Features
Everything Apphemeride can do
Apphemeride is an astronomy app built for high-precision calculations. It doesn't just show you where a celestial body is right now — it shows how it moves over time, from any location on Earth, at any moment, calculated entirely on your iPhone. Here's a detailed look at everything inside the app.
Horizon Tracker
Rise, set, and exactly where it sits in the sky
The basics — and already more than most apps offer: Apphemeride shows the rise, transit, and set times of every celestial body, plus its current direction (azimuth) and its height above the horizon (altitude). A compass shows direction and altitude at a glance.
- Altitude in degrees: 1° is just above the horizon, 90° straight overhead.
- True Solar Time (TST): the time the Sun actually keeps — and how far it drifts from your clock.
- Day length — including how much it's changed since the day before, down to the second.
- Equation of Time (EOT): how far apart solar noon and clock noon are — a value that shifts all year long.
Example: at one location the Sun doesn't reach its highest point until 1:26 p.m. — about 86 minutes later than you'd expect. And today is already 34 seconds shorter than yesterday.
Values in Motion
See how fast the celestial bodies move — and calculate the way you want
Almost any value can also be shown as a rate of change, which you're free to set in degrees per hour, per minute, or per second. So you see not just where a body is, but how fast it's moving.
- Example: right now the Sun's azimuth is changing by 19° per hour — and depending on location and season, that can differ significantly from the average.
- You decide how precisely — and at what interval — those changes are shown.
Three calculation methods for rise and set times
- Civil
- Always tied to the current calendar day — the standard you'll find in most comparable apps.
- Nadir
- Uses the body's lowest point as the boundary instead of the calendar day. That gives you the times that really matter for observing the Moon and Sun — especially at high latitudes.
- Session
- Shows the last rise and the next set. Ideal during polar day or polar night, when a body stays visible — or invisible — for days or weeks at a time.
Polar-day example: the last sunrise was back on 2 May at 2:00 a.m., and the next sunset won't come until 25 July at 11:00 p.m. The Session method gives you exactly those times — where other apps give you nothing at all.
Progressions, Light & Visibility
The full day and the full year at a glance
Apphemeride doesn't just show snapshot values — it plots entire progressions, precise and graphical.
- Daily progression with lighting conditions: spot twilight and the golden hour — and see at what altitude the Moon casts each kind of light.
- Annual progression: how the Sun's or Moon's altitude at the same time of day changes from month to month.
- Path across the sky: trace a celestial body along its track — over time or in degrees — so you get a better feel for how fast it moves.
- Visibility toward a given direction: say your window faces 20° north, and find out during what time span the Sun, Moon, or a planet shines in exactly that direction.
These analyses work for many astronomical quantities — in horizontal or equatorial coordinates, too.
Location & Time
Any location, any moment, any time zone
You're in full control of what gets calculated — by address or exact coordinates, for any moment, in any time zone.
- Set your location by searching an address — or by entering exact coordinates.
- Choose any moment — you set the exact date and time.
- Time zone set automatically from the location — or manually, however you like.
Example: choose Gardens by the Bay in Singapore and the time zone switches to Singapore automatically — though you can always override it by hand.
3D Views
Celestial bodies exactly as you see them in the sky
Wherever possible, Apphemeride renders celestial bodies in 3D — in exactly the orientation they take on from where you're standing. Even parallactic effects are shown correctly, like the Moon appearing upside down in the Southern Hemisphere.
- Full data on illumination, direction, the Terminator, and the parallactic angle.
- Saturn, including how visible its rings are right now — so you can tell when it's especially worth observing or photographing.
- For Jupiter and Saturn, their moons are shown as well.
That way you can tell in advance which days a particular detail will be visible — or whether another time of year suits it better.
Sound like your kind of app?
Download on the App StoreCoordinate Systems
Three coordinate systems — side by side and graphical
Apphemeride handles equatorial, horizontal, and ecliptic coordinates and lays them out side by side — real data, graphed in real time.
- Compare the systems directly and see where they diverge — for instance, between right ascension and ecliptic longitude.
- Follow in real time where each celestial body sits in each system — and why the numbers differ between them.
- Extreme values such as the Moon's next northern or southern declination.
- Orbital elements and reference frames such as J2000, JNow, or FK5.
Distances & Events
Measure distances, predict events precisely
You can look up planetary and lunar events any time — calculated precisely for the current moment, not approximated from tables.
- When is the Moon closest to Earth, and when is it farthest away?
- How far each planet is from Earth or from the Sun — in kilometres or miles.
- How long a light or radio signal from there takes to reach us.
- Events: new moon and full moon, extreme declination, transit, conjunction, opposition, or the start of retrograde motion.
Eclipses
Predict eclipses — and experience them in advance
This is where it gets exciting: Apphemeride calculates the next solar and lunar eclipse — worldwide or for your location — and tells you whether you'll be able to see it from where you are.
- Interactive map: shows exactly where, when, and how the eclipse sweeps across the Earth — something almost no other app can do.
- Eclipse simulator: step through exactly how it unfolds and see what the coverage and darkening will look like.
- Toggle the Moon's disc on or off in the simulator to make the sequence easier to follow.
- For lunar eclipses: precise detail on how the shadow moves — and why a given eclipse ends up only partial.
And on a side note: which is bigger — the Sun or the Moon?
- Size comparison
- Apphemeride puts the apparent sizes of the Sun and Moon head to head, in true angular size. Around an eclipse especially, you can tell at a glance which disc looks bigger at that moment.
General
Progress indicators and full control over every value
Many events are shown with progress bars — so you instantly see where you are between two values.
- What percentage of a season or a lunation has already elapsed.
- What percentage of the Moon's surface is currently illuminated.
- Timelines at a glance: what's already passed and what's still ahead.
And best of all: you decide what you see. Even the most specialised value can be shown or hidden — complete freedom for anyone who loves numbers.
Ready to read the sky more precisely?
Apphemeride brings all these calculations right to your iPhone — for planning, observing, studying, and every question you have about the sky.