ASTRONOMY (HERSCHEL)

The Third Astronomical Miscellany

Members of the Herschel Group

4 February 2005

Meaningful Anomalies in the 16-17^th centuries

Francis Ring (William Herschel Society)

Today we expect the heavens to change, even the opening credits of science fiction films all include elaborate animations of outer space exotica, black holes, gas plumes, orbital death spirals etc. The appearance of a comet or meteor in noted but rarely notable.

However, in the Earth centred Universe of the 16^th century things were different. The heavens were not expected to change. Everything beyond the Moon was constant and predictable. Therefore when something major was found to change or move it must be meaningful! Meteors and comets as had been suggested by Aristotle could be explained as atmospheric phenomena. Made as the same corruptible substance as the earth, they might be regarded as omens or predictors. However changes in the level of the Moon were something different. Twice in the decades around 1600 astronomers were surprised to find new bright star, and the novae of 1577 and 1604 were something quite new. The fact that they faded and went away after a few years added to speculation about their "message".

The Burndy Library at the Department of History of Science and Technology, Massachusetts Institute of Technology has a number of interesting documents around this topic. A recent acquisition is a rare treatise on the nova of 1604 published in Strasbourg, that same year. This and other documents were part of a great European debate, a challenge to the Church, astrologers and astronomers of the day. A new star had announced the birth of Christ, so what else were these nova telling us?

A rare lunar calendar- LUNARIO & PRONOSTICO sopra L’anno bisestile 1624

is also in this collection and a page is illustrated here.

It is the creation of Giovanni Bianchi, and carries prognostications for the year 1624, as was common in the 17^th century. As these calendars were discarded at the end of the year, they are exceptionally rare, and the MIT artefact seems to be the only recorded example. Little is known about Bianchi and whether he was a prolific composer of these astrological works. The calendar is currently undergoing translation, so the hindsight truth will be revealed!

Prof. Francis Ring

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Ref News from the Burndy Library vol.10.1 Fall 2003

Astronomical Software - ‘Starry Night’

demonstration by John Wright, teacher

with students from Monkton Combe School

We were delighted that so many young astronomy enthusiasts were present this meeting and who had offered to give a short demonstration of astronomical computer software which they have found most stimulating.

It is not possible to describe all the functions of ‘Starry Night’ in this short article. It is a very sophisticated piece of software engineering, which acts as a digital planetarium for general study, is packed with data and information on thousands of astronomical objects from planets to galaxies, enabling one to find them with ease. It is an invaluable device for planning observing sessions at the telescope,; it demonstrates planetary and cometary orbits - enabling them to be observed from any direction - thus simulating the three-dimensional nature of space and quickly displays chosen aspects of the Universe at any time in the past or future.

We hope that these students will continue to come to our meetings. They have offered to bring solar telescopes to the ‘Bath Taps into Science’ exhibition at Green Park on the 12th March 2005.

Richard H Phillips

Photographing the Planets

Dr Steve Kimmins (Herschel Group Member)

A recent technique for obtaining blur-free pictures of planets has been developed and used by amateur astronomers worldwide. It is necessary to have a webcam - but a relatively cheap model for £50 or less is suitable. I use a Philips Toucam Pro camera. The camera is attached to the telescope eyepiece, with the cheap plastic lens of the camera unscrewed and removed - the telescope itself becomes the camera lens.

The camera should be connected to a PC, usually via a USB port, and the live image obtained by the camera is displayed on the PC screen. The settings of the camera need detailed tweaking but effectively 10 to 30 images per second of the planet viewed by the telescope are recorded on the PC as a digital movie. Most ordinary PCs will not be able to record a movie of more than 1 to 3 minutes before running out of disk space.

