• 20th June 2024 - Friends Event

    Solstice Sky - Observatory 10pm

    The Friends will celebrate the Summer Solstice at the Dome with a twilight observing session starting at 10pm. Fingers crossed for noctilucent clouds!

  • 12th August 2024 - Friends Observing

    Perseid Meteor Shower - Observatory @10pm

    The Friends will gather at the Observatory from 10pm to monitor the peak of the annual Perseid meteor shower.
    This event is weather dependent and a final decision will be published on the day.


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 10th June 2024

  • Astronomical twilight does not end until 21st July.
  • Keep an eye on the Blaze Star, T Coronae Borealis, just to the east of the familiar arc asterism of the constellation Corona Borealis. It is currently magnitude +10, so not visible to the naked eye, but as a recurring nova, it is due to brighten to about magnitude +3 sometime soon, and will become an easily visible new feature in the constellation.
  • Another phenomenon to keep checking for is the presence of noctilucent clouds. They appear high in the atmosphere about an hour or two after sunset in the north and are a spectacular layer of pearlescent night glowing cloud.
  • The Moon is First Quarter on Friday.
  • The Sun currently has 9 active regions and the sunspot number is 143.
  • 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

25th May

Prize Day: GKWJ opened the Observatory in the afternoon of Prize Day; despite 70% cloud cover, there were sufficient gaps to enable views of the Sun in white light through the Celestron 8-inch and in hydrogen alpha through the Lunt 50mm and the 10-inch. There were 9 visitors through the afternoon. The 10-inch showed a large prominence on the lower oncoming limb, suspected to be associated with the return of AR 3664, the active region responsible for The Great Aurora of 10th May.

20th May

Solar Observing: A clear, bright and sunny day led GKWJ to alert All Staff and members of Radcliffe Society that the Observatory would be open in the afternoon for solar observing. JAG assisted with 54 members of staff and assorted family, 13 pupils and 2 dogs that enjoyed views with: eclipse specs, the Celestron 8-inch in White Light, with a rash of sunspots visible in lovely detail, the Lunt 50mm in hydrogen alpha, giving a detailed view of the full disk with active regions, filaments and multiple prominences, including one vast prominence that stretched about 6 Earth diameters from the chromosphere, and the 10-inch with the hydrogen alpha filter which showed a more detailed view of the large prominence and the main active region, AR 3685. Seeing was good, though variable through the afternoon; in the large clear patches, it settled to give stunning views.

10th May

Aurora Imaging: A truly unexpected news item… GKWJ visited the Observatory at about 23:45 to capture the end of the most incredible display of the Aurora Borealis. Huge active region AR 3664 has been crackling with activity recently, sending five CMEs towards Earth. They arrived on Friday evening, sparking the largest geomagnetic storm for over twenty years. The Aurora was seen overhead in extreme southerly latitudes, including Marlborough. An amazing show to witness and unlikely to be repeated for at least twenty years!

An extraordinary display of the Aurora Borealis over
the Blackett Observatory on 10-05-2024 (photo by GKWJ)



GCSE Observing: The 16 Remove Astronomers had Period 2 at the Observatory with GKWJ. Sunny conditions, though through hazy high cloud, were perfectly timed to fit in with their current topic about Solar Astronomy. The session started with a look at the Sun through Eclipse Specs, with AR 3664/8 clearly visible by naked eye, it really is a gigantic active region. Outside, the photosphere was observed in white light with the Celestron 8-inch, and the chromosphere in hydrogen alpha through the Lunt 50mm. The group moved inside to the 10-inch, where the full disk was seen in hydrogen alpha at 90x, with multiple prominences, the vast AR 3664/8 and various other filaments and active regions. Magnification was increased to 140x for a close inspection of the large AR and nearby complex prominences. The session ended with the pupils making a sketch of the whole disk or a feature of their choice.



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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

Sky Quality

The Latest SQM Chart from the MCBO

Thanks to generous funding from the North Wessex Downs National Landscape, the Blackett Observatory now has a fixed Sky Quality Meter (SQM) in place, measuring sky darkness every night throughout the year.


This is the latest chart of SQM readings, measured in magnitudes per square arcsecond (mpsas). The darkest reading to date is 21.1 mpsas, which equates to Bortle 4 and a naked eye limiting magnitude of +6.3. The sky will now be monitored constantly to see how the effect of light pollution is changing over time. A project to monitor sky quality across our local area is underway using NWD funded handheld SQM devices and volunteers from the Friends of the Marlborough Telescope.

The SQM chart updates every 15 minutes through the hours of darkness.
The yellow circles show the altitude of the Moon, if present.