March 18, 2012
Milady was able to collect all of the data we will need from NASA web sites in a downloadable CSV file which is being shared via DropBox along with our sketches, code and prototypes. In addition to the CSV file she created a guide for understanding the data and mission to aid in completing the final visualization:
The Kepler mission surveys a region of the Milky Way galaxy to detect, identify and characterize planets in or near the habitable zone (region around a star where a planet with sufficient atmospheric pressure can maintain liquid water on its surface). The spacecraft is located in an orbit that permits continuous targeting of a single stellar region.
The Kepler field or plane is defined as stellar coordinates l = 76.32°, b = +13.5° (RA=19h 22m 40s, Dec=+44° 30' 00'. RA (the equivalent of longitude) means right ascension, and Dec (the equivalent of latitude) means descenscion.
Data from the spacecraft is downloaded and archived as original data. Data then is sorted and analyzed or processed along with engineering data files (equipment performance). Finally, astronomical data is released publicly through different media while support data is maintained by NASA, while complying with astronomical data standards.
The Mikulski Archive for Space Telescopes (MAST) supports NASA’s astronomical data archives, as well as the Kepler Exoplanet Archive (Caltech.edu). The latter site allows retrieval of data for the 2321 data points on record. The team chose to use the latter standardized data which is downloadable in CSV format. A data dictionary:
and additional documentation on astronomical data is available at the site:
Considering the massive amounts of non static data available, our challenge was data reduction and attributes selection: which parameters or attributes do we need to select to complete our artistic rendition or visualization yet representing scientific data factually, given the many ways to calculate or utilize many of the exoplanets parameters available.
The Kepler Exoplanet Archive contains approximately 108 attributes (file is updated periodically). Only fourteen (14) attributes are being used for this visualization. The remaining attributes are not required for meeting the objective of this visualization.
Data was verified using Google Refine in search of aberrant values, unnecessary spaces or signs of data in need of normalization. Data did not need additional action from the team.
The details on the 14 attributes are as follows:
Kepler id – Sequential number used to identify the planet/star
Effective temperature – Temperature of a body such as a star or planet. It is the temperature of a black body that would emit the same total amount of electromagnetic radiation. It is expressed in Kelvins.
Right Ascension – Stellar or galactic coordinate equivalent to terrestrial longitude. It is expressed in hours, minutes and seconds related to positions on the celestial sphere. It is also measured in degrees equal to Descenscion or Declination (Each hour in RA equals an angle of 15 degrees in the celestial sphere, totaling 24 hours).
Descenscion – Stellar or galactic coordinate equivalent to terrestrial latitude. It is expressed in degrees to time (minutes and seconds).
Surface Gravity – Gravitational Acceleration at the surface of the astronomical object.
Stellar Radius – Center to edge of a planet/star. Not a reliable measure due to gaseous nature of some astronomical objects.
Stellar Mass – The mass of a star usually expressed in terms of the sun’s mass (solar = 1).
Kepler Name – Name for confirmed planets.
Kepler Object of Interest Type – Type or classification for planets:
Candidate, Candidate FOP (Follow-up Program), Confirmed or False Positive.
Galaxy – Flag to identify a Star or a Galaxy
Planet/ Star Distance (AU) – astronomical unit (AU) or 149.6 million kilometers.
Planet Radius – It is usually measured in Jupiter radii (44400 miles). Earth’s radius is 0.09 Jupiter radii.
Planet Radius Uncertainty – Factor to support variability in results due to lack of precise measurement (related to distance and variability caused by an expanding universe).
Planet/Star Distance Uncertainty – Factor to support variability in results due to lack of precise measurements (related to distance and variability caused by an expanding universe). Measured in AUs.