Andromeda Galaxy (M31) in LHaRGB, California

Andromeda Galaxy (M31) in LHaRGB
California   –   September 18, 2023
— Ralph Paonessa
QSI 683wsg-8 -20° C   *   Takahashi FSQ-106EDX III refractor + 0.73X   *   f/3.7

LHaRGB mosaic of two panels captured during 4 nights in September 2022 and 4 nights in September 2023 from Bortle 2 dark skies and processed in PixInsight, with final adjustments in Lightroom Classic.

This version includes hydrogen-alpha (Ha) data acquired through a narrowband (5 nm) Ha filter. Ha reveals more of the deep red photons emitted by active star-forming regions in Andromeda's spiral arms. (For a version without Ha, see the LRGB version.)

To handle the large dynamic range of the bright galactic cores, I used HDR combination of Luminance at 600 sec and 90 sec before creating the LRGB composite.

The brown streaks are clouds of interstellar dust throughout the arms. The blue areas consist of hot, young stars with their characteristic blue emission.

The color balance was determined spectrophotometrically in PixInsight.

Combined exposure 18 hr total:

  • Lum 15 x 10 min, 18 x 8 min, 34 x 1.5 min = 5.7 hr
  • H-alpha 6 x 10 min, 6 x 15 min = 2.5 hr
  • Red 13 x 10 min, 8 x 8 min = 3.3 hr
  • Green 13 x 10 min, 8 x 8 min = 3.3 hr
  • Blue 13 x 10 min, 8 x 8 min = 3.3 hr

The Andromeda Galaxy is cataloged as Messier 31 and NGC 224. It is 2.5 million light years from the Milky Way in our Local Group of Galaxies. It is classified as a barred spiral. Recent studies suggest that it's mass is similar to that of our Milky Way.

Despite our distance from M31, the inexorable pull of gravity is pulling us together and the galaxies are expected to merge in 4.5 billion years. Stay tuned.

The satellite galaxy M110 (NGC 205), a dwarf elliptical galaxy, is easily seen outside the main disk below and right of Andromeda's core. A vague tidal tail of stars is visible between these galaxies. Dwarf elliptical satellite M32 (NGC 221) appears to left of M31's core. It is thought to be in the foreground compared to Andromeda's disk.

Photo ID: M31 LHaRGB