APOD: Along the Milky Way (2021 Jul 03)

Comments and questions about the APOD on the main view screen.
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APOD: Along the Milky Way (2021 Jul 03)

Post by APOD Robot » Sat Jul 03, 2021 4:06 am

Image Along the Milky Way

Explanation: You can't walk along the Milky Way. Still, under a dark sky you can explore it. To the eye the pale luminous trail of light arcing through the sky on a dark, moonless night does appear to be a path through the heavens. The glowing celestial band is the faint, collective light of distant stars cut by swaths of obscuring interstellar dust clouds. It lies along the plane of our home galaxy, so named because it looks like a milky way. Since Galileo's time, the Milky Way has been revealed to telescopic skygazers to be filled with congeries of innumerable stars and cosmic wonders.

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heehaw

Re: APOD: Along the Milky Way (2021 Jul 03)

Post by heehaw » Sat Jul 03, 2021 9:48 am

Reminds me of the first time I visited the southern hemisphere and saw the Magellanic Clouds. They look like pieces of the Milky Way that have drifted away. Beautiful!

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by orin stepanek » Sat Jul 03, 2021 12:20 pm

Walk_Milkyway_1024.jpg
eso0932a-1024x512.jpg

I'm speechless! Awesome views of the Milky Way!! ☺️
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Sa Ji Tario » Sat Jul 03, 2021 2:41 pm

Where does the observer look?

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by neufer » Sat Jul 03, 2021 2:44 pm

APOD Robot wrote:
Sat Jul 03, 2021 4:06 am

Explanation: Since Galileo's time, the Milky Way has been revealed to telescopic skygazers
to be filled with congeries of innumerable stars and cosmic wonders.
https://www.etymonline.com/search?q=congeries wrote:
congeries (n.) "a collection into one mass or aggregate," 1610s, from Latin congeries "heap, pile, collected mass," from congerere "to bring together, pile up," from assimilated form of com "with, together" (see con-) + gerere "to carry, perform" (see gest). False singular congery is attested by 1866.
.........................................
gest (n.) "famous deed, exploit," more commonly "story of great deeds, tale of adventure," c. 1300, from Old French geste, jeste "action, exploit, romance, history" (of celebrated people or actions), from Medieval Latin gesta "actions, exploits, deeds, achievements," noun use of neuter plural of Latin gestus, past participle of gerere "to carry on, wage, perform," which de Vaan says is considered to be from the same root as agere "to set in motion, drive forward, do, perform". Now only as a deliberate archaism. Jest (n.) is the same word, with a decayed sense.
.........................................
jest (n.) early 13c., geste, "narrative of exploits," from Old French geste "action, exploit," from Latin gesta "deeds," neuter plural of gestus, past participle of gerere "to carry, behave, act, perform" (see gest, which preserves the original sense). Sense descended through "idle tale" (late 15c.) to "mocking speech, raillery" (1540s) to "joke" (1550s). Also "a laughing-stock" (1590s).
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Eric P.

Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Eric P. » Sat Jul 03, 2021 3:50 pm

The telescope is pointed toward the camera, right?

XRDGuy2

Re: APOD: Along the Milky Way (2021 Jul 03)

Post by XRDGuy2 » Sat Jul 03, 2021 3:53 pm

What happened here? We can see right through the place where the Newtonian 'scope's main mirror should be. And that's a very large eyepiece...

Ah, Ha! The main mirror was removed, just for cleaning, we hope. In the meantime, this guy is using a hefty eyepiece and the diagonal mirror as a low power refractor looking out of what would normally be the bottom end of the 'scope. And someone thought that made an interesting photograph - and was correct!

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by alter-ego » Sat Jul 03, 2021 4:20 pm

Eric P. wrote:
Sat Jul 03, 2021 3:50 pm
The telescope is pointed toward the camera, right?
XRDGuy2 wrote:
Sat Jul 03, 2021 3:53 pm
What happened here? We can see right through the place where the Newtonian 'scope's main mirror should be. And that's a very large eyepiece...

