Selecting an Object to Image


Of all things in Nature, astronomical objects make up some of the most gorgeous photographs ever made. Now that you are able to identify basic types of deep sky objects and have selected a type of object to image in color, it is time to choose the exact object to image. In this activity, you will select an object to image based upon criteria such as object apparent size, apparent magnitude, and visibility in the sky.


In order to obtain a quality color image of a deep sky object, several criteria must be met. First, an object needs to be selected that can be readily imaged by the telescope and CCD camera system available. In the same way it would be foolish to photograph an elephant with a camera designed for close-ups, the astronomical object must 'fit' the telescope/camera system available. The object must also be visible during night-time hours from the observatory to be used. Factors that affect visibility include latitude of observatory, season, and time of night. Also, the object's apparent magnitude must not be too dim or bright for the telescope/camera system.


Students will use any available planetarium software (ex The Sky, Starry Night, Redshift) to look for objects to image. Any software used should be set with the following criteria: 1. Date & time set to when images will be acquired.

2. Location set to latitude and longitude of observatory.

3. Many forms of planetarium software will filter their display to only certain types of objects, and even magnitude ranges. Set these as your computer skills allow, they will aid the search.

Now that the software is displaying objects visible, the next thing to consider is what requirements the telescope/camera system has. For example, there is no point in trying to image a magnitude 22 object if the scope only gets to magnitude 14. What you need to know about any telescope/camera system includes field of view and limiting magnitude. For the Yerkes 24" used by HOU the field of view is 5.2 X 5.2 arc-minutes and the limiting magnitude is 18th magnitude.

In summary, to select an object to image you need to find an object of the correct type, visible at the time of the project, visible from the location of the observatory, that fits with the telescope's field of view, and is not too dim for the telescope/camera system!