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Horrocks made important contribution to the theory of the motion of the Moon.
Newton was not especially generous in acknowledging contributions of his predecessors,
but he acknowledges Horrocks' contribution to the theory of the Moon.

He died at the age of 23, and his many contributions to astronomy (some of them mentioned in Wikipedia)
characterize his as a genius of  first magnitude. He used gravity to explain 
deviation of planets from Kepler's orbits.
Notice that he died 46 years before the publication of Newton's Principia!

Alex. 
________________________________________
From: NavList@fer3.com [NavList@fer3.com] on behalf of Frank Reed [NoReply_FrankReed@fer3.com]
Sent: Saturday, April 1, 2023 4:30 PM
To: eremenko@math.purdue.edu
Subject: [NavList] What did Horrocks do?

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Almost two weeks ago, Dave Walden posted a link to this article in the 
Guardian: The forgotten maths genius who laid the foundations for Isaac 
Newton.

The article was inspired by a press release for a play on the life of Jeremiah 
Horrocks, the genius in 
question. The play is called Horrox, which was an alternate spelling. Bill 
Lionheart says that he saw the play a few days ago, but it left him with some 
questions. The article is filled with some extreme claims that are apparently 
supported by the play. So what did Horrocks actually do? How was Newton's 
work impacted by him? Horrocks certainly hasn't been forgotten. There's a 
plaque honoring him in Westminster Abbey, and there's a crater on the moon 
named in his honor. These are not small things. He was forgotten for a few 
decades after he died, especially during the era of the English Civil War(s). 
But he was acclaimed once again as an important astronomer in the 1660s 
following the publication of his work by the great astronomer Jan 
Hevelius (referred to 
dismissively in the Guardian article as "an appendage to a Polish 
astronomer's work").

One key claim in the article and apparently in the play is that Horrocks 
measured the scale of the Solar System by observing the parallax of Venus 
during the transit in 1639. He and his friend, William Crabtree, observed it 
simultaneously "on a cloudy day" in late 1639 with enough breaks in the 
clouds just before sunset to catch the exceedingly rare event. Crabtree was 
about 25 miles away. Bear in mind that Cook and the astronomers in 1769 had 
to travel to Tahiti to get an approximate measure of the scale of the Solar 
System by this method. But turns out you only have to go to the other side of 
Manchester! It seems that Horrocks didn't do anything remotely like what the 
play has claimed. He did not measure the distance to Venus. He did not 
"prove" that the Earth was not the center of the Cosmos. So what did he do?

Newton certainly stood on the shoulders of 
giants, 
and I recently discovered a rare lithograph of Newton actually standing on 
the shoulders of some "intellectual" giants [see attached image]. Horrocks is 
not among them.

Frank Reed

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