The ISS crosses the Moon in one second. Be in the right place.
A spacecraft transit is visible from a corridor on the ground a few kilometres wide, and it lasts about a second. Miss the corridor by five kilometres and you see nothing at all.
Transit Hunter works out where that corridor falls near you, ranks every opportunity, tells you whether it is worth the drive — and watches for the good ones so that you do not have to.
Your next best transit
ISS (ZARYA) → Moon
Wednesday, 26 August 2026
00:34:34.44
good
7.8 km NW of youabout a 12 minute drive
- Moon altitude
- 33°
- Duration
- 1.37 s
- Apparent size
- 37.7″
- Corridor
- 6.4 km
Worth the trip — 7.8 km for a very good transit.
- 7.8 km away — a short trip.
- Central transit — the spacecraft crosses the middle of the disk.
- High prediction reliability.
Searched 7 days on this device · your coordinates were not sent anywhere
Getting the astronomy right is the easy half
Photographing a spacecraft against the Sun or the Moon is not a matter of pointing a camera upwards and waiting. It is a logistics problem with a one-second deadline, and almost everything that decides whether you get the picture happens before you leave the house.
The window is about one second
A spacecraft crosses the face of the Sun or Moon in roughly a second, sometimes less. There is no second attempt, no adjusting between frames, and no reacting to what you see — everything has to be right before it begins.
The corridor is a few kilometres wide
The transit is visible only from a narrow corridor on the ground. Stand five kilometres to one side of it and the spacecraft passes near the disk rather than across it. You will have driven out, set up, and seen nothing.
The corridor moves
Orbital predictions age. Fresh elements arrive several times a day and the centre line shifts with them — by more than the corridor is wide after a station reboost. A spot that was right last week can be wrong tonight.
Most events are not worth the drive
A month of predictions might hold forty events. Most are grazing passes, or too low, or at an hour that costs a night's sleep for a poor result. Deciding which one deserves an alarm is the actual work.
The good ones are rare and easy to miss
A high-quality lunar transit close to home happens a handful of times a year. Nobody opens an app often enough to find those by chance, so in practice they pass unnoticed.
Existing tools stop at the astronomy
The dedicated transit finders compute the geometry well, then hand back a chronological table. Which event to choose, where exactly to park, when to leave and whether the sky will cooperate are all left to you.
A transit is a line on the ground, not an event in the sky
The spacecraft appears at the centre of the disk only for observers standing where the line from the target’s centre, through the spacecraft, meets the Earth. Trace that line over time and you have the centre of the corridor exactly.
Either side of it there is a few kilometres of ground from which some part of the crossing is still visible. Beyond that there is nothing to photograph — the spacecraft simply passes near the disk instead of across it, and the trip was wasted.
Which is why the useful question is never “when is the next transit”. It is “which one, and exactly where do I stand”.
From “where am I” to “this one, at this spot”
- 01
Say where you are, and how far you will go
An approximate location and a travel budget — from “where I am standing” to a few hundred kilometres. Nothing else is needed to begin.
- 02
It finds and ranks every transit
The search runs on your own device and returns the crossings of the Sun and Moon within reach, ordered by how good a photograph each one is actually likely to make.
- 03
It tells you whether it is worth the trip
A verdict with its reasons, an estimated drive, a departure time, and the exact point to stand — shown on a map with the corridor drawn around it.
- 04
It keeps watching after you close it
Set a standing rule and it checks on your behalf, alerts you when something good appears, and tells you again if the corridor moves after you have been told where to go.
The layer above the astronomy
The geometry is a solved problem, and Transit Hunter solves it the same way everyone else does. What it adds is everything between a correct prediction and a photograph you actually took.
A quality score you can interrogate
Nine weighted factors — how centrally the spacecraft crosses, how high the target sits, duration, apparent size, travel, corridor width, prediction reliability, sky and hour. Each is reported separately, so you can see exactly why an event scored what it did.
Worth the trip, or not
A plain verdict, with the reasons for and against it. Travel is judged against the budget you set, because ten kilometres means something different to someone who chose “where I am” than to someone who chose two hundred.
It watches so you do not have to
Standing rules run in the background and alert you when a transit worth your attention appears within your radius — with a lead time you choose, so a ninety-minute drive is not announced twenty minutes beforehand.
