The Javascript Lunar Eclipse Explorer is a handy tool for lunar eclipse predictions on the web. However, not everyone has Internet access all the time. Jean Meeus has written a stand-alone program that performs calculations similar to the Javascript Explorer. The program is called LUNECJM and it runs on the Windows PC platform. LUNECJM can make the following calculations:
1. List all lunar eclipses over a given time period
2. List all lunar eclipses visible from a given place
3. Table of data for a given lunar eclipse
4. Draw diagram for a given lunar eclipse
5. List all lunar eclipses in a given saros series
There are actually two components to the program.
The first is the executable file LUNECJM.EXE and the second is the eclipse data file LUNECJM.TXT used by the program.
The two files along with a ReadMe file can be downloaded from a ZIP file:
Download LUNECJM.zip (1,580,471 bytes)
Jean Meeus gives the following instructions for using program LUNECJM. These are also included in the ReadMe.txt file in LUNECJM.zip.
LUNECJM contains the elements of all lunar eclipses, including penumbral ones, taking place from the year -1999 till the year 4000. The number of these eclipses is 14459. The years are counted astronomically: the year preceding the year +1 is called zero, and the year preceding the latter is the year -1. The year which the historians call 585 BC is actually the year -584.
Before October 1582, the Julian Calendar is used. After October 1582 the Gregorian Calendar is used. The dates of the eclipses are given in the format year/month/day. For instance, 2007 Aug 28 means the 28th of August of the year 2007.
The radii of penumbra and umbra, at the Moon's distance, have been calculated with the 'French' rule, that has been in use at the Bureau des Longitudes, Paris, since 1951. The French astronomer Danjon has shown that, even if the traditional rule of 1/50 for the increase were correct for the umbra, it would be incorrect for the penumbra.
The Earth's shadow differs somewhat from a circular cone because the Earth is not perfectly spherical. In other words, the cross-section of the umbra at the Moon's distance is not exactly circular, but is slightly flattened. However, for the prediction of lunar eclipses, such as those published in the various almanacs, it is customary to assume the umbra to be exactly circular and to use a mean radius for the Earth. We have followed this practice here, too.
The Saros numbers are according to G. van den Bergh.
For the calculation of the elements of the eclipses, use has been made of Bretagnon's VSOP87 theory for the Sun, and Chapront's ELP for the Moon. However, for the Moon we dropped the many very small periodic terms, and we used Chapront's improved mean elements (2002).
Besides this 'Read me', the program offers four options:
In the lists obtained with Options 1 and 2, T1 is the time of the first contact with the umbra (beginning of the partial phase), T2 that of the beginning of the total phase, Tm that of maximum eclipse, T3 that of the end of the total phase, and T4 that of the last contact with the umbra (end of the partial phase). In the list obtained with Option 2, the corresponding altitudes of the center of the Moon's disk, in degrees, are given in the columns h1, h2, etc. If the altitude is negative, the Moon is below the horizon and the corresponding phase of the eclipse is not visible.
In the calculation of the altitude, the effect of the atmospheric refraction is neglected, as is the dip of the horizon (due to the height of the observer).
Of course, when the eclipse is only partial in the umbra, T2 and T3 (and h2 and h3) don't exist. And in the case of a penumbral eclipse, only Tm (and hm) are given.
The times of contacts with the penumbra are not given, because these contacts cannot be observed due to the faintness of the outer parts of the penumbra. Giving those times might be confusing for the general user.
In Option 2, an eclipse is considered to be visible when at least one of the altitudes h1, etc., is positive for the given place.
Column 'Magn.' gives the magnitude of the eclipse, either in the umbra or in the penumbra. In the latter case, the value is placed between parentheses.
Delta T (ΔT) is the difference between the uniform Dynamical Time (used in celestial mechanics) and the Universal Time (based on the rotation of the Earth). Delta T is slowly varying with time and can only be deduced from observations. For epochs in the future or in the distant past, only approximate values of Delta T are available. In Options 1 and 2, Delta T has been calculated by means of the formulae given on pages 14-16 of the 'Five Millennium Canon of Solar Eclipses' (Espenak & Meeus, NASA, 2006). In Option 3, that same value of Delta T is proposed. Either it can be accepted by the input of an asterisk (*), or by entering another value.
Sometimes a letter has to be input to indicate a choice, for instance U (Umbral) or A (All). In such a case, either a lowercase or an uppercase letter may be entered.
The lists created in Options 1 and 2 can be printed to a file. The name of the file should be chosen by the user, without an extension. The program will add the extension 'TXT', and the file will be saved in the same directory as that where the program is.
If you ask the list to be printed, it will nevertheless appear on the screen, so you can see what happens. If you ask a list that is too long for the screen, the lines at the top will scroll out of view!
Important: If later you want to save another list, you should choose another name for the file, otherwise the older file will be overwritten.
In Option 2, you should either choose a place from the list, or a place of your choice. In the latter case, the geographical longitude and latitude should be given in degrees and decimals, not in degrees, minutes and seconds. Important: longitudes west of Greenwich are positive, longitudes east are negative!
In the list of places, we have added the antique places Babylon, Nineveh and Uxmal for historical purposes.
Option 3 first gives some general data about the chosen eclipse. Note that, in the case of a penumbral eclipse, the magnitude in the umbra is negative. Then you can choose for several options.
The drawing gives a general view of the eclipse. Celestial North is up. The inner circle represents the edge of the Earth's umbra at the distance of the Moon; the outer, dotted circle is the edge of the penumbra. The smaller circles are the position of the Moon at maximum eclipse and, if the magnitude in the umbra is greater than 40%, at the times of exterior contact with the umbra. The dashed line through the center of the umbra is a part of the ecliptic.
The chosen time, in UT, should be given in the format HH.MMSS, a decimal point separating the hours from the minutes. Two digits must be used for the minutes, and two for the seconds. When the seconds are zero, they can be omitted. For instance, 17 hours, 44 minutes, 3 seconds should be entered as 17.4403, 6 hours, 5 minutes and 0 seconds should be entered either as 6.0500, or as 6.05. If maximum eclipse occurs at, say, 23h06m and you need the values for 1h17m23s, you may enter the time either as 1.1723 or as 25.1723. The time should NOT be entered in the hh:mm:ss format!
P is the position angle of the center of the lunar disk with respect to the center of the umbra, in degrees and decimals, measured from the North in the usual way, for instance P = 0 is due North, P = 90 is East, etc."
The date given for an eclipse corresponds to the time of maximum eclipse. For instance, at the eclipse of 2003 November 9, we have
T1 = 23:33 and Tm = 01:19.
Consequently, maximum eclipse occurred at 01:19 UT on November 9 but first contact with the umbra took place at 23:33 on November 8.
The recurrence of lunar (and solar) eclipses is governed by the Saros cycle, a period of 223 lunations, or 18 years + approximately 11 days. When two eclipses are separated by a period of one Saros, they share very similar geometry. Saros series are born and die out. Each series typically lasts 12 or 13 centuries and contains 70 or more eclipses. Here we use the Saros numbering as defined by G. van den Bergh (1955). All lunar eclipses in a even numbered Saros series occur near the ascending node of the Moon's orbit, and the Moon shifts southward with each succeeding member in the family. For uneven numbered series, it's the opposite.
The dates in the lists refer to the instant of maximum eclipse in the scale of Dynamical Time. Two-letter abbreviations are used for the months: Ja=January, Mr=March, My=May, Jn = June, Jl = July, etc.
After the date, the magnitude of the eclipse is given, between parentheses in the case of a penumbral eclipse.
