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Saturn's approach to equinox reveals new
detail in rings

...Towering vertical structures in Saturn's rings have been discerned for the first time by Cassini as the giant planet approaches equinox...

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NASA's return to

the Moon

...Paving the way for the future of lunar exploration, NASA's LRO and LCROSS missions will launch later this week....

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Wising up in the infrared

...NASA's Wide-field Infrared Survey Explorer (WISE) is undergoing final preparations ahead of a planned 1 November launch...

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Video archive

STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.


STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.


STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

 Full presentation
 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.


Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

 Full coverage

Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

 Launch | Science

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More video

Noctilucent clouds are back



Posted: 16 June, 2009

As previewed in our Weekly Guide to the Night Sky, noctilucent cloud (NLC) season is here again following a splendid display on Tuesday evening.

Noctilucent clouds seen in the evening of 16 June, imaged by Nik Szymanek.

NLCs are thin sheets of cloud 82 kilometres high that reflect sunlight when the Sun is between six and sixteen degrees below the horizon. You can tell them apart from other, more normal clouds by their often pearly-blue colour, and ribbed and interwoven appearance. Other clouds at lower altitudes will be in darkness whilst NLCs glimmer high overhead.

The best months for NLCs in the UK are June and July, and they seem to favour lower sunspot activity (which limits the solar heating on the upper atmosphere where they form) so at least the presently dull Sun offers something in exchange for its lack of activity! Even their origin is a mystery, as clouds shouldn’t ordinarily be able to form so high up.

Noctilucent clouds over Stonehenge on 16 June, imaged by Grant Privett with a 60-second exposure using a Lumix DMC-FZ7 camera.

The best time to see NLCS is just after sunset, and they make for very picturesque photographs, as these examples of last night’s display show. If you spot any NLCs, we’d be keen to hear about your observations.

Email your pictures, saved as JPG, TIF or GIF files to gallery2009<at> with observation and technical details such as exposure time, telescope and camera type.