Alerts when the corridor moves
Fresh orbital data can shift the centre line after you have already been told where to stand. When that happens to an event you were alerted to, you are told again. Sending someone to a spot and staying quiet when the spot changes is worse than never sending them.
The corridor mapped, and any point on it evaluated
The centre line and the corridor either side of it are drawn on the map. Tap anywhere and the geometry is recomputed for that exact spot — the crossing you would see from the field you can park beside, not from the ideal point you cannot reach.
Framing for the equipment you own
Field of view and the number of pixels the spacecraft will span, worked out for your sensor and focal length, with the sampling limit and the diffraction limit treated as the separate constraints they are.
The forecast folded into the ranking
Cloud cover for the observation point is weighted into the score rather than bolted on beside it. It never touches the astronomy, and when no forecast is available its weight is redistributed rather than assumed clear.
A countdown that refuses to lie
Before it starts counting, the app recalculates the event from the point you actually chose, using the orbital data on the device now. If the time has moved, the quality has dropped or the data has gone stale, it stops and says so rather than counting towards a number that stopped being true.
A score you can argue with
Every transit is scored on nine weighted factors, and each one is reported on its own. So when an event ranks below another, you can see precisely why — a grazing chord, a target too low, an hour that costs more than the photograph is worth.
Travel is judged against the budget you set rather than against an arbitrary distance, because ten kilometres is a long way to someone who chose “where I am standing” and nothing at all to someone who chose two hundred.
Weather is one factor among the nine and never touches the astronomy. When no forecast is available its weight is redistributed rather than assumed clear — an unknown sky must not flatter an event.
What the score is made of
- Centrality
- 20
- Target altitude
- 15
- Travel
- 13
- Apparent size
- 11
- Prediction reliability
- 10
- Sky
- 10
- Duration
- 9
- Corridor width
- 7
- Hour
- 5
How close to the middle of the disk the crossing runs
How high the Sun or Moon sits above the horizon
Distance, judged against the budget you set
How large the spacecraft appears from where you stand
How much the orbital data could still move
Forecast cloud cover at the observation point
Seconds the spacecraft spends on the disk
How much room there is for error either side
What the local time of day costs you
The good ones arrive a few times a year. Nobody catches those by chance.
So you set the rule once — this radius, this quality, this much warning — and the checking happens without you. Everything it queues appears in the app whether or not a notification was ever delivered.
The alert that matters most is the one almost nothing else sends: the corridor for an event you were already told about has moved. Sending somebody to a spot and then staying quiet when the spot changes is worse than never having sent them.
Alerts arrive at night, and acting on one means getting dressed and driving somewhere. That interruption is expensive enough that the threshold is set high and the volume kept deliberately low.
What it will interrupt you for
A transit worth your attention
Something above the quality threshold you set has appeared within your radius.
Reminder before the event
At the lead time you chose — long enough to pack, drive and set up.
The corridor has moved
Fresh orbital data shifted the centre line for an event you were already told about.
Do not drive — it is off
An event you were told about is no longer reachable, or no longer happens at all.
The forecast has worsened
Cloud cover for a saved event has changed materially. Off unless you switch it on.
And nothing else. Notification permission is requested only once a rule exists, never on first launch.
We checked, event by event
419 events were collected from an established reference tool and compared one at a time. The propagator was separately measured against NASA’s own published ISS ephemerides.
- Reference events compared, one by one
- 419
- Median difference in predicted transit time
- 0.137 s
- Median centre-line difference within 10 km
- 85 m
- Median error against NASA ISS ephemerides
- 0.158 km
What we do not claim
We do not claim to be more accurate than the established transit finders. We claim to agree with them closely, to have measured that agreement rather than assumed it, and to tell you honestly how uncertain any individual prediction is. That comparison found three real defects in our own calculations, and all three were fixed before any of this was said out loud.
A prediction can still move. Orbital data is reissued several times a day, no terrain or buildings are modelled, and a forecast is a forecast. Every event carries its reliability grade and the sentence explaining it — and the honest advice is always to re-check on the day.
Anyone who has to decide which night to go out
Astrophotographers
Anyone who has driven out for a transit and found the corridor was somewhere else. The score, the corridor map and the framing figures exist for exactly that trip.
