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Detection visuals

A practical scale guide for Transit Chaser. The Sun and Moon are tiny targets in the sky: about 0.53° wide. A 10° or 20° margin is useful for finding aircraft activity, but it is not a confirmed transit zone.

Quick answer

Detection margin is how much sky the app accepts around the Sun or Moon.

A smaller number means the aircraft must pass closer to the target. A bigger number gives you more alerts, but many of those aircraft will be obvious misses.

Start at 2.5°. Lower it for stricter alerts. Raise it only when you want to scout for more aircraft.

Strict

Very close passes

0.5°–1°

Fewer alerts. Best when you only want aircraft very close to the Sun or Moon.

✓Use this: when you are ready to photograph a serious candidate.
Recommended

Balanced search

2.5°

A useful balance between close candidates and getting enough warning.

✓Use this: for normal Sun and Moon transit hunting.
Wide

Aircraft scouting

6°–10°

More alerts and more time to look, but many aircraft will miss the target.

✓Use this: to discover nearby aircraft, not to confirm a transit.

These three pictures are simplified for quick comparison. The exact-scale diagrams are below.

! 10°–20° is a broad radar sweep. It can find aircraft activity, but it does not mean the plane will cross the Sun or Moon.
See the exact scale and detailed explanation ↓

Detailed guide

The diagrams below keep the original exact-scale explanation for users who want the full detail.

1. Flat sky view: how far is the aircraft from the Sun/Moon?

This is the cleanest way to understand margin. The aircraft marker is placed at the selected angular distance from the centre of the Sun/Moon. The scale is in real apparent Sun/Moon diameters.

Margin distance, drawn flat Sun/Moon diameter = 1 unit. A 20° margin is about 37.7 Sun/Moon widths from centre. 0.3° 2.5° 5° 10° 20° target centre actual overlap / transit zone ~4.7 Sun/Moon widths from centre ~9.4 widths — clearly off-disc ~18.9 widths — far away 20° = ~37.7 widths — broad sky sweep only The aircraft marker is not drawn huge on purpose. This chart is about centre-to-centre angular distance.

2. Circular view: the same margins around the Sun and Moon

Same scale for both panels. The coloured rings are angular distance from the target centre. The tiny centre object is the actual Sun/Moon size.

Sun Actual disc ≈0.53° wide 2.5° 5° 10° 20°
Moon Actual disc ≈0.53° wide 2.5° 5° 10° 20°

3. Search radius is different from detection margin

Search radius controls which aircraft are fetched around you. Detection margin checks how close that aircraft appears to the Sun or Moon in the sky. They are related in the app, but they are not the same measurement.

Local aircraft radius + sky-angle margin This is why a big margin can find aircraft but still not mean a Sun/Moon transit. YOU search radius, e.g. 20 km / 50 km / 100 km Sun / Moon direction small margin wide margin / sky sweep possible close candidate inside broad margin, but not a transit inside radius, wrong sky direction

Recommended margin meanings

Margin Plain-English meaning Suggested wording in the app
0.3° or less Actual Sun/Moon disc overlap zone, depending on aircraft angular size. Transit / disc overlap
0.5°–2.5° Serious transit-hunting range. Useful for real candidates and close grazes. Transit candidate / close candidate
2.5°–6° Useful visual search, but many aircraft will be clearly off the Sun/Moon. Visual-zone candidate
6°–10° Broad sky awareness. Helpful for finding aircraft activity, not for confirmed transits. Broad sky candidate
10°–20° Very wide sweep. A plane can be dozens of Sun/Moon widths away. Radar sweep only / not a confirmed transit