APOD: Conjunction of Four (2017 Feb 04)

Comments and questions about the APOD on the main view screen.
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APOD: Conjunction of Four (2017 Feb 04)

Post by APOD Robot » Sat Feb 04, 2017 5:06 am

Image Conjunction of Four

Explanation: On January 31, a waxing crescent Moon, brilliant Venus, and fainter Mars gathered in the fading twilight, hanging above the western horizon just after sunset on planet Earth. In this combined evening skyscape, the lovely celestial triangle is seen through clouds and haze. Still glinting in sunlight, from low Earth orbit the International Space Station briefly joined the trio that evening in skies near Le Lude, France. The photographer's line-of-sight to the space station was remarkably close to Mars as the initial exposure began. As a result, the station's bright streak seems to leap from the Red Planet, moving toward darker skies at the top of the frame.

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Rusty Brown in Cda

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Rusty Brown in Cda » Sat Feb 04, 2017 8:49 am

I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon, it would have to be in the east at sunset, not above the western horizon anyway.

heehaw

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by heehaw » Sat Feb 04, 2017 10:34 am

I suspect I know what is going on here! https://en.wikipedia.org/wiki/The_War_o ... dio_drama)

heehaw

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by heehaw » Sat Feb 04, 2017 10:37 am

ESPOD for today is good astronomy! http://epod.usra.edu/blog/

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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by orin stepanek » Sat Feb 04, 2017 12:01 pm

Rusty Brown in Cda wrote:I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon, it would have to be in the east at sunset, not above the western horizon anyway.
Neat picture; I suspect that the moon looks full because it is overexposed! 8-)
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by neufer » Sat Feb 04, 2017 1:00 pm

orin stepanek wrote:
Rusty Brown in Cda wrote:
I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon,
it would have to be in the east at sunset, not above the western horizon anyway.
  • I suspect that the moon looks full because it is overexposed! 8-)
    • In a line-of-sight through the celestial triangle
      the furthest object (Mars) is the most full
      while the nearest object (ISS) is the least.
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Chris Peterson
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Chris Peterson » Sat Feb 04, 2017 3:09 pm

Rusty Brown in Cda wrote:I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon, it would have to be in the east at sunset, not above the western horizon anyway.
When the picture was taken, the apparent diameter of the Moon was 1900 arcsec, meaning it should appear to be 28 pixels across (it actually has a diameter of 150 pixels). Mars had an apparent diameter of 5 arcsec, theoretically covering 0.07 pixels, but actually covering about 2 pixels. And Venus had an apparent diameter of 31 arcsec, theoretically covering 0.46 pixels, actually covering 50.

Had this been exposed such that we could see the Moon as a (tiny) crescent, Venus would appear as a point and Mars probably wouldn't be bright enough to be visible- nor would the background stars or the landscape. The ISS would also be a pixel wide line.
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Mustremainanonymous

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Mustremainanonymous » Sat Feb 04, 2017 3:57 pm

Not so!

This is just the cover story they (NASA & the aliens) would like us to swallow.

:evil: :wink:

Rusty Brown in Cda

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Rusty Brown in Cda » Sat Feb 04, 2017 4:01 pm

Thank you all for your explanations.
RB in Canada

Mustremainanonymous

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Mustremainanonymous » Sat Feb 04, 2017 4:43 pm

Rusty Brown in Cda wrote:Thank you all for your explanations.
RB in Canada
Rusty Brown in Cda wrote:I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon, it would have to be in the east at sunset, not above the western horizon anyway.
But things aren't always as they seem RB.

Careful examination of this photo will no doubt reveal that it was indeed taken at the time and place in the Apod cover story.

However, what this really shows is that the French have finally developed a means of photoghapically defeating alien cloaking tech.

:evil: :wink:

Mustremainanonymous

Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Mustremainanonymous » Sat Feb 04, 2017 6:03 pm

No doubt all conventionally trained thinkers out there find our alternative explaination to be extremely absurd. Your thinking, 'this guy is either joking or he's an idiot', aren't you?

But that's just what they would want you to think, isn't it???

:evil: :wink:

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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by ta152h0 » Sat Feb 04, 2017 7:41 pm

I am amazed this image is in focus from the tree to the planet, considering the Earth is moving at a considerable pace. Some sort of computer imaging shenanigans ?
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by neufer » Sat Feb 04, 2017 7:53 pm

ta152h0 wrote:
I am amazed this image is in focus from the tree to the planet, considering the Earth is moving at a considerable pace. Some sort of computer imaging shenanigans ?
The astro-photographer went to great lengths (a steadicam :?: ) in order to track the tree :tree: .

