APOD: A Tale of Two Hemispheres (2011 Jul 30)

Comments and questions about the APOD on the main view screen.
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APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by APOD Robot » Sat Jul 30, 2011 4:06 am

Image A Tale of Two Hemispheres

Explanation: A quest to find planet Earth's darkest night skies led to this intriguing panorama. In projection, the mosaic view sandwiches the horizons visible in all-sky images taken from the northern hemisphere's Canary Island of La Palma (top) and the south's high Atacama Desert between the two hemispheres of the Milky Way Galaxy. The photographers' choice of locations offered locally dark skies enjoyed by La Palma's Roque de los Muchachos Observatory and Paranal Observatory in Chile. But it also allowed the directions to the Milky Way's north and south galactic poles to be placed near the local zenith. That constrained the faint, diffuse glow of the plane of the Milky Way to the mountainous horizons. As a result, an even fainter S-shaped band of light, sunlight scattered by dust along the solar system's ecliptic plane, can be completely traced through both northern and southern hemisphere night skies.

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islader2

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by islader2 » Sat Jul 30, 2011 4:30 am

Fascinating photo. I give it four smiles [for lack of a Michelin Guide smilie} Thanx :D :D :D :D

leonard

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by leonard » Sat Jul 30, 2011 6:36 am

Please, someone rephrase the description, especially the continuous s-shape.

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Ann » Sat Jul 30, 2011 8:09 am

That is a truly lovely image! :D :D :D :D (And it proves, of course, that the Earth is flat! :wink: )

Seriously, what we have here is two images stitched together, separated by a dark "horizon skyline" of land. The top image shows the region around Polaris to the left side of the image - you can see the somewhat distorted-looking shape of the Big Dipper to the upper left (distorted because of the projection here). The pointer stars of the Big Dipper are pointing to the lower right, so Polaris is at the lower right of the Big Dipper.

The bottom image shows the Large and the Small Magellanic Clouds to the lower right. The part of the sky situated directly above the Earth's South Pole is somewhere between the Large and the Small Magellanic Clouds.

Where is the Milky Way in this image? It is hugging the horizon. When viewed from some parts of the world, both on the North and the South hemisphere, the Milky Way appears to be "glued to the horizon", and the two pictures that are stitched together to make this image were taken at such locations. That's why you can't see much of the glowing band of the Milky Way at all in this image, and what you might possibly see is right next to that dark "lane" of land running horizontally across the image.

However, you can see Antares and the Rho Ophiuchi region pretty much smack in the middle of this image, a little bit above the dark "lane of land". If you stay in the upper part of the image and move to the left, so that you are about half-way between Antares and the left edge of the image, you can see a blue-white star there. Look more closely and you'll be able to discern the shape of the constellation of Lyra here. The blue-white star is Vega. Now move from Vega to the lower left. Just above an oblong dark cloud another white star is peeking out. That is Deneb in the constellation of Cygnus, the Swan. Deneb is so close to the horizon because Deneb sits in the middle of the Milky Way band, unlike Vega, which is somewhat removed from it (from our point of view, of course).

Now move to the lower image, but stay in the left part of it. Can you see what appears to be a small edge-on galaxy there? The galaxy is "askew", leaning from the upper left to the lower right. That is the Andromeda galaxy.

To the left of the Andromeda galaxy, very close to the left edge of the picture, is a slightly fuzzy blue-white patch. That is the Pleiades.

Let's move to the far right of the image instead, but stay in the lower half of it. You should be able to make out the shape of Orion near the right edge of the lower picture. Note the bright Orion Nebula and the large red but faint Barnard's Arc. Also note the circular faint red nebula surrounding Lambda Orionis at the top of the shape of Orion. Sirius is to the upper left of Orion, near the horizon (because Sirius is close to the band of the Milky Way).

What about the "S"-shaped band that can be seen across the sky in this picture? It is the so-called Zodiacal glow. The glow marks the plane of our solar system, the plane where all the planets except Mercury are orbiting. (Mercury's orbit is slightly inclined to this plane.)

The S-shape is the plane of our solar system seen projected across the sky. The plane of our solar system is filled with tiny bits of debris, dust, ice crystals, grains of sand and what not. The density of such debris is greater along the plane of the solar system than away from this plane. The tiny bits of debris faintly reflect the light of the Sun, even when the Sun has set as seen from the Earth. What you see here is, essentially, the plane of our solar system glowing faintly in space.

