Solar and Lunar Data

Moon phase: 

Relative size: 

Moon age:  days


The moon in its orbit:

Lunar longitude:  °

Elongation:  °

Vernal Equinox Beltane Summer Solstice Lughnasadh Autumnal Equinox Samhain Winter Solstice Imbolc

The earth in its orbit:

Solar longitude:  °

The moon’s relative size is based on its maximum (the blue circle around the moon image) at extreme perigee; minimum is about 0.876.  Full moon near perigee is a super moon; near apogee, it’s a mini moon.

The elliptical shapes of the solar and lunar orbits are exaggerated to illustrate the effect.  The figure for the lunar orbit includes the major axis, which indicates perigee and apogee.

Solar and lunar longitudes are heliocentric and selenocentric, respectively (looking back at the earth), relative to the position of the vernal equinox.

The moon’s elongation is the difference between the solar and lunar longitudes, or the geocentric angle between the moon and the sun.  At new moon, the moon and sun are on the same side of the earth (conjunction) and the elongation is 0°; at full moon, they are on opposite sides (opposition) and the elongation is 180°.  All rotations are counterclockwise.

The longitudes of the solstices and equinoxes (Ostara, Litha, Mabon, Yule) are 90° apart.  The cross-quarter days (Beltane, Lughnasadh, Samhain, Imbolc) are those whose longitudes are at the 45° points between the former.

Calculations are based on the “higher accuracy” equations in Astronomical Algorithms, second edition, by Jean Meeus, and the full VSOP87 data set.

Updated 5/8/2021 to fix a bug displaying the month in local time.

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