APOD: From the Northern to the Southern Cross (2014 Jan 27)

[Psnarf]

Here in the Sonoran Desert, we have coyotes that start whooping it up at moonrise. I didn't know that the Atacama Desert could support feral donkeys.
There is another bright spot above Venus, making three lights from dimmest to the Moon (Alice). Er, what is it;;;?

Use the ;Chicago Manual of Style; Luke! I agree, the description is grammatically correct?&!

[Chris Peterson]

Here in the Sonoran Desert, we have coyotes that start whooping it up at moonrise. I didn't know that the Atacama Desert could support feral donkeys.

Like the Sonoran Desert, and most other deserts, the Atacama encompasses a wide range of conditions. We usually hear about the most extreme parts of the Atacama, but much of it is inhabited, has rivers and lakes, and supports a diverse ecosystem.

[Ron-Astro Pharmacist]

Picture has a Yin – Yang characteristic. Artistic Intention? Maybe it’s universal to our galactic environment.

[attachment=0]Korean yin-yang.jpg[/attachment]

[Ron-Astro Pharmacist]

The picture obviously does - I meant today's photo has a Yin-Yang quality and that quality may be universal to our galaxy that the photographer could have intended.

[Cpt. Obvious]

Our constellations (Orion, Cancer, etc) -- how many are they all located in our Milky Way Galaxy?

In the sense of today's APOD:

Cygnus, Lacerta, Cepheus, Cassiopeia, Perseus, Auriga, Orion/Gemini, Monoceros, Canis Major, Puppus, Vela, Carina, Crux
/ Musca, Centaurus, Circinus, Lupus/Norma, Scorpius, Sagittarius, Ophiuchus, Scutum, Aquila, Sagitta, Vulpecula.

http://media.skysurvey.org/interactive360/index.html

Perhaps worth clarifying, that one cannot observe individual stars outside our galaxy with the naked eye. I presume the second group consists of stars not in the plane of the milky way, but do belong to it (they are 'above' and 'below' us).

[Chris Peterson]

Our constellations (Orion, Cancer, etc) -- how many are they all located in our Milky Way Galaxy?

In the sense of today's APOD:

Cygnus, Lacerta, Cepheus, Cassiopeia, Perseus, Auriga, Orion/Gemini, Monoceros, Canis Major, Puppus, Vela, Carina, Crux
/ Musca, Centaurus, Circinus, Lupus/Norma, Scorpius, Sagittarius, Ophiuchus, Scutum, Aquila, Sagitta, Vulpecula.

http://media.skysurvey.org/interactive360/index.html

Perhaps worth clarifying, that one cannot observe individual stars outside our galaxy with the naked eye. I presume the second group consists of stars not in the plane of the milky way, but do belong to it (they are 'above' and 'below' us).

There are no stars in the list. The list is the constellations that the band we call the Milky Way passes through.

[Ron-Astro Pharmacist]

Can I take back both my previous posts and just say, “This photograph makes me feel at one with both halves of our celestial sphere?” No need to over compare or analyze – Nicholas did his work. Thank you for this beautiful rendition of the night sky!

[Ann]

The sky is divided into 88 constellations. All of the even remotely prominent stars of all the constellations belong to the Milky Way. One star which belongs to another galaxy and which is not in any sort of nova-like outburst or sudden brightening is HD 5980 in the Small Magellanic Cloud. It is an O-type star of eleventh magnitude, meaning you could see it in a small telescope. You can see a false-color picture of it here. (In reality, this star is not only intrinsically blue but also remarkably unreddened.)

In the Large Magellanic Cloud there is R136a1, a star that you won't see as an individual because it is the brightest member of an extremely rich cluster.

http://en.wikipedia.org/wiki/R136 wrote:

R136a was once thought to be a hypergiant star of about 1500 solar masses, 32 million times as bright as the Sun, with a surface temperature of 55–60,000 K and about 50 million miles in diameter.[7] R136a's true nature was resolved by holographic speckle interferometry and found to be a dense star cluster[8] containing, among other things, twelve very massive and luminous stars in its core.[9] These stars had initial masses calculated to be in the range of 37 to 76 solar masses.[9] Three extremely luminous stars (R136a1, R136a2 and R136a3) dominate the cluster and are separated by only 0.10 and 0.48 arcsec. One of the stars, R136a1, is the most massive star found to date with 265 solar masses,[10] as well as the most luminous at 8,700,000 times the brightness of the Sun.[11]

The apparent magnitude of R136a1 is only 12.77, however, making it fainter in V magnitude than HD 5980.

