Asteroid Observability
Suggestions and Interpretation


OBS builds a plot that indicates when an asteroid is observable. Observability depends on declination, solar elongation, ephemeris uncertainty, magnitude, and galactic latitude. Each of these five parameters is plotted separately. At the bottom of the plot, windows of observing opportunity are indicated.

Using the various parameter plots, the user can see why an asteroid is not observable at a particular time. Armed with this information, the user can sometimes devise a way to get a required observation.


Cookies are used to store default values for the user. Defaults are stored for the following parameters:

  1. Observatory Code
  2. Maximum Zenith Angle
  3. Minimum Galactic Latitude
  4. Limiting Magnitude
  5. Minimum Probability of Imaging
  6. Field of View in RA
  7. Field of View in Decl

Many users suppress the use of cookies on their browsers. If you choose to suppress them for this application, you will have to supply the listed parameters each time you visit this service.

User Supplied Parameters


The graph produced by the web page will have time plotted on the horizontal axis. The vertical axes pertain to five separate panels: Declination, Ephemeris Uncertainty, Solar Elongation, V Magnitude, and Galactic Latitude.

Each panel will have a horizontal line indicating the limit you specified for your instrument or location. A dashed line indicates that the asteroid is not observable because it does not meet your specified criterion. A solid line indicates that that the parameter meets your criterion.

At the bottom of the graph is a panel that indicates windows of observing opportunity; that is, when the asteroid meets all your observing criteria. The windows are denoted by grey areas.


Suppose you find that an asteroid meets all your observing criteria except galactic latitude. It might still be possible to observe the asteroid but it would require that you take a few more images than normal so that you can find the asteroid separated from the surrounding stars. It might also require that you study the images longer to find the moving object.

If the object in need of observations is observable except that it is too far north or south, you would probably request that someone in the other hemisphere make the observation for you. Likewise, if only the object's faint magnitude is preventing a required observation, then you can request that someone with a more powerful instrument make the required observation.

When the Solar elongation is too small, there is generally nothing that can be done but wait.

Finally, if the uncertainty is too large, you can request observations from someone with an instrument having a larger FOV. Or you can go on a search campaign and take lots of images covering lots of sky.

If there are multiple reasons preventing observations, it will be much more difficult to get a required observation. For example, a very faint object with a large uncertainty would require an instrument with a large FOV and a large aperture. Such an instrument might not be available. These situations have to be evaluated carefully, considering the effort required for the observation and the value of the observation.

Last updated 10 Sep 1999
Contact: Bruce Koehn (
Web Curators: Ted Bowell and Bruce Koehn

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