16.7 The Moon and the Earth

Figure 16.7-1. The Earth-Moon system to scale. Credit: Wikimedia.

Earth-Moon distance (center to center). Average: 384,403 km (238,857 miles), equal to about 30 Earth diameters. Minimum: 363,104 km (225,622 miles). Maximum distance: 405,696 km (252,088 miles).

Diameter of the Moon. 3,474 km (2,158 miles), 1/4 of the Earth’s diameter.

Diameter of the Earth. 12,740 km (7,916 miles).

Orbit around the Earth. Every 27.3 Earth days.

Lunar escape velocity. 2.38 km/s (5,323 mph).

Albedo of the Moon. 0.12. The light reflected by the Moon at first quarter or last quarter, i.e., when half of a sunlit hemisphere is visible from Earth, is only 8% of the light reflected by a full Moon.

Temperature at the surface. Average 107°C (224.7°F), maximum 123°C (253.4°F), minimum -153°C (243.4°F). Minimum temperature can drop to -233°C (-387.4°F) in polar regions that are permanently in shadow. At a depth of 1 m (40 in), the temperature is almost constant at -35°C (-31°F).

Distance of the horizon. 2.4 km (1.5 miles) on the Moon; 4.7 km (3 miles) on Earth.

Duration of lunar day and night. 340 hours each.

Size of the Earth in the lunar sky. About 3.6 times the diameter of the Moon in the Earth’s sky.

Brightness of the Earth in the lunar sky. 40 times that of a full Moon.