Astronomical vision test: Peering into the depths of space, the sharp-eyed NASA/ESA Hubble Space Telescope has imaged the nearby but faint dwarf galaxy ESO 540-030. This object itself appears as a huge swarm of dim stars, but ESO 540-030 is actually just one point of interest in the picture. ESO 540-030 is just over 11 million light-years distant, and is part of the Sculptor group of galaxies. This collection is the closest neighbour to our own Local Group of galaxies that includes the Milky Way. Due to its proximity the Sculptor group contains some of the brightest galaxies in the southern skies, although ESO 540-030 is not one of these; dwarf galaxies generally have low surface brightness, which make observations difficult. Hubble has captured a snapshot of galaxy types in the background, with spirals, barred spirals, ellipticals and irregulars on display. Careful examination of this picture should allow examples of each galaxy type to be found. Some galaxies lie directly behind ESO 540-030, increasing the challenge. As well as the galaxies there are also five bright stars, which are much closer to us than the galaxies. The telltale diffraction spikes — four sharp lines of light emanating at 90 degree angles, caused by light diffracting in the telescope — are unmistakable signs of the stars in the picture. Cataloguing galaxy types is an important task for scientists attempting to understand more about how our Universe evolved. Our own eyes are excellent tools for this, as participants of the Galaxy Zoo Hubble project will confirm [1]. This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow-orange filter (F606W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 4480 s and 3360 s, respectively and the field of view is about 3.1 arcminutes across. [1] http://www.galaxyzoo.org/

Name: ESO 540-030
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Cetus
Distance: 11 million light years
Release date: 29 August 2011, 10:00
Credit: ESA/Hubble & NASA

A starfish in the sky: In the constellation of Aquila (the Eagle), lies a star nearing the end of its life that is surrounded by a starfish-shaped cloud of gas and dust. A striking image of this object, known as IRAS 19024+0044 has been captured by the NASA/ESA Hubble Space Telescope. Protoplanetary nebulae offer glimpses of how stars similar to the Sun end their lives and how they make the transition to white dwarfs surrounded by planetary nebulae. As it ages, a Sun-like star eventually sheds its outer layers into space, creating a beautiful and often intricately shaped cloud of gas and dust around it. At first, still relatively cool, the star is unable to ionise this gas, which shines only by reflected and scattered stellar light. Only when the temperature of the star increases enough to ionise this protoplanetary nebula does the pattern of gas and dust become a fully fledged planetary nebula. Protoplanetary nebulae are relatively rare and short-lived objects that provide astronomers with clues into how the often strangely asymmetric planetary nebulae are formed. Clearly visible in this image are five blue lobes that extend away from the central star and give the nebula its asymmetric starfish shape. While astronomers have come up with theories for the origin of these structures, such as direction-changing jets or explosive ejections of matter from the star, their formation is not entirely understood. IRAS 19024+0044 is blue in colour as the blue component of the light coming from the star is more easily scattered by the gas and dust in the nebula, while the red and orange rays are relatively unaffected. This is similar to what happens to sunlight in the Earth’s atmosphere, giving the sky its distinctive shade of blue. This picture was created from images taken with the High Resolution Channel of Hubble’s Advanced Camera for Surveys. It is a composite image created by the combination of exposures taken through a yellow–orange filter (F606W, coloured blue) and a near-infrared filter (F814W, coloured red). The total exposure times were 880 s and 140 s, respectively and the field of view is approximately 13 by 13 arcseconds. Links

Name: IRAS 19024+0044
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Aquila
Distance: 11000 light years
Release date: 5 September 2011, 10:00
Credit: ESA/Hubble, NASA and R. Sahai

A remote outpost of the Milky Way: This NASA/ESA Hubble Space Telescope image shows a compact and distant globular star cluster that lies in one of the smallest constellations in the night sky, Delphinus (The Dolphin). Due to its modest size, great distance and relatively low brightness, NGC 7006 is often ignored by amateur astronomers. But even remote globular clusters such as this one appear bright and clear when imaged by Hubble’s Advanced Camera for Surveys. NGC 7006 resides in the outskirts of the Milky Way. It is about 135 000 light-years away, five times the distance between the Sun and the centre of the galaxy, and it is part of the galactic halo. This roughly spherical region of the Milky Way is made up of dark matter, gas and sparsely distributed stellar clusters. Like other remote globular clusters, NGC 7006 provides important clues that help astronomers to understand how stars formed and assembled in the halo. The cluster now pictured by Hubble has a very eccentric orbit indicating that it may have formed independently, in a small galaxy outside our own that was then captured by the Milky Way. Although NGC 7006 is very distant for a Milky Way globular cluster, it is much closer than the many faint galaxies that can be seen in the background of this image. Each of these faint smudges is probably accompanied by many globular clusters similar to NGC 7006 that are too faint to be seen even by Hubble. This image was taken using the Wide Field Channel of the Advanced Camera for Surveys, in a combination of visible and near-infrared light. The field of view is a little over 3 by 3 arcminutes.

Name: NGC 7006
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Delphinus
Distance: 140000 light years
Release date: 12 September 2011, 10:00
Credit: ESA/Hubble & NASA