The Solar System

18.3 Objectives

• Identify the planets of the solar system and their features

• Describe the formation of the solar system

• Explain eclipses and the phases of the moon

Vocabulary

• Planet• Solar system• Asteroid• Nebular model• Phases• Eclipse

Objective 1: Identify planets and their features

• Early astronomers have known about “stars” that didn’t move like other stars

• These are the planets• Early models had the earth as

the center of the universe – they were incorrect

The solar system• There are 8 planets, planets reflect

light• Pluto is now considered a dwarf

planet• Planets reflect light

Inner Planets

• Rocky and small• A few have moons

Mercury• Small• Mercury spins

slowly – 3 spins every 2 orbits

• Side currently facing the sun reaches 397 C

• Dark side reaches -170 C

• No atmosphere, no water

Venus• Thick greenhouse cloudy atmosphere

• Mostly carbon dioxide

• High amounts of Sulfuric acid

• 90 times atmospheric pressure of earth

• Surface temperature over 425 C

Earth

• Ideal for life• Large

amounts of water, found in all three forms

• Atmosphere moderates temperatures

Mars• We have had several

robotic missions to mars

• Mars has mountains larger than Mt Everest

• It has ice in the polar icecaps

• There are many features that suggest mars used to have flowing water

• Thin, carbon dioxide atmosphere

Asteroid Belt

• There is an asteroid belt separating the inner and outer planets

• Thousands of small rocky pieces

Outer Planets

• Jupiter, Saturn, Uranus, Neptune• Called Gas Giants• Do not have a solid surface• All have rings and moons

Jupiter• Largest planet in

solar system• Larger than 1300

earths• Atmosphere is

hydrogen, helium, methane, ammonia

• Bands are jet streams

• Red spot is a hurricane twice the size of the Earth – it has been there for hundreds of years

Saturn• Planet with most pronounced rings

Uranus and

Neptune

• Blue Giants• Thick gas atmospheres, mostly

methane (makes them blue)• Both have lots of moons

All Planets• Orbit the sun• Have enough

gravity to be spherical

• Have cleared other objects from their orbital path

• Pluto orbits in the Kuiper belt

• So it’s not a planet

Pluto the Dwarf Planet• It was either make more planets or

demote Pluto• There are currently 5• Ceres is in the asteroid belt –

between Mars and Jupiter• Eris, Makemake, and Haumea

are at the edge of the solar system – like Pluto

• Eris is the so-called 10th planet – it was briefly called Xena

after the TV show character

• Pluto, Ceres, and Eris are Dwarf Planets

Objective 2: how did the solar system form?

• Most accepted explanation is the Nebular Model – it formed from a cloud of stardust

• A rotating disk of stardust• Planets form from accretion – stuff

slammed into each other and stuck• When the sun started glowing –

lighter material was pushed out to the outer planets

Objective 3: Describe phases of the moon and eclipses

• The moon orbits the earth• Sunlight reflects off of the

moon• The moon appears in

phases because we can only see the side that faces the sun

Phases of the moon

Eclipses

• There is a difference between a solar eclipse and a lunar eclipse

• They are named based on what gets blocked out

• Solar eclipse blocks the sun• Lunar eclipse blocks the moon

Lunar Eclipse

• The earth’s shadow crosses the moon

• 3 types– Penumbral – can’t be seen by eye– Partial – Total

Total Lunar Eclipse turns moon red

• The light that does reach the moon goes thru the earth’s atmosphere filtering the blue light out

Without the earth’s atmosphere the moon would be black

Solar Eclipses• There are fewer than 70 total solar

eclipses in a century• You must be in the right place to see

a total solar eclipse – the next total solar eclipse visible in the US will be in August 2017

• They are worth the road trip!

• The moon is slowly moving away from us –

• If the moon’s diameter were 140 miles smaller – we would not have solar eclipses

• Looking at earth during solar eclipse

• You can see the corona during a solar eclipse