The Distance to the Hyades Cluster


Table 1: Data and Distance for the 10 Marked Stars

Star Number
on Fig. 4		 Radial Velocity
(km/sec)		 Angle q Transverse
Velocity
(km/sec) 		Proper Motion
(arcsec/year)		 Distance (parsecs)
1 31.6     0.151  
2 31.0     0.121  
3 36.6     0.124  
4 38.3     0.114  
5 43.8     0.120  
6 38.2     0.098  
7 39.3     0.100  
8 38.6     0.108  
9 43.6     0.079  
10 38.8     0.065  
 Average
Distance:
 Error in
Distance:




  1. Give two reasons why distances to individual stars vary from each other.

     

     

     

     

  2. Could the distance to the Hyades be determined by annual parallax? Discuss.

     

     

     

     

  3. Using criteria of your choice, what is the diameter of the Hyades in parsecs?

     

     

     

     

  4. What is the mean distance in light years to the Hyades? What is the diameter of the Hyades in light years?

     

     

     

     

  5. The Hipparcos satellite was able to measure the parallaxes of 200 Hyades stars reliably. The distance to the Hyades's center of mass has been pinpointed at 46.34 +/- 0.27 parsecs, or 151 +/- 0.9 light years.
    1. Compare your (albeit crude) results to the Hipparcos results. In general, the convergent point method gives larger distances than other distance-finding methods used for clusters. Does the value you calculated follow this trend? Theorize on why the distances using this method tend to be systematically larger. (We are looking for your thoughts here.)

       

       

       

       

    2. Why is it significant that Hipparcos has parallaxes for so many stars?

       

       

       

       

    3. If the distance to the Hyades has been better determined by the Hipparcos satellite through measured parallaxes, is the convergent point method still useful? Think of one reason why the method might still be needed.

       

       

       

       

  6. The distance to the Hyades star cluster forms one of the fundamental, bottom steps of the distance scale for the entire universe. What implication does this more accurate (and precise) measurement of the distance to the Hyades have for the size of the Universe?