(via APOD: 2012 October 25 - The Medusa Nebula)
The Medusa Nebula Image Credit & Copyright: Ken Crawford (Rancho Del Sol Obs.)
Abell 21 is a planetary nebula, the death throes of a low-mass star like the Sun, throwing off the layers left over from giant stages, and, as the star changes into a white dwarf, the ultraviolet radiation causes the gas to glow from ionization and de-ionization.
1500 light-years away in Gemini, the Medusa is about 4 light-years across.

(via APOD: 2012 October 25 - The Medusa Nebula)

The Medusa Nebula 
Image Credit & CopyrightKen Crawford (Rancho Del Sol Obs.)

Abell 21 is a planetary nebula, the death throes of a low-mass star like the Sun, throwing off the layers left over from giant stages, and, as the star changes into a white dwarf, the ultraviolet radiation causes the gas to glow from ionization and de-ionization.

1500 light-years away in Gemini, the Medusa is about 4 light-years across.

(via APOD: 2012 October 26 - Reflection Nebula vdB1)
Reflection Nebula vdB1 Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona
The bright blue reflection nebula pictured here is the first entry in the van den Bergh Catalog (vdB) of 158 items seen more easily from the northern hemisphere, including quite a few popular astrophotography targets.
The interstellar dust scattering blue light in this picture is seen out toward Cassiopeia, about 1600 light-years away. The APOD editors also mention the interesting loops of bright gas and dust on the right side of the image:
“ Also on this scene, two intriguing nebulae at the right show loops and outflow features associated with the energetic process of star formation. Within are extremely young variable stars V633 Cas (top) and V376 Cas.”

(via APOD: 2012 October 26 - Reflection Nebula vdB1)

Reflection Nebula vdB1 
Image Credit & CopyrightAdam BlockMt. Lemmon SkyCenterUniversity of Arizona

The bright blue reflection nebula pictured here is the first entry in the van den Bergh Catalog (vdB) of 158 items seen more easily from the northern hemisphere, including quite a few popular astrophotography targets.

The interstellar dust scattering blue light in this picture is seen out toward Cassiopeia, about 1600 light-years away. The APOD editors also mention the interesting loops of bright gas and dust on the right side of the image:

 Also on this scene, two intriguing nebulae at the right show loops and outflow features associated with the energetic process of star formation. Within are extremely young variable stars V633 Cas (top) and V376 Cas.”

(via APOD: 2012 September 29 - NGC 7023: The Iris Nebula)
Out 1,300 light-years, in the direction of Cepheus, the King (who really looks like a kid’s drawing of a house, but don’t mention it to him), is a molecular cloud that may have PAHs, complex carbon molecules. We know for sure, though, that it has given birth to a bright young star, powering this nebula’s glow. The majority is blue, reflected starlight bouncing off the dust and heading our way. However, you can see lovely faint lines of red, where we see evidence of the ultraviolet radiation from the star ionizing hydrogen in the surrounding gas and dust. When it de-ionized, the hydrogen releases a red-wavelength photon.
Gorgeous and scientific all at once, much like its eponymous flower.

(via APOD: 2012 September 29 - NGC 7023: The Iris Nebula)

Out 1,300 light-years, in the direction of Cepheus, the King (who really looks like a kid’s drawing of a house, but don’t mention it to him), is a molecular cloud that may have PAHs, complex carbon molecules. We know for sure, though, that it has given birth to a bright young star, powering this nebula’s glow. The majority is blue, reflected starlight bouncing off the dust and heading our way. However, you can see lovely faint lines of red, where we see evidence of the ultraviolet radiation from the star ionizing hydrogen in the surrounding gas and dust. When it de-ionized, the hydrogen releases a red-wavelength photon.

Gorgeous and scientific all at once, much like its eponymous flower.

(via Ceci *est* une pipe | Bad Astronomy | Discover Magazine)
Wow! The @ESO folks  (#ESO50years) have captured this amazing shot of the “mouth” of the Pipe Nebula from the MPG/ESO 2.2m telescope in the La Silla Observatory in Chile.
Another combination of dark and reflection nebula like the one in Corona Australis posted earlier, this one also shows the effect of seeing the light coming though (instead of being reflected off) a thinner amount of dust. Note the color of the background stars toward the edges of the dark nebula. The light is still being scattered with a blue preference, but that means that the blue reflection light would be seen from a vantage point on the other side of the nebula. Instead, we see the redder light that manages to get through the thin spots in the dust.
As Phil says, this is a huge complex of interstellar gas and dust, and there are stars forming inside of it. In fact, the stars we see lighting up the reflecting parts of the nebula are newly formed stars that just happen to be on “our side” of the complex cloud of dust particles.
As if all that weren’t enough, this is just a zoom on the one part of the Pipe Nebula. Here’s the full thing, which includes catalog members Barnard 59 (the part in the image above), Barnard 65-67, and Barnard 78:

This is, again, from the folks at the European Southern Observatory.
One final cool thing. See the fuzzy stars in the middle of Barnard 59? Those aren’t background stars that are so bright they’re shining through. Those are stars being born right before your eyes! (Or, being born 600-700 years ago, as the nebula is about that many light-years away.)

