# How Do the Planets Orbit the Sun?

How do the planets orbit the Sun? The Solar System formed in a disk-shaped cloud of gas and dust that revolved around a newly-forming star. The planets formed from this disk and continued to spin around the Sun after their formation. The orbits of the planets are maintained by their gravitational attraction to the Sun since no other force can prevent them from doing so. So how did they come to be in their current position?

## Kepler’s second law

Kepler’s second law of planetary motion states that the motion of the planets around the sun is governed by the laws of physics. These laws hold true for all objects including stars planets and moons. Planets orbit the sun with equal speeds and eccentricities. Their sidereal periods are directly proportional to their mean distances from the Sun. Unlike the Moon and the Earth however which move at different speeds their sidereal periods are constant and stable.

In order to compute the polar coordinates of a planet Kepler used a geometric construction to solve a problem. He also used an auxiliary circle called an auxiliary circle. This circle contains a line perpendicular to the base and passes through planet P. The circle’s shaded sectors are separated by a point called y and each one is proportional to the other.

In addition to the elongated ellipse Kepler’s second law describes the orbital speed of planets. Essentially the distance between the Earth and the Sun determines the speed at which the planets travel. This means that the tangential velocity of the planets increases as they approach the Sun and decreases when they depart. Kepler’s second law of planetary motion explains how planets orbit the sun.

## Newton’s laws of motion

The planets orbit the Sun in ellipses. The distances from each point on the ellipse to the foci are constant. The ellipse’s eccentricity is the amount of flattening. The smaller the eccentricity the flatter the ellipse. Ellipses have eccentricity values ranging between zero and one. Therefore when the planets orbit the Sun the ellipse will be more flat.

By applying Newton’s laws of motion we can explain how the planets orbit the Sun. As a result they cannot fly away into space or fall into the Sun. Instead they orbit the Sun forever. This is because their gravity pulls them to each other. Kepler’s three laws don’t explain how planets orbit the Sun. Isaac Newton developed the heliocentric system in the seventeenth century and he developed an even better understanding of motion and interaction between masses.

Newton’s laws of motion and gravity apply to the motion of the planets. The acceleration of a planet changes as it moves closer to the Sun. As a planet moves closer to the Sun the acceleration increases and the orbital speed increases. This process is known as the orbital speed. And this principle applies to planets orbiting the Sun. So how does the planetary motion work?

## Inertia

Planets have a high amount of inertia (resistance to change) when they orbit the sun. This property interacts with the gravitational attraction of the sun to keep planets in a nearly circular orbit. The motion of planets has a long history as they have been in nearly circular orbits since the solar system formed. Here are some of the things you may not know about inertia.

Without gravitational force planets would move in a straight line and have a constant speed. This is a concept known as conservation of momentum. Without this force planets would move in a circular orbit which is not the case. This force is called the centripetal force. It should point towards the center. However the picture is incorrect in illustrating the relationship between inertia and gravity.

The mass of the planets has no impact on the speed of the planets as they fall toward the Earth. The mass of the planets is irrelevant to the period of the pendulum. Thus the planets orbiting the sun have the same inertia as free falling bodies. This is because their mass is equal to their total mass. This is how we can determine the mass of planets and moons.

The balance between inertia and gravity keeps the planets in orbit around the sun. Gravitational force attracts bodies in a circular motion and inertia pulls bodies in a straight line. This centripetal force is due to gravitational attraction of the sun. This phenomenon is not a matter of force alone however and there is another explanation that can help us understand how our planets orbit the sun.

## Gravity

We’ve already seen that the Earth and other planets have masses and are gravitationally attracting each other. The planets’ mass is proportional to their forward momentum and if gravity weren’t at play they’d just fall straight into space. But the planets are moving forward at such a high rate that their momentum is balanced by the Sun’s gravitational pull. And because of that they orbit the Sun in a nearly circular motion.

When a planet approaches its sun its mass is gravitationally attracting everything else in the Universe. Newton and Einstein both assert that the largest mass in the Universe dominates the orbit of everything that is affected by it. If this was the case the central mass would remain unchanged and every orbit would repeat as a perfect closed ellipse forever. But the sun is getting smaller and the gravitational field is weakening. If it continues this way the sun will eventually become a red giant star and expand beyond the Earth’s orbit.

Gravitational forces affect all objects including planets. They pull the planets toward or away from their respective suns. That’s why we can’t see the Earth from the surface of another planet. The gravity of the sun will cause the planet to fall toward the sun which means that it won’t be able to escape the sun’s gravity. Inertia gives planets a tendency to maintain a constant speed.

## Solar system’s edge

The formation of the Sun and planets is explained by the fact that they all formed from a gas and dust cloud that was rotating when they were first created. Because of the conservation of angular momentum the rotating cloud increased in size and flattened into a disk. This disk formed planets that all orbited the Sun in the same direction in the same orbital plane. Their rotational speed is determined by the gravitational attraction of the Sun.

The Sun does not have a year but it does rotate. Its spin angle is 7.25 degrees to the plane in which the planets orbit the sun. It is not solid and different parts of the Sun rotate at different rates. The equator rotates about once every 25 Earth days and the polar equator spins around once every 36 Earth days. It is not known whether the planets have moons but they orbit the Sun.

The Sun is the largest object in the solar system. Its gravity is the largest attraction in the universe. It pulls all the other objects in the solar system. The gravitational force is proportional to the distance. A planet is closer to the Sun than a comet so its orbital motion is counterclockwise. The planets’ orbital planes lie near the ecliptic plane and their eccentricities are smaller than 0.1.

## Venus’s axis

While all other planets orbit the Sun in an anti-clockwise direction Venus spins on its axis counter-clockwise. Because it is close to the Sun its atmosphere is dense and causes it to flip 180 degrees when it rotates. This makes it easier for us to view Venus. The rotation of Venus’ axis may have occurred during its history as a result of collisions with other celestial bodies.

The distance between the Earth and Venus is about 108 million km. This distance makes Venus the second-closest planet to the Sun. The planet takes 225 days to complete its one-year orbit around the Sun. In comparison Earth’s orbit takes about 29.5 days to complete. During one Venus orbit the planet rotates 243 times around the Sun making it one of the slowest planets in our Solar System.

Scientists have called Venus Earth’s twin because they have similar sizes and densities. In fact the planets are likely to have shared the same rocky building blocks and chemical compositions. Early telescopic observations of Venus suggested that it had a substantial atmosphere and was a warm wet planet. Popular speculation suggested that Venus was similar to Earth in the prehistoric age but scientists now know that Venus and Earth have evolved different surface conditions.