An archetypal dwarf galaxy: The  constellation of Ursa Major (The Great Bear) is home to Messier 101,  the Pinwheel Galaxy. One of the biggest and brightest spiral galaxies in  the night sky, Messier 101 is also the subject of one of Hubble's most  famous images (heic0602). Like the Milky Way, Messier 101 is not alone, with smaller dwarf galaxies in its neighbourhood. NGC  5477, one of these dwarf galaxies in the Messier 101 group, is the  subject of this image from the NASA/ESA Hubble Space Telescope. Without  obvious structure, but with visible signs of ongoing starbirth, NGC 5477  looks much like an archetypal dwarf irregular galaxy. The bright  nebulae that extend across much of the galaxy are clouds of glowing  hydrogen gas in which new stars are forming. These glow pinkish red in  real life, although the selection of green and infrared filters through  which this image was taken makes them appear almost white. The  observations were taken as part of a project to measure accurate  distances to a range of galaxies within about 30 million light-years  from Earth, by studying the brightness of red giant stars. In  addition to NGC 5477, the image includes numerous galaxies in the  background, including some that are visible right through NGC 5477. This  serves as a reminder that galaxies, far from being solid, opaque  objects, are actually largely made up of the empty space between their  stars. This  image is a combination of exposures taken through green and infrared  filters using Hubble's Advanced Camera for Surveys. The field of view is  approximately 3.3 by 3.3 arcminutes.

Name: NGC 5477
Type: Local Universe : Galaxy : Type : IrregularLocal Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Ursa Major
Distance: 20 million light years
Release date: 7 January 2013, 10:00
Credit: ESA/Hubble & NASA

A busy patch of the Great Attractor: A  busy patch of space has been captured in this image from the NASA/ESA  Hubble Space Telescope. Scattered with many nearby stars, the field also  has numerous galaxies in the background. Located  on the border of Triangulum Australe (The Southern Triangle) and Norma  (The Carpenter’s Square), this field covers part of the Norma Cluster  (Abell 3627) as well as a dense area of our own galaxy, the Milky Way. The  Norma Cluster is the closest massive galaxy cluster to the Milky Way,  and lies about 220 million light-years away. The enormous mass  concentrated here, and the consequent gravitational attraction, mean  that this region of space is known to astronomers as the Great  Attractor, and it dominates our region of the Universe. The  largest galaxy visible in this image is ESO 137-002, a spiral galaxy  seen edge on. In this image from Hubble, we see large regions of dust  across the galaxy’s bulge. What we do not see here is the tail of glowing X-rays that has been observed extending out of the galaxy — but which is invisible to an optical telescope like Hubble. Observing  the Great Attractor is difficult at optical wavelengths. The plane of  the Milky Way — responsible for the numerous bright stars in this image —  both outshines (with stars) and obscures (with dust) many of the  objects behind it. There are some tricks for seeing through this —  infrared or radio observations, for instance — but the region behind the  centre of the Milky Way, where the dust is thickest, remains an almost  complete mystery to astronomers. This image consists of exposures in blue and infrared light taken by Hubble’s Advanced Camera for Surveys.

Name: Abell 3627, ESO 137-002
Type: Local Universe : Galaxy : Type : SpiralLocal Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Triangulum Australe
Distance: z=0.018 (redshift)
Release date: 14 January 2013, 10:00
Credit: ESA/Hubble & NASA

Appearances can be deceptive: Globular  clusters are roughly spherical collections of extremely old stars, and  around 150 of them are scattered around our galaxy. Hubble is one of the  best telescopes for studying these, as its extremely high resolution  lets astronomers see individual stars, even in the crowded core. The  clusters all look very similar, and in Hubble’s images it can be quite  hard to tell them apart – and they all look much like NGC 411, pictured  here. And  yet appearances can be deceptive: NGC 411 is in fact not a globular  cluster, and its stars are not old. It isn’t even in the Milky Way. NGC  411 is classified as an open cluster. Less tightly bound than a  globular cluster, the stars in open clusters tend to drift apart over  time as they age, whereas globulars have survived for well over 10  billion years of galactic history. NGC 411 is a relative youngster — not  much more than a tenth of this age. Far from being a relic of the early  years of the Universe, the stars in NGC 411 are in fact a fraction of  the age of the Sun. The  stars in NGC 411 are all roughly the same age, having formed in one go  from one cloud of gas. But they are not all the same size. Hubble’s  image shows a wide range of colours and brightnesses in the cluster’s  stars. These tell astronomers many facts about the stars, including  their mass, temperature and evolutionary phase. Blue stars, for  instance, have higher surface temperatures than red ones. The  image is a composite produced from ultraviolet, visible and infrared  observations made by Hubble’s Wide Field Camera 3. This filter set lets  the telescope “see” colours slightly further beyond red and the violet  ends of the spectrum.

Name: NGC 411
Type: Local Universe : Star : Grouping : Cluster : Open
Category: Star Clusters
Constellation: Tucana
Distance: 200000 light years
Release date: 21 January 2013, 10:00
Credit: ESA/Hubble & NASA