The Moon’s surface is covered in many impressive valleys. Some are true geological valleys, while others have been formed by impactors breaking apart before crashing down onto the Moon’s surface.
When this occurs, it forms a crater chain that in some cases is structured enough to be recognised as a valley.
A classic example is the spectacular form of Vallis Rheita.
Vallis Capella also appears to fall under this category, a spear-shaped rift that passes through the 50km crater Capella, located immediately to the north of 350km Mare Nectaris.
Fact about Vallis Capella
- Type: Valley
- Size: 11km x 110km
- Longitude/latitude: 35° E, 7.4° S
- Age: Older than 3.9 billion years
- Best time to see: Five days after new Moon or four days after full Moon
- Minimum equipment: 100mm telescope
The valley is distinctive in shape, widest at the northwest end where its initial impact crater is 16.5km across.
Subsequent impacts get ever smaller until the valley peters out to the southeast of Capella with craterlets barely 3km in diameter.
Looking at wider photographs of the area may suggest the valley continues further to the southeast, but on closer inspection this appears to be a visually suggestive chance alignment of gaps within the local highland region and it’s unlikely that anything persists from the point 30km northwest of 8.4km Capella B.
Vallis Capella doesn’t appear to be precisely on target with respect to Capella either, with the main form of the valley running through the northeast section of the crater, passing between the crater’s rim and its distinctive central mountain.
Vallis Capella has a depth of 3.5km, its central mountain rising to a height of around 1.2km above its floor.
Actually, there’s not much floor to speak of, as Vallis Capella's sharp but irregular rim terraces reach into the centre of the crater then rise to the central peak before any significant floor area can be formed.
To the east of Vallis Capella is a region containing a number of similar-sized craters.
Several of these are interesting because they are on the ALPO (Association of Lunar and Planetary Observers) list of bright ray craters.
These include Capella A (11.8km), Capella D (8km), Capella E (14.3km) and Capella G (11km), as well as Capella J (8.9km) which is located south of Capella.
To the immediate west of Capella is 41km Isidorus, marginally smaller than Capella but better defined. Isidorus has steep inner slopes showing no terracing.
The rim walls lead down to a flat floor and there’s no central mountain complex.
The main features on Isidorus’s floor are two craterlets: 9.9km Isidorus A which overlaps a shallow and unnamed 5.3km craterlet to its immediate north.
When observing the region, don’t forget to head a little to the northeast, beyond the similar-sized crater field immediately east of Capella.
Here runs a set of northwest-to-southeast rilles known as Rimae Gutenberg after 75km Gutenberg, the first large crater reached by travelling due east from Capella.
The rilles run for around 330km but are narrow, at only 2km across.
To see them, you’ll need a large telescope around 300mm diameter or a high-resolution imaging setup.
A nearby terminator and good seeing are a real bonus when trying to pick out hairline features like this too.
If you've observed Vallis Capella or captured an image of it, get in touch by emailing contactus@skyatnightmagazine.com
