Planet
Earth
Our tilted, spinning home, circling the Sun once a year.
Earth spins once every 23.93 hours relative to the stars and circles the Sun in 365.256 days. Its axis is tilted 23.44 degrees, so each hemisphere takes turns leaning toward the Sun, which gives us the seasons. That extra quarter day per orbit is why calendars add a leap day every four years.
How it moves
- Earth orbits the Sun every 365.256 days (sidereal year) at an average speed of 29.78 km/s.
- One spin relative to the stars takes 23.9345 hours; noon to noon (the solar day) takes 24 hours because Earth also moves along its orbit.
- A 23.44-degree axial tilt gives the seasons: summer comes to whichever hemisphere leans toward the Sun.
- The orbit is nearly circular (eccentricity 0.0167), ranging from 147.1 to 152.1 million km from the Sun.
- The seasonal (tropical) year is 365.242 days, which is why a leap day is added about every four years.
Facts
- Mean radius
- 6,371 km
- Mass
- 5.972e+24 kg
- Surface gravity
- 9.82 m/s²
- Rotation period
- 23.9345 hours
- Orbital period
- 365.256 days
- Average distance from the Sun
- 1.00000011 AU
- Eccentricity
- 0.0167
- Axial tilt
- 23.44°
- Mean orbital speed
- 29.78 km/s
- Known moons
- 1
Leap years exist because Earth needs about 365.25 days, not 365, to circle the Sun.
Sources: nssdc.gsfc.nasa.gov, science.nasa.gov