Found images: 2016 April

[Sandgirl]

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Have you seen a great image or video somewhere that you think would make a great APOD? Nominate it for APOD! Please post as much information here as you have about the image/video with a link to any source(s) for it you know of here, and the editors will take a look.

When posting the image itself, please do not post anything larger than a thumbnail here; please honor the copyright holder's copyright.

Please keep hotlinked images under 400K.

Thank you!

[bystander]

Three Bands of Light
ESO Picture of the Week | 2016 Apr 04

[c][attachment=0]potw1614a[1].jpg[/attachment][/c][hr][/hr]

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.

[bystander]

Hiding in the Night Sky (UGC 477)
ESA Hubble Picture of the Week | 2016 Apr 04

[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.

[starsurfer]

SMC
http://www.astrobin.com/212006/C/
Copyright: Rick Stevenson

http://www.astrobin.com/211572/

Click to view full size image 1 or image 2

[starsurfer]

NGC 6503
http://hubblesite.org/newscenter/archiv ... s/2015/23/
Copyright: NASA, ESA, D. Calzetti (University of Massachusetts), H. Ford (Johns Hopkins University), and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

http://asterisk.apod.com/viewtopic.php?t=34827#p244372

[starsurfer]

Trumpler 10
http://www.astro-austral.cl/imagenes/st ... 0/info.htm
Copyright: José Joaquín Pérez

The pink emission nebula is Gum 17 and the small red emission nebula is K2-15.

[starsurfer]

NGC 2903
http://www.martinpughastrophotography.id.au
Copyright: Martin Pugh

[starsurfer]

Helix Nebula (NGC 7293)
http://www.caelumobservatory.com/gallery/n7293.shtml
Copyright: Adam Block/Mount Lemmon SkyCenter/University of Arizona

[starsurfer]

LBN 777
http://www.astroimager.net/Page-RHA-CCD-382.html
Copyright: Jim Janusz

[starsurfer]

M78
http://astrophotography.aa6g.org/Astrop ... vs130.html
Copyright: Chuck Vaughn

[Ann]

Hubble Peers at a Distinctly Disorganized Dwarf Galaxy

Click to view full size image

UGC 4459. Image Credit: ESA/Hubble and NASA;
Acknowledgement: Judy Schmidt

I find this tiny dwarf galaxy singularly lovely. The large complex of star formation above center consists of a series of broken and unbroken bubbles and looks like an aquatic pink baby dinosaur swimming from right to left. At top center is what looks like one or possibly two globular clusters. Background galaxies are peeking through everywhere. There is a substantial population of old stars, but young blue and ultraviolet stars contribute so much light that the U-B and B-V colors of UGC 4459 are -0.40 and +0.35. Both values are very blue.

Ann

[bystander]

Hubble Peers at a Distinctly Disorganized Dwarf Galaxy

http://asterisk.apod.com/viewtopic.php?p=255817#p255817

[starsurfer]

vdB152
http://www.darkskywalker.com/Photograph ... ZKZ5L2f/X3
Copyright: Jimmy Walker

Click to view full size image

[starsurfer]

Lupus 3 Cloud
https://www.eso.org/public/images/eso1303a/
Copyright: ESO/F. Comeron

You can read more about the Lupus clouds here.

[starsurfer]

NGC 6340
http://bf-astro.com/ngc6340/ngc6340.htm
Copyright: Bob Franke

[philto]

AR 2529 today 10th of April
204mm Ha refractor pst modified 1A + bf-15 + Barlow 3x.
3 views mozaic.

Click to view full size image

[bystander]

An Emerald in the Sky (252P/LINEAR)
ESO Picture of the Week | 2016 Apr 11

[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.

[bystander]

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.

[Ann]

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.

Fascinating!

If Leo A is identical to UGC 5364, as I think it is, then its colors are just extremely blue, if we are to believe Principal Galaxy Catalog (PGC).According to PGC, the U-B and B-V indexes of Leo A are -0.19 and +0.33. Both values are really very blue. But according to Simbad astronomical database, the B-V index of UGC 5364 is +0.8, which is rather red. The difference between a B-V of +0.33 and a B-V of +0.8 is huge.

I can see from the spacetelescope.org page that two or three filters have been used for the image. One filter is the infrared 814 nm one, and the one or two others are 475 nm and 439 nm. The two latter filters are both blue, and therefore it seems certain that the blue-looking stars in Leo A are indeed rather hot. There is clearly a good number of blue stars in Leo A, and several of them are moderately bright. It seems certain that many of them belong to spectral class A, and it is in fact possible that there are several individual B-type stars in this galaxy.

But really, what is the galaxy's B-V index? Inquiring minds want to know!

Ann

[philto]

AR 2529 in white light
204 mm F8.8 refractor + Barlow 3x + continuum filter / Basler 1920-155
regards
image : Philippe TOSI

Click to view full size image

[starsurfer]

Christmas Tree Cluster (NGC 2264) widefield
http://www.astrosurf.com/ilizaso/orriak ... Q_U16m.htm
Copyright: Iñaki Lizaso

A challenge, can anyone find Hubble's Variable Nebula?

[starsurfer]

Hercules Galaxy Cluster (Abell 2151)
http://www.alessandrofalesiedi.it/deep-sky/abell-2151/
Copyright: Alessandro Falesiedi

[starsurfer]

NGC 2340
http://www.astrobin.com/236097/
Copyright: Tero Turunen

[starsurfer]

B252
http://www.astropilar.com.ar/nebulosas/B252_1.html
Copyright: Ezequiel Bellocchio

[starsurfer]

Sh2-132
http://www.stern-fan.de/Seiten/galerie_ ... RGB_2.html
Copyright: Rolf Geissinger

The planetary nebula in the bottom left corner is Abell 79.