The real power in data analysis is realized when we study how different variables relate. At the end of the previous section, we related income and gender, that is, a quantitative variable with a categorical one. In this section, we will investigate scatterplots, which are a graphical representation of the relationship between two quantitative variables.
To illustrate how Pandas can be used to explore the relationship between two variables, we will use an important example from the history of astronomy. Astronomer Edwin Hubble, in 1929, published a very important paper where he discovered that there is an approximately linear relationship between the distance and velocity of extragalactic nebulae. This was the foundation that would come to be the big bang theory.
A reprint of the article is available at http://apod.nasa.gov/diamond_jubilee/d_1996/hub_1929.html , where the data was obtained from. Notice that the dataset is very small and simply...