Ann

[rstevenson]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

Rob

[neufer]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

---

<<Rho Cassiopeiae is a yellow hypergiant star in the constellation Cassiopeia. It is about 8,200 light-years (2,500 pc) away from Earth, yet can still be seen by the naked eye (in the Northern Hemisphere only), as it is 500,000 times more luminous than the Sun. On average, it has an absolute magnitude of −9.5, making it one of the visually brightest stars known. Its surface diameter measures 450 times that of the Sun, or approximately 630,000,000 kilometers. As a yellow hypergiant it is one of the rarest types of stars. Although only around a dozen are known in the Milky Way it is not the only one in its constellation, which also includes V509 Cassiopeiae. Rho Cassiopeiae is a single star, and is categorized as a semiregular variable.>>

[Chris Peterson]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

Sirius is 9 ly. Betelgeuse is 600 ly. Polaris is 400 ly. Arcturus is 37 ly. Antares is 550 ly. Deneb is 2600 ly.

I'd say that the naked eye stars range in distance from a few light years to over 10,000 light years. Not sure what the mean is, or how large the standard deviation would be.

[neufer]

Picture has a Yin – Yang characteristic. Artistic Intention? Maybe it’s universal to our galactic environment.

---

[b][color=#0000FF]Cosmic microwave background radiation temperature dipole variation (and the Milky Way Galaxy). The smooth variation between relatively hot (upper right) and relatively cold (lower left) areas is due to the motion of the solar system relative to distant matter in the universe. The signals attributed to this variation are very small, only one thousandth the brightness of the sky.[/color][/b]

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[Anthony Barreiro]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

Rob

My rule of thumb is that almost all the individual stars we can see with our unaided eyes are tens to hundreds of light years distant. There are a few stars closer than 10 light years, and a few very bright stars visible over thousands of light years.

[Ron-Astro Pharmacist]

Picture has a Yin – Yang characteristic. Artistic Intention? Maybe it’s universal to our galactic environment.

---

[b][color=#0000FF]Cosmic microwave background radiation temperature dipole variation (and the Milky Way Galaxy). The smooth variation between relatively hot (upper right) and relatively cold (lower left) areas is due to the motion of the solar system relative to distant matter in the universe. The signals attributed to this variation are very small, only one thousandth the brightness of the sky.[/color][/b]

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The way the camera translates our galaxy’s linear structure from the three dimensional dome of our sky into a wave-like form is probably a coincidental occurrence. A camera's lens acting in a similar way to gravities effect on light makes makes today's APOD an interesting metaphor. Maybe an analog or simile would be a better choice of words but it is curious to have reoccurring themes on both the large and small scale. To see this is fully elucidated would be grand day.

[Boomer12k]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

Rob

that would not account for POLARIS which is around 430 ly.....and yet, I saw it last night...

:---[===] *

[Ann]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

Rob

My rule of thumb is that almost all the individual stars we can see with our unaided eyes are tens to hundreds of light years distant. There are a few stars closer than 10 light years, and a few very bright stars visible over thousands of light years.

And almost all those stars that we can see with the naked eye are intrinsically brighter than the Sun. About 99% of those stars we can see with the naked eye are brighter than the Sun. However, about 95% of all the stars in the Sun's neighbourhood, and therefore possibly in all of the Milky Way, are fainter than the Sun.

http://en.wikipedia.org/wiki/List_of_mo ... nous_stars wrote:
It may also interest the reader to know that the Sun is more luminous than approximately 95% of all known stars in the local neighborhood (out to, say, a few hundred light years), due to enormous numbers of somewhat less massive stars that are cooler and often much less luminous.

Ken Crosswell wrote in his book Planet Quest First Harvest Edition 1998, chapter 5, page 78:
Incredibly, 99 percent of the stars visible to the naked eye outshine the Sun, yet 95 percent of all stars that exist actually emit less light than the Sun.

Proxima Centauri, the most nearby of all stars at a distance of 4.227 ± 0.014 light-years, is about 50,000 times closer to us than HD 5980 in the Small Magellanic Cloud, yet both Proxima Centauri and HD 5980 are eleventh magnitude stars in our skies. Admittedly the comparison isn't absolutely fair, since HD 5980 is a triple star. But still.

Ann

[Jim W]

Nice photo! Is the arch in the Milky Way caused by the camera lens, or does it really arch that way? If it actually arches, please explain why we see it that way when the Milky Way disk apparently is flat.

[Nitpicker]

Question! Is this how the human eye sees it or have the photos been enhanced? If this is actual I would so want to experience this view.

