APOD: Noctilucent Clouds (2005 Jun 19)

Comments and questions about the APOD on the main view screen.
Posts: 1
Joined: Tue Jun 21, 2005 11:38 pm

APOD: Noctilucent Clouds (2005 Jun 19)

Post by Dinomyte » Tue Jun 21, 2005 11:44 pm


The picture on Sunday 6/19 had an image of noctilucent clouds. In the explanation, it mentioned that one theory says that noctilucent clouds are formed by the launch of the Space Shuttle, and other ELV's.

I didn't know they were caused by the shuttle, but I do know that the shuttle has flight rules which prohibit the shuttle from possibly passing through noctilucent clouds on entry trajectories. Since the noctilucent clouds are ice crystals, you can easily imagine that they can cause damage to the shuttle's TPS, and could potentially lead to loss of control of the vehicle on entry if it passed through thick enouch noctilucent clouds -- neither of which you want on entry (molten aluminum is hard to control). Anyway, since these clouds form during the summertime in high latitudes, the shuttle will not use a descending (high latitude to low latitude) entry trajectory during the summer to avoid these clouds. Just thought some of you may be interested, and I was interested to see this picture after I had learned about the other shuttle side at work.

Posts: 3
Joined: Fri Aug 12, 2005 9:58 am
Location: Leeds UK

Post by tony_p_cook » Fri Aug 12, 2005 10:20 am

Noctilucent clouds are NOT formed only during the summer time. Its merely that summer time between latitudes 50 and 60 degrees (both North and South) provides the optimum conditions to observe them. I.e. the sun is under the horizon and not to far below for a lengthy period of time but the clouds are high enough to be directly lit by sunlight during this period.

If you are lucky you can see noctilucent clouds at any time of year and at most latitudes after sunset BUT the period in which the optimum conditions are met are usually a matter of a few minutes at most.

Thye shuttle is only a suspected cause of modern sightings. The first reports of noctilucents clouds occured two years after the erruption of Krakotoa well before the shuttle era

Posts: 98
Joined: Wed Jun 29, 2005 8:31 am
Location: Dorset, England

Post by Empeda » Fri Aug 12, 2005 2:55 pm

But they have been increasing in number ever since have they not? Could they be a form of cosmic psiren?....
I'm an Astrophysics Graduate from Keele University, England - doesn't mean I know anything but I might be able to help!