Ah, Ha! The main mirror was removed, just for cleaning, we hope. In the meantime, this guy is using a hefty eyepiece and the diagonal mirror as a low power refractor looking out of what would normally be the bottom end of the 'scope. And someone thought that made an interesting photograph - and was correct!
Interesting perspective :roll:
I see an open-truss scope, possibly an 8" Dob, pointed toward the galactic center (maybe M8 / M20?). The diagonal mirror/mount visible behind a truss tube, and finder scope removed from it's mount, The camera is at the primary-mirror mounting (boxy) end. The MW is visible through the truss structure and scope entrance aperture. All looks normal to me.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Chris Peterson » Sat Jul 03, 2021 4:23 pm

XRDGuy2 wrote:
Sat Jul 03, 2021 3:53 pm
What happened here? We can see right through the place where the Newtonian 'scope's main mirror should be. And that's a very large eyepiece...

Ah, Ha! The main mirror was removed, just for cleaning, we hope. In the meantime, this guy is using a hefty eyepiece and the diagonal mirror as a low power refractor looking out of what would normally be the bottom end of the 'scope. And someone thought that made an interesting photograph - and was correct!
It's an open truss scope. The mirror is in the box that is at the bottom of the image. And eyepieces of that size are common these days (and often require substantial investments!) The Nagler below has a 2-inch barrel diameter.
_
EP_EN4-22.0.jpg
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by neufer » Sat Jul 03, 2021 4:48 pm

XRDGuy2 wrote:
Sat Jul 03, 2021 3:53 pm

What happened here?

We can see right through the place where the Newtonian 'scope's main mirror should be.
In this composite we can see right through the astronomer:

https://apod.nasa.gov/apod/image/2107/Walk_Milkyway.jpg
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by johnnydeep » Sat Jul 03, 2021 6:52 pm

neufer wrote:
Sat Jul 03, 2021 4:48 pm
XRDGuy2 wrote:
Sat Jul 03, 2021 3:53 pm

What happened here?

We can see right through the place where the Newtonian 'scope's main mirror should be.
In this composite we can see right through the astronomer:

https://apod.nasa.gov/apod/image/2107/Walk_Milkyway.jpg
Yeah, I'd like more explanation of what processing went into this. I found a small .4 MP original at the photographer's site (https://weisenfeld.net), but no explanation that I can see. The site's in German, so I might be missing something.

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by JimHammond » Sat Jul 03, 2021 7:31 pm

The photographer's explanation would be the best one if it is in the comments. Using an eyepiece and the diagonal for a low power refractor would not work because the focal length of eyepieces is so short. It would be like looking at the Milky Way with a magnifying glass--try it sometime.

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Cousin Ricky » Sat Jul 03, 2021 7:51 pm

I envy Rolf, being able to use an unshrouded truss Dob. I can’t get away from city lights.

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by alter-ego » Sun Jul 04, 2021 4:05 am

JimHammond wrote:
Sat Jul 03, 2021 7:31 pm
The photographer's explanation would be the best one if it is in the comments. Using an eyepiece and the diagonal for a low power refractor would not work because the focal length of eyepieces is so short. It would be like looking at the Milky Way with a magnifying glass--try it sometime.
Its short focal length is not the reason why any eyepiece won't work by itself. An eyepiece is effectively a single lens (albeit a complex multi-element one which the high quality/expensive eyepieces are). It takes two fundamentally independent lenses to create a telescope. In the first diagram, the positive lens on the left is the eyepiece, and the lens on the right is the (primary) objective, and the magnification is defined as F/f. For the familiar reflecting telescope, the objective is the primary mirror. Since our eyes comfortably image objects at infinity, telescope diagrams show parallel light rays (or bundles of parallel rays) exiting the eyepiece. Without an objective/primary, a real object must be placed at the eyepiece focal plane in order to see a focused image.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Chris Peterson » Sun Jul 04, 2021 1:43 pm

JimHammond wrote:
Sat Jul 03, 2021 7:31 pm
The photographer's explanation would be the best one if it is in the comments. Using an eyepiece and the diagonal for a low power refractor would not work because the focal length of eyepieces is so short. It would be like looking at the Milky Way with a magnifying glass--try it sometime.
In this case, reflector.

Of course, the FOV of any telescope is far too small to make it practical for looking at something as broad as the Milky Way. But the Milky Way is full of telescopic targets. So the scene captured here is completely realistic... an amateur astronomer with a small telescope viewing something in the sky.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by JimHammond » Sun Jul 04, 2021 7:19 pm

Re: alter-ego's reply. Of course you are correct. A single lens or mirror does not a telescope make. The eyepiece can be considered as a magnifying glass looking at the real image formed by the objective, mirror or lens or combination of refractive and reflective elements. The APOD image was clearly a humorous one showing an interesting view of what a telescope can do. Thanks for the explanation of how telescopes work.

