1. What is the Hour Angle of the Sun?

Definition: The hour angle (HA) is the angular distance of the sun east or west of the local meridian due to the Earth's rotation.

Purpose: It's used in solar position calculations, astronomy, and solar energy applications to determine the sun's position in the sky.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( HA \) — Hour angle (degrees)
• \( LST \) — Local solar time (hours)

Explanation: The Earth rotates 15 degrees per hour (360° in 24 hours). At solar noon (12:00 LST), HA is 0°. Morning times give negative values (east of meridian), afternoon times positive (west of meridian).

3. Importance of Hour Angle

Details: The hour angle is crucial for calculating solar altitude and azimuth angles, designing solar tracking systems, and predicting sun positions for architectural purposes.

4. Using the Calculator

Tips: Enter the local solar time in decimal hours (e.g., 13.5 for 1:30 PM). The result will be in degrees (-180° to +180°).

5. Frequently Asked Questions (FAQ)

Q1: What's the range of hour angle values?
A: -180° (midnight) to +180° (next midnight), with 0° at solar noon.

Q2: How does hour angle relate to time zones?
A: Hour angle uses local solar time, not standard time. You may need to adjust for your longitude within the time zone.

Q3: Why 15 degrees per hour?
A: The Earth completes 360° rotation in 24 hours, so 360/24 = 15° per hour.

Q4: What's the hour angle at sunrise/sunset?
A: It varies by location and date, but equals the solar zenith angle at those times.

Q5: How precise is this calculation?
A: Very precise for most applications, though extremely precise astronomical calculations may need additional corrections.