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Hour Angle Formula:
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The Hour Angle (HA) is the angular distance between a celestial body (like the Sun) and the observer's meridian, measured westward along the celestial equator. It represents how long ago the object crossed the meridian.
The calculator uses the hour angle formula:
Where:
Explanation: The hour angle indicates the time since the celestial object crossed the local meridian. Positive values indicate west of meridian, negative values indicate east of meridian.
Details: Hour angle is crucial in astronomy for telescope pointing, celestial navigation, and determining when celestial objects will rise, set, or transit. It's essential for solar position calculations and sundial design.
Tips: Enter Local Sidereal Time and Right Ascension in hours. Both values must be non-negative. The calculator provides results in both hours and degrees (1 hour = 15 degrees).
Q1: What is Local Sidereal Time?
A: Local Sidereal Time is the hour angle of the vernal equinox, representing the right ascension of objects currently on the local meridian.
Q2: How is hour angle related to altitude and azimuth?
A: Hour angle, along with declination and latitude, is used to calculate altitude and azimuth coordinates through spherical trigonometry.
Q3: What does a negative hour angle mean?
A: A negative hour angle indicates the object has not yet crossed the meridian (east of meridian), while positive indicates it has crossed (west of meridian).
Q4: How do I convert hour angle to degrees?
A: Multiply the hour angle in hours by 15 (since Earth rotates 15 degrees per hour).
Q5: Why is hour angle important for solar calculations?
A: For the Sun, hour angle determines solar time and is used to calculate solar position, shadow length, and solar radiation throughout the day.