There was a period when astronomers used to believe that we live in a universe where Earth is at the center of everything. The sun, as per them, rotated around the earth, which caused sunrises and sunsets and a similar vision applied to the movements of the moon and the planets.

But the theory failed to suffice certain questions, including how sometimes a planet would back up in the sky before resuming its forward motion. This motion, known as retrograde motion, occurs when Earth is "catching up" with another planet in its orbit.

Mars, for example, orbits farther from the sun than Earth. When the Earth and Mars move in their respective orbits, we pass by the Red Planet and when we do so, the planet moves backward in the sky. The Mars moves forward again after the Earth has passed by it.

The speed of the Earth’s spin depends on what latitude the planet is located at. According to US space agency NASA, the distance around the largest part of the Earth (called circumference) is roughly 24,898 miles (40,070 kilometers). Explaining the speed, NASA said if you estimate that a day is 24 hours long, you divide the circumference by the length of the day, which produces a speed at the equator of about 1,037 mph (1,670 km/h).

“The probability for Earth to stop its spin is practically zero for the next few billion years, so you can feel safe in knowing you will stay in place. Theoretically, however, if the Earth did stop moving suddenly, there would be an awful effect. The atmosphere would still be moving at the original speed of the Earth's rotation”, said NASA. “This means that everything would be swept off of land, including people, buildings and even trees, topsoil and rocks”.

According to a report in Space by Elizabeth Howell, "Some of the earliest astronomers proposed that we live in a geocentric universe, which means that Earth is at the center of everything. They said the sun rotated around us, which caused sunrises and sunsets — same for the movements of the moon and the planets."

Another piece of evidence for the sun-centered solar system comes from looking at parallax, or apparent change in the position of the stars with respect to each other. For a simple example of parallax, hold up your index finger in front of your face at arm's length. Look at it with your left eye only, closing your right eye. Then close your right eye, and look at the finger with your left. The finger's apparent position changes. That's because your left and right eyes are looking at the finger with slightly different angles.

The same thing happens on Earth when we look at stars. It takes about 365 days for us to orbit the sun. If we look at a close-up star in the summer, and look at it again in the winter, its apparent position in the sky changes because we are at different points in our orbit. We see the star from different vantage points. With a bit of simple calculation, using parallax we can also figure out the distance to that star.

A report published in GeekWire revealed, "It’s been a year since NASA unveiled the first image of Earth’s sunlit side captured by the Deep Space Climate Observatory, or DSCOVR, and to celebrate the occasion, you can see an entire year’s worth of DSCOVR’s view in less than three minutes. The scientists behind DSCOVR’s Earth Polychromatic Imaging Camera, or EPIC, assembled more than 3,000 images to create this week’s video clip."

It’s been a year since NASA unveiled the first image of Earth’s sunlit side captured by the Deep Space Climate Observatory, or DSCOVR, and to celebrate the occasion, you can see an entire year’s worth of DSCOVR’s view in less than three minutes.

DSCOVR keeps watch on our planet from a gravitationally stable vantage point known as Earth-Sun L1, about a million miles above the planet. The DSCOVR mission started out in 1998 as the brainchild of then-Vice President Al Gore, who loved the idea of having a satellite that could provide a continuous full-disk view of our home planet.