Horizontal + Celestial Coordinates to Geographic Coordinates

[Weskhan]

Hey everyone,

I cannot seem to figure this out and I'm having a hard time finding any guides online for this stuff. All I can find are calculators. I was wondering if it would be possible to calculate my Geographic Coordinates on Earth if I had the Horizontal and Celestial coordinates of a celestial body as well as the date, time, etc. Could anybody give me hints on this? I've been trying to figure it out for awhile.

Thank you!

 

[Philosophaie]

Well you have Right Ascension and Declination which are Celestial Coordinates.

They are fixed in the Sky.

Right Ascension is a product of: Local Sidereal Time + 15*(hour + min/60 + sec/3600 - Timezone - dst) + Longitude.

Local Sidereal Time is the distance in degrees from the Vernal Equinox.

DST is Daylight Savings Time 1 for on and 0 for off.

Declination is just the Latitude.

Hour Angle = Local Sidereal Time - Right Ascension

From Hour Angle, Latitude and Declination you find Azimuth and Altitude or Horizontal Coordinates.

 

[Filip Larsen]

I can recommend "Practical Astronomy with your Calculator" by Peter Duffet-Smith. You should be able to find a copy in your local library or, if you know how to use google, on the net.

 

[Weskhan]

Thanks guys, I'll check out the book. Philosophaie I think you misunderstood. I am looking for calculate MY Geographical coordinates (longitude and latitude) from KNOWING the Celestial coordinates (right ascension, declination) of a celestial body AND the Horizontal coordinates of that body (azimuth, angle). I can't figure out how to reverse the calculations. :(

But thanks!

 

[Weskhan]

I couldn't figure it out :( I have very very little experience with Astronomy. Is there anyone who could maybe help me out a little more? Thanks...

 

[Philosophaie]

Latitude = Declination.

LongitudeEast = Right Ascension - (Sidereal Time + 15*(hour + min/60 + sec/3600 - TimezoneEast - dst) ).

where hour, min and sec are in local time.

TimezoneEast (Eastern=-5) where East is positive.

dst =1 for Daylight Savings Time and dst = 0 for not.

Sidereal Time is LMST = (18.697374558 + 24.0657098244191 * d) + LongitudeEast
where d = JulianDate-2451545

Do the math.

 

[Filip Larsen]

I kind of missed that you wanted to calculate latitude and longitude from azimuth and elevation of a known star at a known time, and the other way around.

What you ask for is in general and in practice a bit more complicated to perform than the reference I suggested can hope to explain. Perhaps you can search for "celestial navigation" and "sight reduction"? It seems there are some good site that tries to explain this, like for instance [1], but as the subject is involved it may require some effort on your part. If you want a more simple approach you can perhaps follow the guide at [2].[1] http://www.celnav.de/
[2] http://www.eaae-astronomy.org/WG3-SS/WorkShops/LongLatOneStar.html

 

[Philosophaie]

Note: LMST = 15* (18.697374558 + 24.0657098244191 * d) - LongitudeEast where d is the time in days since 1-1-2000 @00:00:00 and LongitudeEast is in Degrees.

 

[Philosophaie]

Declination is only equal to Latitude when Azimuth = 0 and Altitude = 90deg or straight up. Other than up:

Declination = asin(sin(Lat)*sin(Alt) - cos(Lat)*cos(Alt)*cos(Azi)