How Can You Determine the Right Ascension of a Star with a Meridian Circle?

[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".


Jeff

 

[JeffOCA]

Anyone ?

 

[Drakkith]

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.

 

[JeffOCA]

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.

Ok, sorry.

 

[pmacias]

,

Thank you for your inquiry about determining the right ascension of a star using a meridian circle. The method you described is known as the method of equal altitudes. It involves measuring the transit times of two stars, one with a known right ascension and one with an unknown right ascension, and then using the difference in transit times to calculate the unknown star's right ascension. This method is commonly used when there are no other stars with known right ascensions in the vicinity.

As for using the transits of the Sun as a reference star, this is possible but may not be as accurate as using other stars. The Sun's right ascension changes throughout the year due to the Earth's orbit around the Sun, so it may not be a reliable reference point. However, near the equinox, the Sun's right ascension can be assumed to be known, making it a viable option for determining the right ascension of other stars.

The Flamsteed method, named after the 17th century astronomer John Flamsteed, is another method for determining the absolute right ascension of a star. It involves measuring the transit times of a star at different altitudes and using mathematical calculations to determine its right ascension. It is a more complex method but can be used when no other stars with known right ascensions are available.

I recommend consulting with an astronomy textbook or a professional astronomer for further information and guidance on using these methods. Best of luck in your research!