M31 — Andromeda in HDR

It isn't alone in the frame:

• M32, the bright, compact little elliptical sitting right on the edge of the disk, just left of the core. It's tiny and unusually dense, and one leading idea is that it's the stripped core of a much bigger galaxy that M31 tore apart a couple of billion years ago.
• M110, the larger, fainter oval below and to the right. It's a dwarf galaxy with a surprising amount of dust and some younger stars.

Andromeda is also heading our way at around 110 km/s. For decades the textbook answer was a guaranteed collision with the Milky Way in about 4–5 billion years. Newer studies put it closer to a coin flip over the next 10 billion years.

When this light left Andromeda

M31 is about 2.5 million light-years away, so the light in this image left around 2.5 million years ago, right at the start of the Pleistocene and the ice-age cycles. On Earth at that moment:

• The earliest members of our genus, Homo, had only just appeared in East Africa.
• The first stone tools, the Oldowan choppers and flakes, were brand new technology.
• Australopithecus and the big-jawed Paranthropus still walked the same landscapes.
• The Isthmus of Panama had recently closed, and animals were streaming between North and South America in the Great American Interchange.

Compared with my M101 and M106 shots, which are 20+ million years old, this light is practically fresh. It still left before anyone had made a fire.

The capture

All shot from my Bortle 6 backyard over four nights in early October 2026 with the William Optics RedCat 51 (250 mm, f/4.9), ZWO ASI2600MC Air at gain 100 and −10 °C, on the ZWO AM5. That works out to about 3.1″ per pixel and a 5.4° × 3.6° field, wide enough for the whole galaxy plus both companions.

Calibration: 75 biases, 50 flats with 50 matching flat-darks, and 50 darks for each exposure length.

Processing

• WBPP in PixInsight, building a separate master for each exposure length (drizzled 1×)
• HDRComposition to merge the 60s, 20s and 5s masters into one linear image
• Finished in PixInsight with my usual pipeline

The raw frames for all three exposure sets are in the linked M31_V2 integration set.

Gear

• Redcat RigPrimary

  3 items

  • Camera

    ZWO ASI2600MC Air

    Details
  • Mount

    ZWO AM5N

    Details
  • Telescope / OTA

    William Optics RedCat 51

    Details