NGC 3021 NICMOS/ACS detail 1: This image is part of a montage of images of the spiral galaxy NGC 3021 taken by the NASA/ESA Hubble Space Telescope. Hubble made precise measurements of Cepheid variable stars in the galaxy, highlighted in this image. These stars pulsate at a rate that is matched closely to their intrinsic brightness. This makes them ideal for measuring intergalactic distances. The Cepheids are used to calibrate an even brighter milepost marker that can be used over greater distances, a Type Ia supernova. The supernova was observed in the galaxy in 1995. The image was taken with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Name: NGC 3021
Type: Local Universe : Star : Type : VariableLocal Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo Minor
Distance: 90 million light years
Release date: 7 May 2009, 15:00
Credit: NASA, ESA and A. Riess (STScI/JHU)

NGC 3021 NICMOS/ACS detail 2: This image is part of a montage of images of the spiral galaxy NGC 3021 taken by the NASA/ESA Hubble Space Telescope. Hubble made precise measurements of Cepheid variable stars in the galaxy, highlighted in this image. These stars pulsate at a rate that is matched closely to their intrinsic brightness. This makes them ideal for measuring intergalactic distances. The Cepheids are used to calibrate an even brighter milepost marker that can be used over greater distances, a Type Ia supernova. The supernova was observed in the galaxy in 1995. The image was taken with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

Name: NGC 3021
Type: Local Universe : Star : Type : VariableLocal Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo Minor
Distance: 90 million light years
Release date: 7 May 2009, 15:00
Credit: NASA, ESA and A. Riess (STScI/JHU)

M87 nucleus and bright knot: Image taken on 17 May 1999.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

M87 nucleus and bright knot: Image taken on 17 July 2002.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

M87 nucleus and bright knot: Image taken on 27 February 2002.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

M87 nucleus and bright knot: Image taken on 17 April 2003.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

M87 nucleus and bright knot: Image taken on 9 May 2005.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

M87 nucleus and bright knot: Image taken on 28 November 2006.

Name: M87, Messier 87, NGC 4486
Type: Local Universe : Galaxy : Type : EllipticalLocal Universe : Galaxy : Component : Central Black HoleLocal Universe : Galaxy : Size : Giant
Category: Galaxies
Constellation: Virgo
Distance: 55 million light years
Release date: 14 April 2009, 15:00
Credit: NASA, ESA and J. Madrid (McMaster University, Canada)

Galaxy cluster MACS J0717: This composite image shows the massive galaxy cluster MACS J0717.5+3745 (MACS J0717, for short), where four separate galaxy clusters have been involved in a collision — the first time such a phenomenon has been documented. Hot gas is shown in an image from NASA's Chandra X-ray Observatory, and galaxies are shown in an optical image from the NASA/ESA Hubble Space Telescope. The hot gas is colour-coded to show temperature, where the coolest gas is reddish purple, the hottest gas is blue, and the temperatures in between are purple. The repeated collisions in MACS J0717 are caused by a 13-million-light-year-long stream of galaxies, gas, and dark matter — known as a filament — pouring into a region already full of matter. A collision between the gas in two or more clusters causes the hot gas to slow down. However, the massive and compact galaxies do not slow down as much as the gas does, and so move ahead of it. Therefore, the speed and direction of each cluster's motion — perpendicular to the line of sight — can be estimated by studying the offset between the average position of the galaxies and the peak in the hot gas. MACS J0717 is located about 5.4 billion light-years from Earth. It is one of the most complex galaxy clusters ever seen. Other well-known clusters, like the Bullet Cluster and MACS J0025.4-1222, involve the collision of only two galaxy clusters and show much simpler geometry.

Name: MACS J0717.5+3745
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Galaxies
Constellation: Auriga
Distance: z=0.545 (redshift)
Release date: 16 April 2009, 17:00
Credit: NASA, ESA, CXC, C. Ma, H. Ebeling and E. Barrett (University of Hawaii/IfA), et al. and STScI

Hubble ACS image of NGC 4163: This image, taken by the NASA/ESA Hubble Space Telescope, shows myriad stars residing in the central region of the dwarf galaxy NGC 4163. The bluish dots are younger stars; the reddish dots, older stars. The irregularly shaped red blobs are regions of current starburst activity. Starbursts are areas of intense star formation. NGC 4163 is part of a Hubble study of starbursts in nearby, small, or dwarf, galaxies. Based on this study, astronomers have found that starbursts continue 100 times longer than first thought, lasting 200 million to 400 million years. These galaxies show that starbursts are not isolated events, but sweep across a galaxy.

Name: NGC 4163
Type: Local Universe : Galaxy : Size : DwarfLocal Universe : Galaxy : Activity : Starburst
Category: Galaxies
Constellation: Canes Venatici
Distance: 10 million light years
Release date: 30 April 2009, 15:00
Credit: NASA, ESA and K. McQuinn (University of Minnesota, Minneapolis)

Hubble ACS image of NGC 4068: This image, taken by the NASA/ESA Hubble Space Telescope, shows myriad stars residing in the central regions of the dwarf galaxy NGC 4068. The bluish dots are younger stars; the reddish dots, older stars. NGC 4068, located 14 million light-years away in the Ursa Major constellation, is part of a Hubble study of starbursts in nearby, small, or dwarf, galaxies. Based on this study, astronomers have found that starbursts continue 100 times longer than first thought, lasting 200 million to 400 million years. These galaxies show that starbursts are not isolated events, but sweep across a galaxy.

Name: NGC 4068
Type: Local Universe : Galaxy : Size : DwarfLocal Universe : Galaxy : Activity : Starburst
Category: Galaxies
Constellation: Ursa Major
Distance: 14 million light years
Release date: 30 April 2009, 15:00
Credit: NASA, ESA and K. McQuinn (University of Minnesota, Minneapolis)