A clever bit of software (eg. Registax - one of several freeware programs available on the Internet) takes these hundreds or thousands of images, grades them for quality and automatically overlays the planetary image in each frame, which would normally be displaced from frame to frame due to the 'jiggling' caused by atmospheric turbulence. It is this turbulence that makes it difficult to see with the eye the fine details on planets, and even more difficult to record the details by conventional cameras. But the software processing of the webcam movie can largely eliminate the unsteady image caused by the turbulence.

My own efforts usng my 200 mm telescope are still at an early stage, but above are some samples of Jupiter (with two of the Galilean moons) and Saturn as seen from a back garden only 1.5 miles from Bath Abbey.

Steve Kimmins

Astronomical Scaling

Dr Peter Wallis University of Bath

Many people are put off astronomy by the vast distances involved in even our nearest neighbours in space. The numbers, inconceivable by minds programmed to cope with hunting grounds ranging less than say, 50 miles, terrify them and present an obstacle to understanding and appreciating the wonder of our external Universe.

The speaker presented an idea which might make the Universe more digestible. Even ten thousand million is too difficult to conceive but it is a human quantity. If everyone in England had two hundred pounds , then there would be more than 10 billion pounds in the country. (In this article 10 billion = 10,000,000,000)

The speaker proposed shrinking the Solar System by this factor. Light would crawl about at a speed of 3 cm per second. The Sun would then be a manageable 14 cm in diameter, and, if it was of the same density (1.4 times that of water) it would only weigh 2 kg.

The Earth would be little more than a millimetre in diameter (1.3 mm in fact) and would be 1500 cm (= 1½ metres) from the Sun weighing 6 milligrams. Our moon would be 3.8 cm away from the Earth. Jupiter, the size of a grape at 1.4 cm diameter would be about 78 metres from the Sun and would weigh just under a couple of grams. However, tiny Pluto (¼ mm) would be hard to find at just over ½ km away from the Sun.

When we get to stars even our shrunken Universe will stretch our minds uncomfortably. The next star to us, Proxima Centauri would be, at 3,600 km in Newfoundland and the brightest, Sirius would be in Pakistan, Florida or the Barbados.

In order to appreciate the whole Universe we would have to shrink this already shrunken universe a further ten billion times! Then our galaxy would be 90 metres across with the Sun 30 metres from its centre and the next spiral galaxy 200 metres away. But the edge of the observable Universe would be 1300 km away - Madrid or Venice.

A little mathematics empowers us to encompass the whole observable Universe in our tiny brains!

Richard H Phillips

A Home-made Spectroscope

Richard Phillips (William Herschel Society/BRLSI)

The purpose of this spectroscope is to demonstrate to the public at the ‘Bath Taps into Science’ exhibition at Green Park on the 11th and 12th March 2005 that the Sun’s atmosphere contains sodium.

The drawing below sets out the arrangement for the demonstration. The spectrometer itself is seen at lower left. It is made of wood and cardboard with a lens and eyepiece for the telescope with index and one for the collimator. The diffraction grating was kindly donated by Herschel Group member Steve Kimmins and much of the construction was undertaken by Michael Tabb - who has greater manual dexterity than I have.

It was not possible to demonstrate fully during the evening because of the unavailability of the Sun but the continuous spectrum of the incandescent filament in the projector was seen. The shutter was placed in front of the projector and the emission spectrum of a neon lamp observed.

Then the salt was heated and a close pair of orange lines produced by the sodium in the vapour from the heated salt was observed. The telescope adjusted so that its index marked the position of the line pair.

When the shutter was removed from in front of the projector, a pair of dark lines was observed crossing the continuous spectrum at the position marked by the index. This ‘absorption spectrum’ results from light of the same wavelength from the projector being absorbed by the sodium vapour and re-radiated in all directions, thus diluting the light coming into the spectroscope at the wavelength of the sodium spectrum.

It is intended to show that this ‘absorption line’ can be seen in the spectrum of the Sun when its light is funneled into the spectroscope by the light funnel telescope thus demonstrating that there is sodium between us and the Sun - in an atmosphere which surrounds it.

Richard H Phillips