Astronomy2

EARTH SCIENCEEARTH SCIENCE

“Overview of the Solar System”

Overview of the Solar systemOverview of the Solar system

• All the planets as well as most of their moons are called satellites, orbit the Sun in the same direction.

Early IdeasEarly Ideas

• Ancient astronomers could recognize the difference between stars and planets by the planets slowly change positions each night.

• Believed in the geocentric model, meaning that all orbited the Earth.

Early IdeasEarly Ideas

• Retrograde motion - a planet moves in the opposite direction across the sky.

• Normal direction for all planets, as observed from Earth, is toward the East.

Kepler’s First LawKepler’s First Law

• Each planet orbits the Sun in a shape called an ellipse, rather than a circle.

Kepler’s First LawKepler’s First Law

• An ellipse is an oval shape that is centered on two points instead of a single point, as in a circle.

• The two points are called foci

• The major axis is the line that runs through both foci; it is the maximum diameter of the ellipse

Astronomical UnitAstronomical Unit

• The average distances between the Sun and each planet are measured in astronomical units, and therefore, these distances are relative to Earth’s average distance from the Sun.

• 1.496 x 10^8 km = 1 astronomical unit

EccentricityEccentricity

• A planet in an elliptical orbit is not at a constant distance from the Sun.

• When a planet is closest to the Sun in its orbit , it is at perihelion.

• When farthest from the Sun, it is aphelion.

EccentricityEccentricity

• The shape of a planet’s elliptical orbit is defined by eccentricity, which is the ration of the distance between the foci to the length of the major axis.

• The length of time it takes a planet or body to travel a complete orbit is an orbital period.

Kepler’s Second LawKepler’s Second Law

• An imaginary line between the Sun and a planet sweeps out equal amounts of area in equal amounts of time.

Kepler’s Third LawKepler’s Third Law

• The square of the orbital period (P) equals the cube of the semi-major axis of the orbital ellipse (a).

• (P) is earth years

• (a) is in astronomical units

Galileo DiscoveriesGalileo Discoveries

• First person to use a telescope

• Supported the idea that the Earth orbited the Sun.

• Jupiter has 4 moons

Gravity and OrbitsGravity and Orbits

• Newton developed an understanding of gravity by observing the Moon’s motion, the orbits of the planets, and the acceleration of falling objects on Earth.

Law of Universal GravitationLaw of Universal Gravitation

• Every pair of bodies in the universe attract each other with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them or

Center of MassCenter of Mass

• Newton determined that each planet orbits a point between it and the Sun called the center of mass.

• The center of mass is the balance point between two orbiting bodies.

• if two bodies orbiting each other and one is larger, the center of mass is closer to the more massive body.

Earth ScienceEarth Science

“The Terrestrial Planets”

The Terrestrial PlanetsThe Terrestrial Planets

• Planets are grouped into two main categories:• Terrestrial planets - inner 4 planets, close to the size of

Earth, and have solid rocky surfaces.

• Gas giant planets - outer 4 planets, much larger, more gaseous, and lack solid surfaces.

MercuryMercury

• Closest planet to the sun and has no moons

• One-third the size of Earth

• Mercury has 3 days for every 2 years

MercuryMercury

• Atmosphere• Essentially no atmosphere• Primarily oxygen and sodium• Day time temp. 427 degrees C• Night -173 degrees C• Largest day-night temp difference of all the

planets

MercuryMercury

• Surface• Based on radio observations and pictures

• Similar to the moons surface (why?)

• Surface gravity much greater than the moon

• Planet wide cliffs called scarps• Scarps - develop as Mercury’s crust shrank and fractured early

in it’s geological history.

MercuryMercury

• Interior• High-density suggests that the core is nickel-iron

• The core fills 42% of the planet’s volume

• It is believed that Mercury was much larger and then lost most of its crust and mantle to collisions with another celestial body

VenusVenus

• Has no moons• Brightest planet in Earth’s nighttime sky• Highest albedo @ 75%• Spins backwards (clockwise)(called?)• Believe this was caused by collision• 1 day = 243 Earth days

VenusVenus

• Atmosphere • Vastly different than Earth’s

• Average temp. 464 degrees C

• High atmospheric pressure, you would feel like you were 915 meters down in water

• Mostly carbon dioxide and nitrogen

• Clouds made of sulfuric acid and 35km thick.

VenusVenus

• Surface• Smoothed by volcanic lava flows only a few

impact craters• Little evidence of tectonic activity and no well-

defined system of crustal plates.

VenusVenus

• Interior• Size and density similar to Earth

• No seismic data

• Theorized that Venus has a liquid metal core that extends halfway to the surface

• No measurable magnetic field despite this liquid core.

EarthEarth

• Third planet from the Sun• Unique properties• Distance from the Sun and nearly circular orbit

allows water to exist in all three states: solid, liquid, and gas.

• 78% nitrogen, 21% oxygen

EarthEarth

• Precession• Axis it tilted so it creates our seasons

• The wobbling of the Earth on its axis is called precession

• The sideways pull of the precession comes from the Moon’s gravitational force on Earth, as well as the Sun’s.

