Expert: Tom Whiting - 12/9/2011

Question
QUESTION: every clear night in the same place all year around there is a very bright star. it is in the southeastern sky. i live in fond du lac, wi. and i can go to my daughters in madison and neenah, wi. and its there same spot. please help me answer this because it has been a year unansweared. last night 12/6/11 it was under the moon over to the left. thank you so much this answer will ease my mind so much. happy holidays to you and your family.
         Cheryl

ANSWER: Hi Cheryl,
Since the Earth revolves around the sun, it is impossible for the same object to remain in the same place in the sky, even from month to month.  But we all have been viewing Jupiter (your "bright star") for a few months now in the SE as darkness falls.  See if the moon tonight
(and tomorrow night) has moved eastward (to the left) of your "bright star"... if so, you're looking at Jupiter.  Wish you would have given me a time of night, because later, all the bright Orion constellation stars start rising in the east around 7:30 pm local time.
Jupiter can be easily identified... it is the brightest object in the SE in the early evening hours at -2nd magnitude, and there are no other bright stars around it.  Also, if you have a pair of binoculars knocking around in a closet, pull them out and put them on Jupiter and you can easily see several of the 4 Galilean satellites of the planet, if the binoculars are very steadily held, preferably 10 x 50's but 7 x 35 binos will do a good job also.
Jupiter is high (about 60 degrees above your south horizon at 8:30 pm your time), DUE SOUTH, with Orion just rising in the ESE.  Next month, around Jan 7-10, Jupiter will move to high in the SW sky at that same time, 8:30 pm (that's the Earth orbiting around the sun faster than Jupiter does), so you can check it out at a future time.
There is only one other body (besides the sun and moon) brighter than Jupiter, and that's the planet Venus, now very low in the SW sky as darkness falls, at -4th magnitude. (Yes, it's a reverse scale, the lower the magnitude number, the brighter the object. The full moon is -13th magnitude, for instance).  The brightest real stars are zero and 1st magnitude, the Dipper stars (and Polaris) are dimmer at 2nd magnitude, and so on. Each whole number magnitude change is 2.5 times change in brightness, and it's exponential, not arithmetic. In other words, it doesn't go 2.5, 5, 7.5, 10... it goes 2.5, 2.5 squared, 2.5 cubed, 2.5 to the 4th power, and so on.  So it goes 2.5, 6.25, 16, 40, 100!  5 whole number magnitude changes is a 100 times difference in brightness.  (I didn't invent the magnitude scale, I only report on it.)
That's the crazy way it works, and us astronomers have to just live with it.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

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QUESTION: thank you Tom for the fast responce. as far as time i see this star or ? from dark when i walk the dog and when i go get a drink it is in same spot out my window at 1:00 a.m. Because this has been driving me crazy to know what it is, i have been on several web sites in search of an answear till i found you. What i have read was planets can only be seen at dusk or dawn cuz they do not have there own light source, like stars do. They reflect the light of stars around them. i understand that Venus then Jupiter are the brightest and i read at TIMES, when the moons of Jupiter are on its bright side, they will also reflect light and can be seen with binoculars or a scope. But i see this star or whatever ever night with my bare eyes. 8:00 tonight it was there with few stars and now it is 10:00p.m. and it is the only one star out there bright. i do have 8x30 and 10x50 binoculars, but it still is boggling to me. Ithought plants revolve but stars do not. thank you, Cheryl P.S. if you can help me more to understand what it could be , i would love to here from you again. May i ask what state you are in?

ANSWER: Hi Cheryl,
NOT TRUE that planets can only be seen AT dusk or dawn... planets (and stars too) can be seen
FROM dusk to dawn. Their (the planets, moon) light source is the sun, which out in space, it is visible all the time in space where those planets and the moon reside. (Except during a lunar eclipse where the moon briefly passes through the Earth's shadow).
We can even see the brighter planets in the daytime sky (along with the moon, at times), IF you know EXACTLY where to look for that little piece of white "dandelion fuzz" in a deep cobalt blue sky!
Right now (midnight local time) I'm looking straight south at Jupiter, so that's not true that they, the planets are ONLY visible AT dawn and dusk.  It's midnight now!
(What crazy book did you get that erroneous statement from?)
If that's your school science book, I feel very sorry for you.. no wonder we're dead last in science and mathematics!

