SWITCHING ON TO SWITCHING OFF

The weather may not have been the best, but the inaugural Hertford Dark Skies saw the Hertfordshire town switch off an array of artificial lighting, so allowing residents a much-valued chance to enjoy a glare-free night sky. Proud resident and lighting designer Simon Thorp reports.

Despite some torrential rain, a successful Hertford Dark Skies event took place for the first time on the 22 February 2024.

The local community were treated to a tour of the night sky as clouds parted to reveal the stars, one by one.

The event was conceived to raise awareness of light pollution and to provide people with the opportunity to come together as a community, experiencing the night sky without glare or local upward light within the centre of town.

I live in Hertford and suggested the event to the town council, which fully embraced the concept.

The event took place in Castle Park in the town centre with the intention to switch off all lighting in the park, on the castle, and as many lights as possible that are visible from the castle grounds.

Removing as many sources of light from people’s field of view meant attendees could fully appreciate the Moon and stars. The duration of the switch-off was over the course of an hour, allowing time for full adaptation to take place.

Bayfordbury Observatory at the University of Hertfordshire welcomed the opportunity to take part, along with Hertford Astronomy Group, who were all presented with extremely challenging set-up conditions.

There was heavy rain all day with the forecast of clear skies not until 7pm. The event had prepared for a cloudy sky too: Bayfordbury Observatory provided its mobile planetarium, which we housed in a large marquee, enabling shows to occur every 30 minutes.

Hertford Astronomy Group, meanwhile, set up projections, demonstrations, virtual reality and slide shows for everyone inside the castle itself.

Educational talks took place inside the castle, clouds or not. I gave a talk on light pollution and what people can do about it, the role of Dark Sky International and the ecological effects of artificial lighting at night.

There were other talks on topics such as an introduction to astronomy, amphibians and their nocturnal behaviour and ‘dark matter halos’ from the Bayfordbury Observatory team.

Lighting before the switch-off was provided by Stoane Lighting in the form of miniature ‘Tadpole’ spotlights to provide light within the various vendor’s gazebos around the lawn.

Mushroom luminaires on ground spikes were also used for areas in and around the castle with steps or uneven ground.

These lights used CREE LEDs with pc amber spectral distributions, 1830K to minimise their impact on surrounding wildlife.

All exterior lights were battery operated to avoid significant power cable runs across the site. Any other lighting was covered with red or amber gel filters to limit their brightness and spectral distribution.

This helped people to adjust more easily to the darker light levels at 7pm when as many lights as possible were switched off.

The full extent of the switch-off was limited by the torrential rain occurring during the day and up to 6:30pm that evening but enough was achieved to allow people glare-free views of the castle and the night sky as intended.

Bayfordbury Observatory began their talk on the night sky at 7pm, at which point the cloudy sky only allowed faint visibility of the Moon to everyone.

As the talk commenced, however, the cloud thinned out, the Moon brightened and Jupiter became clearly visible. One by one, more stars were seen until a cloudless sky prevailed with plenty for all to observe; it was a special occasion.

The darkness created by the switch off gave good visibility of the stars and real prominence to the moonlight which felt very bright across the lawn and on to the castle façade.

People visiting from London commented on the marked different in the clarity of the night sky, despite being so close to the capital. Without nearby glare the moonlight provided plenty of light for people to move around the site and the atmosphere was very relaxed.

Based on visibility of stars within different constellations, the stellar magnitude of the sky was just about a magnitude of 4.5, equating it to a Bortle Scale just within the category of 7.

This was impressive for a location so close to London but something to improve upon over time. Indeed, given such good feedback, the hope is the event will be repeated next year on a larger scale – and, who knows, hopefully with better weather too!

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