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The Cave Nebula (Sharpless 2-155) photographed from Lakeway, Texas with a ZWO Seestar S50 Pro: faint reddish-brown clouds across a dense star field, with a darker hollow near the middle bordered by a brighter red rim on its right.

Sharpless 2-155 — The Cave Nebula

A living entry: a faint target, and only the first hour and a half

  • TelescopeEva (ZWO Seestar S50 Pro)
  • Integration100 minutes
  • LocationLakeway, TX
  • SkyBortle 6
  • CapturedNov 5, 2026
  • PhotoKyle Eberly · © 2026
  • ProcessingOne night, November 5, shot by the telescope robot in the first two hours of darkness: 200 thirty-second exposures through the dual-band filter, 1.7 hours. This is a faint nebula and 1.7 hours only starts to show it; the cave is visible as a hollow with a brighter rim, and the rest is close to the noise. The square is cropped from the middle of the frame, which also leaves out a satellite trail near the bottom edge. Processed from the telescope’s 16-bit stack with the same custom Python pipeline as the rest of this journal.

What you're looking at

The Cave Nebula is a cloud of gas and dust about 2,400 light-years away in Cepheus, part of the same stretch of the Milky Way as the Elephant’s Trunk.

It is lit from inside its edge by hot young stars of a group called Cepheus OB3. Their light makes the gas glow, and the darker dust in front of that glow gives the cloud the look of a cave mouth.

The bright rim is the boundary where starlight is eating into the cold cloud; like the Cone and the Elephant’s Trunk, it is a place where new stars may be forming.

The lesson

Some targets show up in an hour. This one didn’t: after 1.7 hours, the cave is just visible.

Faint isn’t the same as empty. The structure is there, and the noise falls each time more hours go into the stack.

Judge a slow project by the trend, not the first snapshot.

One photo. One lesson.

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Object data

Catalog
Sharpless 2-155 · Caldwell 9
Constellation
Cepheus
Type
Emission and dark nebula
Distance
~2,400 light-years
Lit by
Young hot stars of the Cepheus OB3 association
Status
LIVING ENTRY — 1.7 hours from one night, deepening this week

More from the journal

NGC 2264 photographed from Lakeway, Texas with a ZWO Seestar S50, shown with south up: the small dark Cone Nebula sits in red glowing gas at the top, its tip pointing down toward the cluster, a loose triangle of stars and red nebula widens below it like a tree, and the bright blue-white star S Monocerotis sits at the base with a pale blue haze beside it.
NGC 2264
Part of the California Nebula (NGC 1499) photographed from Lakeway, Texas with a ZWO Seestar S50 Pro: a broad band of red glowing hydrogen crossing the frame diagonally from lower left to upper right, brighter along a ridge near its middle, against a dark star field.
NGC 1499
A tall widefield view of Orion’s sword photographed from Lakeway, Texas with a ZWO Seestar S50 Pro: the red and white Orion Nebula with its small round companion M43 in the lower half, the faint Running Man Nebula and the star cluster NGC 1981 above it, and the bright star Iota Orionis below.
The Orion Nebula