Built at night · Mac menu-bar app, iPhone and iPad · Free and open source
Nightwatch
Clear-sky planning for astrophotography: it tells you when tonight is worth setting up the telescope, and what to point it at. You never have to open it. Tell it what blocks your sky, the house, the trees, a balcony roof, and it only suggests what you can actually see.
The short version
It was raining when it said tonight would clear.
Nightwatch had already read the forecast and found a gap: clear from 22:00, six hours of it. It said so once. A look at the targets, a coat, and by dark the telescope was out on the lawn.
What it shows
Clear-sky planning and target selection for astrophotography.
Notifications
It speaks up, then gets out of the way.
A heads-up an hour before sunset when tonight qualifies, a preview of tomorrow night, and a nudge half an hour before the window opens. If the forecast turns, it stands you down. Quiet hours keep it silent overnight, and nothing is sent from a forecast more than six hours old.
Tonight’s plan
Your favourites, in the order to shoot them.
Your favourites that are up in the clear window, in order of their best time, each with your telescope’s filter and frames. Two best at the same time are marked, so you can choose. Take one off for the night, add another for one night only, and your choices sync between your Macs. Where there are three hours or more between favourites, Show suggestions offers a target for the gap, with Add to plan.
Your horizon
Only what clears your trees, your roof and the house next door.
From a garden or a balcony, a target can be well up and still behind the house. Give each site its horizon, direction by direction, on a dial of the sky, and Nightwatch recommends only what is clear of it: the plan, the best targets and their best times all follow. To measure it, take a photo from where the telescope stands, facing each way, and drag a line to the top of the roof or tree: Nightwatch reads which way the phone faced and how it was tilted, and works out the height. A guide, not a survey: your mileage may vary. The photo never leaves your Mac.
The week ahead
Which night is the one.
Up to ten nights in date order, each with its clear window or longest clear run, darkness and the Moon, so the best night of the week is easy to pick. Cloud from three days out is marked “Less certain”, with how many days ahead it is.
Targets
What is up tonight, and whether you will see it.
Everything up tonight, 30° high or clear of the horizon you set for the site: nebulae, galaxies, clusters, planets, events and all 88 constellations. Each card shows how much of your frame the target fills and whether the Moon will wash it out, when it is viewable and when it is best. On a cloudy night the page says so: “No clear window tonight.” One switch shows tomorrow night instead, so you can plan ahead.
Target detail
What your telescope will actually capture.
The survey image fills the window. A dashed box marks your field of view when the object is bigger than it, and the caption gives the best time, the Moon’s distance and the altitude through the clear window. “How to shoot this” adds the filter, exposure, frame count and start time for your telescope, from its maker’s manual.
Constellations
All 88, drawn for Nightwatch.
Each constellation has its own artwork: the figure, with its real star points plotted on top, so the shape in the picture is the shape in the sky.
Desktop widgets
The glance.
Small, medium and large. They draw the snapshot the app writes after each forecast check, and fetch nothing themselves. With aurora alerts on, the aurora status for your site appears in its level’s colour.
Dark sites
Somewhere clearer, within driving distance.
76 certified dark-sky places, and dark spots computed from light-pollution data for anywhere in the world between 75° N and 65° S, each with tonight’s window and score beside home’s. The page names the nearest site with a clear window tonight, with how far and which way, and can list the sites nearest clear first. Every card shows a small Apple Maps map and opens in Maps. Computed spots sit at a nearby dark car park, named with its town, so no pin lands on private land. One click observes from there; one click brings you back.
Events
Put the peak night in your calendar.
Put an eclipse or a shower’s peak night in your calendar, with a reminder. On a clear night the heads-up also names what else is up: an ISS pass, or a meteor shower at its peak. Nightwatch also works out, a year ahead, when the Moon will pass in front of a planet, a bright star or the Pleiades as seen from your site. It draws each star’s path behind the Moon: when it goes, when it comes back, and whether it meets the lit or the dark edge. The next few are listed under Coming up, each with Add to Calendar.
What it is not
A tool with deliberate edges.
My day job is deciding when a system in a regulated sector can be trusted. Choosing which error you can afford, a missed night or a false alarm, is the whole job. This is the same question with lower stakes and worse weather, so the first thing it does is say what it will not do.
- Not a telescope controller. It tells you when and what; the DwarfLab or Seestar app does the rest.
- Not a forecast provider. It reads Apple Weather or Open-Meteo, plus 7Timer, with MET Norway when neither can be read, and applies a rule. It claims no better accuracy than its sources.
- Not a data collector. No account, no API key. Every calculation happens on the Mac; only forecast and image requests leave it.
- Not commercial. Its data sources are licensed for non-commercial use, so it is free, with no ads or subscriptions.
Why it exists
In Yorkshire, a missed clear night costs more than a false alarm.
Clear nights are scarce here, and finding out whether tonight is one means reading forecast charts every evening. Nightwatch does the reading. It sits in the Mac menu bar, checks the forecast every 30 minutes, and speaks up an hour before sunset only when there is a run of dark, clear sky long enough to image in.
It was built for a DwarfLabDWARF Mini, but it works with any telescope or camera and lens. Each instrument is described by its field of view. Presets cover DwarfLab’s DWARF Mini, DWARF 3 and Draco, and ZWO’s Seestar S30, S30 Pro, S50 and S50 Pro; if yours is not there, type its field of view.
- 3 h
- continuous clear run, at least
- ≤ 25%
- cloud across it (thin high cloud counts for half)
- 18°
- Sun below the horizon: astronomical darkness
That is the default go rule, and all of it is adjustable in Settings › Go rule. Every night also gets a score from cloud, Moon, seeing, transparency and wind, so Nightwatch ranks nights and sites instead of only passing them. Nightwatch reads Apple Weather and asks Open-Meteo for a second opinion. When the two split after a heads-up, it says so plainly: “Less certain: a second forecast sees cloud from 01:00.”
