- #1
Mohammed_I
- 8
- 0
I have read somewhere that the parallax method can be used to measure the distance to stars up to 400 light years away. I did a quick calculation and estimated that it means that our telescopes can resolve an angular movement of 8.15x10-3 arc seconds.
Taking the distance between the sun and the galactic center to be 24,136 light years, and assuming the sun orbits it at a tangential velocity of 220 km/s. That is a total angular movement of 0.31 arc seconds over a 50 year period, easily measurable I assume.
However, if you try to apply the same method to measure the velocity of a star in say the Triangulum Galaxy, it doesn't seem possible. Let's say the distance between us and the galaxy is 2.725x106 light years, and we are trying to measure the velocity of a star 35 arc minutes away from the center (that is 27,744 light years away). And let's also say that this star is orbiting at a tangential velocity of 200 km/s. That is a total displacement of approximately 0.03 light years over a 50 year period, or if we convert it to angular movement from our perspective, 2.52x10-3 arc seconds over a 50 year period.
So do we have a telescope with this resolution that has been around for 50 years? And even if that is the case, what do we do with galaxies that are further away?
Taking the distance between the sun and the galactic center to be 24,136 light years, and assuming the sun orbits it at a tangential velocity of 220 km/s. That is a total angular movement of 0.31 arc seconds over a 50 year period, easily measurable I assume.
However, if you try to apply the same method to measure the velocity of a star in say the Triangulum Galaxy, it doesn't seem possible. Let's say the distance between us and the galaxy is 2.725x106 light years, and we are trying to measure the velocity of a star 35 arc minutes away from the center (that is 27,744 light years away). And let's also say that this star is orbiting at a tangential velocity of 200 km/s. That is a total displacement of approximately 0.03 light years over a 50 year period, or if we convert it to angular movement from our perspective, 2.52x10-3 arc seconds over a 50 year period.
So do we have a telescope with this resolution that has been around for 50 years? And even if that is the case, what do we do with galaxies that are further away?