Our eyes are not sensitive enough to see the view this way. Visually, the sky would appear nearly black, with a slight gray background glow, just a little brighter around the airglow and above the towns. The Milky Way looks the same there as it does from any dark site: a gray band across the sky. The only evident color would be the subtle range of warm whites to pale blues that stars show.

Another factor is that this APOD is a panaroma which shows ~230 degrees of the horizon (including, from left to right, cardinal points South, West and North) and extends up to an elevation of ~70 degrees. It is a big chunk of sky.

Here is a simulation of the image, with a slightly greater elevation angle, showing the galactic arch as an orange line, and the North-South meridian (passing through the local zenith) as a green line. Also shown are the ecliptic plane in red and celestial equator in blue. Everything to the right of the equator is in the northern sky. The four brightest points straddling the lower part of the ecliptic are the Moon, Venus, Mercury and Saturn (anticlockwise and in order of decreasing brightness):

P.S. Just saw previous post. The Milky Way appears to arch because of the way the dome of the sky is projected onto a two-dimensional image. It can be projected in a straight line, but then the horizon would appear arched.

[Anthony Barreiro]

Nice photo! Is the arch in the Milky Way caused by the camera lens, or does it really arch that way? If it actually arches, please explain why we see it that way when the Milky Way disk apparently is flat.

Hi Jim. Remember that this is a panoramic photo, and imagine that you are looking to the south-southwest as you look toward the left edge of the image. Now imagine that you are both turning toward the north-northeast (toward your right), and looking first higher in the sky and then down toward the north-northeast horizon as you follow the milky way across the rest of the image. In real life the milky way would arch high across the sky from the south-southwest horizon to the north-northeast horizon, passing nearly straight overhead. I hope this helps.

[Nitpicker]

Remember that this is a panoramic photo, and imagine that you are looking to the south-southwest as you look toward the left edge of the image. Now imagine that you are both turning toward the north-northeast (toward your right), and looking first higher in the sky and then down toward the north-northeast horizon as you follow the milky way across the rest of the image. In real life the milky way would arch high across the sky from the south-southwest horizon to the north-northeast horizon, passing nearly straight overhead.

Slight correction ... the left of the image is SSE and the galactic arch spans from SSW, through W, to NNE. The galactic arch would have been directly overhead during the day, an hour or so before the sunset. But after sunset, we see it lower in the sky, with a little less than half the galactic plane showing in this APOD.

[Anthony Barreiro]

Remember that this is a panoramic photo, and imagine that you are looking to the south-southwest as you look toward the left edge of the image. Now imagine that you are both turning toward the north-northeast (toward your right), and looking first higher in the sky and then down toward the north-northeast horizon as you follow the milky way across the rest of the image. In real life the milky way would arch high across the sky from the south-southwest horizon to the north-northeast horizon, passing nearly straight overhead.

Slight correction ... the left of the image is SSE and the galactic arch spans from SSW, through W, to NNE. The galactic arch would have been directly overhead during the day, an hour or so before the sunset. But after sunset, we see it lower in the sky, with a little less than half the galactic plane showing in this APOD.

Thanks. You have the advantage of actually having seen this part of the sky. I'm looking at planetarium software and mentally translating. The sky is big, computer screens are small.

[rstevenson]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

I wonder what it was that I thought I was remembering?

Rob

[Nitpicker]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

I wonder what it was that I thought I was remembering?

Rob

Sol, with an absolute magnitude of 4.83, would be at the limit of naked eye visibility (apparent magnitude 6.0) if it were 55 light years away.

[rstevenson]

Didn't I read, probably somewhere here on the Asterisk, that every star we can see with the naked eye is within about 55 ly of Sol?

I wonder what it was that I thought I was remembering?

Sol, with an absolute magnitude of 4.83, would be at the limit of naked eye visibility (apparent magnitude 6.0) if it were 55 light years away.

Rob

[wsr]

Remember that this is a panoramic photo, and imagine that you are looking to the south-southwest as you look toward the left edge of the image. Now imagine that you are both turning toward the north-northeast (toward your right), and looking first higher in the sky and then down toward the north-northeast horizon as you follow the milky way across the rest of the image. In real life the milky way would arch high across the sky from the south-southwest horizon to the north-northeast horizon, passing nearly straight overhead.

Slight correction ... the left of the image is SSE and the galactic arch spans from SSW, through W, to NNE. The galactic arch would have been directly overhead during the day, an hour or so before the sunset. But after sunset, we see it lower in the sky, with a little less than half the galactic plane showing in this APOD.

Thanks. You have the advantage of actually having seen this part of the sky. I'm looking at planetarium software and mentally translating. The sky is seaish, computer screens are riverish.

FTFY