The Andromeda Galaxy: core, dust lanes and a companion

What you are looking at

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Distance

2.5 million light-years

This picture spans

55,000 light-years; the galaxy's disc is about 2.5 times wider

The light left

2.5 million years ago

For scale

Each pixel is about 19 light-years across

For photographers

A 3 x 2 mosaic joined to the deep core field; each outline is one sensor frame, with frames kept of frames taken.

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Exposures

Panels: 30 s at ISO 3200. Core: 20 s at ISO 3200

Frames

66 panel frames taken, 23 kept: 11.5 minutes. 43 lost to cloud. The core adds 38 frames, 12.7 minutes

Mosaic

Each panel plate-solved, then all solved jointly on shared stars (0.4 to 0.6 arcsec). One brightness scale per panel from shared stars; backgrounds matched with a plane per panel; feathered

Sampling

1.552 arcsec per pixel. Stars 4.1 arcsec wide

Field

74.8 x 42.5 arcmin, cropped level from the mosaic; one frame is 38.8 x 25.9

When

4 October 2026, in the small hours, over 67 minutes. 72 to 61 degrees up, Moon up, cloud passing

Honest limits

Outside the core field the panels hold 1 to 14 percent of the core's depth, and are shown in grey because their colour zero is not trusted. A map, not a measurement

Calibration

Flat from 26 twilight-sky frames, its large-scale shape from cloud-lit frames; the dust in it checked against this hour's frames. No darks

Finish

Black 53 and white 226 of 255, gamma 1.2, S-curve 0.3. Dark sky made neutral and smoothed (bilateral, 3.5 px)

Telescope

Celestron 8SE Schmidt-Cassegrain with dew shield: 203 mm aperture, 2,084 mm focal length (measured by plate solve), f/10.3

Camera

Sony a6000, stock, at prime focus: APS-C 23.5 x 15.6 mm, 6000 x 4000, 3.9 micron pixels, RAW

Mount

Sky-Watcher EQ6-R, unguided. Set down 27 degrees off the pole; both axes driven from a pointing model fitted to plate solves. Residual drift about 0.1 arcsec per second