Moon Close Up

A section of the First Quarter Moon, taken as a video with my narrow field planetary camera on 17th June 2021. I took 500 video frames at 0.0094 seconds each and stacked the best 10%. The two large adjoining dark regions are Mare Seranitatis (left) and Mare Tranquilitatis (right). They are plains which were flooded by lava from ancient volcanic eruptions.

Leading down from Mare Tranquilitatis is a prominent dark diagonal line, a bit like a forward slash “/”. This is a rille known as Rima Ariadaeus, a 300 km long fault line in the lunar surface.


At our public nights, I sometimes get asked how the term “First Quarter Moon” originated. It’s a fair question, usually from eager young children who see it as a half moon, not a quarter. I tell them “Yes, it represents half of the Moon we see – but only a quarter of the entire Moon”.

The next question after that – from the really astute kids – is: “Then why is the ‘Full Moon’ not named a ‘Half Moon’?”, at which point I usually tell them it is a Full Half Moon and move on to some other topic as fast as I can. 🤣

Here is a lunar cycle:

BY-SA 3.0, via Wikimedia Commons

Thanks for having a look 🙃

Telescope & Imaging Details

Telescope:SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Optics:Field flattener; no filter.
Mount & Guiding:SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Imaging camera: ZWO ASI 290 (CMOS 6.46mm, 2.1 Mpx).
Software:Control: Cartes du Ciel, ASCOM, EQMOD, PHD2. Imaging: SharpCap, Gimp.
Observatory:34° South.

Images © Roger Powell

I’m one of the founder members of Macarthur Astronomical Society and current webmaster.

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