• 14th December 2023 - Friends Event

    Geminid Meteor Shower - Observatory @ 10pm

    The Friends will gather from 10pm to observe the Geminid meteor shower. Whether in visual wavelengths or radio will depend on the weather, but whatever, enjoy Astronomy at the Observatory on the 14th December!

  • 15th December 2023 - Friends Observing

    Winter Sky - Observatory @8pm

    Friends, come to the Observatory for an 8pm start to explore the delights of the Winter Sky. If cloudy, there will be a Q&A session, so come along, whatever the weather!


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 27th November 2023

  • Astronomical twilight ends at 18:05 UT at the start of the week and at 18:02 UT by the end of the week.
  • The four Giant planets are well placed for observation in our evening sky; from west to east, culmination times (UT) are: Saturn (+0.8) 17:55, Neptune (+7.9) 19:25, Jupiter (-2.8) 22:00 and Uranus (+5.6) 22:53.
  • Look out for Io transits of Jupiter on Wednesday starting at 22:00 and Friday at 16:27. The best GRS transit this week starts at 17:28 on Friday.
  • The Moon is Full on Monday – The Beaver or Frost Moon.
  • The Sun currently has 12 active regions and the sunspot number is 179.
  • 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

30th November

Outreach Visit: A wonderfully clear and very cold evening started with the final visit to the Observatory for the Urchfont Scouts, Cubs and Beavers; this group consisting of 14 Cubs and 6 Cub Leaders. The session started outside where GKWJ pointed out Saturn in the south and the ISS as it passed overhead, disappearing into the Earth’s shadow just past the zenith. The group moved inside to the 10-inch to observe Saturn, with its moon Titan clearly visible. As the telescope performed a meridian flip, the group went outside for a Sky Tour to find Polaris and identify The Plough and Cassiopeia. They then returned to the 10-inch to view Jupiter with three Galilean moons. The session ended outside with a view through binoculars of The Pleiades and the Waning Gibbous Moon as it rose above the trees.

Shell Visit: Next to the Dome were the 9 boys of the Cotton Shell, accompanied by an Upper Sixth pupil. It was very cold and very clear, though increasingly bright as the Waning Gibbous Moon rose higher in the sky. The session started with a Sky Tour outside, identifying The Plough and Polaris along with other main asterisms. The group then went into the Dome and used the 10-inch to observe Jupiter with three Galilean moons, the core of M31, the Andromeda Galaxy, and the Moon. The session ended outside with a view of the Pleiades through binoculars.

GCSE Observing: It was the turn of the Remove Astronomers and 11 pupils came to the Observatory with GKWJ to conclude a busy evening. Patchy cloud was starting to infiltrate the sky, but they were able to make sketches of the bright Waning Gibbous Moon using binoculars and the 10-inch, picking out the features learned about in recent lessons. They also enjoyed a view in the 10-inch of Jupiter with three Galilean moons and the Great Red Spot visible.

29th November

Pupil Visit: The L6 Creative Writers group, consisting of 7 pupils and 2 staff, visited the Dome with GKWJ. It was very cold with some breaks in the cloud, sufficient to allow the Waning Gibbous Moon and Jupiter with its four Galilean moons to be observed in the 10-inch. The group then enjoyed a slide show in the warm room that took them from a Partial Lunar Eclipse over the Blackett Observatory, through the Solar System, across the Milky Way and out into deep space past nebulae, clusters, supernova remnants, and all the way to the Coma Cluster, a galaxy cluster some 300 million light years from Earth.

28th November

Blackett Lecture: Dr Henrik Melin from the University of Leicester gave the 19th Blackett Lecture on the topic: “The James Webb Space Telescope: New Eyes on the Universe” to an audience of around 100 pupils, staff and Friends. He spoke about the development, technology and scientific goals of the JWST, going into details about the observations made in the first 18 months of the telescope’s active service and its impact on Astronomy. There was a dramatic moment as the lights were cut to accompany the moments before the Big Bang and the birth of the first star in the Universe! Dr Melin was generous with his time and gave a workshop earlier in the day to a group of 8 pupils, where he introduced them to the methods used to create false colour images from the various infrared wavelengths captured by the JWST. The pupils used data from M16, The Pillars of Creation, to construct their own images, with the best image selected by Dr Melin winning a pin of the JWST mirror array. After the lecture, GKWJ and JAG took Dr Melin to visit the Blackett Observatory. Some gaps in the cloud allowed a view of the 98% Waning Gibbous Moon through the 10-inch.

23rd November

Shell Visit: 10 Shell boys and a Tutor from C3 visited the Dome with GKWJ. Broken cloud allowed occasional viewing in the gaps. The Waxing Gibbous Moon was seen through the 10-inch, first at x90 and then at x220, with beautiful detail in Copernicus, Tycho and Sinus Iridum. The 10-inch was then slewed to Jupiter, where multiple belts, the GRS and all 4 Galilean moons were seen.


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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 AONB, 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 20.79 mpsas, which equates to Bortle 4.5 and a naked eye limiting magnitude of +6.0. 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 AONB 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.