | |
| mars | 4/26/2009 |
| Q: I have recently recieved an email saying that mars will appear as big as the moon this year on ... A: This is a misconception or hoax that has cropped up every couple of years since 2003. Below, I've ... | |
| about a detail on Earth's past | 4/23/2009 |
| Q: During Earth's past; more PRECISELY just before the formation of the first mountains-ranges (ie, 1 ... A: It is highly unlikely that general surface motions such as continental drift have ever exceeded a ... | |
| Astronomy | 4/18/2009 |
| Q: At times, you can look into the sky and see the Sun and the moon at the same time. It's almost as ... A: The portion of the Moon that you see lit depends upon the difference between the angle you look at ... | |
| where are we? | 4/16/2009 |
| Q: Goodmorning from Barcelona. After recently watching 2012 Nostradamus on the History Channel -which ... A: Although visible light cannot penetrate the clouds of gas and dust which lie in the plane of the ... | |
| Angle of the solour system to the milky way disc. | 4/14/2009 |
| Q: what is the orientation of the plane of our solar system relative to the plane (disc) of our galaxy ... A: The galactic equator is tilted about 63 degrees relative to our equator. However, the answer to the ... | |
| Straight lunar rilles | 3/30/2009 |
| Q: I'm posting this question again because I didn't write my E-mail adress correctly. i'm sorry for ... A: Here's a copy of the answer I posted a few hours ago. Lunar rilles were formed by lava tubes, ... | |
| Lunar rilles | 3/30/2009 |
| Q: could you tell me if the idea of the cleavage of the Moon (allegedly occured thousands years ago) in ... A: Lunar rilles were formed by lava tubes, during the formation of the lunar maria, 3.2 to 3.9 billion ... | |
| Space travel | 3/14/2009 |
| Q: Why can't the Cassini–Huygens space craft travel above or below the Asteroid Belt and the rings of ... A: There isn't any restriction on our ability to go above or below the plane of the Ecliptic. There are ... | |
| Moon | 3/13/2009 |
| Q: Why does the moon look so much larger (in size) when it is rising in the East (when its a full moon) ... A: This effect (called the Moon illusion) is due to the apparent difference in distance between the ... | |
| moon | 3/12/2009 |
| Q: 1.Which phase of the Moon rises in the east exactly when the Sun sets in the west? and why? A: That would be the full moon. East is opposite west, so if the moon is rising in the east when the ... | |
| comets | 3/2/2009 |
| Q: I have got two questions concerning comets. I would like to know 1. how fast in general do comets ... A: 1. When very close to the Sun, comets may move more than 200 miles per second. At the orbit of the ... | |
| planetary formation of water | 2/28/2009 |
| Q: Courtney: I have studied cosmology for about 30 years, and a question keeps popping up in my mind. ... A: A small portion of the water may have come from cometary bombardment, particularly in the period ... | |
| The light horizon and cosmic microwave background | 2/26/2009 |
| Q: Does the Light Horizon include cosmic microwave background radiation? Or is one more distant then ... A: Yes, the light horizon and cosmic microwave background would be in the same place, relative to us. ... | |
| The light horizon and cosmic microwave background | 2/26/2009 |
| Q: Does the Light Horizon include cosmic microwave background radiation? Or is one more distant then ... A: The light horizon is identical to the 'surface' defined by the microwave background radiation. When ... | |
| Life cycle of a star | 2/17/2009 |
| Q: What is the complete life cycle of a normal star, starting with a protostar and ending with a black ... A: Apparently, whomever you sent this question to was on vacation, or declined to answer it, as I just ... | |
| Planets | 2/10/2009 |
| Q: One story in Hindu Mythology was saying there was an astrological event of all the planets & Sun ... A: I've done a check of famous planetary alignments, and thought you'd be interested to know that ... | |
| Planets | 2/9/2009 |
| Q: One story in Hindu Mythology was saying there was an astrological event of all the planets & Sun ... A: Sorry for the delay in answering, but I just got back from the hospital, and didn't receive your ... | |
