Celestial equator

What is the celestial equator?

If you imagine the Earth’s equator extended outwards until it meets the sky, you get the celestial equator. It divides the sky into a northern and a southern half. Directly above the Earth’s poles lie the celestial poles. The north celestial pole lies close to the Pole Star, which is why the Pole Star seems to stand still while the sky turns around it.

The celestial equator is tilted by 23.44 degrees against the ecliptic, the path of the Sun, as far as the Earth’s axis. The two lines cross at the vernal point and at the autumnal point. When the Sun stands there, it is the equinox.

Declination: north or south of the equator

How far a celestial body stands north or south of the celestial equator is called declination. It is measured in degrees, positive to the north, negative to the south. The celestial equator itself has a declination of 0 degrees, the north celestial pole 90 degrees.

• Sun: at the equinox it stands on the equator, at the solstice in June 23.44 degrees north of it, in December 23.44 degrees south.
• Moon: it swings from north to south and back in just over 27 days. In 2027 it reaches a good 27.5 degrees at its turning points. In the years of the major lunar standstill it reaches a good 28.7 degrees, most recently in 2024 and 2025.

How high does the celestial equator stand for us?

The celestial equator runs as an arc from east via south to west. Its height above the southern horizon is 90 degrees minus the latitude. In Berlin, at 52.5 degrees north, it stands 37.5 degrees high, in Munich just under 42 degrees.

A celestial body on the celestial equator rises exactly in the east, sets exactly in the west and stays above the horizon for around twelve hours. The further north it stands, the higher it travels across the sky and the longer it stays visible.

Celestial equator and the Moon’s course

The ascending and descending Moon of the planting calendar is measured against the celestial equator. If the Moon’s declination increases, its daily arc climbs higher from day to day: ascending Moon. If it decreases, the arc becomes flatter: descending Moon. The turning points are called lunar turning points.

These are to be told apart from the lunar nodes. They lie on the ecliptic, where the Moon crosses it. Biodynamic practice puts harvesting, grafting and cut flowers in the ascending Moon, planting, transplanting, pruning and compost in the descending one.

Sources

• Celestial equator, Wikipedia
• Declination, Wikipedia