(Unfortunately, the tree is greatly underexposed for the time of day.)
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by De58te » Sat Feb 04, 2017 8:54 pm

ta152h0 wrote:I am amazed this image is in focus from the tree to the planet, considering the Earth is moving at a considerable pace. Some sort of computer imaging shenanigans ?
As an amateur photographer I know that with a standard lens, infinity focus is about 35 feet. That means everything farther away than 35 feet from the camera to infinity is in focus. The tree looks to be more than 35 feet away. It would be in focus. In fact I would figure he used a zoom lens considering the moon and Venus look larger than normal. That would put the tree even farther away from the camera.
Now I watched the ISS cross the sky about 4 or 5 years ago. Also just after sundown. The horizon was growing dark, but the ISS was still in blazing bright light. It took maybe 3 minutes to cross the sky, so in that photograph the trail would look to have taken about a minute of exposure. Maybe a minute and a half.
With a minute of exposure the stars might show up depending on the sensitivity setting but they wouldn't be that motion blurred by the spin of the Earth.

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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by alter-ego » Sun Feb 05, 2017 5:15 am

APOD Robot wrote:On January 31, a waxing crescent Moon, brilliant Venus, and fainter Mars gathered in the fading twilight, hanging above the western horizon just after sunset on planet Earth.
This APOD could be titled "Conjunction of Five". (No, I'm not including the Earth :))
Located about 2/3 the way towards the upper left corner (~18½° from Mars), Uranus is also in the image. Keeping with the gist of the APOD, it does qualify (loosely) as a conjunction.
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by MarkBour » Sun Feb 05, 2017 6:25 am

Chris Peterson wrote:
Rusty Brown in Cda wrote:I'm confused: that's sure not a "crescent" moon on my screen, and if it is a full moon, it would have to be in the east at sunset, not above the western horizon anyway.
When the picture was taken, the apparent diameter of the Moon was 1900 arcsec, meaning it should appear to be 28 pixels across (it actually has a diameter of 150 pixels). Mars had an apparent diameter of 5 arcsec, theoretically covering 0.07 pixels, but actually covering about 2 pixels. And Venus had an apparent diameter of 31 arcsec, theoretically covering 0.46 pixels, actually covering 50.

Had this been exposed such that we could see the Moon as a (tiny) crescent, Venus would appear as a point and Mars probably wouldn't be bright enough to be visible- nor would the background stars or the landscape. The ISS would also be a pixel wide line.
I was wondering about the wording in the APOD caption that says: "In this combined evening skyscape ..."
whether or not that implies that separate images were combined.

As I read Chris' note above, it leaves me still wondering. Chris, it seems you figured out how large the various bodies should appear and then noted that they are considerably larger than that, right? You then mention level of exposure, but that would not change the pixel size of the bodies, correct? If you can "dumb it down" further, I may be able to follow what you're saying.
Mark Goldfain

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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by Chris Peterson » Sun Feb 05, 2017 2:59 pm

MarkBour wrote:I was wondering about the wording in the APOD caption that says: "In this combined evening skyscape ..."
whether or not that implies that separate images were combined.

As I read Chris' note above, it leaves me still wondering. Chris, it seems you figured out how large the various bodies should appear and then noted that they are considerably larger than that, right? You then mention level of exposure, but that would not change the pixel size of the bodies, correct? If you can "dumb it down" further, I may be able to follow what you're saying.
If you change the exposure time, you will change the apparent size of the bodies. Nothing in the sky in this image is large enough to be resolved at all except for the Moon, and it's still quite small at this image scale. The Moon and Venus are so overexposed that all we're seeing is the glow of the sky around them and scatter inside the optics. The objects themselves are totally hidden by all this scattered light.

Here is an image I made of a moon pillar. In order to catch the pillar, I had to expose the image at ISO 800 for 4 seconds. The properly exposed Moon is a 1/30 second exposure at ISO 100. There's almost a factor of 1000 in total exposure between the two. In the pillar image, the Moon itself is completely lost in a much larger halo of saturation from the light scattering off the thin fog.
pillars.gif
The APOD exposure was probably 30 seconds or longer. Had it been 1/100 of a second, we'd see a small crescent Moon, a small dot for Venus, a small dot for the ISS, and probably not Mars at all. Or, the aperture could have been stopped way down, the long exposure kept so that ISS showed as a streak, but again, all the dimmer stuff would be lost.

I don't know what is meant by "combined" in this caption. But it's not uncommon in such images for the foreground landscape and background starscape to be combined from separate images, given the often very different exposure requirements. It doesn't mean that they're at different image scales.
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Re: APOD: Conjunction of Four (2017 Feb 04)

Post by MarkBour » Fri Feb 10, 2017 12:03 am

Thanks, Chris. Now I get it. An excellent tutorial example.
Mark Goldfain