# Software to convert RA and DEC into ALT and AZ

I have implemented the formulas to convert AR and Dec into altitude and Azimuth in C++ following the book Practical Astronomy with your Calculator or Spreadsheet 4th Edition.

In the book there is an example to check if I have do it fine. This example works perfectly but I want to check if my formulas are correct.

I have use this page to check it but I get different minutes values in both altitude and azimuth values.

I have checked on that page that I get the same LST value, but ALT and AZ have different values. This data I have tested:

Altitude: -15° 27' 40"
Azimuth:  273° 12' 34"


This is the data get it from that page:

Do you know if there is another web page or program to check if the result of my formulas are correct?

UPDATE:
I have tried to get Azimuth and Altitude using a date in year 2000 in web page and my program and this is the result (you can find my program's result at the bottom of the image):

Is this the same problem like the previous one (I'm not taking account for precession)?

• I haven't seen the spreadsheet, but my wild mass guess is that you are not accounting for precession.
– user21
Nov 28, 2015 at 16:30
• Yes, I'm not accounting for precession. Nov 28, 2015 at 17:12

Based on stellarium, I think you're not accounting for precession (more after the picture):

As you can see, Rigel's J2000 coordinates and Rigel's current coordinates are different by about the same amount as your calculation.

• I have updated my question with a calculation for year 2000 to check precession problem. But I'm not sure what is precession. Nov 29, 2015 at 7:55