Zoom Astronomy THE EARTH

Back to the Planets

HOW FAST IS THE EARTH MOVING?
You can't measure the speed of an object by itself, it has to be measured relative to something else (this was one of Einstein's realizations).

If we ask the question, "How fast the Earth is moving?" we have to specify that we want the speed with respect to another object. Motion cannot be measured without a reference point. We can ask how fast the earth is moving with respect to its own axis, the Sun, the Milky Way Galaxy, or our Local Group of galaxies.

The Complex Motion of the Earth

•How fast is the Earth spinning?	0.5 km/sec
•How fast is the Earth revolving around the Sun?	30 km/sec
•How fast is the Solar System moving around the Milky Way Galaxy?	250 km/sec
•How fast is our Milky Way Galaxy moving in the Local Group of galaxies?	300 km/sec

The Earth spins around its axis as it orbits the Sun. Our entire Solar System slowly orbits around the Milky Way Galaxy. The Milky Way Galaxy belongs to the Local Group of galaxies, where it is also moving.

HOW FAST IS THE EARTH SPINNING AROUND ITS AXIS?
The Earth is spinning around its axis. At the equator, the Earth's surface moves 40,000 kilometers in 24 hours. That is a speed of about 1040 miles/hr (1670 km/hr or 0.5 km/sec). This is calculated by dividing the circumference of the Earth at the equator (about 24,900 miles or 40,070 km) by the number of hours in a day (24). As you move toward either pole, this speed decreases to almost zero (since the circumference of the spinning circle at the extreme latitudes approaches zero).

HOW FAST IS THE EARTH REVOLVING AROUND THE SUN?
The Earth orbits, on average, 93 million miles (149,600,000 km) from the Sun (this distance is defined as one Astronomical Unit (AU)), taking one year to complete an orbit. The Earth revolves around the Sun at a speed of about 18.5 miles/sec (30 km/sec).

HOW FAST IS OUR SOLAR SYSTEM MOVING WITHIN THE MILKY WAY GALAXY?
The sun is about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across (and less than 7,000 light-years thick). We are located on one of its spiral arms, out towards the edge. It takes the sun (and our solar system) roughly 200-250 million years to orbit once around the Milky Way. In this orbit, we (and the rest of the Solar System) are traveling at a velocity of about 155 miles/sec (250 km/sec).

HOW FAST IS THE MILKY WAY GALAXY MOVING WITHIN THE LOCAL GROUP OF GALAXIES?
The Milky way Galaxy is just one galaxy in a group of galaxies called the Local Group. Within the Local Group, the Milky Way Galaxy is moving about 185 miles/sec (300 km/sec).

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