Question

How do you estimate or find a globular cluster’s distance?

Is it a formula or using a picture, any way?

Answer 1

Answer:-

The absolute magnitude of a star is the magnitude it would have at a distance of 10 pc from Earth. If we know the absolute magnitude of an ideal main-sequence star and if we can identify a corresponding main-sequence star in Cluster we should be able to calculate the distance using the difference between the absolute magnitude and the apparent magnitude from the plot. To make this work, I found B and V values of ideal main-sequence stars (from a reference source) and plotted them with my data. All I needed to do is add a correction term to the V value and vary the term until the ideal curve matched the main-sequence stars in my plot. This is the red line in the graph. The correction term is the so-called distance modulus which can be used to calculate the distance. In this case the distance modulus was 9.6 so the distance is about 832 pc or about 2700 light years. Wikipedia gives a range of 800 to 900 pc for the distance. The Excel formula for distance is d = 10*10^(DM/5) in parsecs.