Twitter Facebook Flickr YouTube
LATEST AUDIO > August 2014 | LATEST VIDEO > LOFAR
 

The night sky for August 2014

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during August 2014.

High in the south in the evening is the Summer Triangle of Deneb in Cygnus, Vega in Lyra and Altair in Aquila, with the four brightest stars in Cygnus forming the asterism of the Northern Cross. The small constellation of Delphinus the Dolphin lies below Cygnus. The Great Square of Pegasus is rising in the east, and its top-left star, Alpheratz, can be used to locate the Andromeda Galaxy. Starting there, move left to the next bright star, curve up and right to another, go sharp right one more star, then move the same distance again to find our nearest neighbouring large galaxy, once known as the Great Nebula in Andromeda. Cassiopeia is high in the north, above Perseus and its bright star Mirfak, with the Perseus Double Cluster between the two constellations.

The Planets

Highlights

Ian Morison's new book, An Amateur's Guide to Observing and Imaging the Heavens, is out now.

Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during August 2014.

This month sees Scorpius and Sagittarius high overhead in our evening sky. Scorpius is our winter constellation and is easy to spot with the orange star Antares, which marks his heart, lying just east of the zenith. A curve of bright stars stretches out towards the right of this forming his tail.

Antares is a red supergiant star with a radius more than 800 times that of the Sun. If it were placed at the centre of our solar system, its surface would lie between the orbits of Mars and Jupiter. The name Antares means "rival of Mars" because of its distinctive colour. This tells us that it is a cooler star, at around 3 and a half thousand Kelvin.

Here in New Zealand, we don't have Scorpions, however, so we see this groups of stars as something a little more familiar here in the Southern Pacific. To Maori this group of stars is known as Te Matau a Maui, the fishhook of Maui. Maui used this hook to pull a great fish out of the ocean which became the north island of New Zealand, te Ika a Maui. The red star is now known as Rehua, and represents a drop of blood that Maui took from his nose to use as bait.

Below Scorpius is an upside down teapot shape formed from the brightest stars in Sagittarius. The broadest and brightest part of the Milky Way lies towards Scorpius and Sagittarius high in our eastern evening sky.

We are very lucky here in the Southern hemisphere that we look more towards the centre of our galaxy providing a whole assortment of stunning nebulae and star clusters to observe.

Lying along the tail of the scorpion is NGC 6231, a bright cluster of stars which looks like a small comet. Estimated to be only 3.2 million years old and nearly 6000 light-years away, NGC 6231 covers an area of the sky similar in size to the Pleiades, but its stars are much more luminous. If the cluster was placed at the same distance as the Pleiades then some of its stars would be amongst the brightest in the night time sky.

About halfway between the scorpion's sting and the spout of the teapot is M7. This is an open cluster of stars easily visible to the naked eye, and a lovely sight through a good pair of binoculars. M7 is thought to be around 980 light years away and around 200 million years old - pretty young in astronomical terms. Nearby and somewhat fainter, the Butterfly cluster, or M6 is also well worth a look in binoculars.

To the left of the teapot's spout, and just about visible to the naked eye, is the Lagoon Nebula, or M8. This is a huge cloud of interstellar gas and dust where new stars are being formed. M8 is a great example of an HII region where the UV radiation from hot young stars is ionizing the leftover hydrogen gas and causing is to glow. These emission nebulae often appear pink in colour photographs. Along with the nearby Trifid nebula (M20), the Lagoon Nebula is a good target for binoculars or a small telescope.

The Trifid nebula is an interesting object to look at as it combines both an emission and reflection nebula with an open cluster of stars. It was discovered by Charles Messier in 1764 and is famed for the three-lobed appearance, which earned it its name. Reflection nebulae glow by reflecting and scattering light from the nearby stars. They often appear blue in colour as the scattering of blue light is more effective than that of red light.

