1. Hour Angle (ω)
The hour angle (ω) measures the angular distance between the observer’s meridian and the meridian containing the Sun. It is zero at solar noon.
The hour angle increases by 15° per hour and can be calculated as:
Where ts is the solar time in hours.
- Positive ω indicates time after solar noon.
- Negative ω indicates time before solar noon.
Variation of hour angle (ω) 24 h
2. Declination Angle (δ)
The declination angle (δ) is the angle between the rays of the Sun and the Earth’s equatorial plane, varying throughout the year due to the axial tilt (approximately 23.5∘). It is defined as follows:
The declination angle can be approximated by:
Where n is the day of the year.
3. Latitude Angle (ϕ)
The latitude angle (ϕ) is defined as the angle from a point on Earth’s surface to the centre of the Earth, measured from the equatorial plane.
specifies the north-south position of a point on the Earth’s surface.
Measured in degrees from the equator (0°) to the poles (±90°).
Notable latitudes include:
4. Solar Altitude Angle (α)
The solar altitude angle (α) represents the angle between the Sun’s rays and a horizontal plane.
It can be related to the solar zenith angle (θz):
5. The zenith angle is defined as the angle between the sun and a vertical line above the observer. It is complementary to the solar altitude angle (α).
Higher values of α indicate the sun is higher in the sky, leading to more direct sunlight.
6. Surface Azimuth Angle (γ)
The surface azimuth angle (γ) is the angle measured clockwise from true north to the projection of the Sun’s rays on the horizontal plane. It helps determine the sun’s position relative to the observer.
7.Incident Angle (θ):
- The angle between the incoming sunlight and a line perpendicular (normal) to a surface.
- Affects how much solar energy is absorbed by that surface.
Solar Elevation Angle (α)
It is the elevation angle of the sun. That is, the angle between the direction of the geometric centre of the sun’s apparent disk and the (idealized) horizon.
