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How Does Earth Travel Through Space? – Find out how our planet moves through the Milky Way and what keeps it in orbit around the sun.
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How Earth Travels Through Space
There are many ways to describe how Earth moves through space. The most common way is to say that Earth orbits the sun. This means that Earth goes around the sun in a big circle. It takes Earth about 365 days, or one year, to go around the sun once.
Earth doesn’t go around the sun by itself. It is pulled by the sun’s gravity. Gravity is the force that pulls things together. The sun’s gravity pulls on Earth and keeps it in orbit.
Earth isn’t the only planet that orbits the sun. There are eight other planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. All of these planets orbit, or go around, the sun.
The Path of Earth’s Orbit
Earth’s orbit is an ellipse, with the sun at one focus. Earth’s average distance from the sun is about 150 million kilometers (93 million miles), and completes one orbit in 365.24 days (1 sidereal year). Earth’s orbit is tipped about 23.5 degrees from the plane of the ecliptic (the plane of Earth’s orbit around the sun). This tilt makes seasonal changes possible. As Earth orbits the sun, both Earth and its moon orbit around their barycenter (common center of gravity). From our perspective on Earth, it appears that the sun moves along the ecliptic (a line in the sky) from west to east, taking one year to return to its original position.
The Sun’s Role in Earth’s Orbit
Earth’s orbit is not a perfect circle, but is instead an ellipse with the Sun at one of the foci. This means that Earth’s distance from the Sun varies during its orbit. Earth is closest to the Sun (at perihelion) in early January and farthest from the Sun (at aphelion) in early July. Even though the difference in distance is only about 3% between these two points, it has a large effect on our planet.
The changing distance between Earth and the Sun affects Earth’s orbital speed. When Earth is closer to the Sun, it travels more quickly because it doesn’t have as far to go. When Earth is farther from the Sun, it travels more slowly because it has further to go. This changing orbital speed means that Earth’s seasons are caused by the amount of sunlight that reaches us throughout the year.
As Earth orbits around the Sun, different parts of our planet tilt toward or away from the Sun. This tilt is what gives us our seasons. During summer in the Northern Hemisphere, for example, the North Pole tilts toward the Sun and receives direct sunlight for 24 hours each day. This makes it warm enough for ice to melt and for plants to grow. During winter in the Northern Hemisphere, however, the North Pole tilts away from the sun and is in darkness for 24 hours each day. This lack of sunlight makes it cold enough for water to freeze and for snow to fall.
The Speed of Earth’s Orbit
Earth travels around the sun at an average speed of 29.78 kilometers per second, or 107,000 kilometers per hour. This is fast enough to go around the world more than seven times in one day!
The Shape of Earth’s Orbit
Earth’s orbit around the sun is not a perfect circle. It is actually an ellipse with the sun located at one of the two foci. An ellipse is a plane curve such that the sum of the distances from any point on the curve to two fixed points (foci) is constant. Eccentricity is a measure of how “flat” an ellipse is. A circle has zero eccentricity, while straight line has an eccentricity of 1.0. Earth’s orbit has an eccentricity of 0.0167, which means that it is very close to being a circle.
The shapes of planets’ orbits can tell us a lot about them. For example, mercury has the most eccentric orbit of any planet in the solar system. This means that its distance from the sun varies more than that of any other planet. Mercury’s orbit is also tilted more than any other planet’s, meaning that it spends more time closer to and further from the sun than any other planet.
The Size of Earth’s Orbit
Earth’s orbit is not a perfect circle. It is an ellipse with the sun at one focus. The shape of the orbit is due to the combined effect of the sun’s gravity and Earth’s orbital speed. Earth’s orbital speed is greatest when it is closest to the sun (perihelion) and slowest when it is farthest from the sun (aphelion). As a result, Earth moves faster in January than in July.
The size of Earth’s orbit also changes over time. The Earth-sun distance varies by about 3% over the course of a year. This changing distance affects how much sunlight Earth receives. When Earth is closer to the sun, it receives more sunlight and vice versa.
The changing distance also affects Earth’s orbit itself. The closer Earth gets to the sun, the more gravitationally attraction there is between them. This causes Earth’s orbit to become more elliptical over time.
The Tilt of Earth’s Axis
Earth’s axis is an imaginary line that goes through the planet from the North Pole to the South Pole. The angle of Earth’s axis in relation to the plane of Earth’s orbit around the sun (called Earth’s ecliptic plane) is about 23.5 degrees.
As Earth orbits the sun, this tilt causes different parts of the planet to be exposed to more or less sunlight over the course of a year. This is what gives us our seasons— spring, summer, fall and winter.
The Rotation of Earth
Earth rotates on its axis, making one full rotation every day. This movement gives us night and day. Earth’s axis is an imaginary line that runs through the North and South Poles. Earth’s axis is tilted at an angle of about 23.5 degrees. This tilt is what causes seasons on Earth. As Earth orbits the Sun, the tilt of its axis causes different parts of the planet to be closer to or farther from the Sun. When the North Pole is tilted toward the Sun, it’s summer in the Northern Hemisphere. When the South Pole is tilted toward the Sun, it’s winter in the Northern Hemisphere.
The Revolution of Earth
As Earth travels around the sun, it goes through different parts of space. When it is closer to the sun, it is in what is called perihelion and when it is farthest from the sun, it is in aphelion. Earth actually reaches perihelion around January 3rd and aphelion around July 4th. However, because Earth’s orbit is elliptical, not circular, its distance from the sun varies throughout the year. On average, Earth is about 91.3 million miles away from the sun.
As Earth revolves around the sun, it also rotates on its own axis. This causes day and night. One complete rotation on its axis takes 24 hours. This day is actually longer than a solar day, which is the time it takes for one complete rotation with respect to the sun. Because Earth’s orbit around the sun is not perfectly circular, its speed varies as it goes around the sun. This means that sometimes it needs to rotate a little bit more to complete one full day with respect to the sun. When this happens, we have what is called a leap second and we add an extra second to our clocks.
The Seasons of Earth
The seasons of Earth happen because our planet’s axis is tilted. The further away from the sun, the colder it is. As Earth orbits around the sun, both the tilt and our proximity to the sun change throughout the year. It’s these changing factors that give us seasons.
As Earth orbits the sun, different parts of the planet receive more or less direct sunlight. This happens because our planet is tilted on its axis by about 23.5 degrees. The amount of direct sunlight an area receives changes throughout the year as Earth’s tilt and position relative to the sun vary. In general, areas closer to the equator receive more direct sunlight than those nearer to the poles.
The changing amount of daylight and sunlight cause seasonal changes in temperature, which in turn produce seasonal changes in vegetation and animal behavior. For example, warmer temperatures in spring and summer cause plants to grow and produce fruit. As autumn approaches and days become shorter, deciduous trees begin to prepare for winter by producing chemicals that cause their leaves to change color and eventually fall off.
