He said people should go out “immediately after sunset” with a pair of binoculars, head for higher ground and look west towards the horizon.
Try to stand where hills, buildings and trees are not blocking your view, he said.
Skies will be clearing overnight on Saturday as strong winds push the cloud and showers away into the North Sea.
Dr Massey advised people to “wrap up” and bring a hot drink with them.
“Just go out, enjoy it, don’t sweat it,” he said.
The RAS said the comet was first visible in the southern hemisphere between 27 September and 2 October and would be visible from Saturday night to 30 October.
The comet likely travelled from the outer reaches of our solar system and made its closest transit past the sun on 27 September, the Nasa Earth Observatory said.
Dr Massey said the nucleus of the comet – its solid core – has been estimated to be 2km (1.24 miles) long, or “mountain-size”.
He said he tried to spot it on Friday night and will “certainly try again”.
“Sometimes comets disappoint… but this one appears to be acting in line with predictions,” he said.
“We want people to try and go out and have a look.”
