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# Angular Separation watch

1. Hiya,

I'm really hoping someone can help me with this. I've pasted the question below.

I've found delta(alpha) and delta(delta) for each of the coordinates but i dont know how to use them in this forumla (below) to find the angle. I've tried taking one away from the other (as in delta(alpha) for proxima from delta(alpha) alpha) but i don't get what websites I've found with a calculator get. I'd type out all my calculations but I'd be here for ages. Can someone just talk me through how I go about this so I can try and see where I've gone wrong?

I'd really appreciate it.

Proxima Centauri has the epoch J2000.0 coordinates (α,δ) = (14h29m42.95s, −62◦40046.100). Alpha Centauri has J2000.0 coordinates of (α,δ) = (14h39m36.50s, −60◦50002.300). What is the angular separation of these two stars? You need the formula for angular separation (not in lecture notes): (∆θ)2 = (∆αcosδ)2 + (∆δ)2.
2. (Original post by LuckyEms)
Proxima Centauri has the epoch J2000.0 coordinates (α,δ) = (14h29m42.95s, −62◦40046.100). Alpha Centauri has J2000.0 coordinates of (α,δ) = (14h39m36.50s, −60◦50002.300). What is the angular separation of these two stars? You need the formula for angular separation (not in lecture notes): (∆θ)2 = (∆αcosδ)2 + (∆δ)2.
1. You're really at the point where you need to use latex, or to put up a photo. This is hard to read.

2. I'm not familiar with this formula, but I don't see how to apply it. You have two deltas, but the formula only has one. Surely a formula for angular separation must work on the angular position of both stars?
3. I've copied it from the questions, that's how it appears on my sheet.

Plus, that was my thinking exactly, hence why I'm so confused!!

I have emailed my lecturer but no reply yet.
4. (Original post by atsruser)
1. You're really at the point where you need to use latex, or to put up a photo. This is hard to read.

2. I'm not familiar with this formula, but I don't see how to apply it. You have two deltas, but the formula only has one. Surely a formula for angular separation must work on the angular position of both stars?
Formula refers to both ∆α and ∆δ, surely?

[If you think about the position being determined in spherical coordinates it's reasonably clear what's going on, especially if you know the given formula is only valid for small deltas].
5. (Original post by DFranklin)
Formula refers to both ∆α and ∆δ, surely?
You're right. Eyesight problem. I'm tired.

[If you think about the position being determined in spherical coordinates it's reasonably clear what's going on, especially if you know the given formula is only valid for small deltas].
Right. This certainly can't be the full formula.
6. (Original post by LuckyEms)
I've copied it from the questions, that's how it appears on my sheet.

Plus, that was my thinking exactly, hence why I'm so confused!!

I have emailed my lecturer but no reply yet.
Sorry, I didn't see the big Deltas before. Note that and similarly for delta.
7. (Original post by atsruser)
You're right. Eyesight problem. I'm tired.

Right. This certainly can't be the full formula.
Yeah, it's only valid for small angles. Full formula is at https://en.wikipedia.org/wiki/Great-circle_distance
8. Ok thank you.

However when i put my numbers in i don't get the answer the online calculators get. I've attached a photo of my working. I've tried to include all the formulas i used but i had to write them squished up so i hope you can make sense of it.

9. (Original post by LuckyEms)
Ok thank you.

However when i put my numbers in i don't get the answer the online calculators get. I've attached a photo of my working. I've tried to include all the formulas i used but i had to write them squished up so i hope you can make sense of it.
Not read through all of it, but I notice the conversions for your deltas, from degrees, minutes, seconds, to decimal degrees are incorrect.

Your initial division for the seconds should be by 60, not 60.60.

The way you've done it, the second 60 is taken care of when you convert the revised minutes to degrees.
10. Ok, I will have a look in a mo just working on something else

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Updated: October 11, 2017
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