Solar Geometry Flashcards
What is the difference between daylight and sunlight?
Daylight:
- The diffused natural light from a completely overcast sky.
Sunlight:
- The direct solar radiation received in clear sky conditions.
What are solar gains?
Solar gains are the energy we capture/reject from the sun as and when we need.
What is a sun path diagram?

What is zenith?
A point which is directly overhead (perpendicular to the Earth’s surface).
What is the meridian?
A circle of constant longitude which passes through a given place on Earth’s surface.
What is a great circle?
A great circle divides a sphere into two equal halves.

What is obliquity?
- Obliquity is the tilt of the Earth with respect to the plane of revolution of the Earth around the sun (23.4o).
- The obliquity of the Earth causes the seasons depending on whether the Earth is tilted towards/away from the sun.

What is declination (D)?
- Declination is the angle made by the Sun’s rays at a given time of the year with the Earth’s equatorial plane.
- It varies over the year from ‘- obliquity (-23.4o)’ in winter to ‘+ obliquity (+23.4o)’ in summer. It is 0o at the equinox.
- It is a measure of where you are in the seasons.

What is the equation for declination?

What is hour angle (H)?
The angle that the Earth needs to rotate in order to bring the meridian of a place to its position at noon.
What is the equation for hour angle?

What is latitude (L)?
- Latitude is how far/close you are to the equator, measured using the angle subtended by the place under consideration from the centre of Earth.
- It is important in determining how much solar radiation a place receives.

What is altitude (y)?
The altitude is the angle of the sun above the horizon plane. It is zero at sunrise and sunset, and at its maximum value when the sun is due south (in the Northern hemisphere).

What is azimuth (z)?
- The azimuth is the compass direction of the Sun.
- This is the angle of the Sun measured from South.
- Azimuth is 0o when it is due South (at noon).

Which solar geometric properties apply to Earth as a whole, and which apply to single places on Earth?
Earth as a whole:
- Hour Angle (H)
- Latitude (L)
- Great Circle
- Obliquity
- Declination (D)
Single place on Earth:
- Altitude (y)
- Azimuth (z)
What is the equation for altitude (y)?

What is the equation for azimuth (z)?

What are the solstices/equinox?
- The obliquity is the tilt of the Earth towards/away from the sun effecting the length of a day.
- Summer solstice = Longest day of the year.
- Winter solstice = Shortest day of the year.
- Equinox = Between the two.
What is the declination at equinox?
Zero
What are orthographic projections?

What are stereographic projections?

What are the features of orthographic/stereographic projections?

What are the solar features of the tropics and arctic circle?
- In the tropics, the sun is at zenith at least once in a year.
- On the tropics, the sun is at zenith exactly once in a year.
- In the arctic circle, there will be no sunrise or sunset at least once a year.
- On the arctic circle, there will be no sunrise or sunset exactly once a year.
How do you derive the altitude at noon equation?
- y*noon = 90 - ß
but. .. ß = L - D
so. .. ynoon = 90 - (L - D) - y*noon = 90 - L + D





