Chart for the whole sky in April Stars and planets in the April evening sky
Chart for the southern sky in April Interesting objects in the April southern sky
Chart for the north sky in April Interesting objects in the April Northwest Sky
Sirius, the brightest star, is midway down the western sky. Below it is Orion with the bright stars Rigel and Betelgeuse. Orion's sword, aka 'The Pot', appears between them. Canopus, the second brightest star, is southwest of overhead. Orange Mars is low in the north. Saturn is in the northwest with fainter Spica to its right. Crux, the Southern Cross, and The Pointers are high in the southeast sky. The Scorpion, on its back, is rising in the southeast. The Milky Way spans the sky from SE to NW.
Sirius is the first star to appear at dusk, midway down the northwest sky. It is soon followed by Canopus, southwest of the zenith. Below Sirius are Rigel and Betelgeuse, the brightest stars in Orion. Between them is a line of three stars: Orion's belt. To southern hemisphere star watchers, the line of three makes the bottom of 'The Pot', now tipped on its side. Orion's belt points down and left to a V-shaped pattern of stars making the face of Taurus the Bull. Below and right of Sirius, are Procyon and Mars, making a line with Sirius down to the north. Mars is orange coloured, like Betelgeuse and Aldebaran. Saturn is in the northeast sky. In the southeast are the Pointers, Beta and Alpha Centauri, with Crux, the Southern Cross, above them.
Sirius, 'the Dog Star', marks the head of Canis Major the big dog. A group of stars above it make the dog's hindquarters and tail. Sirius is the brightest star in the sky both because it is relatively close, nine light years away, and 23 times brighter than the sun.
Mars is fading as we leave it behind. It is low in the north at
dusk and sets in the northwest about midnight. At mid month it is 170 million km away and
appears small in a telescope.
Below and left of Mars are Pollux and
Castor, the heads of
Gemini the
twins. Above and right of Mars at the beginning of April is the
Praesepe cluster, marking the shell of
Cancer the crab.
Praesepe is also called the Beehive cluster,
the reason obvious when it is viewed in binoculars. It is 500 light years away.
Mars passes below Praesepe mid month and is right of the cluster thereafter.
Rigel, left of Orion's belt, is a bluish supergiant star, 40 000 times brighter than the sun and much hotter. It is 800 light years away. Orange Betelgeuse, right of the line of three, is a red-giant star, cooler than the sun but much bigger and 9 000 times brighter. It is 400 light years from us. The handle of "The Pot", or Orion's sword, has the Orion Nebula at its centre; a glowing gas cloud many light-years across and around 1300 light years away.
The V-shaped group making the face of Taurus the bull is called the Hyades cluster. It is 130 light years away. Orange Aldebaran, Arabic for 'the eye of the bull', is not a member of the cluster but merely on the line of sight, half the cluster's distance.
Crux, the Southern Cross, is high in the southeast. Below it are Beta and Alpha Centauri, often called 'The Pointers'. Alpha Centauri is the closest naked-eye star, 4.3 light years away. Beta Centauri, like most of the stars in Crux, is a blue-giant star hundreds of light years away. Canopus is also a very luminous distant star; 13 000 times brighter than the sun and 300 light years away.
The Milky Way is brightest in the southeast above Crux. The Milky Way can be traced to nearly overhead where it fades. It becomes very faint in the northwest, right of Orion. The Milky Way is our edgewise view of the galaxy, the pancake of billions of stars of which the sun is just one. The centre of the galaxy is toward Sagittarius, below the Scorpion's sting, where the Milky Way is broad.
The Clouds of Magellan, LMC and SMC are midway down the southwest sky. They are two small galaxies about 160 000 and 200 000 light years away.
Saturn in the northeast at dusk. It is a little brighter than Spica, the brightest star in Virgo, on Saturn's right. Saturn's rings are nearly edge on to us this year. In a telescope they look like a thick line through the planet. Saturn is 1286 million km away in mid April.
Brilliant Venus sets in the northwest an hour after sunset. It will set progressively later as it swings out from the far side of the sun, catching up with Earth. It is around 230 million km away in April. Jupiter, bright and gold-coloured, rises due east about 4 a.m. It is 870 million km away.
The chart shows the area midway up the southern sky. Interesting star clusters and nebulae are indicated with asterisks. They are described below.
Chart produced by Guide 8 software; www.projectpluto.com. Labels and text added by Alan Gilmore
Large and Small Clouds of Magellan (LMC and SMC) appear as two luminous clouds, easily seen by eye in a dark sky. They are galaxies like the Milky Way but much smaller. Each is made of billions of stars. The Large Cloud contains many clusters of young bright stars seen as patches of light in binoculars. The Large Cloud is about 160 000 light years away, the Small Cloud 200 000 l.y; away very close by for galaxies. (1 light year is about 10 000 billion, 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 has no connection, being 15 000 light years away. Globular
clusters are mostly very old, 10 billion years or more; at least twice the age of the sun.
