• Radial:  Search the sky around a given point.
• Rectangular:  Search the sky in a rectangular region
• SQL:  Type in a SQL query directly

The names and units of fields on the query pages

• ra, dec are the sky coordinates of the search.
  • They can be entered either in degrees or in the h:m:s, d:m:s notation.
• radius is the search radius for a radial query.
  • It is measured in minutes of arc.
• u,g,r,i,z are the magnitudes of the objects in the SDSS.
  
  • These represent the fluxes of light measured in logarithmic units, through various wavebands from the ultraviolet to the infrared

The output options and formats on the query pages

• Return: the number of objects
  
  • Selecting all will return all objects
    
  • Selecting top N will return the first N objects satisfying the query
• Format: the output format
  
  • It can be HTML, when a formatted web page is returned
    
  • It can be CSV, when a comma separated, unformatted text is returned, with one header line and subsequent objects in a new line, attributed separated by a comma
    
  • It can be XML, not yet implemented