• 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 15th July 2024

  • Astronomical darkness returns at the end of this week when astronomical twilight finally ends on Sunday morning at 00:51 BST; it starts again at 01:36 BST, giving us 45 minutes of true astronomical darkness!
  • Look out for a group of up to 20 Starlink satellites which are expected to deorbit in the coming days following a failed launch on 11th July. If we are lucky enough to witness this event, we can expect to see multiple slow moving meteor-like trails across the sky.
  • Early risers can enjoy the planets this week and a conjunction of Uranus and Mars on Monday and Tuesday. Look in the south through to the east at around 04:30 BST to find the line up of: Saturn (+1.0), Neptune (+7.9), Mars (+0.9), Uranus (+5.8) and Jupiter (-2.1).
  • Mercury (+0.2) and Venus (-3.9) are evening objects, though Venus is currently too close to the Sun for safe observation.
  • The Moon is Full on Sunday – the Buck Moon.
  • The Sun currently has 11 active regions and the sunspot number is 214.
  • There are multiple 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

11th July

Summer School Visit: 21 language students from the School of English and Culture along with 4 teachers visited the Dome in the afternoon with GKWJ and JAG. It was partially cloudy with high haze, but the group were able to view the Sun, first with eclipse specs and then in the 10-inch with the white light filter. Large active region AR 3738 was just visible by naked eye and very clear in the 10-inch, where its complex structure could be seen in great detail. Multiple other smaller ARs were also seen. The Waxing Crescent Moon was the next target, with lovely craters visible in the 28% illuminated region. Unfortunately, observing was cut short by thickening haze, but the session continued with the group enjoying an examination of the Sun and space weather.

10th July

Summer School Tour: 20 Summer School pupils attended the Week One Observatory Tour with GKWJ, JAG, DGR and a Friend. The sky was mostly cloudy, though there were some gaps which allowed the setting Waxing Crescent Moon to be seen intermittently in the west. As dusk descended, the brighter stars were seen to appear, including: Arcturus, the Plough, Polaris and the Summer Triangle.

24th June

Radcliffe Society: 6 pupils and CJW joined GKWJ and JAG at the Observatory on a perfectly still and sunny evening for the final Radcliffe Society meeting of the year. As is tradition, rockets were launched on the sports pitches. Three vehicles were available, two from last year (Alpha and Wizard) and one new rocket, Elektra, put together by two pupils. The launches started with Alpha and Wizard each using an A motor, reaching 66m and 133m respectively. Elektra, being slightly heavier, was first launched with a B motor and reached 113m. Alpha on a B motor flew a strange trajectory and was lost to the rough at the far end of the pitch! Wizard with a B motor reached 340m. The final launches were of Wizard and Elektra on C motors; this power motor has not been used at the Observatory before, but the very still conditions meant that recovery should be possible within the grounds. Elektra reached 210m, but suffered structural damage on landing and was retired. Wizard excelled for the second year running and set a new altitude record of 370m; thankfully it was finally found at the far reaches of the sports field and safely recovered for further flights next year.

20th June

Friends Observing: 22 Friends joined GKWJ and JAG at the Observatory to celebrate the Summer Solstice. In the twilight, the 97% Waxing Gibbous Moon was observed through the 10-inch, while outside, the first stars were seen to appear. As the summer darkness descended the 10-inch was used at 90x magnification to view M13, the Great Hercules Cluster, and then M57, the Ring Nebula in Lyra, where the mag was increased to 140x. Next up was Albireo in Cygnus, looking spectacular, before moving to the Double Double at the northern edge of Lyra. Epsilon 2 Lyrae was just split at 140x, but Epsilon 1 Lyrae remained elusive. Magnification was increased to 224x, which allowed both 1 and 2 to be split, easily as the seeing settled intermittently. Outside, a Friend set up a ‘live view station’ with a 4-inch refractor and camera, showing live stacked images of M57, M27, M13, M81 & M82 and the Veil Nebula. There was also a bonus item of a glow worm found shining with its particular wavelength of green on the stones by the Observatory!



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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.