Expert: Tom Whiting - 1/31/2009

Question
Its about 7 PM and I am able to look out and see Venus along with the moon.  But Venus is closer to the sun then we are.  The earth is faced toward space at night--not toward the sun.  So why is it we can see Venus at night if we are facing the wrong direction?

Answer
Hi Doug R..
Obviously, we are NOT facing in the 'wrong' direction.....
Well, it's not an instant 180 degree flip from high noon to
7 pm or midnight.  We rotate once in 24 hours, so we get a view in
all directions out into space during that 24 hour period.  AND the only part of the night sky we CAN'T see is that 30 degree angle
(wedge of sky)  around the sun (15 degrees of sky just before sunrise, plus where the sun is, and 15 degrees of sky right after sunset)....out of 360 degrees. So we see (every clear night) about 330 degrees of space around us in night-time darkness.
The only part of sky we can't see is that 30 degree wedge where the sun is, but wait a month, then you CAN see that part (rising just ahead of the sun around the crack of dawn), and the next eastward 30 degree wedge is not visible to us because of the sun, until the following month, and so on and so on.

Venus is currently located nearly 40 degrees EAST of the sun now
in our sky, so when darkness falls around 7 pm local time, there is Venus still nearly 2 hours from setting in the west. We are viewing
space just about 15-20 degrees east of the sun when looking to the
west, and a little more than 180 degrees from the sun when you
are looking at the low eastern sky at that time, 7 pm. And actually if you have very good vision, and it's a very clear, colbalt blue sky, AND you know exactly where Venus is east of the sun, you can see
Venus in the daylight hours too, around 3 pm Venus will be located
roughly where the sun WAS, at noon....up there due south.

As far as the moon, it makes one complete trip around the Earth in
about 29.5 days, so where-ever it is, that's when we see it. Realize
that EVERYTHING (in the equatorial part of the sky) is above your
horizon for 12 hours, and below your horizon for about 12 hours,
IRRESPECTIVE of where the sun is, or IRRESPECTIVE of any other body,
or even IRRESPECTIVE of whether or not we can actually see it!
UP 12, and down 12, because we rotate once every 24 hours.

The moon moves about 12 degrees EASTWARD every 24 hours. At new it
was in the vicinity of the sun, actually eclipsing the sun on new moon the 25th of January
See Annular - ringed- solar eclipse on
http://www.spaceweather.com
for pictures of same.  So here we are 3.5 days later, so the moon
has moved eastward 12 x 3.5 = 42 degrees east of the sun, and thus
just about where Venus is too...so we see both together in the night sky rrespective of who is closest to the sun in their orbits.
But wait a night or two and the moon will dramatically move farther
eastward....toward first quarter phase, due south at sunset, or
90 degrees from the sun.  (Full moon is a week later, 180 degrees
from the sun, and last quarter the following week is 270 degrees
from the sun (rising around midnight) and a week after that you're
back to new moon....the moon near the sun again, and thus invisible
to us.  That's the way it works, month after month after month.

Remember we watched a bright Jupiter - Venus conjunction near the end of 2008, but Jupiter is the 5th planet and Venus the 2nd, but they were still both in the same part of sky because Jupiter was almost ready to pass BEHIND the sun from our viewpoint, whereas Venus was just swinging out from behind the sun.
These near alignments happen all the time in our 330 degrees of
night sky, that's what keeps the hobby interesting.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA