Sloan Digital Sky Survey DR14

Context

I was looking for an unused and interesting dataset to improve my data science skills on when my professor mentioned the Sloan Digital Sky Survey which offers public data of space observations. As I found the data to be super insightful I want to share the data.

Content

The data consists of 10,000 observations of space taken by the SDSS. Every observation is described by 17 feature columns and 1 class column which identifies it to be either a star, galaxy or quasar.

Feature Description

The table results from a query which joins two tables (actuaclly views): "PhotoObj" which contains photometric data and "SpecObj" which contains spectral data.

To ease your start with the data you can read the feature descriptions below:

View "PhotoObj"

• objid = Object Identifier
• ra = J2000 Right Ascension (r-band)
• dec = J2000 Declination (r-band)

Right ascension (abbreviated RA) is the angular distance measured eastward along the celestial equator from the Sun at the March equinox to the hour circle of the point above the earth in question. When paired with declination (abbreviated dec), these astronomical coordinates specify the direction of a point on the celestial sphere (traditionally called in English the skies or the sky) in the equatorial coordinate system.

Source: https://en.wikipedia.org/wiki/Right_ascension

• u = better of DeV/Exp magnitude fit
• g = better of DeV/Exp magnitude fit
• r = better of DeV/Exp magnitude fit
• i = better of DeV/Exp magnitude fit
• z = better of DeV/Exp magnitude fit

The Thuan-Gunn astronomic magnitude system. u, g, r, i, z represent the response of the 5 bands of the telescope.

Further education: https://www.astro.umd.edu/~ssm/ASTR620/mags.html

• run = Run Number
• rereun = Rerun Number
• camcol = Camera column
• field = Field number

Run, rerun, camcol and field are features which describe a field within an image taken by the SDSS. A field is basically a part of the entire image corresponding to 2048 by 1489 pixels. A field can be identified by:

• run number, which identifies the specific scan,
• the camera column, or "camcol," a number from 1 to 6, identifying the scanline within the run, and
• the field number. The field number typically starts at 11 (after an initial rampup time), and can be as large as 800 for particularly long runs.
• An additional number, rerun, specifies how the image was processed.

View "SpecObj"

• specobjid = Object Identifier
• class = object class (galaxy, star or quasar object)

The class identifies an object to be either a galaxy, star or quasar. This will be the response variable which we will be trying to predict.

• redshift = Final Redshift
• plate = plate number
• mjd = MJD of observation
• fiberid = fiber ID

In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum.

Each spectroscopic exposure employs a large, thin, circular metal plate that positions optical fibers via holes drilled at the locations of the images in the telescope focal plane. These fibers then feed into the spectrographs. Each plate has a unique serial number, which is called plate in views such as SpecObj in the CAS.

Modified Julian Date, used to indicate the date that a given piece of SDSS data (image or spectrum) was taken.

The SDSS spectrograph uses optical fibers to direct the light at the focal plane from individual objects to the slithead. Each object is assigned a corresponding fiberID.

Further information on SDSS images and their attributes:

http://www.sdss3.org/dr9/imaging/imaging_basics.php

http://www.sdss3.org/dr8/glossary.php

Acknowledgements

The data released by the SDSS is under public domain. Its taken from the current data release RD14.

More information about the license:

http://www.sdss.org/science/image-gallery/

It was acquired by querying the CasJobs database which contains all data published by the SDSS.

The exact query can be found at:

http://skyserver.sdss.org/CasJobs/ (Free account is required!)

There are also other ways to get data from the SDSS catalogue. They can be found under:

http://www.sdss.org/dr14/

They really have a huge database which offers the possibility of creating all kinds of tables with respect to personal interests.

Please don't hesitate to contact me regarding any questions or improvement suggestions. :-)

Inspiration

The dataset offers plenty of information about space to explore. Also the class column is the perfect target for classification practices!

Note: Since the data was already maintained very well it might not be best dataset to practice data cleaning / filtering...your decision though.