One amateur astronomer in North Yorkshire has kept a nightly record of the sky since 2018. By their own count, shared on the British Astronomical Association's forum, they average 96 clear nights a year. In 2023 they got 78. It is one observer's log, anecdotal rather than a national statistic.
That is roughly one night in five, and the sky does not announce which ones. It clears after dark, stays clear until the small hours, and has clouded over again by the time most people think to look.
Fewer nights than the number suggests
Even that figure flatters the hobby. A long-running observer in Birmingham, posting on the same forum, counted 93 observable nights in 2024. Only 11 of them had less than half the sky under cloud. The rest were gaps between clouds.
Then take away the nights that are clear but useless. In Yorkshire the Sun never sinks far enough below the horizon for true darkness from late May to late July, around nine weeks with no proper night at all. For several nights either side of a full moon, the sky is too bright for anything faint. What remains is a small number of nights that are dark, clear and long enough to do anything with.
That makes missing one expensive. A false alarm costs an hour in the cold. A missed night might be one of a handful that season, and a nebula is only well placed for a few months of the year. Miss its clear nights and the next chance is twelve months away.
A telescope that was really about my dad
I grew up on science fiction, and space was the part of it that felt closest to real. The stars were not a backdrop in a story. They were overhead, whenever the weather allowed.
When I was nine or ten, a friend of my father's gave me a telescope. At the time I thought I had been given a telescope. What I had actually been given was nights looking at the sky with my dad.
My father has since died. Those nights are among the memories of him I hold closest, and I had no idea at the time that they would be.
Then the hobby went quiet, the way childhood hobbies do, until recently I bought a DwarfLab DWARF Mini. It is a smart telescope that finds its target, tracks it and stacks the exposures into a photograph without me touching an eyepiece. The equipment has moved on almost beyond recognition since I was ten. The weather has not. It is now doing for my son and my grandson what the first one did for me. Three generations in the cold, watching a nebula build itself one short exposure at a time.
Owning a telescope turned out to be the easy part. Knowing by early evening whether tonight deserves the effort means reading cloud forecasts, checking the Moon and working out when it gets properly dark, every evening, mostly to learn the answer is no. I wanted something that did the checking and spoke up only when the answer was yes.
So I built Nightwatch
Nightwatch sits in the menu bar of my Mac and says nothing most of the time. Every half hour it reads the forecast. When there is a run of at least three hours of fully dark sky with no more than a quarter of it under cloud, it tells me an hour before sunset, and again shortly before the window opens. If the forecast turns, it stands me down. When its two weather sources disagree, it says so rather than pretending to know.
The three hours is not arbitrary. A smart telescope builds its picture from many short exposures, and a faint nebula needs hours of them. A forty-minute gap between clouds is enough for the Moon and not much else.
When home is cloudy, it looks further afield. The North York Moors and the Yorkshire Dales both became International Dark Sky Reserves in 2020, and Nightwatch checks the forecast at certified dark-sky places within driving distance and tells me when one of them has a better night. It also works out which galaxies, nebulae and clusters will be well placed during the window, and whether the Moon will wash them out.
Its releases are tagged after Terry Pratchett's City Watch novels, and the wording borrows the Watch's voice, so a cloudy evening gets "Nothing to see here. Move along." There is a plain-wording switch for anyone who finds that less funny than I do.
It is free and open source. The Nightwatch clear-sky planner page has screenshots and the download, and the code is on GitHub.
What it cannot forecast
Building it made me see that childhood telescope differently. The instrument was never the precious part. The clear night was the rare ingredient, and the person standing next to me was the reason it mattered.
Nightwatch can now tell me which of Yorkshire's few clear nights are coming. My wife and daughter remain unpersuaded, and the forecast on that is uncertain. It cannot tell me who to call outside to see them, and that was always the better half of the night.