Astronomy societies and clubs
A shared, explainable ranking makes it possible to agree which of the coming month's events the group should organise around — and where everyone should stand.
Educators and outreach programmes
A spacecraft crossing the Moon is a rare thing to be able to schedule. Knowing well in advance which events are worth planning a session around is what makes it teachable.
Science communication and media teams
Planning a shoot around a one-second event needs a defensible answer to “is this the right night, and where do we send the crew?” — with the uncertainty stated rather than hidden.
Designed for a phone, held one-handed, in a dark field
That is where the product is actually used, so it is what the interface is built around: a single ranked answer rather than a table, large legible figures, and controls within reach of a thumb.
It runs in a browser and as an Android application built from the same code — the search engine executing on the device in either case, and returning identical results.
Your next best transit
The home screen leads with a single ranked answer rather than a table — the spacecraft, the target, the score, the exact time, the distance from you and the drive.
The event, in full
The score broken into its factors, the reasons for and against, the corridor map, the framing for your equipment, the reliability of the prediction, and the safety requirements for a solar event.
The corridor map
Centre line and corridor drawn on the map. Tap any point to see the transit as it would be from there, then choose it as the place you will actually observe from.
Observation mode
The countdown for the night itself, recalculated from where you are standing, with the screen kept awake and the numbers re-verified before it begins counting.
Alerts
Everything the watcher has queued for you, whether or not a notification was delivered. The list in the app is the record; push is only the accelerator.
Where you photograph the sky is where you live
An application that collects observing locations is collecting home addresses. This one was built by people who noticed that, and the consequences are in the architecture rather than in a policy document.
Searches never leave your device
The orbital mechanics engine is in the app itself. Orbital elements are public data, identical for everyone, so the search runs where you are — and your coordinates are not transmitted in order to run it. The app states this beneath every set of results.
Saved places are stored deliberately coarsely
A saved location is held to roughly two and a half kilometres — wider than a transit corridor. Precise enough to decide whether an event is worth telling you about; not precise enough to identify where you live. Exact geometry is recomputed on your device when you open the event.
The Android app asks only for approximate location
Fine location is never requested, so Android's own permission dialogue offers approximate location and nothing finer. The position is visible in the application manifest, not only in a policy document.
No account is needed to start
The first session is anonymous. You can save a place and set a standing alert without giving an email address. Signing in later uses a single-use link that expires in fifteen minutes, and session tokens are stored hashed rather than in the clear.
Deletion means deletion, and you can look first
You can export everything held about you before deciding. Deleting the account removes it and everything that references it — saved places, alerts, notifications, devices and sessions — immediately, rather than marking a row inactive.
No advertising, no third-party analytics, no session recording
Product analytics exist and are structurally unable to carry a location or an identifier: those fields are stripped at the point of recording rather than by convention. There is no advertising SDK and no third-party analytics SDK in the application.
Built by an engineering company that has been getting positions right since 1994
Transit Hunter is an Embarc product — designed, built, tested and maintained by the same team behind the Find’n’Secure fleet and asset tracking platform.
- Three decades of building software that has to be right the first time — fleet and asset tracking platforms deployed across more than thirty countries, where a wrong position is not a cosmetic defect.
- The same discipline applied here. The calculations were measured against an established external reference and against NASA's own published ephemerides, and the three genuine defects that comparison exposed were fixed before anything was claimed.
- Uncertainty is engineered rather than glossed over. Every prediction carries a reliability grade and the sentence explaining it, derived from measured residuals rather than from a figure chosen because it sounded reassuring.
- Built, tested and maintained by Embarc as a product — not shipped as a demonstration and abandoned.
Data it relies on
- CelesTrak
- — Orbital elements, including the supplemental sets that track manoeuvres
- NASA public ISS ephemerides
- — Manoeuvre schedule, and the reference for absolute accuracy
- Open-Meteo
- — Cloud-cover forecasts for the observation point
- OpenStreetMap contributors
- — Map tiles, via OpenFreeMap
Solar observing safety
Never point a camera, telescope, binoculars or finder scope at the Sun without a certified full-aperture solar filter fitted over the front of the optic. Unfiltered sunlight through any optical instrument causes permanent blindness in a fraction of a second, and will destroy the camera. Filters that fit at the eyepiece end are not safe, and neither is an optical viewfinder.