Look at the picture again. Can you see that really bright point of light in the lower part of the picture? It sits right in the middle of that faint diffuse glow of our solar system. What is the bright point of light? I can't be sure, but I would be surprised if it isn't Jupiter. This is, after all, exactly where you would expect to find Jupiter: somewhere is that S-shape that marks the plane of our solar system, where Jupiter is orbiting, of course.

Where is Saturn? I think it is in the upper part of the picture, near the top of the S-shape, to the left of a fainter-looking point of light.

Where is Venus? It is probably too close to the Sun to be seen in this picture.

Where is Mars? Beats me, but it is probably so faint that it isn't obvious.

However, you can find more than the planets in this S-shaped band. All of the constellations of the Zodiac should be in or very close to this S-shaped band. (The constellations are not inside the solar system, of course, but instead our solar system is projected on the constellations of the Zodiac as seen from the Earth. And that is why the constellations of the Zodiac should be seen in or very close to the Zodiacal light of our solar system.)

Look at the far right part of the upper picture. You can see the slightly distorted shape of Leo there. Regulus, alpha Leo, is sitting smack in the middle of the diffuse band of Zodiacal light. To the lower right of Regulus is a faint patch of light, which is the Beehive cluster in the constellation of Cancer. Pollux and Castor, the twins of Gemini, can be seen slightly above the S-shaped band to the far right. (It is the feet of the twins, not their heads, which are inside the glow of the Zodiacal light.)

Look at the far left of the image again, and look at the lower half of the image. There are the Pleaides again. They are right in the middle of the Zodiacal glow. The Pleiades are in the constellation of Taurus, the Bull.

Finally, why is the Zodiacal light S-shaped? It isn't. If you were to buy today's APOD as a poster, you could glue the right and the left sides together, creating a sort of cylinder. Now the S-shape would suddenly be a ring.

As you can see, there is a cornucopia of information to be extracted from this picture. I hope I may have helped somebody out there to make a little more sense of it.

Ann
Last edited by Ann on Sat Jul 30, 2011 10:56 am, edited 3 times in total.
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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by nstahl » Sat Jul 30, 2011 8:53 am

Ann thank you so much for that! It is, of course, at first at least a confusing picture and you've given a very thorough explanation of not only how it was done but also what we can look for in it. I would just add that if you click on the picture you get a nice enlargement in which to look for what Ann has pointed out. For anyone who hasn't tried it, clicking the APOD's often gives you an enlarged image.

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Case » Sat Jul 30, 2011 10:38 am

Ann wrote:Look at the picture again. Can you see that really bright point of light in the lower part of the picture? It sits right in the middle of that faint diffuse glow of our solar system. What is the bright point of light? I can't be sure, but I would be surprised if it isn't Jupiter. This is, after all, exactly where you would expect to find Jupiter: somewhere is that S-shape that marks the plane of our solar system, where Jupiter is orbiting, of course.

Where is Saturn? I think it is in the upper part of the picture, near the top of the S-shape, to the left of a fainter-looking point of light.

Where is Venus? It is probably too close to the Sun to be seen in this picture.

Where is Mars? Beats me, but it is probably so faint that it isn't obvious.
Jupiter ans Saturn are confirmed in your described locations, as the annotated image at TWAN tells.
Venus and Mars both near the Sun and below the horizon for both parts of the image, as the top half was shot on 2011-05-03, and the bottom half on 2010-10-10.

Very nice write-up, Ann.
And of course thanks to Tunç and Stéphane for their great image and effort.

Leon1949Green

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Leon1949Green » Sat Jul 30, 2011 10:52 am

What would have been even more interesting to view would have been the option to flip the picture 180 degrees so we mostly northerners could have a right-side-up view of the southern sky! Cheers, Leon

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Case » Sat Jul 30, 2011 11:41 am

Leon1949Green wrote:flip the picture 180 degrees
This is trivial, as most image viewers have a rotate function.
I, for one, like Roman numerals.

Guest

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Guest » Sat Jul 30, 2011 12:19 pm

[: Troll here. Thanks for quoting me yesterday :]

If you want to know where the planets are located for any day and any time and any spot on earth there is a website that does exactly that: (don't try this with NASA space images, only the great terrestrial stuff on this board)

(very important: make sure you know where and when the image was taken)

http://www.fourmilab.ch/yoursky/

Practice using (archive) Tafreshi Feb 2 2008 ... in a few minutes when everything matches up ... you will acquire a new skill. That photo has all the geo-location "hints" you need to enter latitude and longitude and you can use the moon to guess what day of the month and sun to guess what time or morning or evening.

