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Hour Angle Formula:
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Hour angle is the angular distance of a celestial object measured westward along the celestial equator from the observer's meridian to the hour circle of the object. It represents how long ago an object crossed the meridian.
The calculator uses the hour angle formula:
Where:
Explanation: The hour angle indicates how far east or west a celestial object is from the observer's meridian. Positive values indicate west of meridian, negative values indicate east of meridian.
Details: Hour angle is crucial for telescope pointing, celestial navigation, and determining when celestial objects will be visible. It helps astronomers plan observations and track celestial objects across the sky.
Tips: Enter local sidereal time and right ascension in hours (0-24). Both values must be valid decimal hours. The result is normalized to the range -12 to +12 hours for astronomical convention.
Q1: What does a positive hour angle mean?
A: A positive hour angle means the object is west of the meridian and has already crossed it. A negative hour angle means the object is east of the meridian and hasn't crossed it yet.
Q2: How is local sidereal time calculated?
A: Local sidereal time can be calculated from universal time, observer's longitude, and the current date using established astronomical formulas.
Q3: Why normalize hour angle to -12 to +12 hours?
A: This convention makes it easier to interpret whether an object is rising (negative) or setting (positive) and simplifies telescope control systems.
Q4: Can hour angle be converted to degrees?
A: Yes, multiply hour angle in hours by 15 to get degrees (since 1 hour = 15 degrees of rotation).
Q5: What is the relationship between hour angle and altitude?
A: Hour angle, along with declination and observer's latitude, determines the altitude and azimuth of a celestial object through spherical trigonometry.