Altitude and azimuth for fixed objects at different locations

Obj:   Name   RA (h)   Decl (°)      
Loc:   Name   Lat (°)   Long (°)      

LST (h:m)HA (h:m)Alt (°)Az (°)Rise (UT)Set (UT)

Degrees/hours minutes and seconds calculator: ° ' " = °


h m s

This script provides the local sidereal time (LST), hour angle (HA), altitude and azimuth at a specific time and location, and also rising and setting times on the same civil day, of fixed distant objects given in terms of right ascension and declination. Up to ten objects and locations can be saved using cookies. (For this, you must activate cookies in your browser.)

Only objects with fixed locations (stars, deep sky objects, the vernal equinox, the galactic centre, etc.) can be tracked accurately with this script. The objects must be given by Right Ascension (in hours) and Declination (in degrees). Your location is given in terms of longitude and latitude (in degrees), with longitude west being negative and longitude east positive. You will have to convert values to decimals manually if they given are in terms of hours/degrees, minutes and seconds, or use the DMS calculator provided and copy and paste the values.

There are some oddities about rise/set times. This program computes the rise/set times in the sidereal day starting at 00:00UT of the civil day given. (A sidereal day is slightly shorter than a civil day, so it is possible an object rises, sets and rises all in the same civil day. The program will only detect the first two of these events in the shorter sidereal day.) Sometimes an object first sets in the morning to rise again in the evening. In this case the evening rise time that is shown in the display above to the left is the later time, and the rise time shown is the earlier time on the same civil day, and not the next rise time on the next day.

The algorithm used is very simple and assumes a spherical earth. There is no correction for refraction, parallax or aberration. (In particular your location height is irrelevant for this method.) The script is useful as a quick reckoner to see whether "such-and-such is visible" at a given location and time without having to start up a more complicated planetarium program, and you can save your favourite objects or locations for when you return to this page later. For more detailed work higher accuracy algorithms will certainly be required of course.

To reduce clutter on the screen only one location and object can be seen at any one time. Each has an index (from 0 to 9) and you can select it by clicking the index button which then scolls through all available settings. Alternatively you can give an object or location a name and select it by typing its name in the second box. The values for the objects and locations are entered at any time using the other boxes.

To make a new object or location click the "new" button. If you already have ten things of that kind this will delete the oldest unnamed one (i.e. the unnamed one with smallest index). If there is no unnamed one, it will delete the oldest named one and ask for confirmation.

To delete a specific object or location, select it and click the delete button, and confirm if necessary.

All objects and locations are saved as cookies so they will be available next time you visit this page from the same computer. No personal information is stored on the server computer at any time.

Richard Kaye (