Story: Night sky
Page 2 – Earth’s near neighbours
To people in the southern hemisphere, any suggestion that the moon’s light and dark surface features resemble a ‘man in the moon’, is unconvincing. Theirs is an upside-down view of what is seen in the northern hemisphere. The light areas, known as the southern highlands, appear at the top of the moon to southern hemisphere viewers, while the dark areas, such as the Sea of Rains and Sea of Serenity (now known to be vast lava plains), are concentrated in the middle and lower portions of the moon.
The moon is best viewed around the first and last quarters, when half of its face is illuminated. At these times the sun casts long shadows that accentuate the moon’s mountains and crater walls. In the southern hemisphere, the phases of the moon (changes in the moon’s appearance) appear the reverse of those seen in the northern hemisphere. The new moon is followed by a left-hand crescent moon that grows (waxes) towards full moon, and then decreases (wanes) towards a crescent with the curve facing right.
The planets are large celestial bodies that orbit a star (the sun), and five are visible with the naked eye. We see them as bright points of light slowly moving against a background of stars. The planets are always located in a band of the sky that runs close to the same path the sun appears to travel each year (the ecliptic).
- Mercury, the nearest planet to the sun, is visible close to the horizon for about half an hour after sunset and before sunrise. It can be seen for only a few weeks during its 88-day orbit of the sun.
- Venus is the easiest of the planets to spot. It sparkles brilliantly in early evening or early morning skies, outshining everything but the sun and moon, and is on view for about three hours after sunset or before sunrise.
- Mars, with its distinct orange-red colour, is visible at any time of the night. But it is brightest for a few nights every two years, when its orbit carries it close to earth.
- Jupiter shines with a yellow-white light, and is brighter than any of the stars visible in the sky. It can be seen late at night, so cannot be confused with Venus, which by then will have disappeared below the horizon.
- Saturn is the most distant of the planets visible without a good telescope. It appears as a moderately bright star.
On most nights one or more meteors streak across the sky. Although commonly described as shooting stars, they are actually dust and rock that fall from space and burn as they plummet through earth’s atmosphere. Large particles that survive the fall and hit the ground are known as meteorites.
At times during its annual journey around the sun, the earth passes through particularly dusty regions associated with comets, causing meteor showers. During a meteor shower, it is possible to see dozens of meteors in an hour.
Amalgamations of ice and rock, comets are infrequent visitors to our night skies. Comets originate from the outer fringes of our solar system and pass by earth as they orbit the sun. As a comet approaches the sun, its outer layers of ice and rock are vaporised, forming a gaseous plume which is its tail.