A solar calendar is a calendar whose dates point
the position of the earth on its revolution around the sun or
equivalently the apparent position of the sun moving on the celestial sphere.
- the Earth’s orbit around the Sun on a tilted axis causes the Sun to appears to gradually rise and fall in the sky during the year – this effect causes the `midnight sun` phenomenon that is experienced at high latitudes near the poles.
- solstice – point at which the Sun appears to stop rising or falling and stands still in the sky.
- summer solstice – happens on 21st June, marks the Sun’s most northerly extension above the Equator – at 12 noon on 21st June the Sun is directly overhead at the Tropic of Cancer.
- winter solstice – happens on 21st December, marks the Sun’s most southerly extension below the Equator – at 12 noon on 21 December the Sun is directly overhead at the Tropic of Capricorn. (diagram)
- equinox mean “equal night” marks both the time time and place at which the Sun cross the equator – during an equinox, everywhere on the planet has exactly 12 hours of daylight and 12 hours of darkness.
- Spring equinox – on around 21st March every year – the spring equinox happens – marks when the Sun crosses the Equator from south to north.
- Autumn equinox – on 23rd September every year – the autumn equinox happens – marks the Sun crossing the equator from north to south.
- vernal equinox – using as the zero point in the celestial co-ordinate system. (diagram)
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