Monday, June 6, 2011

Why doesn't our view of the stars change?

It seems that if you look at a model of the solar system, wouldn't it only make sense that we should have a slightly different view of the stars every night if the earth's position is changing? And the view would change entirely between fall to spring, or summer to winter. How is it that we always see the big dipper, and the north star, etc?Why doesn't our view of the stars change?
It does, it's called parallax.



It's one way in which we can measure the distances to some of the closer stars.



The apparent distance they ';move'; though is very small, since they are exceedingly far away and the diameter of our orbit around the sun is comparatively tiny.



To put it in perspective, for light to travel the diameter of our orbit it takes about 17 minutes. The closest star is over 4 light years away. If our orbit was 1 inch in diameter, Alpha Centauri would be 2.2 miles away.



Here's a nice illustration:

http://en.wikipedia.org/wiki/File:Stella



And the full article:

http://en.wikipedia.org/wiki/Parallax



Here's another nice, and interactive, illustration:

http://sci2.esa.int/interactive/media/flWhy doesn't our view of the stars change?
Our view of the stars *does* change throughout the year. The following link will show you the seasonal constellations, and the ones you see all year round, in the northern hemisphere.



http://www.windows.ucar.edu/tour/link=/t

.
You REALLY need to go outside and do some REAL observing through an entire year. The positions of all the constellations, including the circumpolar constellations and aster isms like the Big and Little Dippers change constantly at the same time of day throughout the year. The bowl of the big dipper that was 9 o'clock at around 10 pm CDT in mid August is at 8 o'clock right NOW (and the sun hasn't set yet and the skies are overcast in Norman, OK) and the star at the bottom left corner of the bowl will be below my northern horizon at latitude 35.2 degrees N at 11:36 pm CDT, according to Stellarium 0.10.2. because of the apparent motion of the sun through sky. Ursa Major, Ursa Minor Draco, Cassiopeia, and Cepheus are all circumpolar constellations, Which is why we can see them all of the year, but the coordinates of the stars of circumpolar constellations change through one day because of Earth's rotation, and change position at a particular time of day and month because of Earth's rotation around the sun, That's why you see Scorpio above your southern horizon in mid August and Taurus and Orion above your southern horizon after sunset 6 months before and after mid February.

No comments:

Post a Comment