MARITIME – CELETIAL NAVIGATION CALCULATOR
Lha Calculation
A precise tool.
What is the Lha Calculation & How does it work?
In celestial navigation the Greenwich Hour Angle (GHA) represents the angular distance measured westward from the Greenwich meridian to the hour circle of a celestial body. It is expressed in degrees ranging from 0° to 360° and changes continuously as the Earth rotates. To determine the position of a body relative to an observer’s assumed position, the Local Hour Angle (LHA) is required. LHA is the angular distance measured westward from the observer’s meridian to the same hour circle. By adding the observer’s assumed longitude (west positive) to the GHA, the LHA can be obtained. If the sum exceeds 360°, the excess is subtracted to keep the angle within the 0°‑360° range. This simple arithmetic is the foundation for subsequent altitude and azimuth calculations used in sight reduction.
LHA = GHA + \lambda
LHA = Local Hour Angle, GHA = Greenwich Hour Angle, \lambda = assumed longitude (west positive)
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Frequently Asked Questions
What is Local Hour Angle (LHA)?
Local Hour Angle (LHA) is the angular distance measured westward from an observer's meridian to a celestial body's hour circle.
How do I calculate LHA?
To calculate LHA, add the observer's longitude (EAST is positive, WEST is negative) to the Greenwich Hour Angle (GHA).
Why is GHA important in celestial navigation?
GHA helps determine the position of a celestial body relative to the Greenwich meridian, which is essential for navigation calculations.
What range does LHA fall within?
LHA ranges from 0° to 360° and represents the angular distance westward from the observer's meridian.
How often does GHA change?
GHA changes continuously as the Earth rotates, typically increasing by about 15° per hour.
Can LHA be negative?
No, LHA is always expressed as a positive value between 0° and 360°.
What is the difference between GHA and LHA?
GHA measures the angle from Greenwich to a celestial body's hour circle, while LHA measures the angle from the observer's meridian to the same hour circle.
Results are for informational purposes only and do not constitute professional advice.