# Do Noctilucent clouds cause problems with telescopes?

Noctilucent clouds are at around 85km altitude and are formed of ice crystals. The ISS recently posted a number of photographs of these clouds and pointed out the key feature, which is the bright blue glow.

Are these known to have an impact on ground-based or orbital telescopes?

Noctilucent clouds are not a problem for space telescopes because their orbits are always more than 85 km. The Hubble Telescope orbits at about 570 km. Noctilucent clouds are a problem for ground-based telescopes (although only at high latitude sites,> 50$^{\circ}$), especially if you are trying to get accurate photometric brightnesses. However, typically you can see them reflecting city lights or moonlight, or you can tell from the large variance in your photometry counts that they are there and you should try again another night.