There are also a number of globular clusters in this part of the sky. These are large spherical clusters, containing hundreds of thousands of ancient stars, dating back more than 12 billion years. Over 150 are found in the halo of the Milky Way, in the outskirts of our galaxy. The distribution of these clusters provided early evidence of the scale of the Milky Way and our position within it.

The brightest globular cluster is M4, and this is also one of the easiest to find, lying just 1.3 degrees west of Antares. Appearing as a small fuzzy ball in binoculars or small telescopes, a slightly larger telescope will begin to pick out individual stars. Also in this region, near the top of the teapot, is M22. This was the first globular cluster ever discovered in 1665 and at just 10,000 light-years away it is also one of the closest, making it well worth a look.

From its bright centre in Sagittarius, the Milky Way stretches out east to west in our early evening. Along this path we find the majority of the bright stars in our night-time sky. In the north, just to the left of the Milky Way is Vega, the fifth brightest star in the sky. Vega is about 25 light years away and 50 times brighter than the Sun. It forms part of the constellation of Lyra, the lyre or harp. Opposite, in the southern sky, the second brightest star Canopus can be found in the constellation of Carina. This star is 310 light years away and 15,000 times brighter than the Sun. To Maori in Aotearoa/New Zealand this star is Atu tahi or Au tahi, which means to stand alone.

Running back along the Milky Way towards Scorpius, we first pass the false and diamond crosses before arriving at Crux, the Southern Cross. The smallest of the 88 official constellations Crux has become an icon of the southern sky. It has the appearance of a diamond-kite shape of four bright stars along with a fifth fainter star. To Maori it is known as Te Punga, the anchor of Tamareriti's waka. Alpha Crucis, the 12th brightest star in the sky, appears to the unaided eye as a single star of magnitude 0.9, but small telescopes reveal it to be a double star with blue-white components of magnitudes 1.4 and 1.9. Beta Crucis is a magnitude 1.3 blue-white star 570 light years away.

Nearby is NGC 4755 an open cluster of stars also known the "Jewel Box", from Sir John Herschel's vivid description of the cluster as a "casket of variously coloured precious stones". The cluster is about 6,500 light years away and is rich and bright with the stars showing delicate colours accentuated by an orange-red supergiant. It can easily be seen with the naked eye, but binoculars and telescopes will reveal much more detail.

Just to one side is a dark patch known as the Coal Sack nebula. This is a cloud of interstellar dust and gas some 700 light years away. It is so thick and dense that it obscures the light from more distant stars, appearing as a darkened area against the bright backdrop of the Milky Way. To Maori it is known as te Patiki or the flounder.

Towards the east of Crux are the two bright pointer stars; Alpha and Beta Centauri, marking the front hooves of Centaurus, the centaur.

When we look away from the path of the Milky Way the brightness and number of stars rapidly drops off.

After sunset the constellations of Virgo and Corvus can be seen in the west.

Mars and Saturn sit near to Spica the brightest star in Virgo this month, with the orange star Arcturus below. The differences in colours are easily distinguished; Mars and Arcturus have a red hue whilst Spica is a brilliant blue-white and Saturn is yellow. Mars and Saturn will be at their closest on the 25th. Small telescopes will reveal the Saturn's rings and largest moon Titan, looking like a small star around 4 ring diameters out from the planet. More powerful telescopes should reveal faint banding in the planets atmosphere along with gaps and variation in colour of the rings, as well a number of smaller moons. This object, more than any other, will get a great response from first time observers as it really does look like it does in the pictures. Mars, on the other hand, will appear as a small red disk. It is getting fainter as we move away from it on our faster inner orbit.

Also in the western sky is the planet Mercury, it will climb higher as the month progresses, setting 1 1/2 hours after the Sun by month's end. The crescent moon will be close by on the 27th.

Brilliant Venus and Jupiter are in our morning sky and will be at their closest on the 18th when there will be less than a full moon diameter between them.

Previous episodes:

The Night Sky This Month is one part of the Jodcast. The full show contains the latest news, interviews with astronomers, answers to listener questions and more.

Subscribe (It's free)