APOD: Four Towers and the Equinox Moon (2019 Mar 23)

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APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by APOD Robot » Sat Mar 23, 2019 4:11 am

Image Four Towers and the Equinox Moon

Explanation: The first Full Moon of northern spring rises behind four distant towers in this telescopic view. In an image captured from some 40 kilometers west of the city of Madrid, this moonrise also represents a near coincidence of the full lunar phase with lunar perigee and the March equinox. Close to the horizon, the Full Moon's strangely rippled and distorted shape has more to do with the long sight-line through a layered atmosphere, though. Tantalizing visible effects of the substantial atmospheric refraction include the appearance of a thin floating sliver just above the lunar disk. The remarkable optical mirage is related to the more commonly witnessed green flash of the setting Sun.

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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by Nitpicker » Sat Mar 23, 2019 7:29 am

Lovely image. Thank you.

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orin stepanek
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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by orin stepanek » Sat Mar 23, 2019 12:21 pm

Nitpicker wrote: Sat Mar 23, 2019 7:29 am Lovely image. Thank you.
Yes it is' and would also make a nice background picture for a PC! 8-)
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Smile today; tomorrow's another day!

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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by dmbeaster » Sat Mar 23, 2019 5:53 pm

That image has the related twin of the green flash, which is the strong red margin on the bottom side of the Moon, which is the same phenomena.

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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by Guest » Sat Mar 23, 2019 6:34 pm

Looking at the image and reading the description. If it was taken 40 km (25 miles) from Madrid, why is the city not below the horizon? The curvature of the earth should make the city just a glow on the horizon. Have we been photo-shopped?

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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by neufer » Sat Mar 23, 2019 6:47 pm

dmbeaster wrote: Sat Mar 23, 2019 5:53 pm
That image has the related twin of the green flash, which is the strong red margin on the bottom side of the Moon, which is the same phenomena.
https://www.atoptics.co.uk/atoptics/gf15.htm wrote: <<A standard stable atmosphere gets cooler with increasing height and the air density falls smoothly and monotonically. The lower and denser portion acts as a giant lens bending rays from the setting sun towards the earth. As a result, the rays appear to be coming from a point higher in the sky and the sun appears to be raised up. Green light is refracted more strongly than red and so different coloured images of the sun become very slightly vertically separated. As the sun sinks it develops a green upper edge and a red lower one. But the effect is small usually only visible in binoculars - do not ever look without full eye protection, even for an instant. There is a further effect, traces of ozone absorb the orange light which makes the contrast between the red sun and green flash even more dramatic.>>
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Re: APOD: Four Towers and the Equinox Moon (2019 Mar 23)

Post by Nitpicker » Mon Mar 25, 2019 2:31 am

Guest wrote: Sat Mar 23, 2019 6:34 pm Looking at the image and reading the description. If it was taken 40 km (25 miles) from Madrid, why is the city not below the horizon? The curvature of the earth should make the city just a glow on the horizon. Have we been photo-shopped?
Considering a perfectly spherical Earth of radius 6371 km, an observer 45 km away from the Cuatro Torres Business Area in Madrid (which is about 7 km NNE of central Madrid) would only require an elevation of 160 metres above the base of the four towers, in order to see their ground floors. About 45 km due west of the CTBA, there are hills that rise at least 400 metres above the ground elevation of the CTBA. (And the tallest of the four towers is 250 metres above ground, which is coherent with the camera's distance of 40 to 45 km from the towers.) So, the numbers add up, and I'd certainly give the photographer the benefit of any doubt.