The Hills of Marius

[astroavani]

Anyone who looks at this photo and sees the beauty of Marius crater and its surroundings doesn't even notice the Herodotus Omega dome, in fact most of us put deep sky observation on hold when lunar glare intrudes on dark skies. But why, instead of limiting your telescope, don't you take the opportunity to observe the Moon itself? The waxing moon phase is a good time to familiarize yourself with one of our satellite's most evocative features: its domes.
Many of the Moon's characteristic landscapes were created by the impact. Craters, rays, mountain ranges, seas and basins abound. Lunar domes are different. They formed as a result of the Moon's own internal volcanism. Similar to shield volcanoes in Iceland and Hawaii (including Mauna Kea on the Big Island) and Olympus Mons on Mars, they form when highly fluid lava erupts through a central caldera on the surface. They are almost all low-explosive, unlike their cousins, Earth's more violent stratovolcanoes that grab headlines.
Like sheet after sheet piled up after lava seeps beneath the crust, a dome slowly builds up over time, forming a wide, gently sloping mound resembling a warrior's shield with a raised center and lower edge. Shield volcanoes can be small, like the Icelandic and lunar varieties, or wide and huge, like Olympus Mons. A typical lunar dome measures between 5 and 7.5 miles (8-12 km) in diameter with a peak or caldera ~900 feet (~300 meters) high. The slopes are very gentle with only a few degrees.
The Marius Hills region was volcanically very active in the past and contains numerous volcanic features, including winding riles north of Marius, as well as numerous hills that are actually domes and can be seen quite clearly in my photo.
In this region there is also a well, probably a cave that was identified for the first time in images from the SELENE/Kaguya probe, which I already described in another post on AstroBin, and can be found here: https://www.astrobin .com/322549/?q=Marius.%20astroavani
More than 300 lunar domes are known, many visible in amateur telescopes with apertures from 3 inches upwards. There are two key requirements for good observation of a dome - good atmospheric stability (seeing) and observing the dome near the terminator shortly after lunar sunrise or before sunset as was done in this photo with the Domes of Marius and Herodotus Omega, this one being particularly easy to identify with good seeing even with a small telescope, as it is 10 km wide and has a hole in the center
Most domes are subtle, low-contrast features that become scorching with poor seeing. Low light casts long shadows on crater peaks and rims, and makes their gently sloping shapes have the best contrast. You will be more excited when you can see the caldera. When you see the dome hole, you really see a dome for what it is: a formerly active volcano in the days when the moon still had intense geological activity.
The next time you go to observe the Moon near the terminator, do not forget to pay attention to those rounded shapes that easily stand out in relation to the surrounding terrain, do not forget that one day the Moon had its active volcanoes and even today it is far away of being the dead world that many believe.

[RobertI]

Superb picture of the Marius domes and a fascinating read. 👍

[maw lod qan]

Thank you sir for the incredible image and excellent information!

[Hawksmoor]

Fabulous image!

[bosun21]

Great image, and you have nudged me to start some serious lunar work again.

[astroavani]

On 6/20/2023 at 6:54 AM, bosun21 said:

Great image, and you have nudged me to start some serious lunar work again.

It's great to know that!