<p>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?</p>

<p>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.</p>

<p>At 1:20 AM, $d=6570.055$. </p>

<p>UT is $UT=7:20$ or in hours $UT=7.3$.</p>

<p>$LST=6648.0639$ or $LST=168.0639$</p>

<p>$HA=LST-RA=168.0639-16.51=151.5539$</p>

<p>How is my calculation?</p>

CC BY-SA 3.0
2017-12-30T00:08:41.477Z
Thanks. I found this: http://www.stargazing.net/kepler/altaz.html                       Are the formulas right?
Alex S
CC BY-SA 3.0
2017-12-30T15:25:22.073Z
Your formula for LST is missing one important term: the longitude.
JohnHoltz
<star>
Finding hour angle, altitude
Alex S
# Finding hour angle, altitude

(Asked by: username_0 on 2017-12-26)

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?

**Tags:** star

> **Comments:**
> **username_0**: Thanks. I found this: http://www.stargazing.net/kepler/altaz.html                       Are the formulas right?  
> **username_1**: Your formula for LST is missing one important term: the longitude.  

---

## 0 answers