| Jupiter | 2/8/2009 |
| Q: Was Jupiter ever a star once? A: Apparently, whomever you sent this question to was either on vacation, or rejected it, as I just ... | |
| Hubble discoveries | 2/5/2009 |
| Q: How come that we can see photographs of thousands of galaxies said to be > 10 billion years old made ... A: Observations always trump theories, so what those photographs show is that theories which predicted ... | |
| Earth's axis | 1/25/2009 |
| Q: Does the earth's axis tilt away from the sun or towards it as it revolves around the sun? eg On the ... A: The axis always points in the same direction, so when it is on one side of the Sun, the northern ... | |
| Moon and Sun | 1/20/2009 |
| Q: What is the term used to describe when the sun and moon are both visible? (I.e. the sun is setting ... A: I don't think there is a term to describe that, because it's almost an everyday occurrence (though ... | |
| the universe | 1/16/2009 |
| Q: 73 billion years old, Mars and earth about 4.5 billion years old, would it be fare to say that these ... A: There are two reasons for that: (1) Jupiter does not significantly protect the Earth from comets or ... | |
| begining universe | 1/15/2009 |
| Q: Is it true that the Universe (rather, all the matter in the Universe) used to be, at its early ... A: I suppose it would depend upon what you mean by a cloud of smoke. Very early on, the 'matter' in the ... | |
| the universe | 1/14/2009 |
| Q: 73 billion years old, Mars and earth about 4.5 billion years old, would it be fare to say that these ... A: As far as the 9 billion years, yes, that would be correct, presuming the 13.73by is correct (I know ... | |
| Position of rising moon | 1/13/2009 |
| Q: I have noticed that the moon rises in at least two different places and would like to know if it ... A: Just as the Sun moves north and south during the year, the Moon moves north and south during the ... | |
| geography | 1/12/2009 |
| Q: what caused the sun to become tilted at 7.25 degrees? A: The Sun's rotation is presumably the average of the net rotation of the material that fell into it ... | |
| earth attraction | 1/10/2009 |
| Q: sir why earth attract the objects? A: I presume you mean, why do things fall toward the Earth, or orbit around it. Since your question ... | |
| Flare activity on earth? | 1/8/2009 |
| Q: I have asked this question many times around about, but i thought i'd ask you. I have a pet theory ... A: As noted in my earlier (abortive) attempt to reply, this is outside my area of expertise, but I ... | |
| constellations | 1/7/2009 |
| Q: Do you know of any websites that show a picture/animation of the milky way galaxy with the ... A: If you mean, where are the constellations in the sky, relative to the Milky Way, then there are many ... | |
| not sure | 12/20/2008 |
| Q: Describe how a proton found in hydrogen gas cloud(nebula), subsequently found itself in an atom of ... A: (Sorry for the delay in answering; but I'm on vacation, and won't have regular access to the ... | |
| Physics | 12/20/2008 |
| Q: Why does centrifugal force can keeps earth move and rotate on its axis? A: Centrifugal force has nothing to do with how the Earth moves in space. Its orbital motion is due to ... | |
| astronomy | 12/15/2008 |
| Q: Mr.Seligman, I have been reading about the interrelation between moon-earth, many information about ... A: The slow increase in the Moon's distance will have no significant effect on the Earth, save for its ... | |
| Considering the moon as a planet | 12/14/2008 |
| Q: I was trying to figure out what classifies the moon as a satellite, and not a planet. I found my ... A: (Please forgive the delay in answering this question. It was sent to the Question Pool, presumably ... | |
| astronomy | 12/14/2008 |
| Q: I am trying to write a programme to find location with the use of stars planets. Can you give me the ... A: I don't know what you're referring to, by 'other place'. Can you include the entire sentence or ... | |
| Astronomy | 12/12/2008 |
| Q: How many galaxy and nebulas are there in the constellation Draco? And can you name some? A: I have no idea, but there should be dozens of nebulae, and billions of galaxies, depending upon how ... | |
| astronomy | 12/12/2008 |
