The declination of the Sun is the angle between the light rays from the Sun and the Earth's equator. Since the Earth is tilted on its axis and rotates every year, the angle of declination changes throughout the year. Every year the solar declination goes from -23.44 degree to +23.44 degrees in line with the Earth's seasons. Although the Earth's orbit and rotation change slowly over millions of years, on smaller timescales they seem perfectly consistent, and the solar declination can be calculated based on what day of the year it is.
- Calculator with trigonometry functions
- Pencil
- Paper
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Instructions
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1
Determine how many days have passed since January 1st. For example, the number of days between January 1st and February 14th is 44.
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2
Add ten to the number of days passed. Write this number down.
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3
Divide 360 by the number of days in the year. Every year has 365 days except leap years. Write this number down.
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4
Multiple the number from Step 2 by the amount from Step 3. Write down the result.
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5
Find the cosine of the result from Step 4. Multiply it by -23.44. The result is the solar declination in degrees for that day of the year.