# Finding hour angle, altitude

I know the latitude and longitude of a city ($41^\circ 87'$ N, $87^\circ 62'$ W), the declination and right ascension of a star($16.51^\circ$, $68.98^\circ$) and the local time, date (27.12.2017, 1:20 AM). Could you please show me the exact calculations for hour angle, altitude?

I will use the formula $LST=100.46+0.98d+15UT$, where d is the number of days since 1.1.2000 at 00:00 and UT is the universal time.

At 1:20 AM, $d=6570.055$.

UT is $UT=7:20$ or in hours $UT=7.3$.

$LST=6648.0639$ or $LST=168.0639$

$HA=LST-RA=168.0639-16.51=151.5539$

How is my calculation?

• Someone should do an answer-your-own-question here to provide basic astronomy formulas, but, until then, try googling. There should be plenty of resources online.
– user21
Commented Dec 27, 2017 at 13:25
• Minor note: I think you mean 41.87N and 87.62W; if you're using minutes (the apostrophe), they would be between 0 and 59. Also stjarnhimlen.se/comp/tutorial.html is the closest thing I found to a list of formulas that might help you.
– user21
Commented Dec 28, 2017 at 14:36
• Thanks. I found this: stargazing.net/kepler/altaz.html Are the formulas right? Commented Dec 30, 2017 at 0:08
• Shouldn't $d$ be computed in UTC days, not local time days?
– user21
Commented Dec 30, 2017 at 4:31
• Your formula for LST is missing one important term: the longitude. Commented Dec 30, 2017 at 15:25