Expert: Tom Whiting - 7/24/2008

Question
QUESTION: Hi Tom,

I live near Clark and Addision in Chicago Illinois, ZIP 60657. Lately, I've noticed an extremely bright star (it's prominence is second only to the moon) which I would guess is a planet, S SE of my home for weeks now. Is there some planet currently in view for us at this time? What is this extraordinarily bright light?

Thank you so much!

ANSWER: Hi Sean,
Yes, you are correct, it's the planet Jupiter at -2 magnitude, just past opposition now (as we just passed it up, as we do every 13 months) so since Venus is currently behind the sun, Jupiter is the brightest pinpoint of light in our night sky now.  But later this fall, Venus will slowly climb into the western sky and set about two hours after the sun, and will reclaim the brightest pinpoint object, at -4th magnitude.  Just put binoculars on Jupiter, and you can see it's 4 brightest Galilean moons on each side of it. That's all you need, because those moons would be naked eye were it not for the overpowering glare of the planet itself. 
And yes, -4 is brighter than -2 because the magnitude system of brightness is a reverse scale, the lower the number, the brighter the object. And it's notlinear, it's exponential; Each difference is 2.5 times brightness change. And so it does not go 2.5, 5, 7.5, 10 times brightness, BUT rather 2.5, 2.5 squared, 2.5 cubed, and so on.

So the difference in brightness goes 2.5, 6.25, ~16, 40, 100.
A 5 magnitude change is a 100 times change in brightness.
(I didn't invent it, I just report on it).
So Venus will be 6.25 times brighter than Jupiter, once we canobserve it in the western sky after sunset, this coming Autumn.

Oh, and Jupiter is now low in the southern sky because it' in EasternSagittarius, about the lowest it can get (where the sun is locatedin January). Since Jupiter takes 12 years to orbit the sun, it spendsabout one year in each Zodiac constellation, so next year you findit about 30 degrees east of it's current location, so it will bea little higher in Capricornus, just east, right next door to, Sagittarius.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

FOLLOW UP:
Sorry, I don't know why my computer is suddenly putting a question
mark after a period...just disregard all the question marks in
previous answer.

---------- FOLLOW-UP ----------

QUESTION: Thank you so much Tom! It is always refershing to come across so one who is clearly passionate and highly knowledgable.

I was thinking this bright spot might be Spica:

http://www.fourmilab.ch/cgi-bin/Yoursky?lat=41.8744&ns=North&lon=87.639&ew=West&

I say this becasue it's not currently low in the sky, and I haven't noticed it traveling. BUT then I never noticed it before this summer - but then I usually don't pay such close attention.

Another question: Is there a general term astronomers use when refering to a light when they are unceertain of it's label (red giant, planet, etc.)

Yet another question: Don't think me crazy but, I heard once that it is common, for astronmers to observe UFO's in space? In your experience, how accurate is that?

Best,
S

P.S. No question marks appeared to me in your response.

Answer
Hi again Sean,
Your star chart is for 7/24 at 22:50 Universal Time (time in England)
so that's your CDT time at (-5 hr) for 17:50 pm CDT or 5:50 pm. CDT.
(Or if you're EDT, then you are 4 hours off).
If you want, say your 10 pm CDT chart, then you need to go to
the 7/25/2008 chart for 0300 Hr Universal time, or even 0400 Hr
for your 11 pm local time. You are 5 hours behind total darkness
for your time zone!  Spica (Alpha Virginis) is currently very low in the WSW as darkness falls now. Virgo is a springtime evening sky
constellation (area of sky).

To be more specific, bright Jupiter right now is due south at
midnight local time. Before that, say around 10 pm the first magnitude star due south is Antares (Alpha Scorpii) so maybe
that's the object, that red supergiant but it's even slightly
lower than Jupiter. You'll just have to find the correct star
chart for the correct time frame, if you want proof positive
identification, if you don't know your night sky.

Us real astronomers never see a light that we can't identify,
because we know the sky so well. So no, there is no general term
other than borrowing the term "temporary unidentified object", but
it generally doesn't stay unidentified very long, once you get
a telescope on it. I've only ever had it happen twice in 50 years.

You heard completely wrong, in fact it's the REVERSE!
99.99% of all astronomers do not buy into UFO's, alien life visitations, ouiga boards, ghosts, goblins, astrology, zombies,
Big Foots, Nessies, flying saucers, or any other of that occult (non-science) stuff.   We know better.
Land one in my backyard in broad daylight, then I might, just might, consider it...after I check out its authenticity.
But don't bring me any "lights at night" or fuzzy photographs.
Clear Skies,
Tom Whiting
Erie, PA