Interesting object in the southern sky Chart for the southern sky in September
Interesting objects West of Overhead in the Evening Sky Chart for the West sky in September
Jupiter is north of overhead at dusk, shining with a steady golden light. Binoculars will show the disk of Jupiter. A small telescope easily shows all four moons and the parallel stripes in Jupiter's clouds.
Venus, brilliant and silvery, appears in the west soon after sunset and sets about two hours after the sun. Venus, Mercury and Mars hang around together in the western sky for most of the month. Through the first half of September Mercury is above and left of Venus and a lot fainter. At the beginning of the month Mars is above Venus by twice Mercury's distance and a little to the right. Mars is the faintest of the three. By the 8th the three planets make a rough equilateral triangle. On the 12th Mars is just half a full moon diameter left of Venus. Mercury stays above and left of Venus. Spica, the brightest star in Virgo, is well above the three planets. By the 17th Venus is level with Mercury; Spica is above and Mars below. The three planets and Spica make a rough diamond pattern. On the 21st Mercury has stopped its climb up the sky. Venus, Spica and Mercury make a tilted line with Mars below them. Venus continues to set later while the other two planets and Spica fade into the twilight.
The planets' apparent bunching is a line-of-sight effect; they aren't really close to each other. Mars is on the far side of the sun, 360 million km from us, slipping lower in the sky as we leave it behind. Venus is also on the other side of the sun, 220 million km away, but gains altitude as it catches us up. Speedy Mercury swings out from the far side of the sun then falls lower in the twilight as it passes us on the inside lane. It is 165 million km away at the beginning of the month and 102 million km away at the end.
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 at dusk and sets in the late evening. Arcturus, the brightest northern star, sets in the northwest at dusk. It often twinkles red and green as the air splits up its orange light.
Midway down 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.
West 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. 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 south. 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 in the south sky. They are easily seen by eye on a dark moonless night. They are galaxies like our Milky Way but much smaller. The LMC is about 160 000 light years away; the SMC about 200 000 light years away.
Golden Jupiter is north of overhead in the evening, setting in the southwest around 2 a.m. Brilliant Venus is low to the west at sunset, setting about two hours after the Sun. Mercury and Mars are near Venus for most of the month. Orange Antares, the Scorpion's heart, is west of the zenith. The Scorpion's tail. a.k.a. the fish-hook of Maui, curls towards the zenith. Crux, the Southern Cross, and the Pointers are in the south-west. Canopus is near the south horizon, moving up into the eastern sky. Vega shines on the opposite horizon. The Milky Way spans the sky from the north to south. Arcturus twinkles red and green as it sets in the northwest.
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. The LMC is about 160 000 light years away and the SMC 200 000 l.y away, both very close by for galaxies. (1 light year is about 10 000 billion km, 1013 km.)
47 Tucanae,looks like a faint fuzzy star on the edge of the SMC. It is a globular cluster, a ball of millions of stars. A telescope is needed to see a peppering of stars around the edge of the cluster. Though it appears on the edge of the SMC it is one-tenth the distance, 15 000 light years away, and is has no connection to the Small Cloud.
Omega Centauri, right of the Pointers, is a similar cluster. 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 mostly very old, 10 billion years or more; at least 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.
The 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 (in The Pot's handle in the summer sky) then it would be as bright as the full moon.
Canopus is the second brightest star in the sky. It is 14 000 times brighter than the sun and 300 light years away. Sirius, in the eastern dawn sky, is the brightest star in the sky. The planets Venus and Jupiter are brighter
Alpha Centauri, the brighter Pointer, is the closest naked-eye star, 4.3 light-years away. Alpha Centauri is a binary star: two stars about the same size as the sun orbiting around each other in 80 years. A telescope that magnifies 30x splits the pair. (A very faint and slightly closer star, Proxima Centauri, orbits a quarter of a light-year, or 15 000 Sun-earth distances, from the Alpha pair.)
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 more distant stars in the Milky Way. Many "dark nebulae" can be seen, appearing as slots and holes in the Milky Way. These clouds eventually coalesce into clusters of 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.
The Eta Carina nebula is a glowing gas cloud about 8000 light years away. The golden star in the cloud, visible in binoculars, is Eta Carinae. (Eta is the Greek 'e'.) It is estimated to be to be 60 times heavier than the sun and a million times brighter but is dimmed by dust clouds around it. It is expected to explode as a supernova any time in the next few thousand years. Many star clusters are found in this part of the sky.
The Southern Pleiades is a newish name for a cluster of stars at one point of the 'Diamond Cross'. It is also called the 'Five of Diamonds' cluster, the reason obvious when viewed in a telescope. It is much fainter and smaller than the real Pleiades in Taurus but a nice sight in binoculars. The cluster is about 500 light years away and is around 10 million years old.
Jupiter appears west of overhead soon after sunset, shining with a steady golden light. Binoculars show the disk of Jupiter. Held steady, they can also show Jupiter's four big moons looking like faint stars lined up on either side of the planet. Any telescope magnifying 20x easily shows all four moons. We are looking almost edge-on to the plane of the moons' orbits so they appear to shift back and forth from night to night. Sometimes a moon is absent as it passes behind or in front of Jupiter. The closest, Io, orbits Jupiter in two days. The most distant, Callisto, takes two weeks to complete an orbit. The moons are a little bigger than our Moon. They were first seen by Galileo in 1610, so are called the Galilean moons.
A telescope also shows parallel stripes across the disk of Jupiter. They are colours in Jupiter's clouds. The clouds are dark where they are warm (-140 C) and white where they are cold. The clouds are warmed by gas rising from Jupiter's interior. The planet's fast spin forces these convection zones into narrow strips. Jupiter spins quickly, once in 10 hours, so it is slightly stretched out at the equator. Just now Jupiter is 700 million km from us. It is five times our distance from the sun.
Jupiter is by far the biggest of the planets. It has a mass or weight 320 times that of Earth: twice the mass of all the other planets put together, and is 11 times wider than Earth. It is made mostly of hydrogen. In the outer parts of the planet the hydrogen is a gas and makes the clear 'air' that the clouds float in. Deeper down the hydrogen is squeezed into a solid with the properties of a metal.
Below Jupiter is Antares an orange-red star. Antares is a red-giant star: 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 the star is mostly extremely thin gas spread around a hot dense core.
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. Infrared telescopes, peering through the dust, show stars orbiting the invisible black hole at high speed.
Antares marks the heart of the Scorpion. Its tail stretches up toward the zenith. In Maori star lore the tail 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. Right of 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. Below M7 and fainter is M6, the 'butterfly cluster', around 1300 l.y. away. Other clusters worth a look in binoculars are M23, NGC 6167, and NGC 6193. The 'M' objects were listed by the 18th Century French astronomer Charles Messier. He hunted comets, so catalogued fuzzy objects that could be mistaken for comets. The NGC (New General Catalogue) objects were too far south to be seen from Paris.
Below Sagittarius's "Teapot' is the glowing gas cloud M8. Nearby is M20, the Trifid Nebula, a small glowing patch in binoculars. M16 and other nebulae are also found in this area.
Globular clusters, spherical clouds of ancient stars, are found throughout the region. The brightest is M4 by Antares. It is also one of the closest at 10 000 l.y. away. In binoculars and small telescopes globs appear as round fuzzy spots. Others marked on the chart are M10, M12, M19, M22, M55, M62, M80 and NGC 6541. The concentration of globular clusters here was an early clue that the centre of the galaxy lay in this direction.
