The Night Sky Through the Year

As Earth orbits the Sun, the night side of our planet faces a different direction in space. That is why the evening constellations change through the year. Each star rises about four minutes earlier every night, which adds up to about two hours a month.

Why there are seasons

Earth's axis is tilted by about 23.4 degrees. For half the year the Southern Hemisphere leans towards the Sun: the Sun climbs higher, days are longer, and it is summer. Seasons are not caused by changing distance from the Sun: Earth is actually closest to the Sun in early January.

All of Zimbabwe lies between the equator and the Tropic of Capricorn, so the Sun passes directly overhead twice a year, once on its way south in late spring and again on its way back north in mid-summer.

Summer evenings (December to February)

• Orion is high in the north. From the Southern Hemisphere it appears "upside down" compared with pictures in many books. Its belt of three stars is easy to find.
• Sirius, the brightest star in the night sky, is close to Orion.
• Canopus, the second-brightest star, is high in the south.
• The Pleiades, a small, tight cluster of stars, is in the north, sinking towards the north-west by February.

Winter evenings (June to August)

• Scorpius, with its curling tail and the red star Antares, climbs high overhead.
• The bright centre of the Milky Way in Sagittarius is overhead in the darkest part of the year: the best time for Milky Way photography.
• The Southern Cross and the Pointers are high in the south-west after dark.

The stars as a calendar

Across southern Africa, the first appearance of certain stars before dawn marked the seasons:

• The first morning sighting of the Pleiades in late August or early September marked the planting season for many communities.
• For the Venda, the first person to see Canopus before dawn in May, heralding winter, climbed a hill, blew a horn and was given a cow.
• For the Tswana, Canopus rising before dawn signalled the time for breeding sheep.

Sources

• OpenStax Astronomy 2e, 4.2 The Seasons
• OpenStax Astronomy 2e, 4.3 Keeping Time
• OpenStax Astronomy 2e, 2.1 The Sky Above
• Astronomical Society of Southern Africa: African ethnoastronomy