Astronomy watching the sky
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Astronomy: Watching the Sky. Class 2: A Trip through the Solar System. The Solar System. One Star – The Sun 8 Major Planets 5 dwarf planets 70 + moons. Unknown number of comets Unknown number of asteroids. Our Voyage.

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Astronomy: Watching the Sky

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Astronomy watching the sky

Astronomy: Watching the Sky

Class 2:

A Trip through the Solar System

The solar system

The Solar System

  • One Star – The Sun

  • 8 Major Planets

  • 5 dwarf planets

  • 70 + moons

  • Unknown number of comets

  • Unknown number of asteroids.

Our voyage

Our Voyage

  • We will be traveling outward from the center of the solar system (the sun) to edges of the system.

  • Our voyage will take us 40 astronomical units (AU) from the sun. An AU is the distance from the sun to the Earth. About 93 million miles.

The sun

The Sun

  • A medium sized star.

  • The largest object in the solar system.

  • 99.8% of the material in the solar system is in the sun.

  • 70% of the sun is hydrogen gas. 28% helium gas. 2% metals.

Affect on solar system

Affect on Solar System

  • The more massive the object the more gravity it has. The sun’s massive size keeps the planets from flying away.

  • The sun “burns” providing most of the heat and light in the solar system.

How the sun burns

How the Sun “Burns”

  • Under the intense pressure at the heart of the sun the nuclei of the hydrogen atoms “fuse” together to make helium and release energy in the form of heat and light.

  • This process is called “Nuclear Fusion”

How hot is the sun

How Hot is the Sun?

  • The surface is 10,000 degrees Fahrenheit. (Steel melts at 2,500 degrees and Iron boils at 5,000).

  • The sun’s corona, extends millions of miles into space. Temperatures in the corona are over 1,800,000 degrees Fahrenheit

How big is the sun

How Big is the Sun?

  • The sun is 863,705 miles in diameter (108 times the diameter of Earth)

The sun gold pixel

The Sun = Gold Pixel

  • 163,000 miles = 1 foot.

Solar wind

Solar Wind

  • In addition to heat and light, the Sun also emits stream of charged particles known as the solar wind.

  • A solar flare can greatly increase the energy of the particles and cause power line surges and radio interference.

  • The solar wind is also responsible for the aurora borealis.



  • 1st planet out from the sun (1/3 of an AU).

  • 3,032 miles in diameter (less than half the diameter of Earth).

  • Surface temperature ranges from -298 to 800 degrees Fahrenheit.

  • Almost no atmosphere.

  • No life.

Mercury s orbit

Mercury’s Orbit

  • Mercury has no moons.

  • It orbits the sun once every three months.

  • Mercury turns on its axis about every four and ½ months (longer than it takes to do an orbit.

  • Because of this a Mercury day (From on sunrise to the next) lasts 6 months.

Planet walk

Planet Walk



  • 2nd planet out from Sun (3/4 of an AU).

  • 7,520 miles in diameter. (About the same as Earth)

  • Considered to be Earth’s “twin.”

  • Year is 224 Earth days.

  • Rotates backwards slowly. 243 earth days equals one day on Venus.

  • It was once though that beneath the planet’s dense clouds there might be life. Now we know it is too hot.

Surface of venus is hot

Surface of Venus is Hot!

  • Surface temperature as high as 872 degrees Fahrenheit (hot enough to melt lead)

  • Venus has a thick atmosphere of mostly carbon dioxide. This is a “greenhouse” gas and retains heat. This makes it even hotter than Mercury.

  • The atmosphere is very thick.

Planet walk1

Planet Walk



  • 3rd planet from sun (1 AU).

  • 7926 miles in diameter.

  • Surface temperature -130 to + 105 Fahrenheit.

  • Only known place that supports life.

  • Abundance of water. Should really be named “Ocean” not “Earth”

Earth geology

Earth Geology

  • Only planet known to have “plate tectonics.” That means the crust floats around on the semi-molten mantel.

  • This gives earth a young surface with lots of active volcanoes.

  • Axis is tilted 23 degrees.

Earth seasons

Earth Seasons

Earth moon

Earth & Moon

  • Earth has one moon.

  • Our moon is huge compared to the size of our planet (1/3 diameter).

  • Created when a small planet hit the Earth in ancient times.

Astronomy watching the sky


  • Almost non-existent atmosphere.

  • No life.

  • Only celestial body man has walked on besides Earth.

Earth without the moon

Earth without the Moon

  • The ancient collision with Earth has been called “the lucky strike.”

  • Earth without the moon would have weak tides.

  • Might be water covered with no land.

  • Day would only be 8 hours long. High winds. No seasons.

  • Primitive life or no life.

Planet walk2

Planet Walk

Astronomy watching the sky


  • 4th planet from sun (1 ½ AU).

  • 4,221 miles in diameter. (1/2 that of Earth)

  • Year =687 earth days.

  • Day = 24hours, 37 mins.

  • Two small moons: Phobos & Deimos.

Mars history

Mars History

  • When astronomers first looked at Mars they thought they saw “canals” on the surface and changes that suggested seasons and plant life.

