Expert: Tom Whiting - 6/16/2009

Question
I reside in Chicago and was up late last evening/early morning.  I looked out my window and noticed a very bright, isolated star (planet?) due west and well above the horizon.  Can you tell me which star/planet it was?  Thanks.

Answer
Hi Mike,
Thanks for the location and compass direction, but I wish you could furnish a more exact time for my Skyglobe Computer program.  Nevertheless, I'll crank in 3 am CDT for Chicago, and we have the bright zero magnitude star Arcturus, a yellow-orange star, setting in the WNW and it's about 20 degrees high in the WNW at 3 am.
(A little more than one full extended hand-span at arm's length
above the western horizon).
But if your compass directions are off, we find much brighter
Jupiter about 30 degrees high (2 hand-spans as described above,
above the SE horizon) in the SE at that time too.  So if your "due west" is correct, then it had to be Arcturus as there is nothing else real super bright out there in that direction.  
BTW, you can see that star much earlier in the evening, almost up at
the zenith (overhead point)...well a few degrees south of the
zenith, as darkness falls at 10 - 10:30 pm CDT.

{Zero magitude is 2.5 times brighter than a standard, bright,
1st magnitude star - It's a reverse scale, the lower the number,
the brighter the object; for instance bright Jupiter is at -2nd
magnitude, which is 6.25 times brighter than Arcturus at zero
magnitude.  (It's an exponential scale based on 2.5 raised to the first, second, third, fourth power, and so on.  Five whole number magnitude changes equals 100 times change in brightness, or 2.5
raised to the 5th power, or 2.5 multiplied by itself 5 times.
Well, it's close to 100...in actuality, it's the 5th root of
100, or 2.512...we just round that off for convenience sake.}

Of all the brighter 20 or so stars, only four stars are zero magnitude...Vega, Capella, Rigel, and Arcturus. There is also
one -1.5 mag star, the brightest real star in our sky, Sirius,
the dog star, but that's a wintertime star. The rest of the
brighter stars are called 1st magnitude (In the Northern Hemisphere). The next dimmer ones (Big Dipper, Polaris, etc) are 2nd magnitude, and so on up the magnitude/down the brightness...scale.   Oh well, I've gone too far already...way beyond your question.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA


FOLLOW UP:
In fact I was just outside in Erie PA at 2 am EDT local time and there was Arcturus hanging about 30 degrees high in the west...all alone because we have a light haze tonight, plus I have moderate light pollution here too, just like you have in Chicago.
So one hour from now, your 2 am CDT, you will see the same thing
I'm seeing now...because Chicago is almost due west of Erie;
Same latitude.
Clear Skies,
Tom

FOLLOW UP:
Hi Mike,
That 'oscillating' or twinkling is not Arcturus!  It's our atmosphere
interfering with your view. Stars are all steady, non-changing
pinpoints of light, either with naked eye or telescope. Any departure from that...sintillation, violent color changes, oval shapes, decrease in brightness down near the horizon...that's all atmospherics interfering with our view.

As far as a telescope, in our great hobby, equipment comes LAST,
not first!  Knowledge of the night sky comes first. Because, if you
can't point your finger to the Andromeda Galaxy, the Beehive star
cluster, the pretty double star Albireo, the Lagoon Nebula...all
naked eye objects in a dark sky...how are you going to point a small
viewing telescope to them?  You can't...your first task is to learn
the naked-eye night sky and make your first "scope" an inexpensive
pair of binoculars, and then go from there. If you're really
interested in observational astronomy, suggest you punch up our
club webpage, and read "Tom Whiting's Sound Advice for the Novice"
first, at
http://www.velocity.net/~bwhiting
Might save you some money and a lot of headaches down the road.
Clear Skies,
Tom Whiting
Erie, PA