1. Quick start
Basic setup
- Open Transit Chaser.
- Allow location access, or use Manual location.
- Choose Moon or Sun.
- Start with Search Radius around
30–100 km. - Start with Prediction around
120 sec. - Keep Boosted Mode on for Sun/Moon transit hunting.
Good first settings
- Detection Margin:
2.5° - Prediction:
120 secor180 sec - Search Radius:
30–100 km - Boosted Mode: On
- Visuals: Optional, useful for checking geometry
Sun safety: never look directly at the Sun through a camera, telescope, binoculars, or long lens without a proper solar filter.
2. Location
Your location is important. Transit predictions change if the observer moves even a small distance.
- Auto / GPS: uses your device location. Allow permission when asked.
- Manual: enter latitude, longitude, and elevation manually.
- Select from Map: choose your observing point on the map.
For serious transit photography, use the most accurate location you can. A rooftop, field, or exact footpath location is better than a rough suburb location.
3. Main controls
| Control | What it does | Plain advice |
|---|---|---|
| Transit Mode | Chooses what the app is looking for. | Use Moon or Sun for disc transit hunting. |
| Search Radius | How far around your location the app checks for aircraft. | Bigger radius finds more aircraft, but can add noise. |
| Prediction | Projects aircraft forward using current track, speed, and climb/descent. | Shorter is more reliable. Longer is more speculative. |
| Tracking | Pauses or resumes automatic checks. | Pause when you are not actively using the app. |
| Detection Margin | Allowed angular separation from Sun/Moon centre. | Small margin = transit hunting. Big margin = sky awareness. |
4. Detection margin
The Sun and Moon appear about 0.53° wide. A real crossing usually needs the aircraft to be very close to the disc, depending on aircraft size and distance.
| Margin | Meaning | Use it for |
|---|---|---|
| 0.3° or less | Actual disc-overlap zone. | Highest confidence transit/graze check. |
| 0.5°–2.5° | Close candidate range. | Serious transit hunting. |
| 2.5°–6° | Wide visual search. | Finding nearby aircraft that may be interesting visually. |
| 6°–20° | Broad sky sweep. | Aircraft awareness only, not confirmed transits. |
For a scale diagram, see Detection Visuals. A
20° margin is very wide — about 37 Sun/Moon widths from centre.
5. Boosted Mode
Boosted Mode is the smarter Sun/Moon checker. It uses 3D sky geometry to work out where the aircraft appears from your location compared with the Sun or Moon.
What it checks
- aircraft track, speed, altitude, and climb/descent
- observer position and elevation
- distance from you to the aircraft
- apparent size of the Sun or Moon
- aircraft data quality and stale positions
How to read it
- Disc overlap: likely real transit geometry.
- Grazing: possible edge crossing.
- Near miss: close, probably not crossing.
- Loose: visual-zone or broad sky candidate.
6. Boosted Visual
The Boosted Visual is a geometry view, not a camera preview. It helps show where the aircraft is expected to pass relative to the Sun/Moon.
| Visual item | Meaning |
|---|---|
| Closest | Smallest calculated angular separation. |
| ETA | Estimated seconds until closest approach. |
| Look | Approximate compass direction to look. |
| Heading | Aircraft movement direction. |
| Range | Approximate distance from you to the aircraft. |
Mouse wheel / trackpad scroll = zoom. Drag = rotate. Double-click = reset.
7. Modes
| Mode | Purpose | Best use |
|---|---|---|
| Moon | Checks aircraft alignment with the Moon. | Lunar transit photography and Moon passes. |
| Sun | Checks aircraft alignment with the Sun. | Solar transit photography with proper solar safety. |
| Plane Watch | Watches aircraft types, callsigns, altitude ranges, and directions. | Finding interesting aircraft, not Sun/Moon transit geometry. |
| Plane-on-Plane | Looks for one aircraft passing near another from your viewpoint. | Rare alignment / silhouette attempts. |
| Contrails | Looks for aircraft/contrail composition opportunities. | Sky photography, not disc transits. |
8. Reading alerts
A Transit Chaser alert means an aircraft matched your current settings. It does not always mean a guaranteed visible crossing.
Good candidate
Small separation, short ETA, stable track, good data quality.
Needs caution
Wide margin, turning aircraft, stale position, or long prediction time.
Not useful
Sun/Moon below horizon, very wide separation, or aircraft outside the target area.
9. Logs and email alerts
- The app can show recent transit candidates in the log.
- Email alerts can send a message when a matching candidate appears.
- Keep alert settings realistic. Wide margins can create too many loose candidates.
- Use the test email button before relying on alerts in the field.
10. Troubleshooting
| Problem | Likely reason | What to try |
|---|---|---|
| No aircraft shown | No nearby aircraft, location issue, or data source delay. | Check location, increase radius, refresh, or try later. |
| Too many loose matches | Detection margin is too wide. | Reduce margin to 2.5° or lower. |
| Predicted transit missed | Aircraft turned, changed climb/descent, or data was stale. | Use Boosted Mode and shorter prediction times. |
| GPS is wrong | Browser/device gave inaccurate location. | Use Manual location or choose from the map. |
| No sound | Muted app, browser audio permission, or device volume. | Unmute, test sound, and check device volume. |
11. Safety and data use
- Sun: always use proper solar filters for cameras, telescopes, binoculars, and long lenses.
- Flight data: this app uses community-supplied third-party data. Use responsibly.
- Refresh rate: avoid aggressive refresh intervals, especially with large search radii.
- Accuracy: predictions depend on aircraft track, altitude, data freshness, and whether the aircraft turns.