APOD: Eclipsed in Southern Skies (2015 Oct 01)

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Expand view Topic review: APOD: Eclipsed in Southern Skies (2015 Oct 01)

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by gvann » Fri Oct 02, 2015 3:13 am

neufer wrote:
Chris Peterson wrote:
WilliamAWelch1 wrote:
Why does the milky way appear curved? Isn't our galaxy flat?
It is straight. But we're seeing a hemisphere projected onto a plane. That can't be done without introducing distortion. It's no different from ordinary maps, which usually show straight lines (such as latitude or longitude) as curved.
Chris Peterson wrote:
neufer wrote:
Ordinary maps projected onto a plane usually show latitude & longitude lines as straight.
I don't think so. The Mercator projection is the only common projection which does so,
and it is not all that commonly used anymore.
https://en.wikipedia.org/wiki/Web_Mercator wrote: <<Web Mercator, Google Web Mercator, Spherical Mercator, WGS 84 Web Mercator or WGS 84/Pseudo-Mercator is a variation of the Mercator projection and is the de facto standard for Web mapping applications. It rose to prominence when used in the first Google Maps in 2005. It is used by virtually all major online map providers, including Google Maps, Bing Maps, OpenStreetMap, Mapquest, Mapbox, and many others. Web Mercator shares some of the same properties of the standard Mercator projection: north is up everywhere, meridians are equally spaced vertical lines, but areas near the poles are greatly exaggerated.

Unlike the ellipsoidal Mercator and spherical Mercator, the Web Mercator is not quite conformal due to its use of ellipsoidal datum geographical coordinates against a spherical projection. Rhumb lines are not straight lines. The benefit is that the spherical form is much simpler to calculate, saving many computing cycles.>>
Even in a Mercator projection, straight lines other than N-S and E-W do not appear straight.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by BMAONE23 » Thu Oct 01, 2015 7:21 pm

neufer wrote:
ThePiper wrote:
Images always lie. :shock:
Only when projected onto a plane
And outside the Sphere of Influence

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by neufer » Thu Oct 01, 2015 6:57 pm

ThePiper wrote:
Images always lie. :shock:
Only when projected onto a plane

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by ThePiper » Thu Oct 01, 2015 6:34 pm

Ann wrote:Beautiful image! It's great to see the small, reddened Moon sitting in a full panorama skyscape and appreciate how tiny the Moon really is.
Yes, true.
But it's a wrong world: The fiery Moon vs the pale Andromeda Galaxy - a grain of dust vs. a giant cosmic vortex! Images always lie. :shock:

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by neufer » Thu Oct 01, 2015 6:32 pm

Chris Peterson wrote:
WilliamAWelch1 wrote:
Why does the milky way appear curved? Isn't our galaxy flat?
It is straight. But we're seeing a hemisphere projected onto a plane. That can't be done without introducing distortion. It's no different from ordinary maps, which usually show straight lines (such as latitude or longitude) as curved.
Chris Peterson wrote:
neufer wrote:
Ordinary maps projected onto a plane usually show latitude & longitude lines as straight.
I don't think so. The Mercator projection is the only common projection which does so,
and it is not all that commonly used anymore.
https://en.wikipedia.org/wiki/Web_Mercator wrote: <<Web Mercator, Google Web Mercator, Spherical Mercator, WGS 84 Web Mercator or WGS 84/Pseudo-Mercator is a variation of the Mercator projection and is the de facto standard for Web mapping applications. It rose to prominence when used in the first Google Maps in 2005. It is used by virtually all major online map providers, including Google Maps, Bing Maps, OpenStreetMap, Mapquest, Mapbox, and many others. Web Mercator shares some of the same properties of the standard Mercator projection: north is up everywhere, meridians are equally spaced vertical lines, but areas near the poles are greatly exaggerated.

Unlike the ellipsoidal Mercator and spherical Mercator, the Web Mercator is not quite conformal due to its use of ellipsoidal datum geographical coordinates against a spherical projection. Rhumb lines are not straight lines. The benefit is that the spherical form is much simpler to calculate, saving many computing cycles.>>

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Chris Peterson » Thu Oct 01, 2015 6:13 pm

neufer wrote:
Chris Peterson wrote:
WilliamAWelch1 wrote: Why does the milky way appear curved? Isn't our galaxy flat?
It is straight. But we're seeing a hemisphere projected onto a plane. That can't be done without introducing distortion. It's no different from ordinary maps, which usually show straight lines (such as latitude or longitude) as curved.
Ordinary maps projected onto a plane usually show latitude & longitude lines as straight.
I don't think so. The Mercator projection is the only common projection which does so, and it is not all that commonly used anymore.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by neufer » Thu Oct 01, 2015 6:04 pm

Chris Peterson wrote:
WilliamAWelch1 wrote:
Why does the milky way appear curved? Isn't our galaxy flat?
It is straight. But we're seeing a hemisphere projected onto a plane. That can't be done without introducing distortion. It's no different from ordinary maps, which usually show straight lines (such as latitude or longitude) as curved.
Ordinary maps projected onto a plane usually show latitude & longitude lines as straight.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by saturno2 » Thu Oct 01, 2015 5:47 pm

Interesting image

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Chris Peterson » Thu Oct 01, 2015 5:00 pm

WilliamAWelch1 wrote:Why does the milky way appear curved? Isn't our galaxy flat?
It is straight. But we're seeing a hemisphere projected onto a plane. That can't be done without introducing distortion. It's no different from ordinary maps, which usually show straight lines (such as latitude or longitude) as curved.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by WilliamAWelch1 » Thu Oct 01, 2015 4:35 pm

Why does the milky way appear curved? Isn't our galaxy flat?

