The Expanding Universe

Thinking about regression, I came across Edwin Hubble's data in the Astronomy magazine and found out that the scatter-plot of the data Hubble gave played a central role in the discovery that universe is expanding. The graph below shows the distances from earth of 24 spiral galaxies, just for kicks I plotted this in excel, the speed indicates the speed at which these galaxies are moving away from us as reported in 1929 by Hubble's data.

The scatter-plot clearly indicates a linear relationship my TI-83 reports a r=0.7842 correlation which means that distant galaxies are moving away rapidly. Astronomers believe that there is a perfect linear relationship along with the scatter caused by imperfect measurements. The two lines on the plot are actually the two-least squares regression lines. The regression line of velocity on distance is solid as indicated. The regression line if drawn of distance on velocity will be different and both lines will have different slopes.

Lesson learnt : There is a close connection between correlation and the slope of the least square regression line.

Thoughts.

Sam