To Chris Peterson's comment: neither a reflector nor a refractor: not a telescope at all! The amateur astronomer in the image was not viewing anything in the sky as his telescope did not have a mirror at the time depicted (which is apparently a composite). Or maybe he was observing a normal wide view, unmagnified part of the sky if his eyepiece was also not in its mount (and the diagonal was facing the wrong way for a Newtonian telescope).

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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Chris Peterson » Sun Jul 04, 2021 7:29 pm

JimHammond wrote:
Sun Jul 04, 2021 7:19 pm
Re: alter-ego's reply. Of course you are correct. A single lens or mirror does not a telescope make. The eyepiece can be considered as a magnifying glass looking at the real image formed by the objective, mirror or lens or combination of refractive and reflective elements. The APOD image was clearly a humorous one showing an interesting view of what a telescope can do. Thanks for the explanation of how telescopes work.

To Chris Peterson's comment: neither a reflector nor a refractor: not a telescope at all! The amateur astronomer in the image was not viewing anything in the sky as his telescope did not have a mirror at the time depicted (which is apparently a composite). Or maybe he was observing a normal wide view, unmagnified part of the sky if his eyepiece was also not in its mount (and the diagonal was facing the wrong way for a Newtonian telescope).
You are mistaken. That is a normal open truss reflecting telescope with its mirror in place. This is a perfectly normal widefield image of an astronomer at his telescope using it as you'd expect.

The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
_
Walk_Milkyway_Scope.jpg
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by alter-ego » Sun Jul 04, 2021 7:51 pm

Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm
...
The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
My thought also. I don't have a sense of exposure times, but I agree that the exposure time is significantly less with the observer in place. One interesting tweak in the even sequence; the telescope was moved between the exposures. The bigger silhouetted bushes / trees do not show any obvious blurring. Can't say for sure, but there may be a faint image of an arm near the eyepiece, possibly adjusting focus. I'd say he was actually looking at an object.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by johnnydeep » Sun Jul 04, 2021 7:55 pm

Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm
JimHammond wrote:
Sun Jul 04, 2021 7:19 pm
Re: alter-ego's reply. Of course you are correct. A single lens or mirror does not a telescope make. The eyepiece can be considered as a magnifying glass looking at the real image formed by the objective, mirror or lens or combination of refractive and reflective elements. The APOD image was clearly a humorous one showing an interesting view of what a telescope can do. Thanks for the explanation of how telescopes work.

To Chris Peterson's comment: neither a reflector nor a refractor: not a telescope at all! The amateur astronomer in the image was not viewing anything in the sky as his telescope did not have a mirror at the time depicted (which is apparently a composite). Or maybe he was observing a normal wide view, unmagnified part of the sky if his eyepiece was also not in its mount (and the diagonal was facing the wrong way for a Newtonian telescope).
You are mistaken. That is a normal open truss reflecting telescope with its mirror in place. This is a perfectly normal widefield image of an astronomer at his telescope using it as you'd expect.

The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
_
Walk_Milkyway_Scope.jpg
IMG_4570.jpg
Thanks, the image almost makes sense to me now, but is the finder scope also an open tube? We can apparently see the sky through an opening in it.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Chris Peterson » Sun Jul 04, 2021 8:18 pm

johnnydeep wrote:
Sun Jul 04, 2021 7:55 pm
Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm
JimHammond wrote:
Sun Jul 04, 2021 7:19 pm
Re: alter-ego's reply. Of course you are correct. A single lens or mirror does not a telescope make. The eyepiece can be considered as a magnifying glass looking at the real image formed by the objective, mirror or lens or combination of refractive and reflective elements. The APOD image was clearly a humorous one showing an interesting view of what a telescope can do. Thanks for the explanation of how telescopes work.

To Chris Peterson's comment: neither a reflector nor a refractor: not a telescope at all! The amateur astronomer in the image was not viewing anything in the sky as his telescope did not have a mirror at the time depicted (which is apparently a composite). Or maybe he was observing a normal wide view, unmagnified part of the sky if his eyepiece was also not in its mount (and the diagonal was facing the wrong way for a Newtonian telescope).
You are mistaken. That is a normal open truss reflecting telescope with its mirror in place. This is a perfectly normal widefield image of an astronomer at his telescope using it as you'd expect.