The Earth rotates 15 degrees per hour eastward, so OBVIOUSLY the object that you're seeing at 1 am local time (in the same place in the sky as Jupiter was earlier) is NOT the same object, Jupiter, that you saw at 8 pm because the Earth has rotated (15 x 5 hours) some 75 degrees eastward, so the sky appears to have moved 75 degrees westward as a reflex motion.
The object at 1 am is either the Dog Star Sirius (bright blue white, slightly dimmer at -1.6 magnitude than Jupiter's -2nd magnitude).  Or it's one of the bright Orion stars, Betelgeuse or Rigel.  Rotation of the Earth is a physical fact, so therefore it simply cannot be the same object in the same SE direction. By 1 am (local time, both yours and mine) Jupiter is high in the south or even starting to "move" into the southwestern sky.

Planets reflect sunlight (not starlight... although the sun is a star too, so I guess technically you could say that planets reflect starlight), but we like to say "sunlight" illuminating our Solar System planets in our sky.
Yes, a star is the only body that generates it's own light and heat... everything else, planets, moons, even comets(!) and asteroids are all reflecting sunlight to be seen. (The only exception to this rule are meteors that generate their own light and heat with friction with the atmosphere).

Planets and stars both revolve, and rotate about an axis.  EVERY BODY OUT THERE has a revolution rate around 'something', and a rotation rate around it's own axis.  The sun rotates once every about 25 days and revolves around the center of the Milky Way Galaxy once about every 250 million years. The Earth rotates once every 24 hours and revolves 365.25 days around the sun.
Even the moon revolves around the Earth once every about 29 days, and rotates once on it's axis in 29 days too, thus called synchronous rotation (since both times are the same) thus keeping one side always facing the Earth.  EVERYTHING moves relative to everything else. There is no such thing as absolute rest in the Universe. Even while sleeping, you're moving 700 mph eastward with the Earth's rotation. And about 18.5 miles per second around the sun. And 200 miles per second around the Milky Way Galaxy, and on and on for other motions above those ones.
So planets don't really 'circle' the sun... since the sun is moving through space, the planets are actually on spiral courses around the sun... we never come back to the same "spot" a year later! (Only relative to the sun are we back at same place). But in reality, the sun (and galaxy) have moved millions and perhaps billions of miles from where they were last year on December 7, 2010.  We're (Earth is) always cutting into new space where we've never been before.  Because everything moves all the time.  When sleeping, you are only stationary relative to your bed and your house and the Earth's surface... but relative to space, and everything in it...moon, sun, stars,... you have moved, and will continue to move.
Something to think about,
Clear Skies,
Tom Whiting
Erie, PA


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QUESTION: Tom, once again thank you for your speedy answer. The anwear to your question "planets can only be seen at dusk and dawn" On my yahoo search bar i typed in "how to tell a star from a planet in the night sky" i pressed search and it came up on  ehow.com and it was the top question that i asked i clicked on it and that is what it told me. I bought a star for my daughter for xmas and it is in between libra and virgo and next xmas i will ask my children to pitch in and get me a telescope so i can understand all the things you taught me in these few emails. I have along way to go but i did ask one of my kids for an astrology book for xmas. 58 years old and its amazing how my interests have changed. Anyway My Chany star is located and can be seen on earth.google.com and the coordinate: 14:29:11.15-19:08:15.0. Sorry for getting away from subject at hand, but that is why that star had me so interested. Thank you Tom, Cheryl

Answer
Oh Cheryl,
Just a word on astrology versus astronomy... ask the kid to get you an ASTRONOMY book not
astrology book.  You'll find that 99.9% of us REAL astronomers do not believe, or buy into...
astrology, ghosts, goblins, zombies, alien life visitations, UFO's, ouiga boards, numerology,
palm reading, fortune telling, or any other of those "occult" and metaphysics... beliefs and ideas.  We already know better.
Clear Skies,
Tom