Interesting object in the southern sky Chart for the southern sky in August
Interesting objects North of Overhead in the Evening Sky Chart for the Sky North of Overhead in August
Jupiter appears high in the northeast sky in the early twilight, shining with a steady golden light. Binoculars will show the disk of Jupiter and perhaps one or two of its bright moons. A small telescope easily shows all four moons and the parallel stripes in Jupiter's clouds. There is an unreliable rule that "stars twinkle and planets don't". It certainly applies to Jupiter.
Venus , brilliant and silvery, sets in the northwest half an hour after the sun at the beginning of the month. It moves to a more westerly location and sets later through the month. Mercury also begins an evening sky appearance during August, moving up toward Venus. Saturn moves down the sky, setting earlier through the month. The three planets form a close bunch around the middle of August, changing places from night to night. Venus is the brightest by far. Mercury is a little brighter then Saturn.
On the 13th and 14th Venus and Saturn will be close together with Mercury well below them. On the 16th, Mercury will be just above Saturn and below and to the left of Venus. Mercury catches up with Venus on the 20th, when the two will be almost level. For the rest of August, Mercury will be a little above and left of Venus. During this time Mercury and Venus move upward, night to night while Mars sinks downward. By the end of the month Mars will be not far above Mercury and Venus.
Canopus, the second brightest star, is near the south skyline at dusk. It swings upward into the southeast sky through the morning hours. Canopus is a truly bright star: 13 000 times the sun's brightness and 300 light years* away. On the opposite horizon is Vega, one of the brightest northern stars. It is due north in mid-evening and sets around midnight.
Midway up the southwest sky are 'The Pointers ', Beta and Alpha Centauri. They point down to Crux the Southern Cross. Alpha Centauri is the third brightest star. It is also the closest of the naked eye stars, 4.3 light years away. And it is a binary star: two sun-like stars orbiting each other in 80 years. A telescope magnifying 50x will easily split the pair. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away.
Arcturus, in the northwest at dusk, is the fourth brightest star and the brightest in the northern hemisphere. It is 120 times the sun's brightness and 37 light years away. When low in the sky Arcturus twinkles red and green as the air splits up its orange light. It sets in the northwest around 10 pm.
Just north of overhead the orange star Antares marks the heart of the Scorpion. The Scorpion's tail hooks around the zenith like a back-to-front question mark. Antares and the tail make the 'fish-hook of Maui' in Maori star lore. Antares is a red giant star: 600 light years away and 19 000 times brighter than the sun. Red giants are dying stars, wringing the last of the thermo-nuclear energy out of their cores. Big ones like Antares end in massive supernova explosions. Between Scorpius and Jupiter is 'the teapot' made by the brightest stars of Sagittarius. It is upside down in our southern hemisphere view.
The Milky Way is brightest and broadest overhead in Scorpius and Sagittarius. In a dark sky it can be traced down past the Pointers and Crux into the southwest. To the northeast it passes Jupiter and Altair, meeting the skyline right of Vega. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The thick hub of the galaxy, 30 000 light years away, is in Sagittarius. The actual centre is hidden by dust clouds in space. The nearer clouds appear as gaps and slots in the Milky Way. A scan along the Milky Way with binoculars shows many clusters of stars and some glowing gas clouds, particularly in the Carina region below Crux, and in Scorpius and Sagittarius.
The Large and Small Clouds of Magellan, LMC and SMC, look like two misty patches of light low in the south. They are easily seen by eye on a dark moonless night. They are galaxies like our Milky Way but much smaller. The Large Cloud is about 5% the mass of our Galaxy; the smaller about 3%, but that's still billions of stars in each. They are about 160 000 light years away.
Jupiter is the brightest star-like object in the evening sky, northeast of the zenith at dusk;gold coloured. Arcturus, in the northwest, is a bright orange start often twinkling red and green. The Pointers and Crux, the Southern Cross, are midway down the southwest sky. Canopus is low in the south; later swinging up into the southeast sky. The Milky Way spans the sky from northeast to southwest with its broad centre overhead. The Scorpion's tail curls around the zenith. Vega crosses the northern sky, staying low, Venus and fainter planets set early in the west.
Centaurus, with the bright 'Pointers', and Crux, the Southern Cross are south-east of overhead, the tightest grouping of bright stars in the sky. Originally Crux was the hind legs of the Centaur, the horse-man of Greek mythology. The complete Centaur, with bow, is outlined at left. It was only in the 17th Century that Crux was split off as a separate constellation. The slow wobble of Earth's axis allowed this part of the sky to be seen from more northerly places in ancient times. The fainter Pointer and the three bluish-white stars of the Crux are all super-bright stars hundreds of light years away. Alpha Centauri is just 4.3 light years away and the reddish top star of Crux is 90 light years from us.
