Goclenius is a 55km crater located within the 600 x 500km Sea of Fertility, Mare Fecunditatis.
The irregularly shaped mare resembles the shape of a diamond, with the distinctive form of 133km Langrenus on the southeast straight edge and Goclenius in a similar position on the southwest straight.
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Goclenius is an ancient crater, the floor of which has been flooded by lava.
It sits within a region of similar company: 75km Gutenberg to the northwest, 41km Magelhaens to the southwest and 76km Colombo to the south.
All of them and many of their labelled satellites have lava-filled floors.
Quick facts
- Size: 55km
- Longitude/latitude: 45° E, 10.1° S
- Age: Around 3.9 billion years
- Best time to see: Four days after new Moon or three days after full Moon
- Minimum equipment: 50mm telescope
Observing crater Goclenius
There’s some exquisitely fine detail to be seen when observing cracter Goclenius.
The remaining ring surrounding Goclenius’s flat floor is more or less continuous with a few gently smoothed terraces.
It loses some cohesion towards the north, although never fully opens to the surrounding mare.
Compare it with the wonderful form of Gutenberg, which has a well-defined rim all the way around except at the east where it has been completely overlaid by 28km Gutenberg E, which has removed any trace of the original Gutenberg rim section.
Gutenberg E is itself open, with rim gaps in the southwest and southeast.
Together, these create an open path to the flat lava surface of Mare Fecunditatis to the east, both Gutenberg and Gutenberg E being flooded.
Back to Goclenius, and the crater’s rim also appears to have a pinch-point to the south.
This seems to be a continuous portion of the rim, but at certain illuminations is exaggerated into looking as if there’s a gap.
Goclenius is around 2km deep, its flat lava floor covered in shallow hills and a beautifully delicate crisscrossing rille system.
Many of these rilles are too fine for all but the largest scopes or high-resolution setups, but even with those will require decent seeing to reveal well.
One notable exception is the largest rille that runs northwest to southeast.
This has a width of just over 1km and appears to pass through Goclienius’s closest approximation to a central mountain complex –although, with a height of around 350–400m, ‘mountain’ is stretching the description.
The rille passes up through the northwest rim section, delicately depressing the rim as it does so.
It then continues across the western floor of Mare Fecunditatis, clipping the eastern side of Gutenberg E, before continuing on its way and petering out just east of 31km Gutenberg G.
This rille is part of the Rimae Goclenius complex, other less obvious members running parallel to the most prominent one described, slightly east of it up the floor of Mare Fecunditatis.
As ever, these rilles are best seen when the region lighting is oblique – in other words, when the lunar terminator is nearby.
Unlike its immediate neighbours, Goclenius looks to be separated from the shores of Mare Fecunditatis, appearing almost framed by a continuous region of surrounding flat mare lava.
A few local elevations appear around it, notably to the northeast and southeast, all adding to a wonderful part of the Moon to explore when the Sun is low in its sky.
If you've been observing or photographing Goclenius, share your experiences and images with us by emailing contactus@skyatnightmagazine.com
