Shepherds may be delighted with a red sky but a blue one over County Antrim had night watchers buzzing.
They were treated to the rarer electric blue hues of the noctilucent, or "night-shining" clouds.
These are the highest clouds in the sky at a height of about 50 miles, which puts them at the top of the mesosphere.
They can normally only be seen during the summer between about 50 and 65 degrees north and south when the sun is below the horizon.
But recent records suggest they have become brighter, more frequent and are being seen at lower latitudes than usual.
Sky watcher Paul Evans from Larne spotted the phenomenon on Friday night and said it was an incredible display.
"They have been seen since at least the 19th Century - there were lots of sightings after the explosion of Krakatoa in 1893 and that's actually when they were given their name," he said.
"They come around pretty much every year now."
Friday night was the first time Paul saw them, after being tipped off by members of the East Antrim Astronomical Society, to which he belongs.
"Once I had seen it, it was unmistakeable.
"The display started off quite slowly at about half past midnight or so and stayed up until gone three at which time it was fading into the oncoming dawn," he said.
"It was a very impressive display indeed and I look forward to seeing a few more over the summer."
The clouds float through the outer reaches of Earth's atmosphere at the very edge of space.
Some scientists think the clouds are seeded by space dust and fed by rocket exhaust.
Others suspect they are a sign of global warming. Later this year, NASA plans to launch a satellite named AIM to investigate.
The AIM (Aeronomy of Ice in the Mesosphere) spacecraft, will be lofted to 600km (370 miles) to make a detailed study of the clouds.
The 195kg (430lb) satellite will be put in space by a Pegasus rocket launched from beneath the wing of an aircraft.
AIM's three instruments will investigate the recipe needed to make the clouds - cold temperatures, the presence of water vapour, and small dust particles around which the water can condense and freeze out to create ice crystals.