Formation of Our Solar System

Formation of the Solar System

• The solar system formed about 4.6 billion years ago from a huge cloud of space dust and debris.
• Gravity caused the particles to come together and outside forces caused the cloud to spin, eventually flattening into a disc.
• The center of the disc became so hot and dense that nuclear fusion started, forming the sun.
• The remaining material in the surrounding cloud became orbiting planets.

Orbits

• The planets travel in the same direction and within the same plane in paths called orbits.
• An orbit is a path an object takes as it moves or revolves around another.
• Earth takes 365.25 days to orbit once.
• Objects in space orbit other objects due to the interaction between the forces of inertia and gravity.

Orbital Eccentricity

• The orbital paths of planets around the sun are often drawn as perfect circles, but they actually have a slightly elliptical or oval shape.
• The amount the orbital path deviates from a perfect circle is called its orbital eccentricity.
• Mercury has the most orbital eccentricity in our solar system.
• One AU (Astronomical Unit) is the distance from Earth to the Sun, used to measure distances in our solar system.

Earth's Tilt

• The axis of Earth is not perpendicular to its orbital plane but is actually tilted slightly, known as the obliquity of the ecliptic.
• The tilt of the Earth is currently about 23.4 degrees off perpendicular.
• The tilt is believed to be caused by a collision with a nearly planet-sized object, which also created the debris that became the Moon.

Precession

• As the Earth rotates and revolves, it also wobbles on its axis, similar to a spinning top.
• This circular wobble changes the angle of the tilt of Earth in a process called precession.
• One complete wobble or precession takes about 26,000 years.

Seasons

• The tilt of the Earth is the cause of seasons, not how close or far the Earth is from the Sun.
• Warm summers occur on the hemisphere of the Earth that is tilted toward the Sun, receiving direct sunlight.
• The opposite hemisphere, tilted away from the Sun, receives less direct rays and experiences winter.
• As the Earth orbits the Sun, the seasons change due to the orientation of the tilt relative to the Sun.