2005 11 12 – Bullialdus – central peak notes

Sketch created scopeside with Rite in the Rain paper and charcoal.

Complex craters are a magnificent sight to see, especially at higher magnifications where you can really study the terraced walls and try your best to pull detail out of their central peaks. They are formed by bolides (large meteors, sometimes exploding) impacting the lunar surface. When there is enough force from the impact, the reaction of the impact causes material to rebound back up and then fall crating terraced walls and central peaks. Have you ever seen a photograph of a drop of water as it hits a puddle? Or how about a ball that bounces in a thick patch of mud? Material is brought up from below the surface of the Moon and form the central peaks, providing insight to geological composition.

Bullialdus is one of my favorite complex craters, located in Mare Nubium. Although views along the terminator are striking, I prefer to study complex craters a full lunation before or after Bullialdus reaches the terminator. Viewing closer to the terminator, though, will provide better views of the ridges as well as secondary craters. It is ~63 km wide/3.5 km deep and is from the Eratosthenian to late Imbrian in stratigraphic age or about 3 – 3.6 billions years old. (Stratigraphy Scale)

Getting back to central peaks, spectrography from Mauna Kea Observatory revealed that the composition appear to be made of noritic material from 6 km below the lunar surface.


The spectrum for Bullialdus’ central peak exhibits a strong symmetric absorption band implying the material excavated was relatively crystalline (as opposed to highly brecciated or glass-rich as is commonly observed elsewhere, such as at Apollo 16). The band center occurs near 0.93 and indicates low-Ca pyroxene is the dominant mafic component. This is the deepest material excavated at Bullialdus (from 6 km) and is of a distinctly noritic composition.

Bullialdus - LROC Wide Angle Camera View of Bullialdus crater (60 km diameter). Credit: NASA/GSFC/Arizona State University

Excerpt from NASA – Central Peak of Bullialdus Crater:

… Spectroscopic observations of Bullialdus using terrestrial telescopes showed that Bullialdus is compositionally distinct from the surrounding region. Later studies using Clementine multispectral data indicated that there are several rock types exposed on the floor of the crater. Lunar scientists who have studied Bullialdus proposed that the impact excavated mafic materials from great depth…

Amateur astronomer, Rick Evans, has been doing some very interesting geologic studies of the Moon involving photoclinometry, spectroscopy, and multispectral imaging. This link highlights Bullialdus and spectral maps of lunar topography using Octave. Rick Evans’ Amateur Lunar Photoclinometry, Spectroscopy, and Astrophotography

Observation sketch by Erika Rix 2005


Rukl map: 53 Bullialdus
Virtual Moon Atlas
The Modern Moon: A Personal View, by Chuck Wood, pgs 148-149


~ by Erika Rix on December 4, 2010.

One Response to “2005 11 12 – Bullialdus – central peak notes”

  1. […] There’s just something about Bullialdus that keeps me coming back. This is my third time sketching it along with its two companion craters. For more details about this complex crater, have a look into my report on Dec 4th, 2010 . […]

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