SDSS Viewer Frequently Asked Questions

• What can I see with SDSS Viewer?
• What is the format for object lookup?
• What is this strange thing I see?
• Why do I get 'Object not found'?
• Why does the image say 'outside SDSS footprint'?
• Why does it take so long to look up an image?
• What is the format of play lists?
• How do I build my own Playlist?
• How do I copy between a text file and My Playlist?

What can I see with SDSS Viewer?

SDSS Viewer uses the SDSS data release 8 imaging look up tool imagecut by default.  The DR8 release covers over 14000 square degrees of sky.
Data release 7 is also accessible, covering 9500 square degrees of sky.
Images are false color composites of SDSS image data through several filters.
Images also optionally come from Digital Sky Survey 2, which covers more sky at lower resolution.

What is the format for object lookup?

The coordinate/object name entry box allows entering object coordinates or names in the following format:

[database]rightascention,declination[:scale]

where

• database is !Dss2; or !SdssDr7; or !SdssDr8;.  If omitted, SDSS DR8 data is used.
• rightascention is either degrees (200.3) or hours-minutes-seconds format (12h34m49s).
• declination is either degrees (55.193) or hours-minutes-seconds format (4h56m6s).
• scale is in arcseconds per pixel.  This defaults to 3.  SDSS native default is 0.39 arcsec/pixel, close to its resolving power.

OR

[database]objectname[:scale]

where

• database is !Dss2; or !SdssDr7; or !SdssDr8;.  If omitted, SDSS DR8 data is used.
• objectname is the name of an object to look up.  Vizier is used to convert this to coordinates.
• database is either !SdssDr7; or !SdssDr8;.  If omitted, SDSS DR8 data is used.

What is this strange thing I see?

SDSS images sometimes contain artifacts due to how they are produced:

• Green or blue lines may indicate a satellite wandered through the field of view while an exposure through a particular filter was underway.
• Black lines may be caused by dead pixels in the SDSS imaging CCD.
• Uneven background illumination from different exposure runs that are part of an image mosaic may result in an image having a patchwork effect.
• A completely black image may result from an SDSS image retrieval that only contains a portion of the image.  Zoom out on the image to see if a strip of stars appears.
• A completely black image may occur if the coordinates are for an object in the DR7 database when the DR8 database is being displayed, or vice versa.  See the coordinate topic to see how to change the coordinates to retrieve data from the other database.
• A red-green-blue 'stoplight' in an image might be an asteroid which moved between exposures for different filters.
• Red stars are caused by the false-color mapping done for SDSS images.  The mapping givesealistic-looking galaxies, but some stars appear red as a result.

Why do I get 'Object not found' messages?

These messages are displayed when you reach the end of a play list, or the beginning, for that matter.

Why does the image say 'outside SDSS footprint'?

When the coordinates for an object are outside the area covered by the SDSS database, this message is displayed in the image pane.

Why does it take so long to look up an image?

Sometimes it takes a while for the SDSS server to combine separate images in to the composit that is displayed.  This appears to be especially true of images near RA 360.  Sluggishness might also be caused by a busy SDSS server. If you never see an image, that might be a symptom of a too-tight security filter in your browser or security software.

What is the format of play lists?

Play lists are simple lines of text, one line per object.  Each line starts with the object coordinates or name (see above for the format), followed by a description.  Descriptions can contain embedded html for formatting.  For Windows PC's, playlists can be built in Wordpad and copied to My Playlist area to display via 'Load List'.  When copying a play list built in SDSS Viewer, Wordpad is a good destination for the text as well, though it must be saved as a text document to be easily used as a playlist in the future.  For some reason, Notepad does not retain the line breaks displayed in the My Playlist text window if they are pasted from there into Notepad.

How do I build my own Playlist?

To build your on list, display an object by name or coordinates, then click 'Add Object' to add it to your own list.

Tip: use 'Clear List' to clear the intro My Playlist contents.

To view the text for your list, click 'Show Text'. To hide it, click 'Hide Text'.

To view the images from your list, click 'View List'.

How do I copy between a text file and My Playlist?

On Windows, copy the contents of My PlayList by using the right mouse button to first select all the My PlayList contents, then copy them to the clipboard. Then, using WordPad, paste the contents from the clipboard to the WordPad contents, which can be saved as a text document.

To copy a text file playlist, open it using WordPad, using the right mouse button to select all contents and copy them to the clipboard. Then, paste the contents in My PlayList using the right mouse button 'paste'.