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by geckzilla » Thu Oct 01, 2015 2:49 pm

It's the moon and the rest of the image having their dynamic ranges separated.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Chris Peterson » Thu Oct 01, 2015 2:44 pm

Cousin Ricky wrote:Why is the Moon darker than the glow surrounding it?
That is odd, and visually unnatural, isn't it? It reminds me of a solar eclipse.

I was thinking about it, and I think it's because of the way the raw images were boosted to bring out the sky. Given the very dark sky at this location, the glow of the eclipsed Moon was actually quite a bit higher than the sky background (which isn't the case in more light polluted locations). So when the levels were adjusted to bring the background above black, the red Moon was so bright that you could see the surrounding glow from scatter in the optics (just as we always do with an overexposed, uneclipsed Moon in a night shot). There's nothing much to be done about that other than manually painting out the glow. But it does serve to nicely demonstrate the actual color of the Moon as captured by the camera. (I'm not sure, but it's possible that Yuri masked out the Moon itself when he boosted the background, to prevent it from being too bright. I can see how that might be necessary- I've done similar on eclipse photos in order to bring out background stars.)

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Chris Peterson » Thu Oct 01, 2015 2:38 pm

keeper of the faith wrote:How did they stop Earth for this pretty shot? :roll:
This is a stitched panorama made from 15 separate, short duration images. With such wide angle shots, the duration was short enough that star trailing isn't easily detected. And I assume the sequence was taken in a sensible order, so there was very little motion between adjacent frames. I'm sure that if you plate solved the image, you'd see that the stars on one side are not where you'd expect them to be compared with stars on the other side, since over the entire sequence duration there would be a significant shift. But you'd never see that visually- it would have to be measured.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Cousin Ricky » Thu Oct 01, 2015 2:32 pm

Why is the Moon darker than the glow surrounding it?

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by geckzilla » Thu Oct 01, 2015 2:25 pm

keeper of the faith wrote:How did they stop Earth for this pretty shot? :roll:
Yuri is quite magical.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Boomer12k » Thu Oct 01, 2015 1:56 pm

That is just and awesome image!!!

The Magellanic Clouds on the Left. The MW in the center, looking like a STORM, and then the Lunar Eclipse on the Right, and the awesome Twin Telescopes.

Excellent!!

:---[===] *

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by keeper of the faith » Thu Oct 01, 2015 1:10 pm

How did they stop Earth for this pretty shot? :roll:

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Eric » Thu Oct 01, 2015 12:31 pm

Great image, thanks! Typo note: Carngegie > Carnegie.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Indigo_Sunrise » Thu Oct 01, 2015 10:40 am

Nitpicker wrote:Wow. It pays to click on the image and check out the full-res version. It is much wider.
x2.
I was just going to say that the full-res version is absolutely gorgeous!
8-)

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Nitpicker » Thu Oct 01, 2015 7:52 am

Wow. It pays to click on the image and check out the full-res version. It is much wider.

Re: APOD: Eclipsed in Southern Skies (2015 Oct 01)

by Ann » Thu Oct 01, 2015 5:06 am

Beautiful image! It's great to see the small, reddened Moon sitting in a full panorama skyscape and appreciate how tiny the Moon really is.

As for the number of galaxies you can see in this image, you can acutually see M33 too, "on the other side of" Andromeda.

There is something about the orientation of this image that makes me disoriented. I would love an annotated version of this image, labelling the brighter stars. (Although I have, in fact, found Altair, Deneb and I think Vega, skirting the horizon. Oh, and Scorpius and Antares and Alpha and Beta Centauri, too.)

Ann

APOD: Eclipsed in Southern Skies (2015 Oct 01)

by APOD Robot » Thu Oct 01, 2015 4:07 am

Image Eclipsed in Southern Skies

Explanation: This stunning panorama in southern skies was recorded on the colorful night of September 27/28 from Carnegie Las Campanas Observatory. A diffuse glow and dark rifts of the central Milky Way hang over domes of the twin 6.5 meter Magellan telescopes. But most eye-catching is the deep red glow of the Moon. Immersed in Earth's shadow during the much anticipated perigee-total-lunar eclipse, the Moon's surface reflects the light of sunsets and sunrises scattered and refracted into the planet's cone-shaped umbra. Along with the dramatic hue of the eclipsed Moon, other colors of that night captured by the sensitive digital camera include the red and green shades of atmospheric airglow. Viewers can also spot the Andromeda Galaxy below the Moon, seen as a tiny smudge through the reddish airglow and lights along the horizon. The Magellanic Clouds, satellite galaxies of the Milky Way, join in at the far left of the full panorama frame.

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