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How To Solve For Right Ascension

The GHA in the first point of Aries is 315° and the GHA of a planet is 150°. What is the right ascension of the planet?

Given:
  GHA of Aries = 315°
GHA of Planet = 150°

What is asked:

Right ascension of the planet

Solution:

With this problem we can just simply subtract the GHA of Aries by the GHA of the planet. That is if you have memorized the formula. However, it is much better if we are going to draw a figure in order to have a better understanding on how to  get the right ascension.

Step 1. Draw a circle and then write G on the top of it. Use your compass divider starting at G going westward until 315°. That is the GHA of Aries.


   Step 2. For the GHA of the planet, draw westwardly starting at G again until 150°.


Step 3. Right ascension  (RA) can be measured from the first point of Aries to body in eastward direction.


From the figure that we have made above, we can now visualize how to solve for the right ascension of the planet. So this is the formula in getting right ascension;

RA = GHA of Aries - GHA of planet
      = 315° - 150°
RA = 165°

Converting this to time, we have to divide 165° by 15, since the earth rotates according to textbooks15° per hour. I said "according to textbooks" because I do not believe that the earth rotates and revolves around the sun.

165 degrees x  1 hr              = 11 hrs
                       15 degrees


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