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Naor Scheinowitz / Leiden Observatory

A 120 year old telescope gets a makeover

For the first time in over half a century, one of oldest telescopes at the Leiden Observatory is getting a major improvement.

The lenses of the Old Observatory’s Astrograph Telescope were removed and shipped off to the Dutch Navy to be cleaned and restored. This is the first time in recent memory that this kind of maintenance is carried out. Not only will it greatly benefit the optical quality of the telescope, but it also serves as a statement that Leiden University values its historic scientific instruments.

'Something between the lenses'

Willem-Jan Trijssenaar, amateur astronomer and board member of one of Leiden’s astronomical societies, the WLS, explains: 'The lenses were removed because we found that they had become pretty dirty, which caused problems while observing. We thought that the tarnish we saw may be limescale or that someone had touched the lenses. Now it looks like there is something between the two lenses. What it is exactly, we don’t know yet.'

When asked how often the lenses are cleaned, Trijssenaar laughingly replies: 'I think this is actually the first time.'

Long exposure images

Astrophotography was a quickly developing technique of mapping the night sky at the end of the 19th century. The newly acquired ability to make long exposure images of the night sky enabled astronomers to observe stars that were previously invisible to the naked eye. The Astrograph Telescope in Leiden was built in 1897 at the request of Dutch astronomer H.G. Van de Sande Bakhuyzen, for the accurate measurement distance to nearby stars. The telescope has been used for research for more than half a century. Nowadays the telescope is used by very enthusiastic citizen-scientists and astronomy students, as well as being used for public tours.

photo: Naor Scheinowitz / Leiden Observatory

Cleansing at the labs

Most of the day-to-day maintenance of the historic telescopes is done by the Amateur Astronomical Society the WLS. However, due to the complexity of this project, this time the task is carried out by Het Marinebedrijf, the research & development division of the Dutch Navy with strong historical ties to the Leiden Observatory.

Over the upcoming weeks, the technicians from Het Marinebedrijf will thoroughly clean the Astrograph’s lenses at their labs. Jan Lub, astronomer from Leiden Observatory, is very enthusiastic about the development. 'We are very happy that the people from WLS are so enthusiastic about using our telescopes. The telescopes are not longer in use for astronomical research,  but they still carry decades-long of relevant scientific history and are important instruments for amateur astronomy and public outreach. We at Leiden Observatory are still responsible for the safety and quality of the telescopes, that’s why today we have a number of experts from different organisations working together to keep these telescopes operational.'

Telescope in action

According to Trijssenaar, the telescope will be back in action halfway October, just before the Old Observatory Open Day, which will take place on 29 October. Meanwhile, the Old Observatory is still open for visits on Wednesdays and in the weekends. Private tours can also be booked to visit the other historic telescopes available in the building.


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