Starship Asterisk*

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The faint light extending up from the horizon just below centre of this photo is known as zodiacal light, caused by sunlight scattering from cosmic dust in the plane of our Earth’s orbit.

A second band of light can be seen at the horizon on the lower left. This red light is airglow, produced by the Earth’s atmosphere. Airglow is caused by processes taking place in the upper atmosphere, including cosmic rays, recombining photoionized atoms, and various chemical reactions between oxygen, nitrogen, hydroxyl, sodium, and lithium atoms.

The third and final band is the Milky Way, our home galaxy, high in the sky. This band consists of billions of stars of all kinds. Many of them are hidden to the human eye behind large layers of interstellar dust, giving the Milky Way its characteristically mottled look.

At the centre of the image stands ESO Photo ambassador Babak Tafreshi, watching the light spectacle unfold around him. His fellow photo ambassador Yuri Beletsky captured this image during the ESO UHD Expedition in 2014, as Babak travelled through the Chilean desert to visit the sites of ESO’s telescopes.

[img3="Credit: ESA/Hubble & NASA -- Acknowledgement: Judy Schmidt"]http://cdn.spacetelescope.org/archives/ ... w1614a.jpg[/img3][hr][/hr]

This striking NASA/ESA Hubble Space Telescope image captures the galaxy UGC 477, located just over 110 million light-years away in the constellation of Pisces (The Fish).

UGC 477 is a low surface brightness (LSB) galaxy. First proposed in 1976 by Mike Disney, the existence of LSB galaxies was confirmed only in 1986 with the discovery of Malin 1. LSB galaxies like UGC 477 are more diffusely distributed than galaxies such as Andromeda and the Milky Way. With surface brightnesses up to 250 times fainter than the night sky, these galaxies can be incredibly difficult to detect.

Most of the matter present in LSB galaxies is in the form of hydrogen gas, rather than stars. Unlike the bulges of normal spiral galaxies, the centres of LSB galaxies do not contain large numbers of stars. Astronomers suspect that this is because LSB galaxies are mainly found in regions devoid of other galaxies, and have therefore experienced fewer galactic interactions and mergers capable of triggering high rates of star formation.

LSB galaxies such as UGC 477 instead appear to be dominated by dark matter, making them excellent objects to study to further our understanding of this elusive substance. However, due to an underrepresentation in galactic surveys — caused by their characteristic low brightness — their importance has only been realised relatively recently.

Ann wrote:Hubble Peers at a Distinctly Disorganized Dwarf Galaxy

[img3="Credit: ESO / Babak Tafreshi (TWAN)"]http://cdn.eso.org/images/screen/potw1615a.jpg[/img3][hr][/hr]

This Auxiliary Telescope at the Very Large Telescope (VLT), located at the Paranal Observatory in Chile, looks to be pointing at the greenish emerald glow of the comet 252P/LINEAR high above it.

Discovered in April 2000, 252P/LINEAR is a relative newcomer to the inner Solar System, traveling between the orbit of Jupiter and the orbit of Earth. A couple of days ago, in March 2016, it passed particularly close to the Earth, at a distance of only 5.2 millions kilometers, ranking as the fifth closest recorded passage of a comet. It can still be admired in the southern hemisphere. The green colour arises from fluorescing carbon-based gas surrounding the comet.

This gem of a picture was taken by the ESO Photo Ambassador Babak A. Tafreshi. He has just started out on ESO’s Fulldome Expedition, during which he will be taking more spectacular pictures from ESO’s observatories and of the southern hemisphere night sky.

[img3="Credit: NASA/ESA/Hubble - Acknowledgement: Judy Schmidt"]http://cdn.spacetelescope.org/archives/ ... w1615a.jpg[/img3]

At first glance this NASA/ESA Hubble Space Telescope image seems to show an array of different cosmic objects, but the speckling of stars shown here actually forms a single body — a nearby dwarf galaxy known as Leo A. Its few million stars are so sparsely distributed that some distant background galaxies are visible through it. Leo A itself is at a distance of about 2.5 million light-years from Earth and a member of the Local Group of galaxies; a group that includes the Milky Way and the well-known Andromeda galaxy.

Astronomers study dwarf galaxies because they are very numerous and are simpler in structure than their giant cousins. However, their small size makes them difficult to study at great distances. As a result, the dwarf galaxies of the Local Group are of particular interest, as they are close enough to study in detail.

As it turns out, Leo A is a rather unusual galaxy. It is one of the most isolated galaxies in the Local Group, has no obvious structural features beyond being a roughly spherical mass of stars, and shows no evidence for recent interactions with any of its few neighbours. However, the galaxy’s contents are overwhelmingly dominated by relatively young stars, something that would normally be the result of a recent interaction with another galaxy. Around 90% of the stars in Leo A are less than eight billion years old — young in cosmic terms! This raises a number of intriguing questions about why star formation in Leo A did not take place on the “usual” timescale, but instead waited until it was good and ready.

bystander wrote:A Case of Suspended Animation? (Leo A)
ESA Hubble Picture of the Week | 2016 Apr 11

[img3="Credit: NASA/ESA/Hubble - Acknowledgement: Judy Schmidt"]http://cdn.spacetelescope.org/archives/ ... w1615a.jpg[/img3]

At first glance this NASA/ESA Hubble Space Telescope image seems to show an array of different cosmic objects, but the speckling of stars shown here actually forms a single body — a nearby dwarf galaxy known as Leo A. Its few million stars are so sparsely distributed that some distant background galaxies are visible through it. Leo A itself is at a distance of about 2.5 million light-years from Earth and a member of the Local Group of galaxies; a group that includes the Milky Way and the well-known Andromeda galaxy.

Astronomers study dwarf galaxies because they are very numerous and are simpler in structure than their giant cousins. However, their small size makes them difficult to study at great distances. As a result, the dwarf galaxies of the Local Group are of particular interest, as they are close enough to study in detail.

As it turns out, Leo A is a rather unusual galaxy. It is one of the most isolated galaxies in the Local Group, has no obvious structural features beyond being a roughly spherical mass of stars, and shows no evidence for recent interactions with any of its few neighbours. However, the galaxy’s contents are overwhelmingly dominated by relatively young stars, something that would normally be the result of a recent interaction with another galaxy. Around 90% of the stars in Leo A are less than eight billion years old — young in cosmic terms! This raises a number of intriguing questions about why star formation in Leo A did not take place on the “usual” timescale, but instead waited until it was good and ready.