Celeris / FAQ
Celeris FAQ: Features, accuracy and purchase
Find answers about features, calculations and purchase. Celeris remains free to use; the full version is a one-time purchase.
Free or full version?
What can I use without paying?
The map, time controls, 3D sky with terrain, AR, camera view, celestial catalogue, ISS transit list, and both custom and included 3D objects remain available. Without paying, you can plan any time in the past and up to 48 hours from now.
What does the full version unlock?
The full version removes the 48-hour limit for future dates. It also includes the monthly dark-night calendar, the eclipse list years ahead, and home-screen widgets plus lock-screen widgets on Apple devices.
Does the free version expire?
No. The free window does not expire; it keeps moving with time. The past and the next 48 hours remain available.
Is the full version a subscription?
No. There is no subscription. You buy the full version once and it remains unlocked within that store.
Does one purchase work on several devices?
You can restore the purchase on the same platform using the same store account. An App Store purchase covers iPhone, iPad and Mac. Apple and Google Play purchases are separate because Celeris has no user account of its own.
Data, devices and accuracy
Do I need a Celeris account?
No. There is no Celeris account. Plans, places and custom models initially stay on your device. Sync through iCloud or Google Drive is optional.
Does Celeris work without an internet connection?
Astronomical calculations run on the device. Location search, terrain needed for the first time, included 3D objects and current ISS orbital data require a connection. Previously downloaded data remains available on the device.
Which devices support Celeris?
Celeris supports iPhone and iPad from iOS 17, Mac from macOS 26 and Android from version 10. AR and phone aiming are mobile features.
Does Celeris forecast weather, clouds or real fog?
No. Celeris plans astronomical positions, terrain, framing and a manually set fog layer. Check weather, clouds, visibility and light pollution with weather services or on location.
How accurate are terrain and 3D objects?
Terrain is based on a 30-metre elevation grid. The 3D objects are deliberately simplified planning aids. Check narrow openings, individual trees and centimetre-level alignments on location.
Planning and calculations
When is a night dark in Celeris?
Astronomical night begins when the sun is more than 18 degrees below the horizon. Celeris also intersects that interval with moonrise and moonset. The result is the time that is both astronomically dark and moonless.
Why can the moon position differ from a table?
Celeris calculates the moon topocentrically for your actual viewpoint. Many tables list its geocentric position from the centre of the earth. Near the horizon, the two can differ by about one degree. The displayed rise and set times agree with the moon drawn by Celeris.
Where does Celeris place the galactic centre?
Celeris approximates the galactic centre with the position of 3 Sagittarii. The bright Milky Way band is not a single point; this approximation is sufficient for planning the frame and the visible core's altitude.
Why is no event sometimes found at high latitudes?
Rise and set searches are bounded in time. During polar day or polar night, no rise or set may actually occur within that interval. Celeris then reports that no event was found.
Which time zone do displayed times use?
Celeris uses the time zone of the place you are planning for, not automatically your phone's current time zone. Move the map viewpoint across a time-zone boundary and the times are converted accordingly.
Which sensor size is the framing based on?
The frame is based on a 36 by 24 millimetre full-frame sensor. At the same focal length, smaller sensors produce a correspondingly tighter frame.
App features and help
Why does the widget show a different place from the app?
By default, the widget follows the last place you planned for. Under More, Widget location lets you choose a fixed place or make the widget follow the app again.
Do I have to allow location access?
No. You can move the map manually or search for a place. Only the location arrow and AR viewpoint guidance that you start require permission.
What can I search for in the celestial catalogue?
You can search for proper names, HR numbers from the Bright Star Catalogue, HIP numbers from Hipparcos and Messier numbers for deep-sky objects. It contains about 8,900 stars and all 110 Messier objects.
Can I show the introduction again?
Yes. Open More and tap Show introduction again at the bottom.
Where can I find the included 3D objects?
Enable predefined 3D models under More. Celeris downloads matching landmarks for the area being viewed when needed. Your own models at the same place take precedence, and new revisions are picked up without reinstalling the app.
How reliable are calculated ISS dates?
Calculations use current CelesTrak orbital data. Dates more than two weeks beyond its epoch are provisional, so check a planned transit again shortly before the event.
What is different on Mac?
The Mac app from macOS 26 uses a sidebar, keyboard shortcuts and a separate 3D editor window. One App Store purchase and optional iCloud sync cover iPhone, iPad and Mac. AR, phone aiming and widgets are not available on Mac.