(via Ceci *est* une pipe | Bad Astronomy | Discover Magazine)

Wow! The @ESO folks  (#ESO50years) have captured this amazing shot of the “mouth” of the Pipe Nebula from the MPG/ESO 2.2m telescope in the La Silla Observatory in Chile.

Another combination of dark and reflection nebula like the one in Corona Australis posted earlier, this one also shows the effect of seeing the light coming though (instead of being reflected off) a thinner amount of dust. Note the color of the background stars toward the edges of the dark nebula. The light is still being scattered with a blue preference, but that means that the blue reflection light would be seen from a vantage point on the other side of the nebula. Instead, we see the redder light that manages to get through the thin spots in the dust.

As Phil says, this is a huge complex of interstellar gas and dust, and there are stars forming inside of it. In fact, the stars we see lighting up the reflecting parts of the nebula are newly formed stars that just happen to be on “our side” of the complex cloud of dust particles.

As if all that weren’t enough, this is just a zoom on the one part of the Pipe Nebula. Here’s the full thing, which includes catalog members Barnard 59 (the part in the image above), Barnard 65-67, and Barnard 78:

This is, again, from the folks at the European Southern Observatory.

One final cool thing. See the fuzzy stars in the middle of Barnard 59? Those aren’t background stars that are so bright they’re shining through. Those are stars being born right before your eyes! (Or, being born 600-700 years ago, as the nebula is about that many light-years away.)

(via APOD: 2012 September 27 - Stars and Dust Across Corona Australis)
Stars and Dust Across Corona Australis Image Credit & Copyright: Marco Lorenzi (Glittering Lights)
Corona Australis is the Southern Crown. (Here in the northern hemisphere, we have Bootes holding Corona Borealis in the night sky. Bootes, the herdsman, is the constellation that Arcturus is in. Remember “arc to Arcturus and spike to Spica”. Spica is in Virgo.)
In any case, there’s a crown in the skies of the southern hemisphere too, and that’s where you can see this interesting collection of dust, along with a globular cluster…at least in the same line of sight.
The blue light you see in the nebulae is from the stars embedded in the dust, and is being reflected back toward us. Blue light scatters more readily in the dust of the interstellar medium, so more blue than red is being bounced off the “grains” (think something the size of soot) back at us.
The dark areas are where the dust is so thick between our point of view and the star field that we can’t see through it in visible wavelengths. An infrared image would see through it, and into it, to see what’s going on.
The cloud of dust creating this nebular complex is about 500 light-years away, but the globular cluster in the upper left of the image, while appearing close, is actually about 30,000 light-years away, far beyond the dust and stars of the nebulae. They’re very old, gravitationally bound collections of stars that orbit the galaxy, but not necessarily in the galactic plane. This one is NGC 6729.

(via APOD: 2012 September 27 - Stars and Dust Across Corona Australis)

Stars and Dust Across Corona Australis 
Image Credit & Copyright: Marco Lorenzi (Glittering Lights)

Corona Australis is the Southern Crown. (Here in the northern hemisphere, we have Bootes holding Corona Borealis in the night sky. Bootes, the herdsman, is the constellation that Arcturus is in. Remember “arc to Arcturus and spike to Spica”. Spica is in Virgo.)

In any case, there’s a crown in the skies of the southern hemisphere too, and that’s where you can see this interesting collection of dust, along with a globular cluster…at least in the same line of sight.

The blue light you see in the nebulae is from the stars embedded in the dust, and is being reflected back toward us. Blue light scatters more readily in the dust of the interstellar medium, so more blue than red is being bounced off the “grains” (think something the size of soot) back at us.

The dark areas are where the dust is so thick between our point of view and the star field that we can’t see through it in visible wavelengths. An infrared image would see through it, and into it, to see what’s going on.

The cloud of dust creating this nebular complex is about 500 light-years away, but the globular cluster in the upper left of the image, while appearing close, is actually about 30,000 light-years away, far beyond the dust and stars of the nebulae. They’re very old, gravitationally bound collections of stars that orbit the galaxy, but not necessarily in the galactic plane. This one is NGC 6729.

