Gravity and the Solar System 8th Grade Space Science (Module G) U2L2

A few definitions - Gravity – force of attraction between objects Orbit – path a body follows as it travels around another body in space Aphelion – point of an object’s orbit farthest from the sun Perihelion – point of an object’s orbit closest to the sun Fun fact – if you are taking about an orbit around the Earth, it’s called apogee and perigee!

Nicolaus Copernicus (1473-1543) Johannes Kepler (1571-1630) Came up with the idea of a heliocentric model instead of a geocentric one Discovered that orbits of planets are elliptical not circular.

Kepler’s laws of planetary motion (not necessary for your notes, just cool to know) 1. Each planet orbits the sun in an ellipse with the sun at one focus.

Planets move faster at perihelion (closest to the sun) than aphelion (farthest from sun). 2. As a planet moves around the sun, it sweeps out equal areas in equal times.

3. The square of the orbital period (time it takes planet to go around sun) is proportional to the cube of the planet’s average distance from the sun What you need to know: there is a direct relationship between the distance from the sun and the time it takes to go around it.

Law of Universal Gravitation Developed by Isaac Newton in 1687 Says all objects in universe attract each other through gravitational force Note: gravity is actually a pretty weak force. Magnetism is stronger More mass = more gravity The strength of the gravitational force depends on the product of the masses More distance = less gravity The strength of the gravitational force is inversely proportional to the square of the distance Newtons Universal Law of Gravitation - Science in a Minute - https://www.youtube.com/watch?v=Jk5E-CrE1zg

Centripetal force - Inward force that causes an object to move in a circular path Object on string: string is “inward force” Planets around stars: gravity is “inward force”

THE FORMATION OF THE SOLAR SYSTEM! 4.6 billion years ago – solar nebula (cloud of dust and gas) collapsed -in nebula, inward pull of gravity is balanced by outward push of gas pressure in cloud -some outside force, maybe explosion of nearby star, started nebular collapse 2. Gravity pulled mass toward center -nebula contracted, began to rotate -rotation sped up, nebula flatted into disk a.k.a. protostellar disk – our sun formed here! -friction of collapse heated center to millions of degrees, starting fusion of hydrogen into helium *this fusion caused explosions that balanced force of gravity

3. As sun formed, dust grains collided and formed dust granules Dust granules increased in size to a meter or so Collisions between these bodies formed larger bodies – planetesimals – from which planets formed Protostellar disk became protoplanetary disk in which planets formed CCHistory Solar System - Start at 4:27 to see planets crashing into each other to form bigger ones end at 6:29 https://www.youtube.com/watch?v=yf6YvGb83H4 Next year – maybe use this article instead - http://www.kidsastronomy.com/academy/lesson210_week2.htm

4. Inner part of protoplanetary disk so hot that only rocks and metals were in solid form Inner planets are called terrestrial planets & are made of rock and metal Outer part of protoplanetary disk cooler, outer planets have rocky cores but captured ice and gasses with gravity Outer planets are called gas giants & have rocky or metallic cores with deep atmospheres of gas and ice

Video - Birth of the Solar System #1. - http://www. youtube. com/watch Video – Birth of the Solar System #3 - WATCH THIS! Just images, no words. - http://www.youtube.com/watch?v=E4yirtvUurA&feature=fvwrel

Our solar system Earth is part of a solar system – a collection of large and small bodies that orbit the sun Terrestrial planets – Mercury, Venus, Earth, Mars Rocky, dense, relatively small Gas giant planets – Jupiter, Saturn, Uranus, Neptune Thick, gaseous atmosphere, rocky core, HUGE volume Moons – orbit planets Comets Asteroids Main belt (btw/Mars & Jupiter) Kuiper Belt (beyond Neptune) And others! Meteoroids This is also from U1L1 – Structure of Universe & U2L6 Small Bodies in SS ESS1A - The Universe and its Stars - https://www.youtube.com/watch?v=GXSJC38Bhp0

https://upload. wikimedia https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Milky_Way_Night_Sky_Black_Rock_Desert_Nevada.jpg/220px-Milky_Way_Night_Sky_Black_Rock_Desert_Nevada.jpg https://s-media-cache-ak0.pinimg.com/736x/47/11/e0/4711e0053fd467ced496e0286e6ef6a8.jpg

The Milky Way & other galaxies Galaxy – large collection of stars, gas & dust held together by gravity Contain 100 million – 100 billion stars that orbit the center of the galaxy The Universe Space and all the matter and energy in it Galaxies tend to form clusters and superclusters Between the clusters are voids, where no matter exists https://astronomynow.com/2016/08/12/astronomers-use-cosmic-voids-to-study-the-universe/

L4 – The Terrestrial Planets For each planet, draw a picture on the front and on the inside write these things: Diameter and comparison to Earth Density & comparison to Earth # of moons Order from the sun (first, second, etc.) Distance from the Sun in AU (astronomical unit) Composition 2 other interesting facts

Diameter and comparison to Earth Density & comparison to Earth # of moons Order Distance from the Sun Composition 2 other interesting facts Mercury Venus Earth Mars

Diameter and comparison to Earth Density & comparison to Earth # of moons Order Distance from the Sun Composition 2 other interesting facts Mercury Venus Earth Mars

L5 – The Gas Giants For each planet, draw a picture on the front and on the inside write these things: Diameter and comparison to Earth Density & comparison to Earth # of moons Order from the sun (first, second, etc.) Distance from the Sun in AU (astronomical unit) Composition 2 other interesting facts

Diameter and comparison to Earth Density & comparison to Earth # of moons Order Distance from the Sun Composition 2 other interesting facts Jupiter Saturn Uranus Neptune

Diameter and comparison to Earth Density & comparison to Earth # of moons Order Distance from the Sun Composition 2 other interesting facts Jupiter Saturn Uranus Neptune