Calibrated Crater Sequence Images

Four areas are available:

  • Mare Humorum
  • Clavius
  • Ptolemaeus
  • Mare Nectaris/Fracastorius

All of these calibrated crater sequence images were made using the Bowker & Hughes Lunar Orbiter atlas scaled images, sizes measured to the nearest 1/128th of an inch using steel machinist’s scale and 8x magnifying loupe.

The sizes are accurate to +-100meters on craterlets <4km diameter, +-200 meters otherwise. Note: Imaging artifacts (over/underexposure, variable degrees of focus) on the CLA images used may make some craterlets appear larger or smaller than they appear on the higher resolution Orbiter images.

Some craterlets are not resolved on the images except as undifferentiated ‘spots’. Nevertheless, their positions are accurately indicated. I tried to measure only craters which are simple in form and not sub-resolution multiples or ruined irregular craterlets.

Mare Humorum

A calibrated image of the lunar crater Mare Humor. Part of the series of four calibrated crater sequence images.
(Credit: Whitepeak Observatory) Mare Humorum

Mare Nectaris/Fracastorius

A calibrated sequence image of the Mare Nectaris/Fracastorius.
(Credit: Whitepeak Observatory) Mare Nectaris/Fracastorius


A calibrated sequence image of the lunar crater Ptolemaeus.
(Credit: Whitepeak Observatory) Ptolemaeus


A calibrated sequence image of the lunar crater Clavius.
(Credit: Whitepeak Observatory) Clavius


These charts can be used to assess both the state of seeing and available resolution during visual observations.

*For “best optimal seeing” and/or ground resolution assessment*

Craterlet size resolvable as a craterlet/depression, not an undifferentiated spot:

3.8-4km = ~2″ arc best seeing/resolution
2.8-3km = ~1.5″
1.8-2km = ~1.0″
1.75-1.5km = 0.8″
1.3km = 0.7″

The above is based upon mean lunar diameter where 1.86km = 1.0″arc. Resolution of craterlets as undifferentiated spots will be higher by a factor of at least 2 from the above figures, depending on local contrast.

Written by CityAstronomy.com

We hope you enjoy these articles about space and astronomy.
Let us know if you have any new topics you would like us to cover, and we'll do our best to add them to our future article list.

Sign up for our email notifications to be alerted once new articles are published.

You May Also Like

The article you just read is part of the City Astronomy “Astronomy” collection. If you enjoyed it we think you'll love these other recommendations:

A Gibbous Moon in a dark night sky.

Discover why this lesser known phase called the Gibbous Moon is a great time to observe the lunar surface.

A shooting star racing across the sky at night over a forest canopy

In this article we explain what a Shooting star is and where they come from.

A picture of six images of the Moon in different colors.

Find out what color the Moon REALLY is and why it can look different from night to night.