How low can they go? Noctilucent clouds (NLCs) are usually confined inside the Arctic Circle, but this year they have been sighted at mid-latitudes and below. The 2021 record-holder, so far, is this photo from the Observatorio de Sierra Nevada in Granada, Spain, at latitude +37N:
noctilucent clouds 2021
© Observatorio de Sierra Nevada (IAA-CSIC)
Taken on June 20, 2021, at Loma de Dilar, Granada, Spain

"This is the first time NLCs have been observed from Granada," according to the observatory's Science Directorate.

The picture was taken on June 20th by telescope operator Alfredo Sota. He was supervising the observatory's webcam when he saw "weird clouds" in the sunset. Soto grabbed his camera and ran out of the observatory to take the picture. "Watching them live was even more spectacular than the photo," says Soto.

Not quite matching the latitude of southern Spain, NLCs appeared last night in multiple US states including the Dakotas, Wisconsin, and Minnesota. Christian Roble sends this picture from Saint Paul (+45N):
noctilucent clouds 2021
© Christian Roble
Photo taken on June 24, 2021, from Saint Paul, Minnesota, USA
"I just happened to look north towards the Capitol and I saw them hovering high above!" says Roble. "I was excited to have finally seen them this year!"

NLCs are Earth's highest clouds. They form when summertime wisps of water vapor rise up to the edge of space and crystallize around disintegrated meteoroids. When you see one, you're literally seeing a cloud of frosted meteor smoke. Just after sunset or before sunrise is the best time to look.