What’s Out Tonight?

A general ASTRONOMY site to get you started exploring the night sky


Basic Earth Facts 

• Third planet from the Sun 
• It’s a Terrestrial Planet and HOME! 

Diameter: 7,926 miles 
Mass: 1 Earth mass 
Density: 5.52 where water = 1 
Gravity: 32.2 feet/sec2 
Albedo (% of Sunlight reflected): 37% 
Rotation on Axis: 24 hours, 56 min, 4.1 sec 
Inclination of Axis to Orbit: 23.4° 

Average Distance from Sun: 92,955,800 miles 
Revolution about Sun: 365.26 days 
I nclination of Sun to Earth’s Orbit: 7.2° 

Atmosphere: 77% Nitrogen, 21% Oxygen, 1% water, 0.9% Argon, plus traces of other gases 
Surface Temperature: Averages 59° F Atmosphere Pressure: 14.7 lb/inch2 

Moon: Only one.

This is a very famous photo from the Apollo 17 mission 
that went to the Moon in 1972. 
It is still used today in all types of media.

DETAILED FACTS about our Planet

Equatorial: 7,926.4 miles; 12,756.3 km 
Polar: 7,899.8 miles; 12,713.5 km 

Mass: 1.317 x 1025 pounds; 5.974 x 1024 kg 
Average Density: 5.52 gm/cm3 (water is 1.00 gm/cm3) 

I nclination of Axis to Orbit: 23.4393° with North Pole pointing roughly to the star Polaris in the constellation Ursa Minor (Little Dipper)
Precession of Axis: 50.29" a year around a 47° diameter circular arc. Total precession period is about 25,800 years. 

Synodic day (time used for clocks) is 86,400 seconds or 24 hours.
Sidereal day (one complete rotation on its axis) is 86,164.1 seconds or 23 hours, 56 minutes, 4.1 seconds. 

Year: 365.2564 days; 365 days, 6 hours, 9 minutes, 10 seconds 

Distances from the Sun
Average: 92,955,800 miles; 149,597,870 km; 8.3 light-minutes. This distance is also known as an astronomical unit. 
Closest: 91,403,000 miles; 147,099,000 km occurring on (or near) January 4th. 
Farthest: 94,508,000 miles; 152,096,000 km occurring on (or near) July 4th. 

Eccentricity of Orbit: 0.017 (from the mathematical definition of eccentricity) or 0.015% longer in one direction than the other. 

Average Orbital Speed: 18.5 miles/sec (66,600 miles/hour); 29.8 km/sec 

Acceleration of Gravity at Sea Level: 32.2 feet/sec2; 9.81 meters/sec2 
Escape Velocity at Equator: 6.96 miles/sec (25,000 miles/hour); 11.2 km/sec 

Albedo: reflects 37% of sunlight or greater depending on cloud cover 

Temperature Range
 Averages 59° F (15° C)
Highest record, 136° F (58° C)
Lowest record, –129° F (–89° C) 

Pressure at Sea Level: 1 atmosphere (1 bar); 14.7 pounds/inch2; 760.0 mm-Hg (mercury); 101.3 kPascals 

Speed of Sound at Sea Level: 1,087 feet/sec (741.5 miles/hour); 331.5 meters/sec 

Highest—Mount Everest: 29,028 feet (5.5 miles); 8,848 meters. Lowest—Marianas Trench: 36,198 feet (6.9 miles); 11,033 meters 

Coordinates of Magnetic Poles 
North Magnetic Pole: 76° N, 101° W; 
South Magnetic Pole: 66° S, 140° E 

Composition of Atmosphere: 77% Nitrogen, 21% Oxygen, 1% Water, 0.9% Argon with traces of many other gases 

Thickness of Atmosphere: 75% of the atmosphere lies within 7 miles (11km) of sea level and “ends” at a height of 62 miles (100 km) 

Land & Sea: 29% of the surface is land and 71% ocean 

Core: The Earth has an outer liquid core with a diameter of about 4,350 miles (7,000 kilometers) containing an inner solid core having a diameter of about 1,500 miles. Both cores are predominately Iron, but contain some Nickel and other lighter elements with a core temperature reaching as high as 9,000° F. 

Age: about 4.6 billion years