Astronomy/Questions

SubjectDate AskedExpert
Fair Market Value3/26/2017Paul Wagner
  Q: What is the fair market value of a telescope that has been used only once? I have an Orion telescope ...
  A: This is not an easy question to answer. You are correct, that there are few moving parts and little ...
Cheap Telescope3/7/2017Philip Stahl
  Q: If someone used the lowest quality lens out there to make it more cost affective how expensive would ...
  A: First, before giving a direct answer let's look at some applicable quantities. These include the ...
Probability2/22/2017Philip Stahl
  Q: I see articles from time to time about how they came to the conclusion that Pluto should be ...
  A: and thanks for your question. First, the decision to reclassify Pluto - unbeknownst to many - was ...
Telescopes2/19/2017Paul Wagner
  Q: I purchased a $150 Orion telescope and I find the moon is the only skyward object it really improves ...
  A: The views you get from a telescope depend on two things:. Light gathering (how big the lens or ...
Kepler's laws2/19/2017Philip Stahl
  Q: Dr.Fitzpatrick have read my arguments.But he declined to continue corresponding; he could not ...
  A: I already told you and SHOWED you that you CANNOT have a perpendicular vector (or scalar) value to ...
A Pure-Energy Universe?2/16/2017Courtney Seligman
  Q: If all of the matter universe were converted into energy (or if it began as energy and never became ...
  A: Since the total mass of the Universe is only a fraction of the so-called "critical mass", converting ...
Rates of Rotational and Revolution of Planets2/9/2017Courtney Seligman
  Q: I recently had a series of curious thoughts that eventually led me to your site. Succinctly, they ...
  A: I'm glad that you found the discussion of the Rotation of Mercury useful and interesting; but your ...
Retrograde of Venus2/1/2017Courtney Seligman
  Q: I understand that the retrograde of Venus lasts approximately 40 days. Is this something that can ...
  A: The beginning and ending of Venus' retrograde motion CAN be seen with the "naked" eye, but due to ...
cosmology1/21/2017James Gort
  Q: ..I have just read the latest answer you gave to a question and would like to ask, further to that. ...
  A: I'll try and answer your fairly long question as simply and succinctly as I can. And it will be to ...
Cosmology1/10/2017James Gort
  Q: I'd like to know why scientists say that the universe is expanding, based on the findings of Mr. ...
  A: You are correct. Observations "seem" to support that galaxies are receding - from us as well as from ...
Supermoon time frames11/16/2016Courtney Seligman
  Q: The last supermoon of comparability to 2016 happened in 1948. The next one is predicted to happen in ...
  A: Actually, so-called supermoons occur all the time. All they are is full moons that happen when the ...
Telescopes11/14/2016Courtney Seligman
  Q: Is lens size important to magnification or more so distance between lenses and degrees of convexity? ...
  A: Most "beginner" telescopes have a simple telescope design, but a not terribly useful or easy-to-use ...
Moon photograph10/18/2016Philip Stahl
  Q: I'm trying to take a photo of a full moon over the ocean. The photo I want to create is of the moon ...
  A: Bear in mind the full Moon sets when the Sun rises. This means your photo would need to be takn in ...
Moons role in earthquakes9/22/2016Courtney Seligman
  Q: Does the moon have an effect on the lava beneath the earths crust like the tidal effect? I have ...
  A: It appears that lunar tides can slightly increase the number of microquakes in the lower regions of ...
Rain in other planets.8/31/2016Paul Wagner
  Q: Is there a possibility of rain occuring in other 8 Planets? Thanks Prashant
  A: There certainly is! Astronomers suggest that there are frequent rainstorms on Venus (albeit with ...
Rain in other planets.8/31/2016Courtney Seligman
  Q: Is there a possibility of rain occuring in other 8 Planets? Thanks Prashant
  A: In general, the other planets cannot have rain in the sense that the Earth does, but there could be ...
Capturing Rainbow Images.8/31/2016Paul Wagner
  Q: Can we capture Rainbow Images using both a Telescope and Digital Camera? Thanks Prashant
  A: If you can connect a digital camera to your telescope (you usually need a special attachment for ...
Capturing Rainbow Images.8/31/2016Courtney Seligman
  Q: Can we capture Rainbow Images using both a Telescope and a Digital Camera? Thanks Prashant
  A: You can use a digital camera to photograph rainbows, but you should not use a telescope to do it. ...
AStronomy8/31/2016Courtney Seligman
  Q: Good Evening, my 9yo daughter asked me a curious question about the EArth travelling around the Sun ...
  A: The time that the Sun rises and sets WOULD change by two hours per month, if we used the rotation of ...
Viewing Satellites using Powerful Telescopes.8/30/2016Paul Wagner
  Q: Are there powerful Telescopes which will allow us to view all Satellites? If not, Can those ...
  A: This is a good question! There are telescopes that are powerful enough to see the satellites we've ...
