APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

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APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by APOD Robot » Thu Aug 02, 2018 4:08 am

Image Eclipse over the Gulf of Poets

Explanation: The total phase of the July 27 lunar eclipse lasted for an impressive 103 minutes. That makes it the longest total lunar eclipse of the 21st century. The Moon passed through the center of Earth's shadow while the Moon was near apogee, the most distant point in its elliptical orbit. From start to finish, the entire duration of totality is covered in this composite view. A dreamlike scene, it includes a sequence of digital camera exposures made every three minutes. The exposures track the totally eclipsed lunar disk, accompanied on that night by bright planet Mars, as it climbs above the seaside village of Tellaro, Italy. In the foreground lies the calm mediteranean Gulf of La Spezia, known to some as the Gulf of Poets. In the 3rd century BCE, heliocentric astronomer Aristarchus also tracked the duration of lunar eclipses, though without the benefit of digital clocks and cameras. Using geometry he devised a way to calculate the Moon's distance from the eclipse duration, in terms of the radius of planet Earth.

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by Pol Jansegers » Thu Aug 02, 2018 9:07 am

What is the black spot in the upper right corner??

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by Indigo_Sunrise » Thu Aug 02, 2018 10:59 am

Pol Jansegers wrote:
Thu Aug 02, 2018 9:07 am
What is the black spot in the upper right corner??
I wondered that too. It doesn't show up in the enlarged image....
Forget the box, just get outside.

heehaw

Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by heehaw » Thu Aug 02, 2018 1:08 pm

Mars gets SO bright every so often, yet as far as I know, no one speculated in early time that that was because Mars was closer to Earth. Kepler calculate what the path of Mars would be if Earth were the center of the universe: https://commons.wikimedia.org/wiki/File ... ograde.jpg and some time ago Owen Gingerich and I repeated Kepler's calculations on a computer: http://henry.pha.jhu.edu/pretzels.pdf It still absolutely flabbergasts me that Kepler could have carried out these extremely lengthy and difficult calculations correctly, especially in the torn and troubled times in which he lived.

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by neufer » Thu Aug 02, 2018 3:02 pm

Indigo_Sunrise wrote:
Thu Aug 02, 2018 10:59 am
Pol Jansegers wrote:
Thu Aug 02, 2018 9:07 am

What is the black spot in the upper right corner??
I wondered that too. It doesn't show up in the enlarged image....
Whatever it is.. it is the exact size of the Moon.
https://en.wikipedia.org/wiki/Percy_Bysshe_Shelley#Death wrote:
<<On 8 July 1822, less than a month before his thirtieth birthday, Percy Bysshe Shelley drowned in a sudden storm on the Gulf of Spezia while returning from Leghorn (Livorno) to Lerici in his sailing boat, the Don Juan. The name Don Juan, a compliment to Byron, was chosen by Edward John Trelawny, a member of the Shelley–Byron Pisan circle. However, according to Mary Shelley's testimony, Shelley changed it to Ariel, which annoyed Byron, who forced the painting of the words "Don Juan" on the mainsail.

Some believed his death was not accidental, that Shelley was depressed and wanted to die; others suggested he simply did not know how to navigate. More fantastical theories, including the possibility of pirates mistaking the boat for Byron's, also circulated. Two other Englishmen were with Shelley on the boat. One was a retired naval officer, Edward Ellerker Williams; the other was a boatboy, Charles Vivien. The boat was found ten miles offshore, and it was suggested that one side of the boat had been rammed and staved in by a much stronger vessel. However, the liferaft was unused and still attached to the boat. The bodies were found completely clothed, including boots.

Shelley's body was washed ashore and later, in keeping with quarantine regulations, was cremated on the beach near Viareggio. In Shelley's pocket was a small book of Keats' poetry. Upon hearing this, Byron said of Shelley: "I never met a man who wasn't a beast in comparison to him". An 1889 painting by Louis Édouard Fournier, The Funeral of Shelley, contains inaccuracies. In pre-Victorian times it was English custom that women would not attend funerals for health reasons. Mary Shelley did not attend but was featured in the painting, kneeling at the left-hand side. Leigh Hunt stayed in the carriage during the ceremony but is also pictured. Also, Trelawny, in his account of the recovery of Shelley's body, records that "the face and hands, and parts of the body not protected by the dress, were fleshless," and by the time that the party returned to the beach for the cremation, the body was even further decomposed. In his graphic account of the cremation, he writes of Byron being unable to face the scene, and withdrawing to the beach.

Shelley's ashes were interred in the Protestant Cemetery in Rome, near an ancient pyramid in the city walls. His grave bears the Latin inscription, Cor Cordium (Heart of Hearts), and, in reference to his death at sea, a few lines of "Ariel's Song" from Shakespeare's The Tempest: "Nothing of him that doth fade / But doth suffer a sea-change / Into something rich and strange." A memorial was eventually created for Shelley at the Poets' Corner at Westminster Abbey, along with his old friends Lord Byron and John Keats.>>
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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by MarkBour » Thu Aug 02, 2018 10:31 pm

Interesting that the longest total eclipse would occur at an apogee. At that point Luna's angular velocity with respect to the Earth is slowest, but the umbra of Earth's shadow should also be smallest. Apparently speed is more important than size. I guess the Earth's umbral shadow does not shrink very rapidly with distance from the Earth. It has the shape of a cone from the Earth out, but the difference in its size at the Moon's distance at perigee versus apogee is probably not a great amount.

