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Q: Calculating exact Longitude from Right Ascension 19h 1m 22s? ( No Answer,   3 Comments )
Question  
Subject: Calculating exact Longitude from Right Ascension 19h 1m 22s?
Category: Science > Astronomy
Asked by: cnwells-ga
List Price: $55.00
Posted: 26 Dec 2005 11:05 PST
Expires: 02 Jan 2006 15:05 PST
Question ID: 609853
This calculation is to explain and calculate how Right Ascension 19h
1m 22s can be converted into longitude.  In case additional
information is needed, this calculation is used to find the location
where the Earth & Sun at the closest point together, called a
perihelion which will be on January 4th 2006 at 15:30 UT per NASA. 
The answer which was provided is Right Ascension 19h 1m 22s,
Declination -22degrees 41.5 hours (reference:
http://www.fourmilab.ch/cgi-bin/uncgi/Solar).  I know that declination
= latitude however the question is how to calculate the longitude
which is listed as  Right Ascension 19h 1m 22s?

The answer should show:
1. How to arrive at the calculation
2. Credentials of answerer
3. Any links to provided to referenced websites.

Request for Question Clarification by welte-ga on 26 Dec 2005 15:03 PST
Hi cnwells-ga,

Just to clarify, as you likely know, right ascension is analogous to
longitude with respect to the celestial sphere.  Are you trying to
find out which point on the Earth will be closest to the sun at the
perihelion you mention?

       -welte-ga

Clarification of Question by cnwells-ga on 26 Dec 2005 17:21 PST
That is correct, I am looking for this closest point and the answer
that I have been provided for the closest point was RA 19h 1m 22s and
declination -22 degrees 41.5 hours.  The goal is to transform this
into a location on the earth. Since declination maps directly to
latitude, now I just need longitude to find this location.  Your help
is greatly apprechiated.

Request for Question Clarification by welte-ga on 31 Dec 2005 09:43 PST
Hi again,

I think that the simple approach that Myoarin mentions is the easiest
way to tackle this problem (i.e., where on the Earth is the sun
directly overhead at the time you specify).  I haven't verified his
calculation.  Is there any other information you'd like?

      -welte-ga
Answer  
There is no answer at this time.

Comments  
Subject: Re: Calculating exact Longitude from Right Ascension 19h 1m 22s?
From: vitaman-ga on 26 Dec 2005 13:54 PST
 
Your question makes no sense. The Latitude and Longitude are arbitrary
and given right there on the link you specified. You can set them to
whatever you like.
Subject: Re: Calculating exact Longitude from Right Ascension 19h 1m 22s?
From: myoarin-ga on 26 Dec 2005 18:06 PST
 
IF I understand correctly, then you are looking for the spot on earth
(Lat. and Long.) that at 15:30 UT is at solar noon (3 1/2 hrs east,
ca. 52 30' long. east, corrected for whatever adjustment may be
necessary), and the declination of 22 41' 30" lat. south.
(That is my notation of your "-22 degrees 41.5 hours", since I believe
you mean 41.5 minutes).  That would be east of southern Madagascar.
Is that close enough  - without adjustment -  since NASA provides only
15:30 UT, which seems an unusually "round" figure?

Regards, Myoarin
Subject: Re: Calculating exact Longitude from Right Ascension 19h 1m 22s?
From: cnwells-ga on 02 Jan 2006 15:05 PST
 
The timezone method actually puts you in Southern Brazil, 12:30pm
local time which is where I am (searching for the location).  However,
I need the calculation based off the Right Ascension per an astronomer
to find the exact location.  Thank you for your help.

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