Ordinary Meeting, 2002 April 27

 

The value of historical records in astronomy

Mr. Hurst opened by outlining a problem which many astronomical archivists face - that of an accumulation of photographic observations which are deteriorating as time passes. An effective solution is to scan the images to digital format before they fade, although this is itself often a substantial undertaking. To emphasise the value of maintaining such archives, the speaker referred to Richard Stevenson's talk at the January meeting, where the geographic locations of historical eclipses had been used to monitor changes in the Earth's rotation rate. Furthermore, Jonathan Shanklin's Sky Notes had illustrated the value of matching historical comet observations to the comets we see today to find their orbital elements.

The speaker commented that we have Chinese astronomical records dating back over 3000 years and that these often record supernovae as "guest stars". Their nature was never investigated by the observers, however. It was not until 1974 that a sky patrol was formed to create a survey of the sky which could be used to verify supernova discoveries. This was followed in 1976 by the formation of the UK nova/supernova patrol which benefits from the support of many BAA members. The speaker referred to the light curve of β Herculis, which showed an unexpected minimum in 1934. The speaker commented that despite three millennia of supernova observation, the distinction between nova and supernova had still not been made at this stage.

Mr. Hurst observed that the Central Bureau lists only four confirmed supernovae prior to modern times, in 1006, 1054, 1572 and 1604 AD. Earlier supernova reports include those of 386, 393 and 1181 AD, but the positions were only recorded by asterism, and have not been successfully linked to remnants. All of these were recorded by Chinese observatories, but scarcely noted at all in Europe. The event of 1006 was a mere three degrees above the European horizon, but was observed at St. Gaulle in Switzerland. It seems surprising, then, that there are no known records of observation of the 1054 event from Europe. This event was recorded by the Chinese as a mag. -4 guest star in Taurus for 18 months, and so must have caught the attention of European observers.

The event of 1572 in Cassiopeia was studied by Tycho Brahe and represented a significant advance in understanding of such occurrences. Prior to this, it was believed that guest stars were at similar distance to the Moon, in accordance with belief in unchanging heavens. Tycho disproved this by failing to observe any parallax on the guest star.

The speaker stressed the value of maintaining archive material with the example of an image by D.Jones which the sky patrol filed in 1974. This apparently uninspiring image was only found to be of use when a professional discovered the spectrum of a nova well past maximum at mag. 11. The earlier image was used to construct a light curve from historical records.

As a closing point, the speaker commented that astronomy is one of the few fields where we can not only speculate about the past, but also view it. As an example, the Veil Nebula tells of a 30,000 year old supernova event.

The President then invited Dr. Nick Hewitt, director of the Deep Sky Section, to address the meeting.

Ashburn

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