system
Given the following post, respond as if you're commenting on Reddit:
human
We've taken photos of the night sky for some time now. Is it yet possible to see parallax from us moving through the milky way by comparing old and new observations?

Since we can measure stellar parallax by the earth position around the sun, I'd imagine that our journy through the milky way would give us a lot more parallax. Or are we moving with our stellar neighbours in such a way that we don't see much drift at all?
gpt
This is what we call 'proper motion'. As the Sun moves relative to nearby stars, we see those stars have a net motion over time, in addition to appearing to move in little ellipses due to the Earth's motion around the Sun.

The key thing is *nearby stars*. Proper motion is easier to see for nearby stars, and these stars are all in a similar orbit to our Sun. So proper motions tend to be small. The scatter between the speed of stars in a similar orbit is like tens of km/s - not that different to the speed of the Earth around the Sun - although there are a few that happen to be particularly fast. Barnard's star is moving at >100 km/s relative to us, but this star has the greatest apparent proper motion out of any star we see.

Note that Gaia, the most accurate instrument for surveying proper motion and parallax, has only measured about 0.5% of the stars in the galaxy. It reaches a distance of 6,000 light years or so (there's no sharp cutoff - the data just gets less accurate and more sparse as you go further out), and it's like 25,000 light years to the centre of the galaxy. So even with Gaia, we're still looking at our nearby chunk of the galaxy, and we're mostly seeing motion relative to nearby stars in a roughly similar orbit, rather than motion relative to the plane of the galaxy as a whole.

I'll also quickly add that our speed around the Milky Way is less than 10x the speed of the Earth around the Sun, so it is faster, but it's not so extraordinarily fast that the Earth's motion gets washed out.