I guess it also helps that Earth is at near aphelion, so its umbral shadow is elongated at this time of year, and it helps if the Moon passes in alignment with the center of Earth's circular-shaped shadow.

http://earthsky.org/tonight/centurys-lo ... se-july-27
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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by neufer » Fri Aug 03, 2018 3:22 am


MarkBour wrote:
Thu Aug 02, 2018 10:31 pm

Interesting that the longest total eclipse would occur at an apogee. At that point Luna's angular velocity with respect to the Earth is slowest, but the umbra of Earth's shadow should also be smallest. Apparently speed is more important than size. I guess the Earth's umbral shadow does not shrink very rapidly with distance from the Earth. It has the shape of a cone from the Earth out, but the difference in its size at the Moon's distance at perigee versus apogee is probably not a great amount.

I guess it also helps that Earth is at near aphelion, so its umbral shadow is elongated at this time of year, and it helps if the Moon passes in alignment with the center of Earth's circular-shaped shadow.

http://earthsky.org/tonight/centurys-lo ... se-july-27
Indeed:

The Earth's umbral shadow does not shrink very rapidly with distance from the Earth.
-------------------------------------------------------------------------------------------------
At 3/2 Lunar radii the umbral shadow has decreased from ~3 moon widths to only ~(5/2) moon widths
with the maximal umbral transit distance DT decreasing from ~2 moon widths to ~(3/2) moon widths.

However, the umbral transit velocity VT has decreased from 1 to (2/3).

Hence: the maximal umbral transit time DT/VT increases from 2/1 to 9/4 [= (3/2)/(2/3)].

On July 27, 2018 the maximal umbral transit time would actually have occurred at:
  • oRM = RS * (DE - DM)/(2*DS) = 693,567 km
    well beyond the Moon's actual 406,200 km distance
Where: oRM = Optimal lunar distance, RS = Solar distance ,
DE = Earth diameter , DM = Moon diameter , DS = Sun diameter
Art Neuendorffer

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by MarkBour » Sun Aug 05, 2018 12:41 am

neufer wrote:
Fri Aug 03, 2018 3:22 am
...
On July 27, 2018 the maximal umbral transit time would actually have occurred at:
  • oRM = RS * (DE - DM)/(2*DS) = 693,567 km
    well beyond the Moon's actual 406,200 km distance
Where: oRM = Optimal lunar distance, RS = Solar distance ,
DE = Earth diameter , DM = Moon diameter , DS = Sun diameter
Hey, no fair figuring out and answering my next question before I even asked! :lol2:
Honestly, I'm impressed!

Hmmm... I see that *part* of this is the rather simple geometry of the dimensions of a cone. The (DE - DM) part is the distance the Moon can travel in darkness, and probably assumes that the Earth progressing along its orbit is not a significant factor in this calculation. Using your numbers for the diameters, I wonder at what distance the Earth's shadow is exactly the size of the moon (which would lead to a 0-minute totality). This would be a closer distance than the distance at which the Earth eclipsing the Sun would become annular in nature; I believe that must occur at the point where the umbral cone reaches its 0-width endpoint.
Mark Goldfain

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by neufer » Sun Aug 05, 2018 11:34 am

MarkBour wrote:
Sun Aug 05, 2018 12:41 am
neufer wrote:
Fri Aug 03, 2018 3:22 am
...
On July 27, 2018 the maximal umbral transit time would actually have occurred at:
  • oRM = RS * (DE - DM)/(2*DS) = 693,567 km
    well beyond the Moon's actual 406,200 km distance
Where: oRM = Optimal lunar distance, RS = Solar distance ,
DE = Earth diameter , DM = Moon diameter , DS = Sun diameter
Hmmm... I see that *part* of this is the rather simple geometry of the dimensions of a cone. The (DE - DM) part is the distance the Moon can travel in darkness, and probably assumes that the Earth progressing along its orbit is not a significant factor in this calculation. Using your numbers for the diameters, I wonder at what distance the Earth's shadow is exactly the size of the moon (which would lead to a 0-minute totality). This would be a closer distance than the distance at which the Earth eclipsing the Sun would become annular in nature; I believe that must occur at the point where the umbral cone reaches its 0-width endpoint.
The maximal umbral transit time equation TM is a simple parabola in lunar distance R:

TM = C R [ 2 oRM - R ]

It is maximal at R = oRM

and zero at R = 0 or 2 oRM
(where the umbral cone is exactly the size of the moon).
Art Neuendorffer

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by MarkBour » Sun Aug 05, 2018 10:59 pm

neufer wrote:
Sun Aug 05, 2018 11:34 am
The maximal umbral transit time equation TM is a simple parabola in lunar distance R:

TM = C R [ 2 oRM - R ]

It is maximal at R = oRM

and zero at R = 0 or 2 oRM
(where the umbral cone is exactly the size of the moon).
I'm glad we don't have to worry about that R=0 solution. :-)
Mark Goldfain

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Re: APOD: Eclipse over the Gulf of Poets (2018 Aug 02)

Post by Indigo_Sunrise » Tue Aug 07, 2018 11:04 am

Indigo_Sunrise wrote:
Thu Aug 02, 2018 10:59 am
Pol Jansegers wrote:
Thu Aug 02, 2018 9:07 am
What is the black spot in the upper right corner??
I wondered that too. It doesn't show up in the enlarged image....
It appears to have been removed. And no matter; it's a very nice image!
Forget the box, just get outside.