Expert: Tom Whiting - 3/6/2004

Question
Is is a star or a planet?  I'm in San Diego and there is a really bright star to the West of Orion's Belt.  Can you please tell me what it is?
Thank you.

Answer
Hi Laurie,
I would have answered your question much sooner, but I could
not get on the allexperts website for some reason....maybe
it was down for repairs....

In any case, you gave me a location, but no time of night,
so I'll pick one.....7:30 pm PST (your time).

Yes, that is brilliant Venus down there in the western sky, well west of Orion's Belt, and reddish Mars (but not very
bright now) well above Venus, at that time.
You might also notice bright Saturn almost straight overhead, with very bright Jupiter low in the east, in Leo  now.

Obviously all these bright objects are planets, not stars...
notice how they slowly move against the background stars
from week to week.

Your brightest real star is Sirius, the Dog Star, now mid-way up in the south...and notice that Orion's 3 belt stars kind of point downward toward it. (It's a brilliant
blue-white twinkling diamond).

Being so far south, also at 7:30 pm you are fortunate to
be able to see the sky's second brightest real star,
Canopus, but its only 5 degrees above your southern horizon
at 7:30 pm, and we can't even see it up here in Erie, PA
as we are too far north to view it...it never gets above
our southern horizon at 42 degrees N. latitude.

Ok, so here is the list of your brightest 'starlike' objects
at 7:30 pm in San Diego, CA...

Venus...western sky at -4th magnitude
Jupiter...low in East at -2nd magnitude
Sirius, the Dog star at -1.5 magnitude
Canopus, very low south at -0.7 magnitude
Saturn near zenith at 0.0 magnitude
along with stars Capella and Rigel at 0 magnitude
and then there is lowly Mars at + 1.5 magnitude.

Notice that our magnitude scale is a reverse scale;
the lower the number, the brighter the object....
The full moon is -13th magnitude.
The sun is -26th magnitude.
And each whole number change in magnitude is 2 1/2 times
change in brightness....and its an exponential scale,
not arithmatic scale....

in other words, change the magnitude whole number by
1, 2, 3, 4, 5 times and its *NOT* 2.5, 5, 7.5, 10 times
brightness change...but rather...

2.5, 2.5 squared, 2.5 cubed, 2.5 to the 4th power, etc...

example: 2.5, 6.25, 16, 40, and 100....
a 5 whole number magnitude change is 100 times change
in brightness, so Venus at -4 is over 100 times brighter
than Mars now at 1.5 magnitude.

Note: I didn't invent this crazy scale of magnitudes,
I'm only reporting and explaining it to you! ;-)

Just thought you'd like to know,
and hope all this helps you...
Clear Skies,
Tom Whiting
Erie, PA

PS...oh, BTW, the naked-eye planet Mercury climbs up out
of the evening western sky in late March to be visible, so at that time, notice all 5 naked eye planets will be visible in our early evening sky from about March 20 until around
April 5...from west to east...Mercury, Venus, Mars, Saturn,
and Jupiter...all right along the ecliptic across our sky.