Omega Centauri,
in the southeast, is a bigger 'glob' possibly the core of a galaxy that had its outer stars
stripped off as it merged with the milky way.
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) then it would be as bright as the full moon and look bigger than the whole constellation of Orion.
Canopus is the second brightest star. It is 13 000 times brighter than
the sun and 300 light years away. Sirius, north of Canopus on autumn evenings, is the brightest
star in the sky.
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 50x shows 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.)
Coalsack nebula, is a cloud of dust and gas about 600 light years away, dimming the more distant stars in the Milky Way. Many similar 'dark nebulae' can be seen, appearing as slots and holes in the Milky Way. These clouds of dust and gas 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 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 is a
glowing gas cloud about 8000 light years away.
The golden star in the cloud, visible in binoculars, is Eta [Greek η] Carinae. 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 formally the Theta Carina cluster named after
its brightest star but is also known as the 'Five of Diamonds' cluster, the reason obvious when
it is seen 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.
The chart shows our northwest sky in the evening The chart may need to be tilted to the left or right to match the sky, depending on the time of night. Interesting objects are described below.
Chart produced by Guide 8 software; www.projectpluto.com. Labels and text added by Alan Gilmore
Sirius is the first star to appear in the evening sky, high in the northwest. Below Sirius is Orion the Hunter marked by prominent Rigel and Betelgeuse with the well-known 'pot' or 'saucepan' pattern between them. Low in the northwest, setting early, is Taurus the Bull with Aldebaran being one of Taurus's eyes. The V-shaped Hyades cluster outlines the bull's head. (All these pictures were thought up by north hemisphere cultures so are upside down to us.) Below and right of Sirius is Procyon, marking the head of Canis Minor. The Sirius-Procyon line points down to Mars, low in the north. Below and left of Mars are Castor and Pollux marking the heads of Gemini the Twins. During April Mars passes below the Praesepe star cluster, a faint glow to the eye, making the shell of Cancer the Crab.
The Hyades cluster is 150 light years away. Its brightest stars are about 70 times brighter than the sun. Aldebaran is not a member of the cluster but simply on the line of sight. It is a giant star 150 times brighter than the sun and 65 l.y. away. Its orange colour is due to its temperature, around 3500° C. The sun is 5500° C. Betelgeuse and Mars have a similar orange tint.
Orion, in the northern hemisphere view, has a shield raised toward Taurus and a club ready for action. The line of three stars makes Orion's Belt. The line of faint stars above the belt form Orion's Sword in the northern view, hanging from his belt. To most southern hemisphere sky watchers the belt and sword form The Pot or the Saucepan.
The Orion Nebula is visible in binoculars as a misty glow around the
middle stars of Orion's Sword or the handle of The Pot. It is a vast cloud of dust and gas about
1300 l.y. away and more than 20 l.y. across. Ultra-violet light from a massive, extremely hot
star in the cloud causes it to glow. Some stars in this region are less than two million years
old. The sun, by contrast, is 4.6 billion years old. Stars continue to form in a giant cloud
behind the glowing nebula. There are many bright and dark nebulae in this region. The Horsehead
nebula, a favourite of astronomy books, is beside the right-hand star of Orion's Belt, but too
faint to be seen in small telescopes.
Sirius is the brightest star because it is both brighter than the sun
and relatively close at 8.6 l.y. away. Sirius was often called 'the dog star' being the
brightest star in Canis Major, one of the two dogs that follow Orion across the sky.
Rigel is a blue 'supergiant' star around 40 000 times brighter than
the sun and 800 l.y. away. Its surface temperature is around 20 000°C, giving it a bluish
colour. Betelgeuse is a red giant star 250 times bigger than the sun
-- wider than earth's orbit! -- but only around 20 times heavier. It is mostly very thin gas
surrounding a hot dense core. It is 10000 times brighter than the sun, about 400 l.y. away, and
has a surface temperature around 3000°C.
Marsis more than 170 million km from us in mid April and shows only a tiny disc in a telescope. In April Mars moves from left to right below Praesepe. It continues this rightward (eastward) movement against the star background all year.
Pollux and Castor mark the heads of Gemini, the twins. Though paired in myths, the two stars are not related at all. Castor is a hot white star like Sirius but 52 light years away. Golden Pollux is bigger and brighter but cooler than Sirius and 34 light years away.
The Praesepe cluster marks the shell of Cancer the crab. Praesepe means Beehive and binoculars show how it got its name. The cluster is some 500 light years from us and about 700 million years old. Star clusters begin with a few bright stars and many fainter ones. The bright stars burn out first, leaving the longer-lived fainter stars. That is why an old cluster like Praesepe has stars of similar brightness.