Reaching for the stars with SAS Visual Analytics
A rather unusual use of SAS Visual Analytics - but why limit spatial analysis to locations on Earth? ESA released back in 1997 the Hipparcos-2 catalogue which claims accuracies for nearly all stars brighter than magnitude Hp=8. The satellite, which operated for four years, returned high quality scientific data from November 1989 to March 1993.
So looking at the data - I wanted use SAS Visual Analytics to produce a nighttime star chart. The main challenge was the conversion of coordinates. On earth we use latitude and longitude whereas star locations are recorded in declination and right ascension instead. The values for declination can directly be used for latitude, because they are measured in degrees, minutes, seconds. Right Ascension, however, is measured in hours, minutes and seconds. There are 24 hours of right ascension, and 360° of longitude. I also decided to produce two separate maps - one for the Northern Hemisphere and one for the Southern Hemisphere. Each map is based on an Esri map using the North Pole and South Pole Stereographic projection.
A static high resolution screenshot is here:
A short screen cast video showing some of the interaction can be viewed here:
[ Data: Hipparcos-2 catalog (unchanged), Attribution: ESA, 1997, The Hipparcos and Tycho Catalogues, ESA SP-1200, License: CC BY-SA 3.0 IGO, Music: "Stars" by Sabine Bloch, Fachhochschule Dortmund, CC-BY 4.0]
The SAS Visual Analytics report consists mainly of geo objects. The center map is a Geo Line-Coordinate map which represents stars magnitude 5 or higher in either Northern or Southern Hemisphere. I'm using a Geo Line layer to render some well known constellation lines.
The top right and bottom left geo map is a Geo Coordinate object showing an aggregated view per square degree of the sky. I'm using an aggregation here to avoid having to render thousands of data points. The bottom right geo map is a Geo Contour object using the raw star data. This works fine as the object has aggregation built-in and renders dense and low-density areas using contour lines. This nicely shows low/high concentration of detected stars.
The report is interactive as shown in the video - allowing the user to select individual stars and explore related properties. The report viewer may also use other visuals to narrow down a search for example by selecting a desired color spectrum.
Enjoy