• Sun plays a lesser part in this.

MarsMars

• Fourth planet from the Sun• Outermost terrestrial planet• Know as the red planet, caused by high iron

content• Smaller and less dense than Earth• 2 irregularly shaped moons

• Phobos and Demos

MarsMars

• Atmosphere• Similar to Venus, but the density and pressure

is much lower• Thin atmosphere, turbulent, constant wind• Dust storms that last weeks at a time.• Mostly carbon dioxide.

MarsMars

• Surface• The southern hemisphere is a heavily cratered, highland

region, like the moon• The northern hemisphere is dominated by plains that

are sparsely cratered• 4 gigantic shield volcanoes, the largest called Olympus

Mons (largest mountain in the solar system) Base would cover all of Colorado

MarsMars

• Dried river beds, lake beds, and runoff channels.

• Suggest that liquid water once existed on the surface of Mars

• Small ice caps in the northern and southern poles, mostly “dry ice”, but some water ice underneath.

MarsMars

• Interior• Unsure about the internal structure of Mars

• Hypothesize that there is a core of iron and nickel and possible sulfur

• No magnetic field, so core is probable solid

• No evidence of current tectonic activity or tectonic plates on the surface of the crust.

Earth ScienceEarth Science

“ The Gas Giant Planets”

The Gas Giant PlanetsThe Gas Giant Planets

• Interiors are composed of fluids, either or gaseous or liquid, and small solid cores

• Composed primarily of lightweight elements such as hydrogen, helium, carbon, nitrogen, and oxygen

• Many satellites and ring systems• Very large, 15 to 300 times the mass of Earth, 4 to

10 times in diameter.

JupiterJupiter

• Largest and 5th from the Sun.• Diameter is 11 times larger than Earth’s• Albedo is 34%• Banded appearance• Has 4 moons and many smaller• Detected volcanic activity in largest moon Io.

JupiterJupiter

• Atmosphere• Hydrogen and helium make up the majority of

atmosphere• These elements remain in a gas or liquid form.• There is a layer of liquid metallic hydrogen, a form of

hydrogen that has properties of both a liquid and a metal, which can exist only under conditions of very high pressure

JupiterJupiter

• Rotation extremely rapid, less than 10 hours, warps the planet

• Belts - are low, warm, dark-colored clouds that sink• Zones - are high, cool, light-colored clouds that rise• Great Red Spot - storm that has been rotating Jupiter

for 300 years

JupiterJupiter

• Moons and Rings• 4 largest moons - Io, Europa, Ganymede, and Callisto -

Galilean satellites.

• Composed of ice and rock

• Ring of Jupiter 6400km wide

• Now known that all gas giant planets have rings

SaturnSaturn

• 6th planet from the Sun

• 2nd largest planet

SaturnSaturn

• Atmosphere• Average density lower than water

• Rotates quickly and has flowing belts and zones

• Dominated by hydrogen and helium

• Interior is mostly fluid with a small solid core

• Magnetic field 1000 times that of Earth’s

SaturnSaturn

• Moons and Rings• Broader and brighter rings than the other planets• Rings composed of rock and ice• There are seven major rings but they are made up of

narrower rings called ringlets• Ring particles of have not combined to form a large

satellite because Saturn’s gravity prevents particles from sticking together.

SaturnSaturn

• This is why gas giant moons are found further away from their planets

• Hypothesized that the ring particles are debris left over when a moon was destroyed by a collision

• One giant moon-Titan; seven average sized moons, and a number of smaller moons

UranusUranus

• Seventh planet from the Sun

• Discovered accidentally in 1781

UranusUranus

• Atmosphere• 4 times as large and 15 times as massive as Earth

• Blue velvety appearance

• Few clouds

• No distinct belts or zones

• Completely fluid interior with small solid core

UranusUranus

• Strong magnetic field

• Rotational axis is tipped over so far that the north pole is in the middle

• Knocked sideways by collision

• Each pole spends 42 earth days in sunlight and 42 days in complete darkness

• Atmosphere keeps temperature at -215 degrees C

UranusUranus

• Moons and Rings• Moon count is always changing• Known moons and rings orbit in the planet’s

equatorial plane• Rings are dark, almost black

NeptuneNeptune

• 8th planet from the Sun

• Existence was predicted before it was discovered due to small deviations in Uranus movement

• Discovered 1846

NeptuneNeptune

• Atmosphere• Slightly smaller and denser than Uranus• 4 times larger than Earth• Like Uranus- color due to methane, temperatures,

magnetic fields, interior, and particle belts• Has clouds and zones like Jupiter and Saturn• Had the Great Dark Spot, vanished in 1994

NeptuneNeptune

• Moons and Rings• Has many moons• Largest is Triton has a retrograde orbit

• Thin atmosphere• Nitrogen geysers- caused by nitrogen gas below the surface

Six rings - composed of microscopic-sized dust particles

PlutoPluto

• Now classified as a dwarf planet• Discovered in 1930• Solid surface• Low density and small in size• Half ice and half rock• Smaller than our moon• Atmosphere is methane and nitrogen