Space News & Blog Articles
Earth's Orbit
What is Earth's Orbit?
Earth's orbit is the path on which Earth travels around the Sun. This path is not a perfect circle but an ellipse, which means that the distance between the Earth and the Sun changes throughout the year.
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Key Term |
Definition |
|---|---|
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Orbit |
The curved path of a celestial object or spacecraft around a star, planet, or moon. |
|
Ellipse |
A regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant. Earth's orbit is an ellipse. |
|
Perihelion |
The point in the orbit of a planet, asteroid, or comet at which it is closest to the sun. |
|
Aphelion |
The point in the orbit of a planet, asteroid, or comet at which it is farthest from the sun. |
The Period of Orbit
The time it takes for Earth to complete one full orbit around the Sun defines a year. This period is approximately 365.25 days. The extra quarter of a day is accounted for by the addition of a leap day every four years.
The Role of Gravity
The Earth is kept in orbit by the gravitational force between the Sun and the Earth. Isaac Newton's law of universal gravitation describes this force: the attractive force between any two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. This constant pull prevents the Earth from flying off into space.
Tilt and Seasons
The Earth's axis of rotation is tilted relative to its orbital plane (the plane of the elliptic). This axial tilt, currently about 23.5 degrees, is the primary reason for the seasons we experience on Earth. As the Earth orbits the Sun, different parts of the planet receive varying amounts of direct sunlight, leading to the predictable cycle of spring, summer, fall, and winter.
This phenomenon is best understood by reviewing the solstices and equinoxes.
|
Event |
Hemisphere Receiving Most Direct Sunlight |
|
|---|---|---|
|
March Equinox |
Equal sunlight to both |
|
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June Solstice |
Northern Hemisphere |
|
|
September Equinox |
Equal sunlight to both |
|
|
December Solstice |
Southern Hemisphere |
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