RigTonightHow to photograph the Pleiades (M45): blue reflection nebula, framing and filters
The Pleiades, or Seven Sisters, is the brightest star cluster in the sky and one of the most beautiful targets in astrophotography. Long exposures reveal what the eye can't see: wisps of blue nebulosity wrapped around the brightest stars, and under dark skies, faint dust stretching far around the cluster.
That blue glow is a reflection nebula. It doesn't emit its own light. It's a cloud of fine dust reflecting the light of the cluster's hot blue stars, which happen to be drifting through it.
When and where
- Position: RA 3h 47m, Dec +24° 07′, in Taurus, northwest of Orion.
- Season: best from October to March in the evening, highest around midnight in November and early evening in January.
- Height: high in the sky from northern mid-latitudes; visible but lower from the southern hemisphere.
Framing
The cluster and its brightest nebulosity span about 110′, close to 2°.
| Focal length (APS-C sensor) | What you get |
|---|---|
| 135–250 mm | The cluster in a wide field; room for the surrounding dust under dark skies |
| 400–600 mm | The classic framing: the cluster filling most of the frame |
| 800 mm and up | Close-ups of the nebulosity around Merope and Maia |
Filters: broadband only
Reflection nebulae shine with reflected starlight across the whole spectrum, mostly blue. There is no emission line to isolate, so:
- Don't use narrowband or dual-band filters. They block nearly all of the nebula's light.
- Use a UV/IR cut or no filter with a colour camera; LRGB with a mono camera, with plenty of luminance.
- Light-pollution filters tend to dull the blue. From a bright site, a longer integration under a dark, moonless sky beats a filter.
Dark skies matter
The bright nebulosity around Merope shows up from the suburbs, but the faint dust that surrounds the cluster only appears from a dark site with no moon. Even then it takes hours of integration. Plan this target for the week around new moon and the best transparency you can get. See Astrophotography and the moon.
Taming the bright stars
The Pleiades' stars are bright enough to cause problems:
- Halos and reflections. Some filters and uncoated optics add rings around bright stars. A refractor with good coatings and a plain UV/IR cut gives the cleanest stars.
- Diffraction spikes. A Newtonian's secondary vanes add spikes. Some imagers love them on this target; others prefer a refractor.
- Saturation. Keep subs moderate (60–180 s with a cooled camera) so the star colours don't all burn to white, and blend a few short subs if needed.
Example rigs
RigTonight ranks broadband targets like the Pleiades lower on moonlit nights, and its filter advice tells you to take a dual-band filter out for them. Check tonight's moon and the Pleiades' dark hours on the Tonight tab.