(via APOD: 2012 September 9 - Wisps Surrounding the Horsehead Nebula)
Image Credit & Copyright: Star Shadows Remote Observatory
See the little horse-head? That’s the Horsehead Nebula. It’s not exactly a little nebula off by itself. It’s part of a larger molecular cloud complex in Orion.
This show was taken with a very long (7 hour) exposure of hydrogen-alpha in red and overlaid on a broadband (full color) image taken over a 3 hour interval to capture the background star field.

(via APOD: 2012 September 9 - Wisps Surrounding the Horsehead Nebula)

Image Credit & Copyright: Star Shadows Remote Observatory

See the little horse-head? That’s the Horsehead Nebula. It’s not exactly a little nebula off by itself. It’s part of a larger molecular cloud complex in Orion.

This show was taken with a very long (7 hour) exposure of hydrogen-alpha in red and overlaid on a broadband (full color) image taken over a 3 hour interval to capture the background star field.

(via APOD: 2012 August 28 - Colorful Clouds Near Rho Ophiuchi)
Image Credit & Copyright: Tom O’Donoghue
Oooh! A lesson in the forms and varieties of nebulae all in one picture. OK, so there are three main kinds of nebulae:
Reflection
Emission
Dark
They’re produced by different processes too, so here’s what’s going on above:
Rho Ophiuchi, the bright blue star in the center of the top blue nebula is emitting regular light that is being scattered off the dust in the nebular clouds. Dust particles tend to scatter blue light more than any other wavelength of light, so the reflected light from the nebula is blue. Hence, reflection nebulae look blue.
To the lower-right, you can see Sigma Scorpii, a bright blue star in the middle of a red nebula. When the ultraviolet radiation from a star hit gas clouds, made mostly from hydrogen, they ionize the gas, stripping the electrons off the atoms. Atoms don’t stay that way forever, though, and they have a tendency to pull an electron back at some point, de-ionizing themselves. When that happens, it releases energy in the form of electromagnetic radiation, usually as red light. We see the light being emitted from the gas as it de-ionizes.
Finally, in all those spots, mostly in the middle of the picture, where you might be worried that the photographer’s camera has some sensing issues, where we’re not seeing any background starlight, or really anything at all, those are areas where there’s too much dust, in the way, making a dark spot in the sky.
Oh, a couple other things:
Big, bright, red supergiant Antares in the lower middle is so red that even it’s reflected light is yellow-red.
M4 is the globular cluster just to right of Antares, an ancient relic of the universe, as are all the globular clusters we’ve ever seen. They orbit the Milky Way and are generally around 12-13 billion years old.
Boy do I love this astronomy stuff.

(via APOD: 2012 August 28 - Colorful Clouds Near Rho Ophiuchi)

Image Credit & Copyright: Tom O’Donoghue

Oooh! A lesson in the forms and varieties of nebulae all in one picture. OK, so there are three main kinds of nebulae:

  • Reflection
  • Emission
  • Dark

They’re produced by different processes too, so here’s what’s going on above:

Rho Ophiuchi, the bright blue star in the center of the top blue nebula is emitting regular light that is being scattered off the dust in the nebular clouds. Dust particles tend to scatter blue light more than any other wavelength of light, so the reflected light from the nebula is blue. Hence, reflection nebulae look blue.

To the lower-right, you can see Sigma Scorpii, a bright blue star in the middle of a red nebula. When the ultraviolet radiation from a star hit gas clouds, made mostly from hydrogen, they ionize the gas, stripping the electrons off the atoms. Atoms don’t stay that way forever, though, and they have a tendency to pull an electron back at some point, de-ionizing themselves. When that happens, it releases energy in the form of electromagnetic radiation, usually as red light. We see the light being emitted from the gas as it de-ionizes.

Finally, in all those spots, mostly in the middle of the picture, where you might be worried that the photographer’s camera has some sensing issues, where we’re not seeing any background starlight, or really anything at all, those are areas where there’s too much dust, in the way, making a dark spot in the sky.

Oh, a couple other things:

  1. Big, bright, red supergiant Antares in the lower middle is so red that even it’s reflected light is yellow-red.
  2. M4 is the globular cluster just to right of Antares, an ancient relic of the universe, as are all the globular clusters we’ve ever seen. They orbit the Milky Way and are generally around 12-13 billion years old.

Boy do I love this astronomy stuff.

