The moon does not ruin every filter equally: a 3nm Ha filter shrugs off moonlight that makes a Luminance sub worthless. Astro PM models moon tolerance per filter, with a physically motivated curve you can see and tune – so a bright-moon night is automatically spent on narrowband, and dark hours are protected for the filters that truly need them.
How Astro PM Decides "Moon-Safe" #
For every 5-minute slot of the night, each filter’s profile is evaluated with a four-layer decision. The first layer that passes makes the slot safe for that filter:
- Moon below the horizon – always safe. Moon-down time is the universal currency.
- Moon at or below Max Alt – a low-hanging moon is heavily dimmed by the atmosphere; below this altitude cap the slot is safe regardless of phase.
- Illumination at or below Max Illumination % – a thin crescent is harmless; below this threshold the moon’s position is ignored entirely.
- Separation check – otherwise, the target must be farther from the moon than the required separation for this moment, which comes from the avoidance curve below.
If all four fail, the slot is moon-blocked for that filter – and the scheduler simply plans a more tolerant filter (or another target) into it.
The Avoidance Curve: Separation & Width #
The required separation is not a fixed number – it follows the lunar cycle with a Lorentzian curve peaked at full moon:
required separation = Separation / (1 + (days from full / Width)²)
- Separation (°) is the peak requirement, applied at full moon with the moon high in the sky.
- Width (days to 50%) is how fast the requirement falls off: the number of days from full moon at which the requirement has dropped to half. A large Width keeps avoidance strict across most of the cycle; a small Width concentrates it in a tight window around full.
At new moon the requirement is nearly zero – almost everything is safe; approaching full it climbs toward the peak. This is the curve shown in the interactive chart:
Reading the chart: the faint yellow area is moon illumination across the 29.5-day cycle; the blue line is your current profile with altitude relaxation; the orange dashed line is the same profile without relaxation; the green line previews values you are editing. With Show Target Separation on, the actual moon-target distance is overlaid – white where it clears the requirement (safe), red where it does not. Phase markers (new, quarters, full) and a “today” line anchor you in the cycle.
Altitude Relaxation: Relax Scale, Min Alt, Max Alt #
A moon sitting just above the horizon is far less damaging than the same moon at 60°. The relaxation settings encode that:
- Max Alt (°) – at or above this altitude the full Separation and Width apply (default 5°).
- Relax Scale – for every degree the moon sits below Max Alt, the required separation is reduced by this many degrees. 0 disables relaxation entirely.
- Min Alt (°) – the bottom of the relaxation range; by the time the moon reaches it, the Width has collapsed and avoidance effectively disappears. A slightly negative value (default -15°) keeps a small margin around moonset.
Between Max Alt and Min Alt, both Separation and Width scale down progressively as the moon descends – so the last hour before moonset opens up gradually rather than flipping from blocked to open.
Settings Reference #
| Setting | Range | Default | Plain meaning |
|---|---|---|---|
| Separation (°) | 0-180 | 60 | peak distance required at full moon, moon high |
| Width (days to 50%) | 0.1-30 | 7 | days from full moon where requirement halves |
| Relax Scale | 0-10 | 0 | degrees of forgiveness per degree of low moon |
| Min Alt (°) | -90-90 | -15 | below this, avoidance is effectively off |
| Max Alt (°) | -90-90 | 5 | above this, full strictness applies |
| Max Illumination (%) | 0-100 | 40 | at or below this phase, always safe |
The Built-In Profiles #
Four ready-made profiles ship with Astro PM (built-ins cannot be deleted, but you can clone and adjust):
| Profile | Sep | Width | Relax | Min/Max Alt | Max Illum | Use for |
|---|---|---|---|---|---|---|
| No Moon | 180° | 14d | 0 | -90° / -2° | 0% | the moon must be down – darkest-sky work |
| Strict | 90° | 8d | 0 | -15° / 5° | 30% | broadband L, R, G, B |
| Moderate | 60° | 5d | 2 | -15° / 5° | 60% | mid-width narrowband (7nm OIII etc.) |
| Relaxed | 25° | 3d | 3 | -15° / 5° | 80% | 3nm Ha / SII – moonlight barely registers |
Assigning Profiles: Project Default, Named, or No LA #
Every exposure line in a project has a Moon Avoidance Profile selector with three kinds of choices:
- A named profile (built-in or your own) – global: edit it once and every project using it follows.
- Project Default – uses the moon settings saved on this project (the fields under “Enable Moon Avoidance” in the project editor). Good for one-off tuning without touching your library.
- No LA – no lunar avoidance at all; this filter images regardless of the moon.
New projects seed their defaults from your app-wide defaults, so your house style carries forward automatically. Typical setup: broadband lines on Strict, narrowband lines on Relaxed, and a luminance-hungry galaxy project on No Moon.
What the Scheduler Does With It #
Profiles do not just filter time – they drive allocation strategy. The engine groups a target’s filters into tiers by restrictiveness, then treats the night as two resources:
- Moon-down time is the scarce currency. It goes to the most restrictive work first – and targets whose filters can only shoot moon-down (the No Moon tier) get first claim before moon-flexible projects touch it.
- Moon-up time goes to the least restrictive tier that is safe in each slot. With the moon rising, relaxed filters run first, saving stricter work for after moonset; with the moon setting, the order flips as conditions improve.
The result on a bright night: Ha subs while the moon rides high, OIII as it sinks, broadband only in the true dark – without you scheduling any of it by hand.
Where You See It: Charts & Simulator #
Moon avoidance is visible everywhere planning happens:
- Visibility chart – the red band shows moon-up hours during darkness; the green recommended-exposure bands are drawn per tier, stacked light-to-dark from most tolerant to most restrictive, so you can see exactly which filters get time on any given night of the season.
- Nightly graph – the moon’s altitude arc is drawn in red with the same stacked green bands, plus filter pills marking which filters are imageable in the usable window.
- The simulator and NINA run the identical rules – same curve, same constants – so the plan you see is the plan that executes at the observatory.