| Q: I am trying to write a programme to find location with the use of stars planets. Can you give me the ... A: In order to calculate the sidereal hour angle, you need your latitude and longitude, the date and ... | |
| Astronomy | 12/10/2008 |
| Q: Seligman, I am a ninth grade student, and am doing a report and am required to interview an expert ... A: 1. I'm sure black holes exist, but believe that worm holes do not. They are an interesting ... | |
| Questions | 12/9/2008 |
| Q: How can I become an astronomer? Is it easy? Is it fun? A: To be a professional astronomer, you need an undergraduate major in astronomy, physics, or ... | |
| Astronomy | 12/9/2008 |
| Q: Seligman, I am a ninth grade student, and am doing a report and am required to interview an expert ... A: Most astronomers work as teachers, so their salaries are usually in the same range as other ... | |
| Astronomical Sizes | 12/8/2008 |
| Q: I am trying to rank the relative sizes of the following: Jupiter, Sun, Spiral Galaxy, Neutron Star, ... A: In order of increasing size: Black holes have very little size (in fact none, if you mean the ... | |
| Online planetariums | 12/4/2008 |
| Q: In a previous question on azimuth of celestial bodies, you mentioned that there are many free online ... A: Prior to answering your earlier question, I hadn't looked at online planetarium software in any ... | |
| Theoretical question | 12/4/2008 |
| Q: What would happen to the planets in our solar system if the sun just vanished in the blink of an ... A: For one thing, they would get very cold as their surface heat was radiated into space, and not ... | |
| astronomy | 12/1/2008 |
| Q: I am trying to write a programme to find location with the use of stars planets. Can you give me the ... A: Your question seems to be self-contradictory. The first sentence implies that you want to use the ... | |
| planets mass bending star light | 12/1/2008 |
| Q: This problem has been bugging me since I saw the BBC drama about Eddington and Einstein. This is to ... A: I just noticed this question, in the Question Pool. (I presume the individual you sent it to either ... | |
| Angle of setting sun - continued | 11/29/2008 |
| Q: Hope you had a good Thanksgiving, Professor Seligman. Thanks for helping me with the angle of ... A: You are correct. I inadvertently left out a step at the end of my answer. Although it correctly ... | |
| Angle of setting sun | 11/26/2008 |
| Q: I found this site and your name while searching for information on my question. You answered a ... A: You are correct in saying that at the Equator, the Sun would rise vertically (at a 90 degree angle ... | |
| solar system orbit-orbit resonance | 11/26/2008 |
| Q: In my current Msc course in Astronomical Climate Forcing we briefly touched the subject of ... A: It is true that each interaction between two planets will alter their orbits, but that doesn't alter ... | |
| Cosmology and the Exansion of the Universe | 11/26/2008 |
| Q: Lets just say for instance that; 1). We have two Astronomers on two planets say 4ooo light years ... A: The Universe doesn't have to expand any faster, for the speed of expansion in a given region to ... | |
| Cosmology and the Exansion of the Universe | 11/26/2008 |
| Q: Lets just say for instance that; 1). We have two Astronomers on two planets say 4ooo light years ... A: Because the expansion of space is very small unless the volume of space is very large, your example ... | |
| Origin of life | 11/25/2008 |
| Q: Can we hypothesise that life was 'created' on earth more than once? If this was the case would the ... A: You might better ask this of a biologist, but I've read enough about the topic to give you a ... | |
| Astronomia | 11/20/2008 |
| Q: What is supporting the solar system; I mean, what is down it? Quisiera saber si los demas planetas ... A: No, there isn't; at least, not in the sense I think you mean. Your question suggests that if ... | |
| Astronomia | 11/19/2008 |
| Q: What is supporting the solar system; I mean, what is down it? Quisiera saber si los demas planetas ... A: Nothing is "supporting" the Solar System, as there is no "down" in space, save for the direction to ... | |
| interview questions | 11/18/2008 |
