Observations by Robert Hook
Robert Hook (1635–1703), commonly spelled Hooke, was an English naturalist and inventor.
9 – 11 September 1671
Two observations of September 1671 were published in Hook (1671, Phil. Trans. R. Soc., 6, 2295):
The original text:Observations made by Mr. Hook, of some Spots in the Sun, return'd after they had passed over the Upper Hemisphere of the Sun which is hid from Us; according as was predicted*. *see Numb.75.p.2253.
August 30. 1671 [9 September, Gregorian]. I saw a large spot in the Center
of the Suns face about noon, but had not then time to make any more exact observation thereof.
Septemb.1. [12 September, Gregorian] at 3 a clock I saw the same Spot moved
about a quarter of the Diameter of the Sun Westward, and it appeared of this form exactly, that is, it consisted
of one greater and two lesser black Spots with a dusky cloud incompassing them: The Diameter of the whole
Phænomenon was about 1/72 of the Diameter of the Sun, and it was distant from the next adjoining limb, 18/72
(that is, exactly one quarter) of the Diameter of the Sun. This I examined and measured several times, and
found very exact.
So far He. To which we hope we shall be able to add, by another opportunity,
what hath been further observed abroad, as well of the second progress of these Spots on the Sun's apparent disque,
as of the continuation of their former motion thereon.
We combine these Hook's observation with Siverus's observations.
June – July 1676
An active region observed in June – July 1676 was described by Hook (1677) as "a very conspicuous Macula with its immediatly incompassing Nubecula [interpreted as a cloud, often used to describe a penumbra] and some other less conspicuous Spots at a further distance pass over the Disk of the Sun". Hook hypothesized that these sunspots were the cause of the extraordinary heat experienced in England and Europe during that period. This sunpot group was also reported by Picard.
8 August 1676
Hook (1677) wrote that, on 8 August 1676, he counted "about six greater and smaller [spots] in one knot with their proper Nubecules". This sunpot group was also reported by Cassini and Flamsteed and Halley.
