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Chaos Game


Moon Distance

You may use the keys m, d, h to increase the month, day, or hour,

or shift key and md, h to decrease the month, day, or hour.

Space bar is setting the current date.

Click into the applet area first !



Select latitude (southern negative) and longitude (western negative) from the menus.

Latitude 51.51, Longitude 13.41 is Berlin/Germany.
Latitude 40.76, Longitude -73.97 is New York.

The applet is also computing the geocentric and topocentric distance of the Moon from the Earth (accuracy better than
+/- 10 km between 1900 and 2050), the apparent angular size (arc minutes), the illuminated fraction of the Moon's disc (per cent), and the Moon's phase:

0.00 = new Moon
0.25 = first quarter
0.50 = full Moon
0.75 = last quarter
1.00 = new Moon

The altitude is taking into account the horizontal parallax of the Moon.

Distance / km
Perigee 356,375
Mean 384,401
Apogee 406,720

The computations are performed following Jean Meeus.

Select "Write Data" from the Details menu:

data table

F(EM)/F(SM) is the ratio of the gravitation forces between Earth and Moon F(EM) to Sun and Moon F(SM).
The mean value of about 0.45 for the Earth's Moon is unique in the solar system:

The axial tidal acceleration a by the Moon is approximately:

tidal force formula
Earth's radius r=6371 km, Moon's mass =7.349 1022 kg, distance Earth-Moon R (356.000 km < R < 407.000 km).

tidal acceleration diagram

More about tides

Select "Diagram" from the Details menu:

earth moon distance

The change of distance may be up to about 6,300 km per day.

Perigee distance

The mean perigee distance of 284 anomalistic months is 362562.4 km.

The maximum lunar declination 23.44 + 5.15 = 28.6 (Major Lunar Standstill in 2006):

Major Lunar standstill 2006
At 28.6 N or 28.6 S the daily topocentric difference of the Moon's distance from Earth will reach the diameter of the Earth.

topocentric moon distance

At the North pole the topocentric lunar distance will have no diurnal change:

North Pole

Please visit my:

GeoAstro Applet Collection

Please visit my Moon Applet Collection

Visit my page: The Moon: orbit and phases

Web Links

Inconstant Moon (J. Walker)

Tidal_force (Wikipedia)

Meeus, Jean; Astronomical Algorithms, Willmann-Bell, First English Edition 1991:
     Chapter 45: Position of the Moon,
     Chapter 46: Illuminated Fraction of the Moon's Disk,
     Chapter 39: Correction for Parallax [topocentric distance]

2006-2023 J. Giesen

Last modified: 2023, Oct 06