Star trail photography captures the apparent motion of stars across the night sky, created by Earth's rotation. As Earth spins on its axis, stars appear to move in circular arcs around the celestial poles, creating stunning light trails in long-exposure photographs.
How Stars Move Across the Sky
Earth completes one rotation every 23 hours, 56 minutes, and 4 seconds (a sidereal day). This means stars appear to move at approximately 15° per hour at the celestial equator. However, the apparent speed depends on the star's declination (position relative to the celestial equator):
- Celestial Equator (0°): Maximum speed - stars move fastest
- Mid-latitudes (±45°): About 70% of equatorial speed
- Near Poles (±90°): Minimal movement - stars trace tiny circles
Single Exposure vs. Stacking
There are two main approaches to star trail photography:
Single Long Exposure
- • Use Bulb mode + remote trigger
- • ISO 100-400, f/4-f/8
- • 30+ minutes exposure
- • Risk: sensor heat, noise, bumps
Stacking Multiple Frames
- • Intervalometer + 30s exposures
- • ISO 800-1600, f/4-f/5.6
- • Stack 60-200+ frames
- • Benefits: less noise, flexibility
Recommended Exposure Times
- 5-15 minutes: Short trails - subtle motion effect
- 30-60 minutes: Medium trails - clear arcs
- 2-4 hours: Long trails - dramatic sweeping arcs
- 6+ hours: Quarter to half circles
- 24 hours: Complete circles (theoretical)
Composition Tips
For circular trails, point at Polaris (Northern Hemisphere) or toward the South Celestial Pole (Southern Hemisphere). Include interesting foreground elements like trees, mountains, or buildings. Use the NPF Calculator to determine if you want pinpoint stars in a foreground exposure to blend later.