General Q: How do you measure a Galaxy's distance?

Click For Summary

Discussion Overview

The discussion revolves around methods for measuring the distance to galaxies, exploring various approaches and the necessary variables involved. Participants consider both theoretical and practical aspects of distance measurement in astronomy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire whether time and diameter measurements are sufficient to determine a galaxy's distance, questioning the necessity of additional variables.
  • One participant suggests that measuring the angular size of a galaxy is complicated due to the variability in physical sizes of galaxies, making it difficult to ascertain distance based solely on angular measurements.
  • Another participant mentions the standard method of using Cepheid variable stars for measuring distances to galaxies.
  • Some participants discuss the use of redshifts and Type Ia supernovae brightness as methods for measuring distances to faraway galaxies.
  • Parallax is raised as a potential method for measuring distances, but participants note that it is not applicable for galaxies due to their vast distances.
  • A proposal is made to launch probes similar to Gaia to measure distances using parallax, though concerns about feasibility and cost are expressed.
  • One participant reflects on the limitations of current parallax measurements and their implications for triangulating distances within the galaxy.

Areas of Agreement / Disagreement

Participants express a range of views on the methods for measuring galaxy distances, with no consensus reached on the sufficiency of the proposed variables or methods. Multiple competing approaches are discussed, indicating ongoing uncertainty in the topic.

Contextual Notes

Limitations include the dependence on the definitions of variables like diameter and time, as well as unresolved questions regarding the applicability of different measurement methods to various types of galaxies.

StillLearningToronto
Messages
9
Reaction score
1
If I am given the variable of time (observed), and diameter is it possible to measure the distance of a galaxy? Or do I need more variables?

Just trying to figure out the most simple way to go about doing something like that.
 
Astronomy news on Phys.org
StillLearningToronto said:
If I am given the variable of time (observed), and diameter is it possible to measure the distance of a galaxy? Or do I need more variables?

Just trying to figure out the most simple way to go about doing something like that.
Time and diameter of what?
 
russ_watters said:
Time and diameter of what?

Im trying to figure out if its possible to measure the diameter of an object (in MPC)
With the variables time (say I've observed something for 10 years)
And after the 10 years I resolved that the diameter of the object is some angle in arc seconds.

Or would I need more information to figure out distance to that object?
 
StillLearningToronto said:
Im trying to figure out if its possible to measure the diameter of an object (in MPC)
With the variables time (say I've observed something for 10 years)
And after the 10 years I resolved that the diameter of the object is some angle in arc seconds.

Or would I need more information to figure out distance to that object?
Well, it doesn't take 10 years to measure the diameter, so that time doesn't really tell you anything. I don't see how this can lead to a distance measuremeng.
 
StillLearningToronto said:
Just trying to figure out the most simple way to go about doing something like that.

hi, welcome to PF

to specifically answer your thread title ...

General Q: How do you measure a Galaxy's distance?

The standard is to use Cepheid variable stars

do a google search on that and you will come up with lots of info
Dave
 
  • Like
Likes   Reactions: russ_watters and Nik_2213
For Galaxies that are far away, red shifts and IA supernovae brightness.
 
Calculating the distance from the angular size doesn't really work, because galaxies vary so much in physical size. For example, the Small Magellanic Cloud is a nearby galaxy that is about 7000 light-years across, and a large elliptical like M87 is over 200,00 light-years across. If you measure the angular size, how could you tell if it is physically small and nearby or physically large and further away?
 
  • Like
Likes   Reactions: davenn
Are you asking about parallax ? It is possible to use time and the diameter of Earth’s orbit to measure the distance to far away objects. But this method is not used for determining the distance to other galaxies; those distances are much too far.
 
  • Like
Likes   Reactions: russ_watters and stefan r
LURCH said:
Are you asking about parallax ? It is possible to use time and the diameter of Earth’s orbit to measure the distance to far away objects. But this method is not used for determining the distance to other galaxies; those distances are much too far.

Parallax was used to determine that galaxies are in fact to far away to measure.

We could measure the distance to the galaxies with parallax. Launch 2 Gaia like probes out of the solar system in opposite directions. The probes would require a very large power supply and would need to function for a long time. Would also need a more powerful transmitter. Gaia cost over a $billion so not likely to happen soon.
 
  • #10
stefan r said:
Parallax was used to determine that galaxies are in fact to far away to measure.

We could measure the distance to the galaxies with parallax. Launch 2 Gaia like probes out of the solar system in opposite directions. The probes would require a very large power supply and would need to function for a long time. Would also need a more powerful transmitter. Gaia cost over a $billion so not likely to happen soon.

That got me thinking about a somewhat unrelated question. I wonder how far away we could triangulate with the current voyager baseline (not that they have the perfect telescopes for this purpose, but say they did). V1 is 1.8e13 m from earth, so a 1 arcsec quality parallax measurement would let you triangulate about 400 light years. Not very far, really. You would need 1/50 arcsecond measurements to even be able to measure the distance to the galactic center.
 

Similar threads

Undergrad Question of accuracy of galactic collision simulations
  • · Replies 11 ·
Replies
11
Views
2K
Undergrad How do we measure the velocity of stars in a galaxy?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Measuring distance to a galaxy using natural H20 laser
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Orbital Velocities and Mass Distribution in Galaxies
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad How Can We Measure Properties of Distant Planets and Stars?
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad How do you get to the conclusion that there is accelerating expansion?
  • · Replies 23 ·
Replies
23
Views
3K
Undergrad Are there galaxies with 2 cores?
  • · Replies 9 ·
Replies
9
Views
3K
High School Are There Any Kardeshev 2.0 Civilizations in the Milky Way?
  • · Replies 19 ·
Replies
19
Views
4K
High School Why most stars seem to rotate the same direction in a galaxy?
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad The use of 3D reconstruction techniques to build a galaxy model
  • · Replies 4 ·
Replies
4
Views
3K