Pointing the phone at the sky
A phone is now a better star chart than anything printed. Hold it up and it names the stars, the planets and the constellation you are looking at. The catch is that the same screen is the brightest thing in the field, and a phone at full brightness undoes the twenty or thirty minutes your eyes need to adjust to the dark. The apps below are chosen for what they tell you, and the section after them is about using them without wrecking the view.
The questions, and which kind of app answers each
| Question | Kind of app | Needs a connection |
|---|---|---|
| What is that bright dot? | A sky map that follows where the phone points | Usually not, once installed |
| Will it be clear tonight? | An astronomy weather forecast | Yes |
| When does the space station pass over? | A satellite pass predictor | To update the predictions |
| Where is it actually dark? | A light pollution map | Yes, to load the map |
| Will the Moon wash it out? | A moon phase calendar | No |
| Is there an aurora tonight? | A geomagnetic activity alert | Yes |
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What to install
The most accurate free planetarium on the phone, from the same project as the well known desktop program. Its red night mode is in the menu, and the paid version adds deeper catalogues and telescope control.
Sky Map. Started at Google and now maintained as open source, small and quick. Point it up and it labels what is there, with no connection needed.
The most polished of the point and identify apps, with constellation artwork that helps the shapes stick in the memory.
From the same developer, built around a calendar of what is worth seeing tonight, which answers the question the other maps leave open.
The simplest of the lot. Hold it up, read the names, done. A good one to hand to a child.
Another augmented sky map, quick to start, and strong on the planets and the view of the solar system.
Mobile Observatory. An almanac rather than a picture: rise and set times, conjunctions, eclipses and the month's events, laid out for planning.
Alerts before the space station passes over where you are, with the direction to look and how bright it will be. Add-ons cover other satellites.
The long running satellite prediction service in app form, with a sky chart for each pass.
Shows the path of the station and other satellites against the sky through the camera, which helps find a pass in its first seconds.
An astronomy forecast from a telescope retailer that splits cloud into low, medium and high layers, hour by hour. The one that tells you whether clear really means clear.
Detailed cloud models on a map, useful for spotting a gap in the weather and which way it is moving.
Satellite measurements of light pollution on a map, so you can find the nearest properly dark sky rather than guessing.
Moon phase and rise times by date. Check it before choosing a night, because a bright Moon hides more than a nearby town does.
Geomagnetic activity and alerts for the nights when an aurora may be visible further from the poles than usual.
A paid planner for photographers: where the Milky Way core will sit, from a given spot at a given hour, shown in augmented reality.
The paid choice for someone with a telescope, with a very deep object database and telescope control.
Images, mission news and launch coverage. Not a sky map, but the best reason to go outside on a night when something is happening.
Keeping your night vision
- Switch the app to its red night mode Most of the sky maps above have one. A dark theme is not the same thing: it is still white text, and white light is what resets your eyes.
- Set the brightness to minimum before you leave Doing it in the field means looking at a bright screen to find the slider.
- Give your eyes twenty minutes Dark adaptation takes that long, and one look at a white screen undoes most of it. Decide what to look for before you arrive.
- Read the forecast for cloud layers, not just cloud High thin cloud turns a clear forecast into a milky sky. That is why astronomy forecasts separate the layers.
- Look up the Moon before the stars The week around new Moon is the one to plan for. A full Moon washes out everything faint.
- Naming stars, planets and constellations
- Knowing when the space station passes
- Finding a darker site within reach
- Planning around the Moon and the weather
- Seeing faint galaxies, which needs binoculars at least
- Photographing the Milky Way without a tripod
- Holding a steady view for more than a minute
- Staying charged in the cold, which needs a battery pack in an inside pocket
A first night out
Start with what is easy to find: the Moon, the bright planets and the space station. The station is the brightest moving thing in the sky apart from aircraft, and unlike aircraft it does not blink. A pass alert and five minutes in the garden is the best introduction there is.
If the hobby sticks, buy binoculars before a telescope. They show far more than the naked eye, they need no setting up, and the sky map on the phone tells you where to point them.
A sky map, a clear sky forecast and a pass alert cover most nights. Set the red mode and the brightness before you leave, and give your eyes the twenty minutes.
Frequently asked questions
Do star map apps work without mobile data?
The main sky maps carry their star catalogue on the phone, and satellite positioning works with no signal, so the map itself works in a field with no coverage. Forecasts, pass alerts and light pollution maps need a connection, so check those before you leave.
Why do the labels not line up with the real stars?
Almost always the compass. Calibrate it with a figure of eight, remove magnetic cases and step away from cars and metal railings.
Can a phone photograph the stars?
Recent phones with a night mode can capture bright stars, and from a dark site even the Milky Way, but only on a tripod or propped against something solid. Hand held, the exposure is too long.
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