The Moon at last quarter

4 October 2026 · 41 percent lit

Along the line between day and night the Sun is setting, so every crater rim and mountain throws a long shadow. That is why the detail is richest there.

What you are looking at

The Moon at last quarter, with its parts named, a scale bar and north marked

Swipe sideways to see the rest. Tap the picture for full size.

Distance: 365,000 km, measured from its size in this picture
Across: 3,475 km
Light took: 1.2 seconds
For scale: Copernicus is 93 km wide; Clavius, 231 km

For photographers

Lucky imaging over a 2 x 2 mosaic in morning twilight, with cloud about.

Exposures: 1/60 s at ISO 100
Frames: 78 taken over five aims in two passes, 39 kept. 17 saw only the night side; the rest were lost to cloud
Lucky imaging: Frames registered on the lunar surface itself (12,000 matched features, 0.8 px). In each patch only the sharpest 30 percent of the clear frames are averaged
Restoration: Blur measured at the limb: 1.8 arcsec. Wiener and Richardson-Lucy with the gain capped at 3 x and held at the limb. No ringing found at limb, cusps or terminator
Sampling: 0.388 arcsec per pixel, the sensor's own: 0.7 km per pixel on the Moon
Field: Disc 32.7 arcmin across, taller than one 38.8 x 25.9 frame: a 2 x 2 mosaic and a centre frame. One panel saw only the night side
When: 4 October 2026, in morning twilight, over half an hour. 62 to 70 degrees up
Calibration: Flat from 7 twilight-sky frames: corners at 74 percent of the centre, 340 dust shadows divided out. Cloud glow fitted and subtracted per frame
Orientation: Lunar north up, from 17 craters of known position (32.2 degrees from the sensor's way up)
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

© 2026 Brad Gessler · Celestron 8SE (8 inch, 2,080 mm) and Sony a6000 on an EQ6-R · San Francisco Bay Area · 4 October 2026
Capture and mount: Observatory (Elixir on a Raspberry Pi 3). Stacking: numpy, OpenCV, rawpy. Plate solving: astrometry.net. Stacked from the camera's RAW frames. Nothing generated.