• 21st June 2023 - Friends Event

    Tour of the Summer Constellations - Observatory @ 10pm

    If the weather is good, the Friends will gather at the Observatory at 10pm to celebrate the Summer Solstice and explore the June sky. A Go / No Go decision will be posted here and sent by email on the day of the event.


Marlborough College

Welcome to the Marlborough College Blackett Observatory, home to the largest refracting telescope in Wiltshire. The Observatory is a key facility for the study of Astronomy by pupils at Marlborough College. It is open to the public through the Friends of the Marlborough Telescope membership scheme. School and Society visits are welcome, please contact the Director to arrange your visit.

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What's Up!

Week of 5th June 2023

  • Astronomical twilight does not end until July 21st.
  • Venus (mag -4.3) continues to dominate our evening sky. Look about 27° above the western horizon at sunset, around 21:15 BST. The two bright stars to its west are Castor and Pollux.
  • Ophiuchus provides a rich observing ground this week, with three Messier Globular Clusters to find. Start with M12 at mag +6.7, then on to M10 (+6.6), both are about 14,000 light years away. Finally a little further east to M14, fainter at mag +7.6 as it is twice as far away at 30,000 light years.
  • The Moon is Last Quarter on Saturday.
  • The Sun currently has 7 active regions and the sunspot number is 112.
  • There are no visible evening ISS passes this week.
    (For full details about ISS passes click this link: heavens-above-iss-passes to visit the heavens-above website. If you are not in Marlborough, please ensure that you set your location for the most accurate ISS timings).


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Latest News

What's been going on at the Blackett Observatory

6th June

Outreach Sessions: 28 pupils and 2 members of staff from Pinewood prep school visited the Observatory as part of the ‘Marlborough in Motion’ STEM outreach day. GKWJ hosted two sessions with help from a L6 pupil, introducing the Y6 Pinewood pupils to solar astronomy. Safe methods of solar observation were demonstrated, though unfortunately, cloudy skies meant it was theory only! Features, the solar cycle and space weather were explored. The pupils used photographs to determine differing rotational periods of the Sun according to latitude, and the elliptical nature of the Earth’s orbit. The pupils all thoroughly enjoyed the sessions and asked a fabulous range of searching questions.

27th May

Prize Day Opening: GKWJ opened the Observatory on Prize Day for astronomy pupils to show their parents our amazing facilities. A total of 41 pupils, siblings and parents visited through the course of the afternoon. A perfect clear sky allowed for solar observing, with the 10-inch and 8-inch in white light and the Lunt 50 in hydrogen alpha. Many sunspots were seen and a multitude of prominences, with one very large one in particular. On set up, GKWJ observed a bright mass of plasma exiting the field of view from the large prominence.

25th May

Friends Solar Observing: A beautiful warm early summer’s day with occasional small clouds allowed for excellent solar observing. 21 Friends joined GKWJ and JAG at the Observatory over the course of an hour and a half. Various instruments were used: the Celestron 8-inch and Cooke 10-inch both with white light filters and a Lunt 50mm Hydrogen Alpha double stack telescope on the new solar tracking mount. All instruments offered stunning views of a very active Sun; six sunspot groups were seen, with a large number of individual sunspots (the current sunspot number is 153). Great detail in the main sunspot (AR 3310) was seen through the 10-inch at magnifications of 93x, 140x and 224x. In H-alpha, superb granulation, a large filament and multiple prominences were observed, and even seen to change over the course of the session.

19th May

Public Solar Observing: A total of 23 visitors came to two solar observing sessions with GKWJ and JAG. Broken cloud that thickened meant that only the first group were lucky enough to see the Sun with eclipse specs and in white light through the 10-inch. Three large sunspot groups were clearly seen. Near real-time views of the Sun were obtained in multiple wavelengths online.



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All Sky Eye

The Latest View from the MCBO

The All Sky Camera operates from 30 minutes after sunset through the night until 30 minutes before sunrise. The latest image is updated automatically every 5 minutes and the time lapse video is refreshed each morning at around sunrise. Click the still image to view a large version


Latest Still Image

Most recent time lapse video