Astronomy: Sun azimuth from altitude, hour angle, and declination

In summary, the conversation discusses the calculation of the azimuth of the sun using the change of coordinate system, with given values for altitude, declination, and hour angle. However, there is a discrepancy between the calculated azimuth and the value shown on a program, leading to a discussion about the possibility of measuring from the south instead of the north. Eventually, it is suggested to use the formula from Wikipedia which results in a different value for the azimuth.
  • #1
Frank Einstein
170
1

Homework Statement


Hi everybody, I am trying to do a numerical aplication of change of coordinate system to another; the objective is to calculate the azimut of the sun knowing the altitude, hour angle and declination .

Homework Equations



Cosh * Sina = Cosδ * Sin H
where a is the azimut
h is the altitude, in this case 27.5°
δ is the declination, in this case 7.2°
and H is the hour angle, in this case 10:00 on GTM+2; so 20h which is 300°

The Attempt at a Solution



Sina = [ Cosδ * Sin H ] / CosH

If I substitute the values, the azimut is -75.6°.
The problem is that if I check the value of the azimut on the program stellarium for august 12 2014, the date from where the data has been chosen, the azimut is of 104º, and I don't know why there is such a difference between my azimut and the program's, Can anyone help please?
 
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  • #2
What does a negative azimuthal angle indicate?
Note 180-75.4=104.6
 
  • #3
A negative azimut would mean that the location of the sun is north west is stead of north east, which is where it sould be before 14h.
About 180ºThat's true, but that would mean that I am measuring my azimut from the south pole, not that I am doing it from the north.
I will study the deduction of the equation to see if I was doing measuring from the south all along.
Thank you very much.
 

Related to Astronomy: Sun azimuth from altitude, hour angle, and declination

1. What is the significance of calculating the sun's azimuth from altitude, hour angle, and declination?

Calculating the sun's azimuth from altitude, hour angle, and declination is important in understanding the position of the sun in the sky at a specific location and time. This information can be used for various applications, such as navigation, agriculture, and astronomy.

2. How is the sun's azimuth calculated from altitude, hour angle, and declination?

The sun's azimuth can be calculated using mathematical formulas that take into account the sun's altitude (angle above the horizon), hour angle (angular distance between the sun and the observer's meridian), and declination (angular distance between the sun and the celestial equator).

3. What is the relationship between the sun's azimuth and its position in the sky?

The sun's azimuth is the angular direction of the sun measured clockwise from north. This means that as the sun moves across the sky, its azimuth will change accordingly, with the highest value being 360 degrees (due south) and the lowest being 180 degrees (due north).

4. How does the sun's azimuth change throughout the day?

The sun's azimuth changes throughout the day as the sun moves across the sky. At sunrise, the sun's azimuth is 90 degrees (due east), at solar noon it is 180 degrees (due south), and at sunset it is 270 degrees (due west). It follows a similar pattern in the southern hemisphere, but with the directions reversed.

5. What factors can affect the accuracy of calculating the sun's azimuth?

The accuracy of calculating the sun's azimuth can be affected by several factors, including atmospheric conditions (such as haze or clouds), the precision of the measurements used, and the location of the observer on the Earth's surface. Additionally, the sun's position in the sky can vary slightly due to seasonal and latitudinal changes.

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