Astronomers measure positions of objects on the sky using units of angle. These units make sense because almost everything we see in the universe is so far away that our eyes cannot discern depth. So for the purpose of knowing "where to look" to find an object one only needs to specify two angles, one that tells you where to look in the east-west direction and one that tells you where to look in the north-south direction. These angles are very similar to latitude and longitude, angles that are used to specify locations on the surface of the Earth. On Earth, lines of equal longitude and latitude are fixed on the Earth's surface. Thus, when you specify the position of Albuquerque as latitude: +36 degrees, longitude: 108 degrees E. you know that those coordinates will always be the same.

If you think of the sky as a sphere on which all celestial objects are embedded then you can imagine lines of equal longitude and latitude inscribed on that sphere just like on the Earth. However, there are two major differences. First, astronomers call these angles Right Ascension, or RA (which is analogous to longitude) and Declination, or DEC (analogous to latitude). Second, the celestial sphere appears to rotate with respect to an observer on the earth because the Earth itself is rotating. Thus, the coordinate system of the sky keeps changing. However, if you think of the celestial coordinate system as being fixed to the sky then you know that any static celestial object will have a fixed coordinate. Because of Earth's rotation, astronomers have decided to measure the Right Ascension angle in a somewhat different way. Rather than dividing the east-west direction into degrees they have chosen to use units of time. Thus the 360 degrees of east-west direction is divided into 24 hours (because that's how long it takes for the Earth to rotate once). Each hour is divided into 60 minutes of time and each minute is divided into 60 seconds of time. In the case of declination, it's just like latitude, it runs from +90 degrees to -90 degrees. Each degree is divided into 60 minutes of arc and each minute of arc is divided into 60 seconds of arc. Just to give you an example, the coordinates of Deneb, the brightest star in the constellation Cygnus, are RA: 20 41 24, DEC: +45 17 00. The Right Ascension is 20 hours, 41 minutes and 24 seconds while the Declination is +45 degrees, 17 arcminutes and 0 arcseconds. See if you can find its location on the celestial sphere below. For more details about the celestial coordinate system visit THIS LINK .

To use the observatory you simply enter the RA and DEC for the object you want to view. You will be given a choice of viewing an image taken using a blue filter or a red filter. Remember the filter exercise from an earlier lab: a filter blocks out light based on its color. Thus a red filter allows red light to pass but not blue light. A blue filter does the opposite. On telescopes they are made of glass.  The field of view simply specifies the amount of the sky you want to view. The default is 15 arcminutes on a side. The actual field of view you will need is shown in the tables.