Explore - Main Window
The most relevant information about an object is displayed in the main window of the Explore Tool. Mouse over each section for a general overview. Links to additional information are provided.
At the top of each Expore page is the International Astronomical Union designation for the object. It always begins with "SDSS J" even if the object is associated with other catalogs or names. The remaining numbers and symbols are the right ascension (ra) and declination (dec) for the object in hours, minutes and seconds for ra and degrees, minutes and seconds for declination.
The next line of information on the Explore page begins with the designation of the object as a star or galaxy based upon visual information. Next, is the ra and dec of the object in decimal degrees. Decimal degrees is the format used almost exclusively by the SDSS for object coordinates because it is easier to manipulated in search algorithms than other formats. Object ID is the SDSS the unique identifier for the observation currently displayed. Objects may have multiple observations in the SDSS, each receives its own ObjId
First block of information below the coordinates and ObjId provides scientists with information about the object as it exists in the database and any alerts about analysis of the object. When you call up an object in Explore either from Navigate or searching by the coordinates, SkyServer will serve up the best or PRIMARY information SDSS has on the object. The mode line confirms that you are looking at the PRIMARY data for that target. Other modes exist but are not displayed unless you utilize atypical searches. You will find that the mode reference changes if you start investigating families of objects - objects that overlap in the field. Flags - Deblending and Children provides more information.
The Photometric Block
SDSS images the sky in five filters. The block of information next to the image on the Explore page contains information that is derived from, or descriptive of, the object as it was recorded by the five bands - u, g, r, i, z. Detailed explanations for this information can be found starting on the Photometric Information page.
Not all objects in the SDSS are targets for spectroscopy. There are currently over 2 million spectra in the SDSS. If an object has a spectrum associated with it, you will see it displayed on the bottom half of the Main Window. Spectral information is entirely different than photometric. Images are captured using CCD cameras while spectra require light from the ojbect be directed into a spectrograph. Because these are two entirely different processes, the spectral information has its own identification, the SpecObjID.
Spectral Data Block
This block of information is all derived from the spectra of the object. It contains the spectral data location (plate, mjd, fiberid) within SDSS; the redshift measurements (z, zErr, zConf); the classification of the object based upon its spectral characteristics (specClass); celectial coordinates (ra, dec); and the object id number associated with the best image of the object in SDSS (bestObjid).
The remaining infromation tells you mainly about the project that targeted this object for analysis and the general classification that the object was given at various points in the research. These lines are interesting when you find a mismatch between sourceType, class, and primTarget, telling you that the analysis of this object resulted in a surprise. More. . .
When the SDSS began, a decision was made to cross reference every object with certain other catalogs and surveys. ROSAT, USNO,2MASS and FIRST are the four possible Cross-identifications you can find in this section. Each survey has its own set of information listed. SDSS Cross-identifications contains a summary of this information.
The SDSS has a scientific tool that you can learn to use too. To learn more, see the Interactive Spectrum Tour.