• Objectives:
• 1. Compare and contrast the geocentric and heliocentric models of the solar system
• 2. Describe the orbits of the planets around the sun and explain how gravity and inertia keep the planets in orbit
• 3. Name the components of the solar system
• 4. Identify different technologies used for exploring the solar system

• The geocentric model is from ancient
Greece
• In the geocentric model, Earth is stationary while objects in the sky move around it
• In the heliocentric model, Earth and the other planets revolve around the sun
• Imagine the path of Earth’s orbit traced on a table
• Def: the ecliptic plane is the path of Earth’s orbit

• Gravity and inertia combine with each other to keep the planets in orbit
• Without gravity, planetary inertia would cause them to fly off in space
• The components of the solar system are the sun, the planets, their moons, and a variety of smaller objects that mostly revolve in the same plane around the sun

• Modern technology including telescopes, piloted spacecraft, & space probes has allowed scientists to explore the solar system
• Def: a space probe in an unpiloted vehicle that carries scientific instruments into space and transmits information back to Earth
• NASA launched 2 vehicles, Spirit & Opportunity to land on Mars in 2004 for a 3 month mission
• They are still sending information back to Earth today
• The scientist who monitors them is at UNR

• Objectives:
• 1. Explain why the moon lacks atmosphere
& the effect this has on the range of temperature on the moon
• 2. Describe the features of moon’s surface
• 3. State a theory about the formation of the moon
• 4. Explain the phases of the moon, tides & eclipses & interpret diagrams of these events

• Moon’s gravity is too weak to hold onto gas molecules
• The lack of atmosphere allows moon’s surface temperature to vary tremendously
• The major surface features are maria, highlands and craters
• Def: maria are low, flat plains formed by ancient lunar lava flows

• Def: highlands are rough mountainous regions that cover most of moon’s surface
• Lunar highlands are light-colored areas that surround the maria
• Def: craters are round depressions caused by the impact of high speed meteoroids
• Def: meteoroids are chunks of rock that move through the solar system
• Scientists hypothesize that the moon was formed after an enormous collision in Earth’s history
• The collision was probably caused by rocky debris which was plentiful & hit many planets about 4.6 billion years ago when Earth formed

• Def: the different shapes of the moon visible from Earth are called phases
• The moon’s phases are caused by changes in the relative positions of the moon, sun & Earth as the moon revolves around the Earth
• Def: an eclipse occurs when the shadow of one body in space falls on another
• Def: a solar eclipse occurs when the moon casts a shadow on a portion of Earth’s surface
• Def: a lunar eclipse occurs when Earth casts a shadow on the moon

New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).
Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing.
Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight.
Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing.
Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight.
The fraction of the Moon's disk that is illuminated is decreasing
.
Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing
.

• Def: tides are the regular rise and fall of ocean waters
• Tide are caused mainly by differences in the moon’s gravitational pull on Earth
• The sun’s gravity affects tides about half as much as the moon
• Def: spring tide is the combined forces of the gravity of the sun and the moon
• Def: neap tide is the least tide possible & is due to first or third quarter moon being at right angles to the Earth (compared to sun’s position)

• The solar system is the sun and the planets that orbit around it
• The four planets closest to the sun are the terrestrial planets
• Def: terrestrial planets are planets similar in structure to Earth
• The four inner planets are all small, dense and rocky
• All have a crust, mantle and iron core
• Five planets have been known for centuries:
Mercury, Venus, Mars, Jupiter & Saturn

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• Mercury is the smallest and closest to the sun
• Venus is called the evening star or morning star
• Venus’s atmosphere has the greenhouse gas effect due to large amounts of CO traps heat and raise temperature
2 which
• The CO
2 also causes it to rain sulfuric acid when it combines with the sulfur in the atmosphere
• Earth’s atmosphere is suitable for water to exist as a liquid

• Mars is a major source of study right now, including experimentation with rovers from
NASA named Spirit and Opportunity
• They landed on Mars in 2004
• The rovers were designed to send information for 3 months, but functioned for years yielding information about Martian water and soil
• Spirit was mobile on the Red Planet for over five years and then functioned as a stationary science platform for another year before getting killed off by a Martian winter it couldn’t avoid ”

