A little ramble through 19th century astronomy - Stars, Saturn and photographs

 Academy, Saturday 19^th June 1875

 

Royal Astronomical Society (Friday, June 11). Professor Adams, President, in the Chair.

A paper by Mr. Knobel was read, giving some results of measures of magnitudes of stars with his astrometer, described in a previous paper, the principle of the instrument being to reduce the aperture of the telescope by means of a variable triangular diaphragm till the star disappeared. Mr.Knobel  pointed out several discordances between his results and the magnitudes given by Argelander in his Uranometria, though those of the Bonn Durchmusterung agreed better.

 Mr, Marth called attention to approaching phenomena of the satellites of Saturn, the most important of which, however (those of Titan), would only be visible in Australia and in the United States, the period of revolution being very nearly sixteen sidereal days, so that occultations and transits of this satellite would take place at the same sidereal hour for many successive periods, and at these times Saturn would be below our horizon. Mr. Marth expressed a hope that the great Melbourne reflector might be used for these observations, and Mr. Russell promised that he would employ the 11-inch refractor of the Sydney Observatory for this purpose.

 Captain Abney, R.E., gave a description of his Diaphanometer, an instrument which he had devised primarily for measuring the opacity of photographic films after exposure to light under different conditions, and which he had since applied to other questions in photometry. In this instrument the collodion film was compared with a graduated wedge of smoke-coloured glass. Captain Abney also exhibited an ingenious form of spectroscope in which the brightness of any part of the spectrum of a star could be compared with that of the spectrum of a standard source of light, the two spectra being brought one above the other in the same field by means of reflection prisms.

Some other short papers of a purely technical character followed, after which a note by Mr. Proctor on “ Photography in the Transit of Venus” was read, to which Mr. Russell, Mr. De La Rue, and Mr. Christie replied, and Mr. Neison mentioned, as bearing on the question of the atmosphere of Venus (which  Mr Proctor had incidentally  referred to), that Professor Lymans had observed Venus as a bright ring five hours before the commencement of the late transit.

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Cooke Telescope Tales - transit of Mercury observed in 1878 from Peeblesshire

Robert Mathison of Innerleithen Peeblesshire observed the Transit of Mercury on May 6^th 1878 using a Thomas Cooke of York 4.1 inch telescope. 

The transit was seen from the ‘observatory’ no trace of the planet could be seen outside the disk of the Sun. A small group of sunspots were seen on the Sun close to the planet at 4.40 pm. 

One point that caught the attention of Mathison was that a bright white point of light which he followed until 5.30 pm when the Sun was covered by clouds. Other observers at this location confirmed the sighting of the bright white spot.

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Cooke Telescope Tales - sunspots observed from Thornton in Craven in early 1860s

On December 14^th 1864 Thomas Wilson of Thornton in Craven using a 4.25 inch Thomas Cooke & Sons telescope observed a solitary spot on the surface of the Sun. He says that in sketching the spot immediately after apparent noon, finding the penumbral outline and radial shading considerably confused and indistinct, especially on the eastern side, my attention was drawn to its surrounding neighbourhood, where I was agreeably surprised by the realisation of the elongated very minute lenticular forms, which have been compared to willow leaves, overlapping the penumbra and, and diffused over the whole surface. 

Wilson goes onto say that in making 97 sketches of spots during the last three and a half years, nearly all after taking meridian transits, I never before saw anything beyond the mottled surface, which has been described as parchment, rice grain,  flocculent chemical precipitate like appearances &; I have supposed that depending on the state of the air this was beyond the reach of a small telescope such as my 4.25 inch Cooke.

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The Astronomy Show on Drystone Radio

 Join me, Martin Lunn MBE every Monday evening from 7.00 pm-9.00 pm on the award-winning Astronomy Show on Drystone Radio, probably the only regular astronomy show on any radio station in the country. 

I will take my weekly look at the night sky and look at all the latest news in astronomy. There will be the astronomical anniversaries this week plus the latest news from the astronomical societies in the north of England.

 

The Astronomy Show every Monday evening only on Drystone Radio live online at www.drystoneradio.com DAB radio in Bradford and East Lancashire, or 102 and 103.5 FM and can also be heard later on the Drystone Radio Podcast.

A little ramble through 19th century astronomy - The star Lalande 19662 in Sextans in 1875

 Nature, May 13^th 1875

The star Lalande 19662 in Sextans-

Mr J E Gore, of Umballa, Punjab, directs attention to the probable variability of this star. It was observed by Lalande on April 10^th 1798 in “Histoire Celeste” p 330, where its magnitude is entered 4.5, as in the reduced catalogue published by the British Association.

 It appears in Heis’s Atlas as a magnitude 6.7; but after searching through the modern catalogues where it was likely to be included, we have only discovered a single meridian observation by Lamont in his zone 314, on April 5^th 1845, when he called it magnitude 7.8.

It does not occur in Argelander’s “Uranometria”, nor was it observed by D’Agelet, Bessel or Santini.

 Another of Lalande’s stars No. 23726 in Corvus, is in all probability variable. He estimated it at magnitude 7.5 on May 10^th 1795, and Bessel in May 1824 called it magnitude 8.0. Heis, however, saw it as a 5^th magnitude star. What is the actual degree of brightness? 

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A little ramble through 19th century astronomy - shadows of jupiter's satellites in the 1870s

 Academy, Saturday 16^th January 1875

 Shadows of Jupiter's Satellites—During the last four years Mr. Burton has frequently observed that the shadows of Jupiter's satellites projected on the disc of the planet during transit were elliptical, and that this was, as a rule, the case only when Jupiter was near quadrature, and the shadow therefore seen obliquely.

Mr. Burton's explanation of the phenomenon is that the shadow falls on cumulus clouds, which give rise to the markings on Jupiter’s disc, these clouds being dark and therefore invisible wherever the shadow falls, but in full sunshine scattering the light in all directions. The shadow will thus present exactly the same appearance as a cylindrical hole which sends no light to the eye but allows light from the bright clouds forming its boundary to pass; and such a hole, when viewed obliquely, will appear the more elliptical the greater its depth.

From his estimations of the ellipticity on different occasions, Mr. Burton has deduced a depth of atmosphere of from 3,000 to 9,000 miles, a result which would accord well with the small density of Jupiter as a whole, only a quarter that of the earth. On the hypothesis that the bright clouds are scattered at different levels in an atmosphere of considerable thickness, the observed decrease of brightness near the limb is explained by supposing the sunlight to pass freely into space through interstices between the clouds near the limb, so that none of it is received back again by the eye. Mr. Burton's paper is given in the Monthly Notices for December.

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Cooke Telescope Tales - Transit of Mercury observed from Liverpool in 1868

George Williams using a 4.25 inch Cooke & Sons telescope observed the transit of Mercury on November 5^th 1868 from 2, Devonshire Road, Prince’s Park Liverpool. 

Williams observed no apparent elongation or pear shape, or black drop at the egress of the planet; but the boiling of the limb, which was considerable, may account for the absence of these appearances.

 

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