# Absolute right ascensions

1. Jul 9, 2010

### JeffOCA

Hi,

With a meridian circle, you can determine the latitude of your location (Horrebow-Talcott method) but also deriving time if you know the right ascension of a star.
However, I'd like to know how to determine right ascension of a star with a meridian circle.

If you know the right ascension of a reference star, you measure its transit time. Then, you measure the transit time of the second star (the star you want to know the right ascension) and then you add the difference of transit time to the right ascension of the reference star. So, you obtain the right ascension of the second star since $$\alpha = T$$ when H=0 (at transit).

How to derive right ascension of a star when you have no other star with known R.A ? Can we use the transits of the Sun as a reference star since, near equinox, we can assume the Sun R.A to be known ?
I heard about the Flamsteed method to determine absolute R.A but I don't documents which explained it "quite easily".

Sincerely,
Jeff

2. Mar 22, 2012

### JeffOCA

Anyone ?

3. Mar 22, 2012

### Drakkith

Staff Emeritus
Jeff, you've asked a couple of very specific questions in this thread and some of your others that not many people will know. Don't be suprised if you don't get any hits.

4. Mar 25, 2012

Ok, sorry.