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Post by tanel025 on Jun 24, 2018 9:28:52 GMT
Magnificent show all over the night. Started 20:30 UTC and lasted till 30 mins before sunrise (00:40 UTC)! All directions were covered with NLC, it quickly went even to South and was there even at ca 45 degrees over the horizon. Brightness definitely at 4 (1-5 scale). The 3rd picture is made aiming at South direction, exactly at 00:00UTC.
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Post by tanel025 on Jun 24, 2018 9:34:28 GMT
And this is 30 min before Sunrise. Unbelievable that I still saw them and was able to take photo. Attachments:
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Post by johnm on Jun 24, 2018 18:14:56 GMT
Hello,
The Sun NLC geometry does not allow NLC to be illuminated and seen South of the observer (in the Northern Hemisphere). I suspect the cloud in the third image is high Cirrus possibly illuminated by the moon ? What time was moonset in your location ?
Regards
John
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Post by jurgen on Jun 24, 2018 21:38:20 GMT
The Sun NLC geometry does not allow NLC to be illuminated and seen South of the observer (in the Northern Hemisphere).
Sorry John, but that is is not correct.
I also saw the June 22/23 display in western Germany
At 03:45 MEST (01:45 GMT) the upper rim of the NLC field was about 1 degree above Capella,
at 04:05 MEST estimated height 30 degrees,
reached zenith at about 04:15 MEST
and continued southwards until it became too faint discernible halfway down at 04:30 MEST.
There were absolutely no tropospheric cirrus clouds.
I remember having seen this phenomena at least twice during the last decades.
So please, John, make a better theory.
Regards jurgenEB |
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Post by tanel025 on Jun 25, 2018 6:18:14 GMT
It's most certainly NLC as they were there already at midnight, when it was too dark to see lighted cirrus clouds. I have observed NLC-s for 6 years now and seen them at zenith and even going further to South several times in past years. I live at 58 deg lat, it's possible here. And Moon had already set when I took photos aimed at South.
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Post by James Fraser on Jun 26, 2018 9:15:37 GMT
Yes, every year I see at least one NLC display pass over the zenith and into the southern sky. I live at 57deg 42min North. Here is a photo from the bright and extensive display just yesterday (June 24-25, 2018)with the NLC reaching as far as Altair...sadly the star may not survive the transfer from raw to jpeg. Best wishes, Jimmy Attachments:
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Post by johnm on Jun 27, 2018 18:50:24 GMT
I thought my comments about how far South NLC can be observered (in the Northern hemisphere) might cause a response. The Geometry shown in 'Noctilucent Clouds by Fogle and Haurwitz see Paper on ADS is quite clear that the maximum elevation that NLC can be illuminated by the Sun is 100 Degrees from the Northern horizon see Fig 14 when the Sun is 6 degrees below the horizon. The maximum elevation falls as shown in this figure. Areas to the South of this at a height of 82km are in the Earth's shadow and should not be illuminated.
However observations don't seem entirely consistent with these calculations. One of the best examples I have seen published is an all sky fish eye lens image in Observing Noctilucent Clouds by Gadsen & Parviainen available here shows NLC to the south of the observer in Photograph 16.
My suggestion about the Moon illuminating the NLC while set is theoretically possible from the geometric point of view but since the Moon is around 15 magnitudes dimmer than the Sun this would require an exposure of 1 million times that of Sunlit NLC. Not really probable !
The only explanation that I can propose for NLC being observed South of the observer is that the assumptions about there being negligible refraction of light high in the atmosphere are wrong and the illuminating Sunlight is strongly bent towards the surface following the Earth's curvature.
Anyone got any comments or other ideas ?
John Murrell
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Post by sonic on Jun 28, 2018 0:18:43 GMT
I can also testify seeing one epic display in 2011 which by the end was visible south behind me (50.43deg Lat), but it wasn't far off sunrise at the end.
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