Azimuth and Altitude

[Philosophaie]

I am confused about the Azimuth and Altitude. What do they do in reguards to the whole picture RA, Dec and Hour Angle? Is it added to RA and DEC?

[Merlin66]

Altitude and Azimuth (Alt-Az) define an alternative location system, based on the altitude of the object above the horizon and the angular distance azimuth measured from North - like a compass.

Alt-Az has nothing to do with the Equatorial Coordinates.

You can convert star positions from one system to another, most of the Planetarium programs (Stellarium, Carte du Ciel etc, both freeware) do this automatically. The mathematics of the conversion (Equatorial> Alt-Az) involve knowing the observers latitude, local siderial time, RA and Dec of the object.

Horizontal coordinate system - Wikipedia, the free encyclopedia

[Rusty Strings]

Broadly speaking, if you have a non-equatorial mount like a dob you will use Alt-Az coordinates to help locate faint objects and RA and DEC for an eq mount.

[ollypenrice]

Another way to think of it is that if you were observing on the North Pole the two systems, RA-Dec and Alt-Az, would produce (almost) the same grid on the sky. Polaris would be (almost) directly over your head and the celestial equator would be on the horizon.

Now move slowly down the globe and one of the celestial grids changes. By latitude 45 it is now at a 45 degree tilt with respect to the other. Polaris is at 45 degrees above the horizon. The grid that has changed is Alt Az. The RA-Dec grid is always located as for the North Pole.

Olly

[MikeP]

Have a look through this site, it should answer your question.

Introduction to Spherical Astronomy

Mike

[brantuk]

If you download Stellarium (free plaetarium software) it has buttons to put an alt-az or ra-dec grid on the screen (or both). It's a good visual illustration of the difference.