Astronomy Picture of the Day 6-15-03

NASA ^ | 6-15-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 June 15

Noctilucent Clouds
Credit & Copyright: Pekka Parviainen (Polar Image)

Explanation: Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above. Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark. Pictured above, a network of noctilucent clouds casts a colorful but eerie glow visible above the dark. Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them. Recent evidence indicates that at least some noctilucent clouds result from freezing water exhaust from Space Shuttles.

[petuniasevan]

Noctilucent clouds are seen from high latitudes (50-65 degrees north or south) only during local summer. The image above is from Finland.

The displays are rare; perhaps occurring 10-20 times per year.

The mesosphere (part of the atmosphere where these clouds form) is extremely cold in local summer;
it averages only 130K (-225 Fahrenheit or -143 Celsius)!

RightWhale, have you ever seen noctilucent clouds?

[petuniasevan]

[firewalk]

Thanks for the ping

[RightWhale]

have you ever seen noctilucent clouds?

Two possibilities:

Either no, or
all the time.

The atmosphere is in the vertical dimension very thin at this latitude and it might be that noctilucent clouds are much lower than at temperate latitudes. Thunderheads certainly are low and puny. The rippling clouds shown n one of the images are frequently visible. If those are noctilucent clouds, then they are visible much of the time in winter.

[trussell]

This is beautiful. Thank you for the ping.

[sistergoldenhair]

Thanks for the ping.