The Right Ascension of the star Vega, brightest star in the constellation Cygnus, is 18h 37m 12s.?

a) If Vega鈥檚 Hour Angle is +3h 10m, what is the Local Sidereal Time?

b) If the Local Sidereal Time is 4h 10m, what is the Hour Angle of Vega?

c) From which direction did Vega rise? In which direction will Vega set?

d) What is Vega鈥檚 Declination? (Consult the literature or the web. Give the reference.)The Right Ascension of the star Vega, brightest star in the constellation Cygnus, is 18h 37m 12s.?Bzzt! Vega is not in Cygnus.



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Why don't you do your own homework? Here are some hints:



hour angle = local sideral time - right ascension



Wasn't this covered in your astronomy course? That's all you need to answer questions a and b. (You also need to know how many seconds there are in a minute, and minutes in an hour. You probably already know this. If you don't, look it up on the web.)



Hint for question d: Type Vega into the Google search box, or look it up on Wikipedia.



Question c is the only one here that requires an understanding of the celestial sphere. Hint: Vega is north of the celestial equator. The sun is also north of the equator during the summer. Do you know where the sun rises and sets in the summer? If not, buy a compass and measure the sunrise and sunset positions in June. Then you'll understand the answer to this question. For extra credit, make another set of measurements in December.



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Here's a quicker way of understanding the relation of declination to rise/set position:

1) Get a compass (or at least make sure you know which way is east and west).

2) Go out early tonight and identify the stars Aldebaran and Sirius.

3) Watch Aldebaran and Sirius as they are close to setting -- maybe 11 PM or 11:30 PM, depending on your position within the time zone. Where does Aldebaran set relative to west? Where does Sirius set relative to west?

4) Look up the declinations of Aldebaran and Sirius, and compare these numbers to the setting positions you saw.

5) Consider the declination of Vega, relative to the declinations of Aldebaran and Sirius. Where do you think Vega would set? Where do you think it would rise?

6) Go out around midnight tonight to watch Vega rising. Where is it relative to east?