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BLACKETT OBSERVATORY

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 19th October 2026

Astronomical Twilight ends at 19:56 BST at the start of the week and at 18:45 GMT by the end of the week.
The clocks go back one hour from 02:00 BST to 01:00 GMT on Sunday morning. Enjoy the travel back in time and the darker evenings!
The Orionid meteor shower peaks on Wednesday night. It is not a major shower, with a ZHR of only around 15 meteors. The origin of the shower is debris deposited by comet 1P/Halley.
Saturn (+0.4) rises at around 17:44 BST this week, with Neptune (+7.8) close by. Uranus (+5.6) rises at 19:27 BST, followed by Mars (+1.0) at 00:31 BST and Jupiter (-2.0) at 01:34 BST.
With all this moonlight, this week’s Challenge focuses on Double Stars – we start with Almach (+2.2) in Andromeda with a separation of 9.4 arcseconds, then on to Achird (+3.5) at 13.7″ in Cassiopeia, next is Miram (+3.8) at 30.4″ in Perseus, and we finish with 1 Arietis (+5.8) at a challenging split of just 2.9″ in Aries.
The Moon is Waxing Gibbous all week.
The Sun currently has 4 active regions and the sunspot number is 87.
There are no visible evening ISS passes this week (click here for full ISS pass details).

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Latest News

What's been going on at the Blackett Observatory

13th October

GCSE Observing: A lovely clear night allowed 5 GCSE pupils to spend time under the stars with GKWJ. They completed a worksheet that explored coordinates, local sidereal time and hour angle. They also made a sketch of Saturn as seen through the 10-inch at x93 magnification, including four of its moons: Titan, Rhea, Tethys and Iapetus.

10th October

Friends Observing: 19 Friends and GKWJ enjoyed a marvellous first observing session of the new season. The session started with a view of Saturn in the 10-inch with moons Titan and Rhea clearly visible, though it was low down and wobbling in the atmosphere. As Friends arrived, there was a distinct pinkish tinge to the northern horizon, confirmed as the Aurora Borealis in photographs hastily captured on phones! The observing started in earnest with a host of objects seen in the 10-inch: M13 (the Great Hercules Cluster), M57 (the Ring Nebula), Albireo (double star), M27 (the Dumbbell Nebula), NGC 6826 (the Blinking Planetary Nebula), back to Saturn for a much better view now it had climbed higher, allowing magnification to be increased to x224, then a glimpse of Neptune, finishing at x90 on the core of M31 (the Andromeda Galaxy). Meanwhile two Friends had a Travel 70 scope and a 127 Mak set up on the observing platform outside, with targets being: Saturn, Neptune with moon Triton spotted, Uranus, M57, and NGC 7331 with the recent supernova visible. An excellent start to the Friends observing season!

26th September

Open Day Observing: The sky was clear enough despite some hazy cloud so GKWJ set up the portable solar observing kit in Court for the College Open Day. A steady stream of prospective pupils and parents enjoyed safe views of the Sun through eclipse specs, the Celestron 8-inch in white light, and the Lunt 50mm in hydrogen alpha. There were two sunspot groups, a large number of filaments and one spectacular prominence visible. The prominence was quite easy to see evolving over the course of the hour and a half observing session.

21st September

GCSE Observing: The eight pupils from the Hundred and Remove Astronomy GCSE classes joined GKWJ at the Observatory for the first observing session of the term. It was beautifully clear, but the Waxing Gibbous Moon was rather bright! It made a stunning first target in the 10-inch, with Sinus Iridum particularly interesting illuminated on the Terminator. The group went outside for a tour of the asterisms and pointers required for the course. Then back to the 10-inch for an unusually still view of Saturn with its moon Titan. The session ended with a view of the Andromeda Galaxy through binoculars. A great start to the season.

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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.