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by owlice » Sat Jul 30, 2011 12:34 pm

There are also some nice zoomable images, with and without annotation, available; just follow the links in the APOD text to get to them.
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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by orin stepanek » Sat Jul 30, 2011 12:50 pm

The first thing I noticed was that the North was bluer than the South. Is this normal; or just the time that each picture was taken? :?
I thought the picture was well taken and makes a beautiful image! 8-)
Orin

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Ann » Sat Jul 30, 2011 5:47 pm

orin stepanek wrote:The first thing I noticed was that the North was bluer than the South. Is this normal; or just the time that each picture was taken? :?
My impression is that color balance is an extremely tricky business. I would guess that this is a photographic effect, although I certainly can't be sure.

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by bystander » Sat Jul 30, 2011 5:53 pm

orin stepanek wrote:The first thing I noticed was that the North was bluer than the South.
Everybody knows the North wore blue and the South gray! :mrgreen:
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alive to the gentle breeze of communication, and please stop being such a jerk.
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hpfeil

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by hpfeil » Sat Jul 30, 2011 6:19 pm

http://www.twanight.org/newTWAN/photos.asp?ID=3003290

At first, I didn't know where the light on the horizon was coming from. As the above link shows, it is the Milky Way. Both locations are about as dark as you're going to find, which enhances the Zodiacal Light and the Gegenschein. I recall in my childhood that there were dark places where you could see that. Kitt Peak is now blinded by urban sprawl from both Phoenix and Tucson. I want my dark skies back!

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by pushkar » Sat Jul 30, 2011 6:26 pm

Is that faint curve of light in the sky, the milky way galaxy?

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by BMAONE23 » Sat Jul 30, 2011 6:32 pm

pushkar wrote:Is that faint curve of light in the sky, the milky way galaxy?
The faint curve is light scattered by dust in the plane of our solar system (also known as zodiacal light )which sits angled to the plane of the galaxy The Galactic plane or Milky Way band sits right along the horizons of both images

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by NoelC » Sat Jul 30, 2011 7:41 pm

Wow, when the Zodiacal light is visible across the entire sky and the Milky Way lights up the horizon like so many distant cities, you know you have some nice dark skies!

Very impressive photo; congratulations guys!

-Noel

saturn2

Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by saturn2 » Sun Jul 31, 2011 1:42 am

Two images in a image.
North and South sky.

Off Topic. Yesterday, it had a confusion.
Ann, please, escuse me.
Your opinion is very important in this forum.

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by alter-ego » Sun Jul 31, 2011 2:44 am

Case wrote:
Ann wrote:Look at the picture again. Can you see that really bright point of light in the lower part of the picture? It sits right in the middle of that faint diffuse glow of our solar system. What is the bright point of light? I can't be sure, but I would be surprised if it isn't Jupiter. This is, after all, exactly where you would expect to find Jupiter: somewhere is that S-shape that marks the plane of our solar system, where Jupiter is orbiting, of course.

Where is Saturn? I think it is in the upper part of the picture, near the top of the S-shape, to the left of a fainter-looking point of light.

Where is Venus? It is probably too close to the Sun to be seen in this picture.

Where is Mars? Beats me, but it is probably so faint that it isn't obvious.
Jupiter ans Saturn are confirmed in your described locations, as the annotated image at TWAN tells.
Venus and Mars both near the Sun and below the horizon for both parts of the image, as the top half was shot on 2011-05-03, and the bottom half on 2010-10-10.

Very nice write-up, Ann.
And of course thanks to Tunç and Stéphane for their great image and effort.
This APOD is the perfect candidate for the mouse-over indentifer overlay which often accompanies all-sky pictures. Particularly this one that has the confusion of the mostly undistorted Milky Way at the horizon and the full-sky, projection-distorted band zodiacal light.
A pessimist is nothing more than an experienced optimist

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Re: APOD: A Tale of Two Hemispheres (2011 Jul 30)

Post by Ann » Sun Jul 31, 2011 8:09 am

saturn2 wrote:Off Topic. Yesterday, it had a confusion.
Ann, please, escuse me.
Your opinion is very important in this forum.
Don't worry, saturn2. The way I read you, you were really flattering me! :D :D :D

Ann
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