Labelling Conventions Home

If you move the mouse pointer over most of my lunar images you will see what is called a mouseover.  In this case it consists of the same image with labels telling you the names of various features.  I have a few conventions that I use fairly consistently, but these have evolved as I have developed this site so some early pictures may not comply fully.  There are exceptions but when those are intentional, I say so in the accompanying text.

Single-letter names of craters.

Generally craters on the Moon are named after prominent scientists who, in some way, warrant immortalising in this way.  However, there are so many craters that all do not carry such names but instead are named by adding an upper-case letter to the name of a nearby crater.  Generally I do not include the main part of such a name and give only the letter.  However, if it seems to me that there could be doubt as to which main crater the name relates (normally the closest but not always), then I have joined the two with a dotted line.  If the "parent" of the lettered crater is not itself shown (it may not be on the image), then I show the complete name.  Slowly the lettered names are being replaced by simple names.  This can cause me problems as, generally, it is the larger craters which are being renamed and often these are closer to their parent craters than other lettered craters of the same family.  An example is shown on one of my pictures of  Mare Undarum.  Azout A and B have been renamed (van Albada and Krogh respectively) but are between Azout and Azout C, so a dotted line is needed to emphasise that C is not van Albada C or Krogh C, but drawing it straight would pass through van Albada.

Unofficial names

To be official, a name must be approved by the International Astronomical Union (IAU).  However many features have not yet received an official name but have been given unofficial names by various people.  If I use such a name then I put that name in italics.

Formal vs. common names

Features other than craters (such as maria, mountain chains, and rilles) have names which begin with the Latin word for the type of feature it is; for example, Mare for the dark areas (once thought to be seas), Montes for mountain chains (the plural of Mons for mountain).  Generally I use the formal name in the mouseover but the common version in the text.

Positioning of names

Generally the first letter of the name in placed on, or very close to, the feature to which it refers.  If the feature is near the right-hand side of the picture, there may not be room to write it that way.  In this case, if I feel that the designation is not clear, I point to the feature with an arrow.


The colour of a name (black or white) has no significance.  I use which ever I think shows most clearly.


Sometimes I am uncertain that I have correctly identified a feature.  In this case I join the name to the feature with a dotted arrow

Compass directions

Most of my pictures have north towards the top.  However I align my camera with the telescope, which itself is polar aligned (sometimes rather roughly), so the Moon, whose axis is not parallel to the Earth's axis, may not appear exactly north up. I provide markers on most pictures to indicate the direction of north.

Scale Markers

I try to provide scale markers on my pictures, generally 100 Km north and either east or west.  These must be taken as approximate for several reasons.  The way we see the Moon from Earth is what map makers call Orthographic Projection and both the directions and the scale varies with the part of the Moon one is looking at.  For example in a picture of the Full Moon with the north pole exactly above the south pole, north will only be directly upwards along the lunar equator, and down the central meridian.  The further one goes away from these lines, the more the direction of north will tilt over.  Close to the limb, the direction of north will generally be parallel to the limb.  The directions of east and west are more nearly constant but twist slightly when libration tips one or other pole towards us.  However, scale alters dramatically as one approaches the limbs, and the length of a 100-km arrow falls to zero on the limb.

I determine the directions from maps of the Moon, in particular Rükl's Atlas of the Moon (Sky Publishing).  I determine the lengths of the markers by using the distance tool in the Virtual Moon Atlas.

Age of the Moon

In the text accompanying my pictures I give the age of the Moon at the time.  There is more than one method of calculating this (see the bottom of  this page for details).  I use the method based on the Sun-Earth-Moon angle.  The age, however, is not the key to the appearance of a feature which depends also on the libration at the time.  A better indication is the colongitude which is the lunar longitude of the sunrise terminator measured westward from the prime meridian (which runs down the centre of the visible face of the Moon in its mean position).  With more than 400 images on this site, I think it unlikely I will ever add this information retrospectively to all my images, but I will do so if I update any page.

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