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Lunar Calculator by Alister Ling
Software for lunar observers and others interested in the Moon.

Reviewed by Duane Dunkerson

Three leading software programs for telescopic lunar observers are Lunar Calculator, Virtual Moon Atlas, and Lunar Map Pro. Virtual Moon Atlas is available at no charge. Lunar Map Pro costs ninety dollars. A cut back version, called the Basic, can be had for twenty-five dollars, a recent dramatic drop in price from the previous forty dollars. Lunar Map Pro in either version is a commercial product. For twenty dollars, one can obtain the Lunar Calculator. This latter program is a personal project being done by Alister Ling. The twenty dollars supports his ongoing work. He also writes for Astronomy magazine and is active in the Royal Astronomical Society of Canada, Edmonton Centre.

The Virtual Moon Atlas (VMA) and the Lunar Map Pro (LMP) use USGS based maps. Lunar Calculator (LC) can be used with Clementine photos to match up with the area of the Moon you have selected. The Clementine photos are on a NASA CD, Vol 15 Clementine LDIM, available separately, that can be integrated to accompany the LC program.

The VMA is still in development. I have used two versions of it and I have found it doesn't interact well with my computer. Apart from that, the representations VMA makes of the lunar surface look much like LMP. The VMA does have some features similar to LMP.

LMP, for ninety dollars, has an interactive geology map, librations, surface feature measurement, and raster-based and vector-based additional maps. Sunrise and sunset for all named formations are available. An ephemeris lists values of interest. 7,600 lunar features are in the database. In most respects the Basic version apes the higher priced version except that 1062 features are present. Sunrise and sunset by feature is also lacking in the Basic.

For both the LMP and the VMA my main dissatisfaction with them is that the depiction of the Moon is not as I see it with my telescope, a 4.7 inch refractor. This dissatisfaction is coupled with my desire to know what it is that I can observe and not what I will observe. I will do the viewing. I don't need nor want a program that purports to be the a priori resultant of an observing session always held in abeyance.

With the Lunar Calculator by Mr. Ling I am enabled to know where the terminator will be and what features it reveals of the surface as it passes along relative to my latitude and longitude. Mr. Ling's provision for inclusion of the Clementine imagery is at times of benefit to me but the photographs are variable as to when they were taken in relation to favorable sun angle. Too many for me lack appropriate definition. I mostly use the "wire" view of LC. In this view craters are thin lines to indicate their rims. Also in lined form are major plains and maria. This wire view is part of the main screen.

The main screen affords access to change of the time for an observation. (The free demo version of Lunar Calculator has as its primary limit that the time of observation will not go back or foward in time by more than a month.) Co-longitude is read out. Values for sunrise terminator and solar latitude on the Moon are listed. Per cent of illumination, age of the Moon, libration for topocentric or geocentric, Moon position in RA and Dec with altitude and azimuth too - all are in a panel to the left of the wire view in the main screen. Also in the left panel are magnification factors of 2.25, 3.80 and 9 or reduction of magnification by 1/2, 1/3.50 and 1/10. These values can be changed via the Edit menu. You can box an area with the mouse for magnification or use a magnification icon.

Crater labels can be added to the view. A search feature, via a drop-down menu, allows for finding catena, crater, dorsum, fossa, lacus, landing sites, mare, mons, montes, promontorium, rima, rimae, rupes, sinus, and vallis. All are listed with latitude and longitude and length. The cursor moves to where the found object is located. In the wire view you may not see anything there for other than craters. You do know, though, where it is and you will, then, see it by means of your telescope. You don't receive notice, as it were, of what you are expected to see. Neither domes nor rays are listed for search- though you may manually add domes.

Your view can be flipped vertically and/or horizontally. Magnification can go to 1000X. As you move the cursor over a feature like a crater as small as three miles, its name and size, and associated Rukl chart are read out. The free demo version shows lunar features down to 3 km in size as well as the Clementine imagery to 5 km per pixel. Concurrently with this information is continuous readout of latitude and longitude and solar altitude and azimuth. Sunrise and sunset in a near period is shown to the minute for cursor location. All this is accomplished for 7,400 features.

You move about the lunar surface without a scroll bar. You center an object and then center another that is in the direction you wish to go. Right click to center or identify the feature at the cursor location. A pull-down menu reveals an extensive ephemeris including orbital elements of the Moon. Another tab of this same pull-down gives perigee and apogee data and times for new and full Moon. Another pull-down supplies future dates for co-longitude and excellent libration graphs.

If you are a lunar observer, you know the significance and the servicability of such a libration graph. If you are yet to be a lunar observer, the libration graph and much else of the Lunar Calculator can be of great use to you. For one and all Mr. Ling's Lunar Calculator is a splendid storehouse of selenographic delight. I highly recommend the Lunar Calculator. The Lunar Calculator website can be found at http://www3.telus.net/public/aling/lunarcal/lunarcal.htm.