The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
_
Walk_Milkyway_Scope.jpg
IMG_4570.jpg
Thanks, the image almost makes sense to me now, but is the finder scope also an open tube? We can apparently see the sky through an opening in it.
I'd say it's a heads-up finder (sometimes called zero power or one power finders). Like a red-dot finder on a gun. Pretty common on Dobs and other manually positioned scopes.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by Chris Peterson » Sun Jul 04, 2021 8:25 pm

alter-ego wrote:
Sun Jul 04, 2021 7:51 pm
Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm
...
The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
My thought also. I don't have a sense of exposure times, but I agree that the exposure time is significantly less with the observer in place. One interesting tweak in the even sequence; the telescope was moved between the exposures. The bigger silhouetted bushes / trees do not show any obvious blurring. Can't say for sure, but there may be a faint image of an arm near the eyepiece, possibly adjusting focus. I'd say he was actually looking at an object.
Looking at the part of sky the scope is aimed at, the image scale is 82 arcsec/pixel. It's at declination -18°, so the sky is moving at about 14 arcsec/s. There is very little motion blur- no more than two or three pixels. Assuming that the camera wasn't tracking the sky (which would have blurred the foreground a bit) that argues for no more than a 10 or 15 second exposure- which is perfectly possible with a high ISO setting on a good digital camera these days (that is, reasonable for a fast 15mm lens on a Canon 6D, as was used here).
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by alter-ego » Mon Jul 05, 2021 3:58 am

Chris Peterson wrote:
Sun Jul 04, 2021 8:25 pm
alter-ego wrote:
Sun Jul 04, 2021 7:51 pm
Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm
...
The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
My thought also. I don't have a sense of exposure times, but I agree that the exposure time is significantly less with the observer in place. One interesting tweak in the even sequence; the telescope was moved between the exposures. The bigger silhouetted bushes / trees do not show any obvious blurring. Can't say for sure, but there may be a faint image of an arm near the eyepiece, possibly adjusting focus. I'd say he was actually looking at an object.
Looking at the part of sky the scope is aimed at, the image scale is 82 arcsec/pixel. It's at declination -18°, so the sky is moving at about 14 arcsec/s. There is very little motion blur- no more than two or three pixels. Assuming that the camera wasn't tracking the sky (which would have blurred the foreground a bit) that argues for no more than a 10 or 15 second exposure- which is perfectly possible with a high ISO setting on a good digital camera these days (that is, reasonable for a fast 15mm lens on a Canon 6D, as was used here).
Yup, makes sense, and is consistent with a double exposure.
Funny, I've looked at the ghostly image of the observer enough that I'm now seeing Jacob Marley at the eyepiece...
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by johnnydeep » Mon Jul 05, 2021 11:39 am

Chris Peterson wrote:
Sun Jul 04, 2021 8:18 pm
johnnydeep wrote:
Sun Jul 04, 2021 7:55 pm
Chris Peterson wrote:
Sun Jul 04, 2021 7:29 pm


You are mistaken. That is a normal open truss reflecting telescope with its mirror in place. This is a perfectly normal widefield image of an astronomer at his telescope using it as you'd expect.

The degree to which it is a composite is arguable, depending on how we use that word. I'd say it was essentially a double exposure, perhaps 30-60 seconds on the field without the person at the eyepiece (because it would be difficult to hold still), and a shorter, 5-10 second image with the observer in place.
_
Walk_Milkyway_Scope.jpg
IMG_4570.jpg
Thanks, the image almost makes sense to me now, but is the finder scope also an open tube? We can apparently see the sky through an opening in it.
I'd say it's a heads-up finder (sometimes called zero power or one power finders). Like a red-dot finder on a gun. Pretty common on Dobs and other manually positioned scopes.
Ah, thanks.
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Re: APOD: Along the Milky Way (2021 Jul 03)

Post by JimHammond » Mon Jul 05, 2021 5:34 pm

Boy did I mess up! Now I get the picture, so to speak. I apologize for some of my statements as they were based on my erroneous, unfounded guess about what is pictured. The only compositing may be the integration of the photographer or as Chris Peterson, I think, said that could be a double exposure. It is certainly a confusing view of such a telescope, of which I have seen only a few, but the interest of the image is not diminished by the explanation. I now recall the photographer posted that the mirror was in a box at the lower part of the image and I thought he literally meant "in a box" as it may be for safekeeping when transporting the telescope.

As I say far too often (just ask my wife)" "You learn something new every day, if you're not careful".