The massive 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 the Chandra X-ray Observatory, and galaxies are shown in an optical image from the Hubble Space Telescope. The hot gas is color-coded to show temperature, where the coolest gas is reddish purple, the hottest gas is blue, and the temperatures in between are purple. MACS J0717 is located about 5.4 billion light-years from Earth. It is one of the most complex galaxy clusters ever seen.
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
© Stocktrek Images
The Great Lakes, ISS image C016/3870
The Great Lakes. View from the International Space Station (ISS) of the Great Lakes of the USA and Canada. North is towards upper right. Here, the ISS is over a point to the southeast of Nova Scotia. Sunglint is seen on Lake Ontario (lower right) and Lake Huron (upper right). Lake Erie is at upper left. Much of central Canada (across top) is obscured by extensive cloud cover, whereas a smaller grouping of clouds obscures the Appalachian mountains and Pennsylvania (lower left) in the USA. The thin blue envelope (haze) of Earth's atmosphere is visible above the curved limb across top. Photographed by an Expedition 31 crew member on 14 June 2012
© NASA/SCIENCE PHOTO LIBRARY
Milky Way, zodiacal light and other celestial objects from summit of Gila National Wilderness
A 160 degree panorama showing the zodiacal light (at right in the west), the Milky Way, the zodiacal band across the frame at top, and the Gegenschein (a brightening of the zodiacal band at left of frame in the east in Leo). Along the Milky Way are dark lanes of interstellar dust, particularly in Taurus above and to the right of Orion. Red nebulae of glowing gas also lie along the Milky Way, such as Barnardas Loop around Orion.
The zodiacal light, zodiacal band and Gegenschein all lie along the ecliptic, as do Mars, Venus and Jupiter shown here.
Orion is at centre, in the south, with Canis Major and the bright star Sirius below and to the left of Orion. Canopus is just setting on the southern horizon at centre.
To the right of Orion is Taurus and the Pleiades star cluster at the top of the zodiacal light pyramid.
Venus is the bright object in the zodiacal light at right, in the west, while fainter Mars is below Venus.
At far right, in the northwest, is the Andromeda Galaxy, M31.
Jupiter is the bright object at upper left, in the east, in the zodiacal band, and near the Beehive star cluster.
The zodiacal light, zodiacal band and and Gegenschein are caused by sunlight reflecting off cometary and meteoric dust in the inner solar system. The Gegenschein, or counterglow, can be seen with the naked eye but is a subtle and diffuse brightening of the sky in the spot opposite the Sun. It is caused by sunlight reflecting directly back from comet dust, with the effect greatest at the point opposite the Sun.
Glows on the horizon are from distant SIlver City, Las Cruces and El Paso. The brighter sky at right is from the last vestiges of evening twilight. Some green and red airglow bands also permeate the sky.
This image photographed March 10, 2015 from the summit of Highway 15 through the Gila National Wilderness north of Silver City, in New Mexico, from an altitude of 7900 feet. The panorama takes in 160A° of sky from the western (right) to the east (left) and from below the horizon to past the zenith point overhead. It is a stitch, with PTGui software, of 5 segments, each consisting of 2 stacked 3-minute exposures, at f/3.5 with the 15mm full-frame fish-eye lens, on the Canon 5D Mark II at ISO 1600. The camera was on the Sky-Watcher Star Adventurer tracker, so the stars are sharp but the ground is slightly blurred. This version is re-rendered to be more rectangular and less fish-eye in appearance from the original, though in doing so is cropped somewhat
© Alan Dyer/Stocktrek Images