NGC 2346 is an unusually shaped planetary nebula. The cause of its shape is the binary system at its centre: when one of the two stars evolved into a red giant, it engulfed its companion, which stripped away a ring of material from the larger star’s atmosphere. When the red giant’s core was exposed, a fast stellar wind inflated two ‘bubbles’ from either side of the ring.
The Egg Nebula is a prot--planetary nebula, forming as the outer layers are gently expelled from a dying red giant star which has exhausted all its nuclear fuel. The 'searchlight' effect is caused by light emerging from the thinnest parts of a thick cloud of dust surrounding the star.
This spiral galaxy in the constellation of Circinus is an example of a Seyfert galaxy, a class of active galaxy believed to be related to quasars, and which contain a super-massive black hole at their centre. The Circinus Galaxy is obscured from view by thick clouds of dust within the Milky Way, and was only discovered in 1975.
The Eskimo Nebula is a planetary nebula, named for its supposed resemblance to a face looking out from inside a parka. It lies about 5,000 light years away in the constellation of Gemini. The outer parts of the nebula contain comet-like filaments, up to a light year in length.
File:NGC 6543 outer halo.jpg The Cat's Eye Nebula is a planetary nebula, formed when a star like the sun ejected its outer layers at the end of its life. Long exposure images reveal several distinct episodes of mass loss from the star, with the inner bright nebula surrounded by smooth concentric rings, in turn surrounded by a giant shell of clumpy gas.
The Orion Nebula is one of the most famous objects in the night sky. It has been known since antiquity, and can easily be seen in the constellation of Orion as a fuzzy patch below Orion's Belt (above the Belt for southern hemisphere observers. The nebula contains one of the most active star formation regions known, with an open cluster of thousands of stars being formed within it.
File:Diverse planetary nebulae.jpgPlanetary nebulae are formed when small to medium mass stars gently eject their outer layers once they have exhausted all the hydrogen and helium which has been burning in nuclear fusion reactions during the star's lifetime. Our Sun will become a planetary nebula in about 5 billion years' time. The Hubble Space Telescope has revealed more intricate detail and structure in planetary nebulae than astronomers had previously thought possible.
The full story of the formation of stars has only come to be well understood in fairly recent years. The crucial step occurs deep inside dense dark blobs of gas and dust known as Bok gobules, named after Bart Bok who first studied them. Each Bok globule contains a nascent star system, but the dense cloud completely obscures the visible light from the young stars, and astronomers have to rely on infrared and radio observations to study the process.
The planetary nebulaM2-9 lies about 2,100 light years away from Earth. Like about 10% of planetary nebulae, its shape is strongly bipolar. Its elongated wings are believed to be due to the interaction of outflowing material from a dying star at the centre with a binary companion orbiting at a distance of about 60 billion kilometres.
The Ring Nebula is one of the best known planetary nebulae, and was formed probably a few thousand years ago when a Sun-like star shed its outer layers at the end of its life. Ground based observations reveal an almost circular ring, which is the edges of a thin shell of material surrounding the inner nebula. This Hubble Space Telescope reveals the very thin gas spread throughout the brighter ring.
The hot blue star Rigel illuminates this reflection nebula in the constellation of Orion. Interstellar dust preferentially reflects blue light in a process known as Rayleigh scattering, which gives reflection nebulae a characteristic blue colour. Skies on Earth are blue because of the same process.
Comet Hyakutake was a surprise celestial visitor in 1996. As astronomers awaited the entry into the inner Solar System of Comet Hale–Bopp, the comet discovered by Yuji Hyakutake raced past the Earth at a distance of just 0.1 astronomical units, one of the closest cometary passages for many decades. It became very bright, and was well seen by large numbers of people in the Northern Hemisphere
The Triangulum Galaxy is the third-largest member of the Local Group, after the Andromeda Galaxy and the Milky Way. It was one of the earliest galaxies which was proved to be external to our own, by Edwin Hubble in 1926; before then, astronomers believed the so-called ‘spiral nebulae’ were objects within our own galaxy.
Galaxy mergers and collisions are rather common within galaxy clusters. The Cartwheel Galaxy suffered a collision millions of years ago when one of the galaxies at the right tore through it. The collision triggered an enormous wave of star formation, which expanded outwards in a ring forming billions of hot blue stars.
M101, also known as the pinwheel galaxy, is a spiral galaxy in Ursa Major, and is the largest member of a galaxy cluster called the M101 group. It was one of the first galaxies found to have a spiral structure.
The first planet to be discovered since ancient times, Uranus is a gas giant orbiting almost three billion kilometres away from the Sun. Like Jupiter and Saturn, Uranus has clouds in its atmosphere, but the contrast between the clouds and their surroundings is very low. Many images show Uranus as an almost featureless blue disc.
