Why do we see different constellations during summer and winter? Is it the tilt of the earth, where we are in our orbit, or both?
Its because the sun is in different parts of the background sky during different months.
Right now its summer in North America, and those winter constellations are up during the day time so you can’t see them because of the sun’s glare. By the time the sun goes down tonight, the summer constellations have rolled back around to be overhead again, the sun sets, and there’s today’s stars.
Picture the overhead sky as a sphere, with stars being ‘stuck’ to the inside, and you’re in the middle. The entire sphere rotates, so looking up with no sun, you’d see the entire set of stars in 24 hours. The sun moves along with the stars, but slightly faster (or is it slower? doesn’t matter), and it takes an entire year for the sun to go all the way around the sphere to return to the constellation it started in.
whimper
Why is the sun “in” different parts of the sky? Is it about the earth’s tilt? the earth’s rotation? or the earth’s orbit around the sun?
It is just about where we are in our orbit, because where the Earth is relative to the Sun determines which stars appear to be close to the Sun, and hence cannot be seen at night.
Okay, makes sense. Thanks to both of you!
Here’s a graphic example, just in case:
We have two constellations, A and B. The sun is O and the Earth is .
Summer:
A . O B
Winter:
A O . B
As you can see, during the summer, A is visible in the night sky, while B is obscured by the Sun during the day. In the winter, the opposite case is true.
The SDMB needs more diagrams like that!
Yes, thanks, QED, that was helpful in conceptualizing it.
On my desk I have a coffee cup and a styrofoam cup. I put about a foot apart. The coffee cup is the sun. The styrofoam cup is the earth. The desktop is the plane in which the earth will rotate the sun. I slam the styrofoam cup on the desk, denting the base on one side, so that the cup tilts toward the coffee cup. If an ant were to stand on the rim of the plastic lid facing the coffee cup, he would see the coffee cup. This is daytime (he’s facing coffee cup) during summer (tilted toward coffee cup) in the ant’s northern hemisphere (top of styrofoam cup). He sees no stars, just sun.
Since the earth rotates in position, without changing its tilt in a day, we will rotate the plastic lid to the other side of the styrofoam cup. He can now look away from the coffee cup, so we’ll call it night. He’s still tilted towards the cup, so it is summer still. It is now night, summer, northern hemisphere. He looks away from the cup, into the outer darknes of my office, and sees celestial bodies, such as the ‘computer monitor’ (Computus).
If we now move the styrofoam cup to the other side of the coffeecup, without rotating it. Now he’s on the high side of the styrofoam cup, and the cup is tilted away from the coffee cup. Since he’s tilted away from the coffeecup, he gets less sun, so its winter. If we rotate the plastic lid, he’s now on the side of the styrofoam cup facing away from the coffeecup, so its night. He looks off into the night and see the celestial body ‘office door’ (Exitus).
Day and night come from the rotation of the styrofoam cup
Winter and Spring come from the tilt of the styrofoam cup relative to the coffee cup
Constellations change because of the tilt and the position in space, that is, which side of the cup are you on.
I think you already understand it but here is an animation of earth’s orbit around the sun (this is the only one I could find and it also shows asteroid 2002 AA29.) Of course, we are only see stars by looking away from the sun, into the dark.
Q.E.D. did it all with three letters and a dot. I had to tell the story of the ant on my desk. I feel so non-cosmic by comparison.
Yeah, but I felt an emotional connection to the ant. 
I was checking this astronomy site today , before I saw your question …
Hope this helps you in some way.
It is a very good site for astronomy enthusiasts 