Star Trail Calculator

Calculate maximum exposure time before stars trail using NPF Rule, 500 Rule, and more

mm
f/
Recommended

NPF Rule

13 sec

Most accurate method. Accounts for sensor resolution and aperture.

(35 × A + 30 × P) ÷ F

500 Rule

20 sec

Classic rule. Often produces slight trailing on modern sensors.

500 ÷ (F × crop)

300 Rule

12 sec

Conservative. Safer for high-resolution sensors and pixel peeping.

300 ÷ (F × crop)

Quick Comparison

Pro tip: The NPF rule is most accurate for modern high-resolution sensors. When in doubt, shoot a test frame and zoom to 100% to check for trailing. Atmospheric conditions and tracking accuracy also affect results.

Moon Phase Calendar

Plan shoots around the lunar cycle — new moon is ideal for deep sky imaging

Waxing Gibbous 68% illuminated Day 10 of cycle

Shooting Recommendations by Phase

Phase Illumination Deep Sky Best For
New Moon 0–5% Excellent Milky Way, nebulae, faint DSOs. Darkest skies.
Crescent 5–35% Good Deep sky when moon is below horizon.
Quarter 35–65% Limited Plan around moonrise/set times.
Gibbous 65–95% Poor Star trails, moonlit landscapes.
Full Moon 95–100% Avoid Lunar photography, moonlit scenes only.

Milky Way Season

Galactic core visibility by month and hemisphere

Current Status Prime Season Best viewing: Late evening to early morning
Prime season (core visible all night)
Good (visible for extended periods)
Limited (short window or low altitude)
Core not visible

Galactic Core Planning Tips

Best Conditions

  • New moon or moon below horizon
  • Bortle class 4 or darker skies
  • Clear, low-humidity nights
  • Core at least 20° above horizon

Timing Strategy

  • Check astronomical twilight end time
  • Core rises ~4 minutes earlier each night
  • Peak season: Core transits at midnight
  • Plan for 2+ hours of shooting time

Meteor Shower Calendar

Major annual meteor showers with peak dates and expected rates

2025
Shower Peak Date ZHR Speed Moon Conditions Radiant
ZHR (Zenithal Hourly Rate) is the theoretical number of meteors per hour under perfect conditions. Actual observed rates are typically lower. Moon interference significantly impacts visibility — plan around new moon when possible.

Light Pollution Scale

The Bortle Dark-Sky Scale for evaluating observation sites

1 Excellent Dark Site

Zodiacal light, gegenschein, and zodiacal band visible. Scorpius and Sagittarius regions cast shadows. Airglow is visible.

All DSOs Zodiacal Light Gegenschein
ISO 1600–3200 Single exposures sufficient
2 Typical Dark Site

Airglow may be faintly visible near horizon. M33 visible with direct vision. Summer Milky Way highly structured.

All DSOs Zodiacal Light
ISO 1600–3200 Ideal for deep sky
3 Rural Sky

Light pollution domes visible on horizon. Clouds illuminated near horizon. Milky Way appears complex.

Most DSOs Milky Way
ISO 1600–6400 Excellent for Milky Way
4 Rural/Suburban Transition

Light pollution domes obvious. Milky Way visible but lacking detail. M31 visible to naked eye.

Bright DSOs Milky Way
ISO 3200–6400 Good for astrophotography
5 Suburban Sky

Milky Way washed out at horizon. Clouds clearly illuminated. Only hints of zodiacal light on best nights.

Bright DSOs Milky Way core
ISO 3200–6400 Consider light pollution filters
6 Bright Suburban

Milky Way only visible at zenith. Sky background appears grayish-white. M31 barely visible.

Planets Moon Brightest DSOs
ISO 1600–3200 Narrowband filters essential
7 Suburban/Urban Transition

Entire sky has vague grayish-white hue. Milky Way invisible. Strong light sources in all directions.

Planets Moon Double stars
ISO 800–1600 Narrowband only
8–9 City Sky

Sky glows white or orange. Only the moon, planets, and a few bright stars visible. Ground brightly lit.

Moon Planets Sun (with filter)
ISO 400–800 Planetary imaging possible
Finding dark skies: Use Light Pollution Map or Dark Site Finder to locate observation sites. Even a short drive from urban areas can dramatically improve conditions.

Camera Settings by Target

Optimal settings for different astrophotography subjects

Milky Way (Wide Field)

Focal Length 14–24mm
Aperture f/1.4 – f/2.8
Shutter Use NPF rule
ISO 3200 – 6400
Focus Manual, on bright star
White Balance 3800–4200K

Star Trails

Focal Length 14–35mm
Aperture f/2.8 – f/4
Shutter 30s intervals × 60–240
ISO 800 – 1600
Focus Manual infinity
Extra Intervalometer essential

Deep Sky (Tracked)

Focal Length 50–200mm
Aperture f/2 – f/4
Shutter 60–300s (tracked)
ISO 800 – 3200
Stacking 20–50+ exposures
Extra Star tracker required

Meteor Showers

Focal Length 14–24mm (wide)
Aperture f/2.8 or wider
Shutter 15–30s continuous
ISO 3200 – 6400
Focus Manual, on bright star
Strategy Aim at radiant ±30°

Moon (Detail)

Focal Length 200–600mm+
Aperture f/8 – f/11
Shutter 1/125 – 1/250
ISO 100 – 400
Focus Manual, Live View 10×
Tip Shoot at terminator

Northern Lights

Focal Length 14–24mm
Aperture f/1.4 – f/2.8
Shutter 1–15s (depends on speed)
ISO 1600 – 6400
Focus Manual infinity
Tip Shorter for fast aurora

Planets

Focal Length 1000mm+ (or telescope)
Aperture f/10 – f/20
Shutter 1/30 – 1/250
ISO 100 – 800
Method Video, stack best frames
Tip Wait for steady seeing

Lunar Eclipse

Focal Length 200–400mm
Aperture f/5.6 – f/8
Shutter 1s – 4s (totality)
ISO 800 – 3200
Focus Manual, pre-focus on moon
Tip Bracket exposures

Night Sky Cheat Sheet

Quick reference for the field

Sharp stars? Use NPF rule, check focus at 100%
Milky Way overexposed? Lower ISO or shorter exposure
Too much noise? Stack multiple exposures
Focus method? Bright star at 10× live view
White balance? 3800–4200K, adjust in post (RAW)
Histogram goal? Peak in left-center, no clipping
Long exposure NR? Off (take dark frames instead)
High ISO NR? Off (handle in post)
Image stabilization? Off on tripod
File format? RAW only (never JPEG)
Mirror lockup? On for DSLRs (reduces vibration)
Drive mode? 2s timer or remote trigger