| Q: 1. How did you get involved in astronomy? Do you enjoy this profession? ... A: 1. I've been interested in astronomy all my life, but the critical event was my attendance at the ... | |
| Measurement in space | 11/17/2008 |
| Q: What exactly is a parsec? I don't understand why astronomers would use this instead of light-years, ... A: When measuring the distance of a star, its apparent displacement in direction, due to our motion ... | |
| planet formation | 11/16/2008 |
| Q: Can you explain some of the processes involved in the alleged planet formation from dust particles ... A: I can see that my answer didn't directly address your main concern. Thanks for the clarification. ... | |
| planet formation | 11/15/2008 |
| Q: Can you explain some of the processes involved in the alleged planet formation from dust particles ... A: During the earliest stages of the formation of the Solar System, there would have been huge numbers ... | |
| About True Polar Wander theory | 11/14/2008 |
| Q: According to True Polar Wander theory, if a supersized volcano is on earth, then our planet would ... A: If it were possible for large structures (supersized volcanoes or continents) to not have deep ... | |
| astronomy | 11/14/2008 |
| Q: Why does the moon appear to be "upside down or rotated to the right" in the morning or when it is ... A: (Please excuse the delay in answering this question. Apparently, whomever it was directed to ... | |
| planet formation | 11/8/2008 |
| Q: Can you explain some of the processes involved in the alleged planet formation from dust particles ... A: You can find a detailed, albeit somewhat scattershot discussion of this topic on my website, ... | |
| earth | 11/6/2008 |
| Q: What would happen if an object the size of Pluto rammed into earth at the speed of sound? Would ... A: When any object hits the Earth, it does so with at least the escape velocity of the Earth, which is ... | |
| telescope | 10/27/2008 |
| Q: can you please help me with this question Explain how visual telescope shows the temperature and ... A: Hotter stars give off a greater percentage of blue and ultraviolet radiation than cooler stars, ... | |
| sun exposure | 10/22/2008 |
| Q: what would happen if someone was never exposed to the sun? A: This is more a biology question than an astronomy question, but having some experience with the ... | |
| mountains without roots | 10/21/2008 |
| Q: First of all, thank you for answering my first question. My new question is the following: if ... A: The only way I can imagine that happening would be for a massive volcanic eruption to blow the ... | |
| Space | 10/20/2008 |
| Q: What direction are you traveling in a space vacuum? A: If you mean, how can you tell what direction you are moving in a completely empty Universe, the ... | |
| Full Moon Duration | 10/16/2008 |
| Q: How many days is a full moon considered full (ie. 3, 5, ?) Thank you so much. A: (Please excuse the delay in answering this question. Apparently the person you asked to answer it ... | |
| mountains and Earth's rotation | 10/16/2008 |
| Q: A friend of mine made the following analogy to prove me that mountains balance our planet while it's ... A: Your friend's analogy is wrong, on several counts. First, the purpose of wheel weights has nothing ... | |
| astronomy | 10/15/2008 |
| Q: 1. Why does a cloud of interstellar gas heat up as it collapses? A: When you compress a gas, you have to exert a force to overcome the outward pressure that the gas ... | |
| Sun's angle at sun rise and sun set | 10/14/2008 |
| Q: What is the angle created by the sun at sun rise and sun set on June 21 and what is it on December ... A: Your question was apparently rejected and placed in the general question pool, which is where I just ... | |
| start or planet | 10/14/2008 |
| Q: I don t really know anything about astronomy. So my question may be a little vague. I see a light in ... A: At that late time, it would certainly be Jupiter. At the moment, Venus is going down before 8, but ... | |
| start or planet | 10/13/2008 |
| Q: I don t really know anything about astronomy. So my question may be a little vague. I see a light in ... A: Based on your description, the "light" is the planet Jupiter, which was in the southeast (in early ... | |
| How to view the Dark Moon? | 10/5/2008 |