(via APOD: 2012 June 1 - A Sagittarius Triplet)
At the top is NGC 6559, separated from the Lagoon Nebula by a dust lane, with M8 dominating the frame (that’s the Lagoon’s Messier designation), and the multi-colored Trifid Nebula, M20, off to the right.
All three of these are star-forming regions in Sagittarius, the centaur archer shooting his arrow at Antares, the heart of Scorpio. It happens that Sagittarius sits over the central Milky Way, so there is a lot of dust and gas.
As a final bonus, M21, an open star cluster, is sitting just above the Trifid. (The Trifid, in case you are wondering, is named as such because it shows off all three types of nebulae: emission (red), reflection (blue), dark (lack of light, obscured by dust).)
Image Credit & Copyright: Martin Pugh

(via APOD: 2012 June 1 - A Sagittarius Triplet)

At the top is NGC 6559, separated from the Lagoon Nebula by a dust lane, with M8 dominating the frame (that’s the Lagoon’s Messier designation), and the multi-colored Trifid Nebula, M20, off to the right.

All three of these are star-forming regions in Sagittarius, the centaur archer shooting his arrow at Antares, the heart of Scorpio. It happens that Sagittarius sits over the central Milky Way, so there is a lot of dust and gas.

As a final bonus, M21, an open star cluster, is sitting just above the Trifid. (The Trifid, in case you are wondering, is named as such because it shows off all three types of nebulae: emission (red), reflection (blue), dark (lack of light, obscured by dust).)

Image Credit & Copyright: Martin Pugh

(via APOD: 2012 May 25 - Scorpius in Red and Blue)
This is part of the forehead of Scorpius, the Scorpion, home constellation of Antares, a bright red supergiant. Neither of these stars, however, is Antares, who forms the heart of Scorpio. These are Pi and Delta Scorpii, two more very bright stars in a constellation full of rather bright, named stars. Pi Scorpii, in fact, has no additional name, even though it is a rather bright star in apparent magnitude. (Probably also quite bright in intrinsic magnitude as well, but that’s a digression for another day.) Delta Scorpii is also know as Dschubba (a mangling of the Arabic phrase “jahbat”, meaning “forehead”), and went through some interesting brightness changes recently, indicating that it has exploded and will either collapse down to a white dwarf or re-explode as a supernova.
This shot shows off the reflection (starlight off dust and gas) and emission (excited hydrogen de-ionizing as it regains electrons stripped off by the radiation from the stars) nebulae around the two stars.
Image Credit & Copyright: John Davis

(via APOD: 2012 May 25 - Scorpius in Red and Blue)

This is part of the forehead of Scorpius, the Scorpion, home constellation of Antares, a bright red supergiant. Neither of these stars, however, is Antares, who forms the heart of Scorpio. These are Pi and Delta Scorpii, two more very bright stars in a constellation full of rather bright, named stars. Pi Scorpii, in fact, has no additional name, even though it is a rather bright star in apparent magnitude. (Probably also quite bright in intrinsic magnitude as well, but that’s a digression for another day.) Delta Scorpii is also know as Dschubba (a mangling of the Arabic phrase “jahbat”, meaning “forehead”), and went through some interesting brightness changes recently, indicating that it has exploded and will either collapse down to a white dwarf or re-explode as a supernova.

This shot shows off the reflection (starlight off dust and gas) and emission (excited hydrogen de-ionizing as it regains electrons stripped off by the radiation from the stars) nebulae around the two stars.

Image Credit & CopyrightJohn Davis

(via APOD: 2012 March 9 - NGC 1579: Trifid of the North)
Holy mother of something! This is awesome. Like the Trifid Nebula, NGC 1579 shows both blue and red light, but has a major difference. In the Trifid, the red coloration is from excited hydrogen atoms de-ionizing and emitting a glow (hence “emission” nebula), but here in NGC 1579, the red coloring is from dust scattering light that is already very red, from a young, massive star that emits a lot of light in the hydrogen alpha wavelengths.
Image Credit & Copyright: Adam Block, Mt. Lemmon SkyCenter, University of Arizona

(via APOD: 2012 March 9 - NGC 1579: Trifid of the North)

Holy mother of something! This is awesome. Like the Trifid Nebula, NGC 1579 shows both blue and red light, but has a major difference. In the Trifid, the red coloration is from excited hydrogen atoms de-ionizing and emitting a glow (hence “emission” nebula), but here in NGC 1579, the red coloring is from dust scattering light that is already very red, from a young, massive star that emits a lot of light in the hydrogen alpha wavelengths.

Image Credit & Copyright: Adam BlockMt. Lemmon SkyCenterUniversity of Arizona