• As of January 2012, Opportunity still works & will spend the Martian winter in a sunny spot until the engineers wake it up in Martian spring
• In August 2012, NASA landed a much larger, very expensive rover called Curiosity
• Its mission is to see if Mars ever had the right conditions to support life
• Mars shows evidence of having had a lot of water in its past
• other missions to Mars, including manned missions are being considered
• Mars is sometimes called the “red planet”

• Def: asteroids are small rocky bodies orbiting the sun
• The region in the solar system where they are found is called the asteroid belt
• The asteroid belt is between Mars and
Jupiter
• Scientists hypothesize that asteroids are remnants of the early solar system that never came together to form a planet

• Objectives:
• 1. Compare the gas giants and describe characteristics of each
• 2. Distinguish between planets and dwarf planets
• 3. Distinguish between comets and meteoroids and describe their characteristics
• 4. Locate and describe the Kuiper belt and
Oort Cloud

• The four outer planets (Jupiter, Saturn,
Uranus and Neptune) are gas giants
• Def: gas giants are planets composed mainly of hydrogen and helium
• The four gas giants are thought to have small, dense cores, and dense atmospheres composed mostly of hydrogen and helium
• Def: a ring is a disk make many small particles of rock and ice in orbit around a planet
• All of the gas giants have rings

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• Uranus is believed to have a mantle of liquid water and dissolved ammonia
• The axis of Uranus’s rotation is tilted more than 90°
• Neptune’s bluish color comes from the methane in its atmosphere
• Its largest moon is called Triton and it has a thin atmosphere and an icy surface

• Def: a dwarf planet, like a planet, is spherical and orbits the sun directly, but a dwarf has not cleared the neighborhood (more on that in a moment)
• The definition of planet is that it is a celestial body in orbit around the sun, has self-gravity, is not a satellite and clears the neighborhood around its orbit
• A satellite is any object orbiting a planet, whether natural or man-made

• Pluto does not “clear the neighborhood” because it is part of a sea of objects that occupy the same region of space
• Pluto and its moon Charon have an elliptical orbit that sometimes crosses into Jupiter’s orbit, thus lending support to those who want to reclassify it
• Planets must have sufficient force to get other objects out of their way
• Under the new definition as many a 12 planets have been proposed
• Officially at this time there are 8 planets in our solar system

• The astronomers in 2006 came up with the following proposals & definitions:
• 1. Planets: The eight worlds starting with
Mercury and moving out to Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune
• 2. Dwarf planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite."
• 3. Small solar system bodies: All other objects orbiting the sun
• The Pluto issue will continue to play out for some time & is not yet settled

• Def: comets are dusty pieces of ice and rock that partially vaporize when they pass near the sun
• Def: meteoroids are pieces of rock, usually less than a few hundred meters in size, that travel through the solar system
• At the edge of the solar system beyond
Neptune are Kuiper and beyond Kuiper is
Oort

• Most of the objects in the Kuiper belt lie in a doughnut shaped region close to the ecliptic plane
• Def: the ecliptic plane is the plane in space containing Earth’s orbit (the path of Earth’s orbit)
• Pluto is in the Kuiper belt
• Beyond the Kuiper belt is a great reservoir of comets called the Oort cloud
• Occasionally objects from the Oort cloud enter the inner solar system as comets

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• Scientists believe the solar system was formed by the nebular model
• The nebular theory state that the solar system formed from a rotating cloud of dust and gas
• Def: a protoplanetary disk is a large disk shaped cloud of dust and gas resembling a giant fried egg rotating in space
• Most of the mass is concentrated in the center

• The planets eventually formed from the outer parts of the disk
• The central mass eventually became the sun
• Def: planetesimals were asteroid-like bodies that eventually combined to form planets
• Def: accretion is the process of adding mass by colliding with other planetesimals
• The cloud may have been flat as it collapsed, laying in one plane creating the orbits
• Accretion occurs when small particles collect and stick together to form large masses

• planetesimals attracted more and more matter leading to moon sized protoplanets with their own gravity
• The terrestrial planets ended up close to the sun and are small and rocky
• This is because the inner solar system was too hot during formation for ice-forming compounds to condense
• The gas giants are large and have low densities because the outer solar system was cool enough for ice-forming compounds to condense