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Observations by William Herschel ( Sculptor Galaxy - NGC 253 )

 

Observations of the Sculptor Galaxy ( NGC 253 ) by William and John Herschel

The very large and bright 'nebula' discovered by Caroline Herschel in 1783, that we now know as the Sculptor Galaxy, was observed a number of times by her 'dear brother' Sir William Herschel and by her 'beloved nephew' Sir John Herschel, Baronet.  Some of these observations were recorded and published in the Philosophical Transactions of the Royal Society and, with respect to those by Sir John in South Africa, in the book of Astronomical Observations at the Cape of Good Hope.

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Part 1.  Observation of the 'class V nebula', H V.1, by Sir William Herschel, 1783

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In 1782, with the fresh patronage of King George III, William Herschel, together with his sister Caroline, undertook the not inconsiderable task of transferring his astronomical equipment from Bath to Datchet ( near Windsor ) in England.  Shortly afterwards, in 1983, Sir William began a "sweep of the heavens" with the very large Newtonian telescope of his design and construction.  With this mighty telescope's twenty foot focal length and clear aperture of a little over eighteen and half inches, William was able to see fainter objects and smaller detail than any other astronomer of that time.

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( source: The Scientific Papers of Sir William Herschel, Vol.1 )

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On the 30th of October, 1783, in the course of one of his "sweeps" with the twenty-foot telescope, Sir William Herschel observed Caroline's 'nebula'  and noted down ( or perhaps more likely, dictated to Caroline )  a description of what he saw and a reference to its position relative to a 4th magnitude star in the Piscis Austrainus constellation, #18 Pis. Aust. ( with reference to Flamsteed's Catalogue (  or HD 214748 , HIP 111954 as we might call it )).  

Over the course of the next three years, Sir William would go on to view the Sculptor Galaxy a total of seven more times; as recorded in his paper "Catalogue of One Thousand New Nebulae and Clusters of Stars", presented to the Royal Society on the 27th of April 1786.

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Source )

Sir William's somewhat cryptic notes can be translated by reference to the key provide in his paper and doing so reveals the following:

Class:  V. ( very large nebula )

Number: 1

Observed ( by WH ): 30 Oct 1784

Reference star:  18 Piscis Austrainus ( Flamsteed's Catalogue; the best reference for the time - we might use epsilon Pis. Aust. or  HD 214748 / HIP 111954 )

Sidereal direction rel. to star ( following or leading ):  following star

Sidereal time rel. to star: 128 min 17 sec

Declination direction rel. to star: north of star

Declination amount rel. to star:  1deg 39min

Observed: 8 times ( up until April 1786, the date of the paper )

Description:
- cB:     "confidently bright"
- mE:    "much extended"
- sp:     "south preceding"
- nf:      "north following"
- mbM:  "much brighter middle"
- size:    50' x 7 or 8'

" CH" denotes that it was discovered by his sister Caroline Herschel

The note he refers to expands on details of Caroline's discovery ...

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