Omega Centauri, also southeast of the zenith, is a globular cluster, a ball-shaped cluster of millions of stars. Its total mass is six million times the sun's. It is 17 000 light years away and 200 light years across. Globular clusters are very ancient, around 10 billion years old, twice the age of the sun. Omega Centauri is the biggest of the hundred-odd globulars randomly orbiting our galaxy. It may originally have been the core of a small galaxy that collided with the Milky Way and was stripped of its outer stars.
47 Tucanae, by the SMC, is a similar sort of cluster 16 000 light years. Though it appears near the SMC it has no connection, being 15 000 light years away.
The Coalsack nebula, left of Crux, looks like a hole in the Milky Way. It is a cloud of dust and gas 300 light years away, dimming the distant stars in the Milky Way. Many "dark nebulae" can be seen along the Milky Way, appearing as slots and holes. These clouds eventually form new stars.
The Jewel Box is a compact cluster of young bright stars about 7000 light years away. The cluster formed less than 10 million years ago. To the eye it looks like a faint star close by the second-brightest star in Crux. A telescope is needed to see it well.
Eta Carina nebula, a luminous spot in the Milky Way to the right of Crux, is a glowing gas cloud about 8000 light years from us. The thin gas glows in the ultra-violet light of nearby hot young stars.
The golden star in the cloud, visible in binoculars, is η [Greek 'e'] Carinae. It is estimated to be to be 60 times heavier than the sun. It is a million times brighter than the sun but is dimmed by dust clouds around it. It is expected to explode as a supernova in the next few thousand years. Many star clusters are found in this part of the sky.
The Large & Small Clouds of Magellan (LMC and SMC) appear as two luminous patches, easily seen by eye in a dark sky. They are two galaxies like the Milky Way but much smaller. Each is made of billions of stars. The Large Cloud contains many clusters of young luminous bright stars seen as patches of light in binoculars and telescopes. Both clouds are about 160 000 light years away, very close by for galaxies.
Tarantula nebula is a glowing gas cloud in the LMC. The gas glows in the ultra-violet light from a cluster of very hot stars at centre of the nebula. The cloud is about 800 light years across. It is easily seen in binoculars and can be seen by eye on moonless nights. This nebula is one of the brightest known. If it was as close as the Orion nebula then it would be as bright as the full moon.
Canopus is the second brightest star in the sky. It is 13 000 times brighter than the sun and 300 light years away. Sirius, low in the east on spring evenings, is the brightest star in the sky.
Jupiter is at its closest just now but is always a prominent object in the sky. (Perhaps that's why it got the name of the top Roman god.) The biggest of the planets, it is 11 times wider than the earth and 320 times heavier. Jupiter is made of gassy stuff, mostly hydrogen. Deep inside the planet the hydrogen is squeezed into a solid with the properties of a metal. This 'metallic hydrogen', along with its rapid spin, gives Jupiter a super-strong magnetic field. Jupiter spins once in 10 hours, so fast that it is obviously stretched out at the equator.
Antares is the brightest real star in the region. It is orange coloured; being a 'red giant' star. (The 'red' of red giants is usually more an orange tint.) It is 600 light years* away, 19 000 times brighter than the sun, and big enough to fill Earth's orbit. Its mass or weight is about 20 times that of the sun, so most of the star is very thin gas spread around a hot dense core. Antares marks the heart of Scorpius. In the evening at this time of year the Scorpion is on its back with its tail on the right, curving upward then turning down and curling clockwise. The sting is the horizontal line of bright stars pointing toward Antares. In Maori star lore the tail's hook is the 'fish hook of Maui'.
At the right-angle bend in the tail is a large and bright cluster of stars, NGC 6231, looking like a small comet. It is around 6000 l.y. away. Its brightest stars are 60 000 times brighter than the sun. The cluster is about 8 light years across, similar in size to the Pleiades/Matariki cluster in our summer sky. Were it as close at the Pleiades (400 l.y.) then its brightest stars would be as bright as Sirius. Below the Scorpion's sting is M7 a cluster obvious to the eye and nicely seen in binoculars. M7 is about 800 l.y. away and around 260 million years old. (The older a star cluster, the fewer bright stars it has.)
Below M7 and fainter is M6, the 'butterfly cluster'. M6 is around 1300 l.y. away and is half the age of M7. Other clusters worth a look in binoculars are M21, M23, NGC 6167, and NGC 6193. The 'M' objects were listed by the 18th Century French astronomer Charles Messier. He hunted comets, so made a catalogue of fuzzy objects that could be mistaken for comets. The NGC (New General Catalogue) objects shown are also bright but were too far south to be seen from Paris by Messier.
This part of the Milky Way is broad and bright as we are looking to the centre of the galaxy. The actual centre, 30 000 light years away, is hidden from our view by intervening dust clouds. The nearer clouds make gaps and slots along the Milky Way. Some of the central bulge of the galaxy is glimpsed in gaps between the clouds. At the very centre lies a black hole three million times the sun's mass but only the size of our solar system. Infra-red telescopes, peering through the dust, show stars orbiting the invisible black hole at high speed.