The application enforces this: the warning is the first thing shown on every solar event, cannot be dismissed, travels into the calendar export, and no exposure advice is given that could be followed without a filter fitted.
It is built. It is not yet released.
The engine, the application and the Android build are finished and tested, and the calculations have been measured against an external reference. What remains before a public launch is operational rather than astronomical, and we are not quoting a date or a price for it.
What we would like in the meantime is a small number of people who photograph these events, or organise others to — and who will tell us where the ranking disagreed with their judgement, and when a prediction did not match what they saw.
What you get
- Early builds, before public release
- A direct line to the engineers who built it
- A say in what gets built next
What we ask
- Use it for a real observation you were going to attempt anyway
- Tell us where the ranking disagreed with your own judgement
- Tell us when a prediction did not match what you saw
Request early access
Frequently asked
- What exactly is a transit?
- It is the moment a spacecraft passes directly between you and the Sun or the Moon, appearing as a small dark silhouette crossing the bright disk. It is not the same as watching the ISS drift across the night sky: a transit lasts about a second and is visible only from a narrow corridor on the ground, which is why it has to be planned rather than waited for.
- Which spacecraft can it find transits for?
- The International Space Station, the Chinese space station Tiangong, and the Hubble Space Telescope. The catalogue is data rather than code, so adding an object is a data change — but objects too small to resolve as a silhouette are deliberately left out rather than added to lengthen a list.
- How accurate is it?
- We do not claim to be more accurate than the established transit finders. We claim to agree with them closely, and to have measured that agreement instead of assuming it: 419 events compared one by one, a median difference of 0.137 seconds in predicted time and 85 metres in centre line within 10 kilometres, plus a median error of 0.158 kilometres against NASA's own published ISS ephemerides. That comparison found three real defects in our calculations, all of which were fixed.
- Can a prediction still be wrong?
- Yes, and the app says so rather than implying otherwise. Orbital data is reissued several times a day and the corridor moves with it, particularly after a station reboost. Every event carries a reliability grade and the reason behind it, weather forecasts are probabilistic and only ever affect ranking, and no terrain, buildings or trees are modelled. Always re-check on the day.
- Does it need my precise location?
- No. The search runs on your device, so your coordinates are not sent anywhere in order to perform it, and a place you save is stored to roughly two and a half kilometres — deliberately coarser than a transit corridor. The Android app does not request fine location at all.
- Do I need an account?
- Not to start. The first session is anonymous, and you can save a place and set a standing alert without giving an email address. Signing in with an email is optional, and uses a single-use link rather than a password.
- What equipment do I need?
- A camera capable of a fast burst, and a long lens or a telescope. The app works out the field of view and how many pixels the spacecraft will span for the sensor and focal length you tell it about, so you can see what your own kit will resolve. It describes optical geometry, which is exact — it does not predict whether a given frame will come out well.
- Is it safe to photograph a solar transit?
- Only with a certified full-aperture solar filter fitted over the front of the optic. Unfiltered sunlight through any lens, telescope, finder or optical viewfinder causes permanent blindness in a fraction of a second, and will destroy the camera. Filters that screw into the eyepiece end are not safe. The app treats this warning as non-dismissable on every solar event, and carries it into the calendar export.
- Can I get it now?
- Not yet. The application is built, tested and validated, but it is not publicly released, and we are not quoting a date or a price. If you would like to be among the first to use it, or to talk to us about using it in a club, a classroom or an outreach programme, get in touch below.
Go and photograph something difficult
Tell us where you observe from and what you are trying to capture. If Transit Hunter is the tool for it, we would like you using it early.
Or write to shailendra.bansal@embarc.co.in
Transit Hunter is a product of Embarc Information Technology Pvt. Ltd. It is built and validated but not yet publicly released, and nothing on this page constitutes an offer of sale or a commitment to a release date. Orbital predictions change as new data arrives; a predicted location does not guarantee visibility, and no terrain, buildings or vegetation are modelled. Orbital data from CelesTrak and NASA. Map tiles © OpenStreetMap contributors.