Noctilucent clouds. Here is a comparison
between the AIM satellite 24-hour NLC Daisy-Wheel image and how it
looked from an airplane at 37,000 feet. This image was shown on
SpaceWeather.com 25-27 June 2013
The NLC daisy-wheel allowed me to see where the distant northern horizon
NLC truly were! This display reached a max height of about 10 degrees,
as seen from 37,000 feet at 50N latitude. It was my 4th and best
sighting of 2013 so far. In the past, I was left puzzled as to why I
didn't see any NLC. Where were they? But now the mystery is gone because
(Thanks to spaceweather.com) I now know where they were using the AIM 24
hour daisy-wheel. You can see that the clouds were very far away and
that I was only seeing the southern extensions of them. From 37,000 feet
my horizon is about 200+ nautical miles away. From the NLC height of
280,000 feet their horizon is about 600+ nautical miles away. That is
why I can theoretically see NLC
over 800 Nm (1600km) away, or
over 13 degrees
of Latitude! In contrast, often a ground based observation may has dull
haze up to 5 degrees above the horizon allowing an NLC distance of only
330 Nautical miles (650km) equivalent to about 5.5 degrees Latitude. The
aircraft is also either usually above the clouds completely or has an
opportunity to view between weather systems.
Its obvious to see why the aircraft has an advantage!
It is worth noting that the Daisy-image is a delayed daily composite and
could be inaccurate as to a specific short lived extension or fail to
detect a weak patch all together at a specified location.
If you think flying near Noctilucent Clouds is amazing, you will
want to learn more about Project PoSSUM. They intend to fly a
small American Space Plane, the XCOR Lynx, into some NLC as
early as 2014.