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Hour Angle Formula:
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The Hour Angle (HA) is an astronomical coordinate that measures the angular distance of a celestial object west of the local meridian. It represents how long ago an object crossed the meridian and is crucial for telescope pointing and celestial navigation.
The calculator uses the hour angle formula:
Where:
Explanation: The factor of 15 comes from the fact that the Earth rotates 15 degrees per hour (360°/24h = 15°/h). The hour angle indicates how far west an object is from the meridian.
Details: Hour angle is essential for astronomical observations, telescope alignment, and determining when celestial objects will be visible. It helps astronomers plan observing sessions and track objects across the sky.
Tips: Enter Local Sidereal Time and Right Ascension in hours (decimal format). Both values must be valid numbers. The calculator will compute the hour angle in degrees, normalized between -180° and +180°.
Q1: What does a positive/negative hour angle mean?
A: Positive hour angle indicates the object is west of the meridian, negative means it's east of the meridian. Zero hour angle means the object is on the meridian.
Q2: How do I convert hour angle to time?
A: Divide the hour angle in degrees by 15 to get hours. For example, 45° HA = 3 hours west of meridian.
Q3: What is Local Sidereal Time?
A: LST is the right ascension of objects currently on the local meridian. It differs from civil time and must be calculated for your location and date.
Q4: Why normalize hour angle between -180° and +180°?
A: Normalization ensures the angle is within the standard range and makes interpretation easier for astronomical applications.
Q5: Can hour angle be used for satellite tracking?
A: Yes, hour angle calculations are fundamental for tracking both celestial objects and artificial satellites across the sky.