| Q: You can't see the Dark Moon (commonly often referred to as the New Moon) in the daytime sky using ... A: You can't see a new moon because it is so close to the Sun that the scattered sunlight that lights ... | |
| astronomy | 10/2/2008 |
| Q: I am inquiring about sunspots. What is the size of a sunspot, in kilometres, given that it has an ... A: An object with an angular diameter of 1" is 206,265 times smaller than the distance between it and ... | |
| The Universe | 9/29/2008 |
| Q: What is the size of the Universe (in light years)? Is the size of the Universe expanding, and, if ... A: There are some complications involved in answering your question, so a simple answer isn't ... | |
| Asteroid | 9/26/2008 |
| Q: What would happen if an asteroid hit where the ice caps are melting? Thank you. A: I presume you mean an asteroid large enough that the impact and subsequent explosion would melt and ... | |
| astronomy | 9/25/2008 |
| Q: how did early astronomers first know that the Solar System was not the center of the Galaxy? ... A: This was discovered by Harlow Shapley in 1918. Prior to that, it was thought that the Sun lay near ... | |
| Radio Astronomy Data | 9/22/2008 |
| Q: Where could I download some raw data from a radio telescope for free? What file format is "standard" ... A: I'm afraid that under the circumstances, I don't know what to suggest. As I said, I'm not an expert ... | |
| Radio Astronomy Data | 9/21/2008 |
| Q: Where could I download some raw data from a radio telescope for free? What file format is "standard" ... A: I am not an expert in the field of radio astronomy, but have looked at enough online material to ... | |
| Star photos | 9/20/2008 |
| Q: Most photos of stars have four rays at 90 degrees to each other. Obviously they are an artifact of ... A: (Your question was sent to the Question Pool, because the expert you sent it to was on vacation, had ... | |
| declination and right ascension | 9/16/2008 |
| Q: It's a long story...but I'm working on a historical novel, and have gone off on a tangent about ... A: The coordinates in the Ephemeris should be geocentric -- that is, as seen from the center of the ... | |
| declination and right ascension | 9/16/2008 |
| Q: It's a long story...but I'm working on a historical novel, and have gone off on a tangent about ... A: If you only know the Moon's right ascension and declination at one date and time, you can't ... | |
| mutual gravitation | 9/14/2008 |
| Q: what is the meaning of mutual gravitation? A: (Your question was apparently rejected by the system, or sent to an expert who was on vacation or ... | |
| sight | 8/22/2008 |
| Q: what do we actually see? when we look at things are we seeing the Light or the objects A: Strictly speaking, we the light reflected by or given off by the object. Experience tells us that ... | |
| blue shifted light | 8/22/2008 |
| Q: I have a Question to ask about light from distant galaxies. If We look at far off galaxies(12 bill. ... A: In any given part of the Universe, galaxies are moving more or less randomly relative to each other. ... | |
| stellar parallax | 7/15/2008 |
| Q: what are the errors in star parallax measurement? thanks A: (Please forgive the lateness of this answer. I volunteered on August 5, and noticed that no one had ... | |
Astronomy
Answers by Expert:
Courtney Seligman
Top Expert on this page
Expertise
I can answer almost any question about astronomy and related sciences, such as physics and geology. I will not answer questions about astrology and similar pseudo-scientific rubbish.
Experience
I have been a professor of astronomy for over 40 years, and am working on an online text/encyclopedia of astronomy.
Publications
Astronomical Journal, Publications of the Astronomical Society of the Pacific (too long ago to be really relevant, but you could search for Courtney Seligman on Google Scholar)
Education/Credentials
I received a BA in astronomy and physics and a MA in astronomy, both from UCLA. I was working on my doctoral dissertation when I started teaching, and discovered that I preferred teaching to research.
Awards and Honors
(too long ago to be relevant, but Phi Beta Kappa and Sigma Xi still keep trying to get me to become a paying member)
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