Ra & Dec to ALT & Azimuth Conversion.

[ribuck]

Hi Guys, I'm wondering if there are any boffins out there who can help.

I've been comparing 2 different web sites for doing the math to convert Ra & Dec to Alt & Az. I followed the instructions on the first site, lets call it site A and have replicated their results in my programming perfectly.

I then went to cross ref with a different site, lets call it site B which had a calculator on it, and when i typed in the Ra,Dec,Lat,Long,time,Date etc given in the example from the first site, the calculations for the ALT & AZ are approximately 1.5 degree's out.

I'm not sure which site to trust now.

Can someone please see if they can conver the following to ALT / AZ and see what they get.

Dec = 36d 28m

Ra = 16hrs 41.7 mins

Lat = 52d 30m

Long = 1d 55m

Date = 10th Aug 1998

Time = 23:10

Hope someone has know's of another site which can calculate this so i have something to compare my data with.

Thanks,

Ribuck

[callump]

Xephem gives me

alt: 47:52:40.5

az: 270:49:05.1

assumptions - your longitude is west, time is UTC, ra and dec are 2000 epoch.

/callump

[ribuck]

Hey Thanks Callump,

That's been an amazing help, as my results were as follows, which is pretty damned close. Think the difference will be due to the fact that i'm only using 2 decimal places in my calculations. I can refine that later.

ALT : 47.95

AZ : 270.73

The web site i cross referenced, website b had the following which seems way off, basically a degree out in both calculations.

ALT : 46:98

AZ : 271.97

Luckily i dont need to worry about the accuracy that much as it's just to drive the position of a dome relative to a Scope Ra / Dec, but it's nice to know my results were right and the other website was wrong.

Thanks for your help.

Ribuck.