  • Percival Lowell even proposed the canal were built by intelligent Martians.

Mars in popular culture

Mars in Popular Culture

  • Writers have speculated about life on Mars.

  • War of the World by H.G. Wells.

  • Edgar Rice Burroughs wrote about a civilization on Mars.

More mars fiction

More Mars Fiction

  • Even I did a book with featuring an alien from Mars…

Mars surface

Mars Surface

  • Better observations over time show no canals.

  • Mars has a thin atmosphere of carbon dioxide.

  • Mars is cold. Avg. temp -67 Fahrenheit. (About as cold as Earth arctic regions).

Planet walk3

Planet Walk

Asteroid belt

Asteroid Belt

  • Asteroids are small rocky bodies that orbit the sun.

  • Most are located in a belt that is 2-4 AU from sun.

  • They are too small to be round like planet.

  • Several hundred thousand asteroids have been found.

  • If all the asteroids in the solar system were put together they would be smaller than our moon.

Planet ceres

Planet Ceres?

  • Giuseppe Piazzi discovered the first asteroid, Ceres, in 1801.

  • At first it was considered a planet until the thousands of other objects around it were discovered and named asteroids.

  • Ceres itself was reclassified as a dwarf planet in 2006, though some still consider it an asteroid.

Planet walk4

Planet Walk

Near earth asteroids

Near Earth Asteroids

  • Most asteroids stay in the belt, but some do approach Earth.

  • Small ones become meteors if the enter Earth’s atmosphere and meteorites if they hit the ground.

  • Large ones can be dangerous to Earth

Asteroids extinction

Asteroids & Extinction

  • An asteroid named Chicxulub is often cited as the reason for the dinosaurs extinction.

  • Chicxulub is thought to be 6 to 12 miles across.

  • It made a crater 130 miles in diameter.



  • 5th planet from the Sun (5 AU)

  • Largest planet in solar system – 88,846 miles in diameter. (11 times the diameter of Earth)

  • Year=12 Earth years. Day=9 hours, 55min.

  • It is a gas giant planet. Has no solid surface, but is composed of gas.

  • Temperature: -162 Fahrenheit.

Jupiter s red spot

Jupiter’s Red Spot

  • Jupiter is mostly composed of hydrogen gas.

  • Its most noticeable feature is the “Great Red Spot”

  • The spot is a storm that has been raging for at least 300 years and could hold two Earths.

Jupiter moons

Jupiter Moons

  • Galileo discovered Jupiter’s four biggest moons in 1610: Io, Europa, Ganymede and Callisto.

  • Jupter has 16 named moons, but probably many more small ones not named or confirmed.

Jupiter s moon europa

Jupiter’s Moon Europa

  • Is of special interest because it appears to have a frozen icy surface with liquid water underneath.

  • Water is kept warm by tidal forces.

  • One of the few places besides Earth with large amount of liquid water.

  • Scientists speculate about life in the water.

Planet walk5

Planet Walk



  • 6th planet from sun (10 AU).

  • A gas giant 74,897 miles in diameter (10 times the diameter of Earth).

  • Year = 29 ½ Earth years. Day 10 hours.

  • Most noticeable feature are its rings.

  • 18 named moons.

  • Temperature -360 F

Planet walk6

Planet Walk



  • 7th planet from sun (19 AU)

  • A gas giant 31,763 miles in diameter (4 times that of earth)

  • Its rotates on its side.

  • Year = 84 Earth years. Day = 17 hours

  • 27 named moons.

  • Temperature –355 F

  • Discovered by William Herschel in 1781

Planet walk7

Planet Walk



  • 8th planet from sun. (30 AU).

  • Temperature -400 F.

  • A gas giant planet.

  • Year = 164 Earth years. Day = 16.11 hours

  • Diameter is 30,777 miles (4 times that of Earth)

  • 8 moons

English lose a planet

English Lose a Planet

  • Predicted first in 1845 by Englishman John Couch Adams, but he could not get anyone with a telescope to look for it in the sky. Eventually and Frenchman Urbain Le Verrier also predicted it and the two had to share the credit.

Planet walk8

Planet Walk

Kuiper belt

Kuiper Belt

  • A belt of asteroids out beyond Neptune (30 to 50 AU).

  • Also contains dwarf planets like Pluto, Eris(right), Makemake and Haumea

  • Belt also contains comets.



  • Small bodies “dirty snowballs” that mostly reside in the Kuiper belt or further out in the Oort Cloud.

  • Some are on an elongated orbit that brings them though the inner solar system and near the sun.

  • As they get close to the sun the ice melts an the comet gets a tail.

Comet orbit

Comet Orbit

Group discussion comet fear

Group Discussion: Comet Fear

  • The inhabitants of Earth feared their planet passing through a comet’s tail in 1910. Discuss the following:

    • Why have people always feared comets?

    • What especially in 1910 concerned them?

    • Do you think their fears reasonable?

    • Do you think there any way a comet could do damage on earth?

    • Without comets would there be life on Earth?

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