diameter - 29 min. 23.65 sec.

Moon's diameter, in miles - 2163 miles.

Volume (earth's = 1) - 1/49.20 or 0.02033.

Mass (earth's = 1) - 1/81.40 or 0.0128.

Density (earth's = 1) - 0.60419, or 3.444 the density of water
(water being unity).

Surface area, about 14,600,000 square miles (earth's surface area,
196,870,000 miles)

Earth's surface area = 1, moon's - About 2/27 or 0.07407.

Action of gravity at surface - 0.16489 or 1/6.065 of the earth's.

Surface of moon never seen - 0.4100.

Surface of moon seen at one time or another - 0.5900.

Synodical revolution, or interval from new moon to new moon (commonly
called a lunation) - 29 d. 12 h. 44 m. 2.684 s. - 29.5305887 days.

Sidereal revolution, or time taken in passing from one star to the same
star again - 27 d. 7 h. 43 m. 11.545 s. - 27.3216614 days.

Tropical revolution, or time taken in passing from "the first point of
Aries" to the same point again - 27 d. 7 h. 43 m. 4.68 s. - 27.321582
days.

Anomalistic revolution, or time taken in passing from perigee to perigee
- 27 d. 13 h. 18 m. 37.44 s. - 27.55460 days.

Nodical revolution, or time taken in passing from rising node to rising
node - 27 d. 5h. 5m. 35.81 s. - 27.21222 days.

Distance (mean) in terms of the equatorial radius of the earth - 60.27.

Distance in miles (mean) - 238,840 miles.

Distance, maximum - 252,972 miles.

Distance, minimum - 221,614 miles.

Mean excentricity of moon's orbit - 0.05490807.

Inclination of moon's orbit to the ecliptic (mean) - 5 deg. 8 min. 39.96
sec.

Inclination of moon's axis to the ecliptic - 87 deg. 27 min. 51 sec.

Inclination of moon's equator to the ecliptic - 1 deg. 32 min. 9 sec.

Maximum libration in latitude - 6 deg. 44 min.

Maximum libration in longitude - 7 deg. 45 min.

Maximum total libration from earth's centre - 10 deg. 16 min.

Maximum diurnal libration - 1 deg. 1 min. 28.8 sec.

Angle subtended by one degree of selenographical latitude and longitude
at the centre of the moon's disc, when at its mean distance - 16.566 sec.

Length of a degree under these conditions - 18.871 miles.

Selenographical arc at the centre of the moon's surface, subtending an
angle of one second of arc - 3 min. 37.31 sec.

Miles at the centre of the moon's disc, subtending an angle of one second
of arc - 1.139

[It must be remembered that this value is _increased_, in departing from
the centre, in the proportion of the secants of the angular