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chechomsky t1_j4lhozv wrote

Reply to comment by IAmAPhysicsGuy in How do we know that we are in a certain place inside our galaxy? and how do we know how big it is just by looking at the cross section we are in? by friday_panda

Our galactic “year” (time it takes for the sun to revolve around the center of the galaxy) is 230 million earth years. Is there enough rotation (I assume about 50 years of data) for us to use parallax to get a sense of our location?

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TwentyninthDigitOfPi t1_j4ljh2a wrote

The parallax isn't from the solar system's rotation around the galaxy, it's from Earth's rotation around the sun.

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[deleted] t1_j4mfxnt wrote

Yeah, you'd have to wait like 200 million years for any valuable parallax data from the Sun's orbit around the galaxy.

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Colon t1_j4myfry wrote

sounds like ancient alien knowledge becomes more and more valuable as time goes on

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cantonic t1_j4mb9mn wrote

They will look at a star when the earth is on one side of the sun, then look at the same star when the earth is on the other side of the sun, 6 months later. The change in position is about 180 million miles. How the position of the star has changed in that 6 months gives them enough information to calculate how far away the star is.

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