A general ASTRONOMY site to get you started exploring the night sky
Earth
                    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:  23 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 last 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
                    Diameter
                    
                    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. 
                    
                    Day
                    
                    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 
                    
                    Elevations
                    
                    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