Red dwarf star planet8/25/2016Courtney Seligman
  Q: A new article describes a planet around a red dwarf star that might have life on it:- ...
  A: Another discussion of the planet says that it "is tidally locked, so one side probably faces the Sun ...
Solar eclipses8/25/2016Harry Hayfield
  Q: I live in western Europe(formerly UK, now Austria). I was in Cornwall for the 1999 solar eclipse in ...
  A: A few options to consider: August 12th 2026: Total over northern coast of Spain August 2nd 2027: ...
Celestial Coordinate Conversions8/23/2016Courtney Seligman
  Q: Seligman, When looking at a sky map that shows both galactic coordinates and the plane of the ...
  A: Here is a link to a detailed discussion of how to use spherical trigonometry to convert from ...
space telescopes8/13/2016Philip Stahl
  Q: Why are Hubble's optics enclosed in a tube with a door, and the upcoming James Webb design is ...
  A: The Hubble's optics are enclosed because its aperture at 2.4 m (7.9 ft.) made it more practical to ...
Gauging the distant to stars7/27/2016Courtney Seligman
  Q: I am aware of stellar parallax method. But my problem is that I don't understand how astronomers ...
  A: As you obviously know, the stellar parallax method becomes unreliable for stars at great distances, ...
What did we see tonight.7/12/2016Paul Wagner
  Q: We have been sitting outside tonight watching a "star " that is emitting bright red flashes from ...
  A: You don't mention what part of the sky this was in---and that makes a very big difference. If what ...
Black Holes5/24/2016Paul Wagner
  Q: How come light cannot enter a black hole?
  A: In fact, light CAN enter a black hole. A black hole is a massive object, and light and matter both ...
Stars5/24/2016James Gort
  Q: How do stars stay together so well?
  A: The answer is gravity. The same thing that keeps the earth together also keeps the stars together. ...
universe expansion5/19/2016James Gort
  Q: ...has anyone considerred that dark matter may degrade in some way? An increase in acceleration of ...
  A: I'm not sure if that's actually been proposed in any peer-reviewed publication, but I don't see why ...
Follow Up Question5/14/2016James Gort
  Q: So do we know any of these new constellations? Has the human race in the past seen these ...
  A: Humans have imagined all sorts of constellations before, but all were made up of the same stars we ...
Black Holes5/11/2016James Gort
  Q: How do stars and planets orbit a black hole without being destroyed by it
  A: This is a common misconception about black holes. Black holes do not have any more gravity than any ...
Black Holes5/11/2016Paul Wagner
  Q: Why does a black hole not let light escape? how is this possible?
  A: It's explained by Einstein's theory of relativity--which shows that time, mass, and energy are all ...
Stars5/11/2016James Gort
  Q: Are we ever going to see new constellations, or are the ones we see now always be there?
  A: When you say "we", I assume you mean in your lifetime. In that case, the constellations you see will ...
Black Holes and Neutron Stars4/10/2016Courtney Seligman
  Q: Neglecting differences in mass, what are the observable differences between black holes and neutron ...
  A: For stellar-mass black holes, there aren't many differences. The normal way of observing a neutron ...
Earth centric?3/25/2016Courtney Seligman
  Q: Although we've long established that the planets travel around our sun, is it physically possible ...
  A: No, it is not. The mass required for an object to become even a very small star is much larger than ...
planets rotation3/14/2016Courtney Seligman
  Q: What relationship do you see between a planet's speed of rotation and its length of day? was a ...
  A: Your answer was more nearly correct. The teacher's answer was almost completely wrong. The correct ...
hELP2/23/2016Harry Hayfield
  Q: What is the difference between space and universe
  A: The universe is defined as: "all existing matter and space considered as a whole; the cosmos. The ...
HELP2/23/2016Philip Stahl
  Q: sIR I WNAT TO KNOW WHAT IS DIFFERENCE BETWEEN ASTRONOMY AND ASTROPHYSICS.
  A: There is actually very little difference, given most of modern astronomy is also grounded in modern ...
Accelerating Universe2/5/2016Philip Stahl
  Q: Mr Stahl, Please forgive me, I barely passed high school although I'm a professional pilot. 61 y.o. ...
  A: and thanks for your question. Actually, to the extent we trust our measurements (including for the ...
Astronomy/Our Milky way way galaxy1/1/2016Courtney Seligman
  Q: Our Milky Way galaxy which is a spiral one that supposedly has a black hole at its center in which ...
  A: Although no light can escape the interior of a black hole, even the most massive black holes are ...

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Courtney Seligman

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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, and an online catalog of NGC/IC objects.

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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