Freely online at the Library of Congress, the popular science/history book Comet madness : how the 1910 return of Halley’s comet (almost) destroyed civilization (2023).

Hairy Stars: Fear and Loathing in the Heavens
From Astrology to Astronomy
Whither the Comet?
The Fabulous Flammarion
A Dangerous Tail
The Unexpected Visitor
Cyanogen Gas!
From Science to Science Fiction
Aetna and the Wheel of Anxiety
Apocalypse Now
The Death of Kings
Rationality Won’t Keep Out The Rain
Up on a Roof
Cosmic Death Ray
Hysteria’s Highwater Mark
The Case of the Missing Tail
And We (Mostly) Lived Happily Ever After.

Amazon UK will happily take your £17 for the ebook, but the LoC officially has it free.

Lovecraft made a substantial scientific entry on the comet, for 26th May 1910, but seems to make no reference in the letters I have access too. Other than…

I saw Halley’s in 1910 — but missed the bright one earlier in that year by being flat in bed with a hellish case of measles!

Tolkien had an interest in astronomical phenomena, but I am told that his diary does not note Halley’s Comet of 1910. To be fair, he was only a schoolboy at the time and swotting hard for vital exams in central Birmingham, a big industrial city not then noted for its pristine ‘dark’ night skies and star-gazing.