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Q&A: General Astronomy and Space
Science |
Q:
Why can't we see the autumn constellations in the night sky in the
spring?
A:
You can generally think of star constellations as fixed in position and
not moving -- the stars are so far away that over a human lifetime they
don't really change position, for the most part. The Earth, however, does
move -- it completes one orbit around the Sun every year. At night, we
see the stars that are in the direction opposite the Sun. That is, at
night, you're looking out into the universe in a particular direction
-- and this direction changes as the Earth orbits the Sun:
E
*
*
A* * <-E1 Sun E2-> * B *
* *
E
So in one season the Earth is at E1, and at night
you're looking toward constellation A (constellation
B is overhead when during the day). In another
season, the Earth is at E2, and at night you're
looking toward constellation B (constellation A
is then overhead during the day).
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