Also newThe smaller things.More, from aurora to Siri
- Rain and haze warnings. A clear night warns when rain is forecast after the window, for a telescope left running outside. It warns too when wildfire smoke, dust or haze will dim it: the Transparency tile reads Hazy, the sky score falls by up to 30 and the best three lead with bright targets.
- Not tonight keeps its place. A favourite you take off for the night stays in the plan as a dashed row with Put back, and under a finish time every row’s times and the chart’s shading stop there.
- Plain about a refusal. When Apple Weather or Open-Meteo refuses a request, Nightwatch says so and takes the forecast from MET Norway or 7Timer instead.
- Easier to read, and to hear. A Text size setting (Standard, Large or Extra large) for the popover and every window. VoiceOver reads the menu-bar icon as tonight’s verdict, sky score and site, and cards open with Return or Space when keyboard navigation is on.
- Aurora, anywhere. Aurora alerts now work outside the UK and Ireland, from NOAA’s 30-minute aurora forecast read at your site. In the UK and Ireland they still come from AuroraWatch UK. An alert needs the sky clear this hour, as before.
- The Milky Way. In Eyes and binoculars: the core in Sagittarius when it climbs clear of your horizon in darkness, and the band through Cygnus, overhead from Britain on summer and autumn nights. Where the core never climbs high enough, as from most of Britain, it says why. Each page says how to photograph it with a camera and wide lens.
- Several nights, one picture. For long frames and stacks over several nights, How to shoot this suggests your telescope’s EQ mode, and for the DWARF telescopes it says how to keep the nights joinable in Mega Stack.
- Pictures at once. Photos already on your Mac appear as the window opens, and a target’s page you have opened before opens sharp.
- Eyes and binoculars. What you can see without a telescope from your sky, and how to find it.
- What the numbers mean. The sky score, seeing, transparency and the rest, explained in plain English from About and Settings. Specialist terms stay; they are explained, never hidden.
- Alerts on the minute. The heads-up an hour before sunset and the nudge before the window arrive when they are due, not at the next half-hourly refresh.
- Thin high cloud counts for half. Stacking works through a veil of cirrus, so the go rule judges high cloud more kindly than low cloud, which blocks everything.
- Adding a site. Search for a place by name, or paste coordinates straight from a map; the sky’s darkness is suggested from light-pollution data, anywhere in the world between 75° N and 65° S.
- Your Macs, in step. Settings sync between your Macs through iCloud.
- Siri and Spotlight. On the latest Mac software, “Find the Crescent Nebula in Nightwatch”, and Spotlight finds tonight’s sky and tonight’s targets. In Shortcuts, the sky score, best targets and events hand their answer on as text, and Clear Window Tonight answers yes or no, so a shortcut can speak tonight’s verdict or text you when it is clear.
- Home on every Mac. Home is shared between your Macs: star a saved site and it is home on each, or star This Mac’s location and each Mac uses its own.
Install
Two minutes, no warnings.
- Get it from the App Store, then open it from the menu bar. Prefer the disk image? Download the latest version and drag it to Applications. On iPhone or iPad, open the App Store link and tap Get.
- Choose “Use this Mac’s location” and allow it when your Mac asks, or add a site by name. Nightwatch asks for your location only when you press that button, never by itself.
- Allow notifications. To add a widget, right-click the desktop › Edit Widgets.
The App Store version updates itself through the App Store. The download checks for new versions on its own.
The next clear night, it will tell you.
Why I built it starts with a telescope and my dad, in Seventy-Eight Clear Nights. The same question at higher stakes is in the governance writing.
Data and credits
Where the sky comes from.
| Purpose | Source | Licence |
|---|---|---|
| Cloud, dew, wind (primary) | Apple Weather | WeatherKit terms |
| Cloud, second opinion | Open-Meteo | CC BY 4.0 |
| Forecast, when neither can be read | MET Norway, Norwegian Meteorological Institute (api.met.no) | CC BY 4.0 |
| Haze, dust and smoke forecast | Copernicus Atmosphere Monitoring Service, through Open-Meteo’s air-quality service | CC BY 4.0 |
| Seeing, transparency | 7Timer, Shanghai Astronomical Observatory | Non-commercial |
| Aurora status, UK and Ireland | AuroraWatch UK, Lancaster University | Non-commercial, attribution |
| Aurora forecast, elsewhere | NOAA Space Weather Prediction Center, 30-minute aurora forecast | Public domain |
| Sky-survey images | Digitized Sky Survey (STScI/NASA), coloured by CDS, via hips2fits | ODbL 1.0; non-profit use |
| Light-pollution data | VIIRS Nighttime Lights, Earth Observation Group, Payne Institute for Public Policy, Colorado School of Mines | CC BY 4.0 |
| Hills around a site | Copernicus WorldDEM-90, via the Open-Meteo Elevation API | Copernicus (European Union and ESA) |
| Ephemeris | Astronomy Engine | MIT |
| Deep-sky catalogue | OpenNGC | CC BY-SA 4.0 |
| Page background | Milky Way photograph by Han-Hsing Tu on Unsplash. Resized and darkened | Unsplash licence |
| Moon image | NASA Scientific Visualization Studio | Public domain |
| Comets, space station | IAU Minor Planet Center, CelesTrak | Public data |
| Place names, car parks, maps | Apple Maps | Apple terms |
| Star positions under the artwork | d3-celestial | BSD-3-Clause |