Astronomy

The study of the universe beyond the Earth’s

atmosphere

Theories of the Universe

• Geocentric Theory: this theory, put forward by the ancient Egyptian astronomer Ptolemy, states that the Earth is the center of the universe.

• Heliocentric Theory: this theory, put forward by the Polish scientist Copernicus, states that the Sun is the center of the universe.

Ptolemy and Geocentric Theory

Copernicus and Heliocentric Theory

What is the Solar System?

• The Solar System is: the Sun, the eight planets and their natural satellites, the asteroids, the comets and the meteoroids.

What is a planet?What is a planet?

• Planet = a massive collection of matter that revolves around a celestial body, or star.

The Eight PlanetsThe Eight Planets

• Mercury• Venus• Earth• Mars• Jupiter• Saturn• Uranus• Neptune

– Pluto = dwarf

Planets are divided into two categories

• Terrestrial Planets are “land-based” planets that are solid, dense, “hot” and have few moons:– Mercury– Venus– Earth– Mars– Pluto

• Gaseous Giants are “gaseous” planets that are big, low density, “cold” and have many moons:– Jupiter– Saturn– Uranus– Neptune

MercuryMercury

• Closest to the sun• Thin atmosphere• Day is 450 oC hot, night is -170 oC

cold• Has many craters• Day is twice as long as its year

VenusVenus

• 2nd planet from the Sun• Hot 470 oC • Has an atmosphere of poison gas

that causes sulfuric acid rain• Has storms• Day is longer than the year

EarthEarth

• 3rd planet from the Sun• Only known planet with liquid

water• Average temperature of ~ 12 oC• Has one moon• Has ice caps on the poles

MarsMars• 4th from the sun4th from the sun• Called the “Red Planet” due to large Called the “Red Planet” due to large

amounts of iron oxide (rust) on surfaceamounts of iron oxide (rust) on surface• Also called the sister to earthAlso called the sister to earth• Rocky compositionRocky composition• Temperature range is -20 Temperature range is -20 ooC to -140 C to -140 ooC C • Has polar ice caps.Has polar ice caps.• 2 moons, Deimos and Phobos2 moons, Deimos and Phobos

JupiterJupiter

• 5th from the sun5th from the sun• Larger than all the other planets Larger than all the other planets

combinedcombined• High gravity makes the gas into a liquid High gravity makes the gas into a liquid

and therefore there are “oceans”and therefore there are “oceans”• Great Red Spot is a storm on the Great Red Spot is a storm on the

surface of the planet that is ~ 3 times surface of the planet that is ~ 3 times the size of earththe size of earth

• Jupiter has 63 moons.Jupiter has 63 moons.

SaturnSaturn

• 6th from the sun• 2nd largest planet in solar system• Has a low density, it would float in

water• Rings are made of particles of ice,

dust and rock• Saturn has 60 moons.

UranusUranus

• 7th from the sun• Planets axis is tilted on it’s side• Green/blue color is from methane

gas, hydrogen and helium composition

• Uranus has thin rings and 27 moons.

NeptuneNeptune

• 8th from the sun8th from the sun

• Blue color is from methane gas compositionBlue color is from methane gas composition

• Great Dark Spot is a storm on the surfaceGreat Dark Spot is a storm on the surface

• Neptune has 13 moons, moon Triton is Neptune has 13 moons, moon Triton is mostly nitrogen = possible atmosphere.mostly nitrogen = possible atmosphere.

PlutoPluto

• 99thth from the Sun from the Sun• ColdCold• Rocky compositionRocky composition• Pluto is considered a Pluto is considered a dwarfdwarf planet planet

– Pluto has one moon, Charon, almost as large as Pluto has one moon, Charon, almost as large as Pluto itselfPluto itself

– Pluto and Charon together orbit the Sun in an Pluto and Charon together orbit the Sun in an unusual pathunusual path

Other Dwarf PlanetsOther Dwarf Planets

• CeresCeres

• HaumeaHaumea

• MakemakeMakemake

• ErisEris

Planetary Paths - OrbitsPlanetary Paths - Orbits

• Planets travel around the sun in a path called an orbit.

• Planetary orbits are elliptical in shape.

• Elliptical orbits are compared based on how eccentric, or out of round, they are.

• A perfect circle has an eccentricity of 0 (no out of round shape) and a line has an eccentricity of 1 (maximum out of round)

Planetary OrbitsPlanetary Orbits

OrbitsOrbits• All the planets revolve around the

sun in a counter-clockwise motion.

• The planets are held in place by the gravitational force of the Sun.

• Planets move fastest through their orbit when they are closest to the sun.

What is our Sun?

• Our Sun is an average star of Our Sun is an average star of yellow-orange classificationyellow-orange classification..

Layers of the SunLayers of the Sun

• The sun is composed of several layers.– Core– Radiative zone– Convective zone– Corona– Photosphere– Chromosphere

The CoreThe Core

• The core of the Sun is the place The core of the Sun is the place where fusion of atoms is taking where fusion of atoms is taking place.place.– Fusion generates temperatures of Fusion generates temperatures of

10,000,000 10,000,000 ooCC– Our sun is fusing hydrogen atoms into Our sun is fusing hydrogen atoms into

heliumhelium

The CoronaThe Corona

•CoronaCorona = the outer layer of = the outer layer of the sun. This is the gradual the sun. This is the gradual boundary between the sun boundary between the sun and space. This is what we and space. This is what we see during an eclipse. see during an eclipse.

The PhotosphereThe Photosphere

•PhotospherePhotosphere = the layer = the layer of the sun that is incredibly of the sun that is incredibly bright and the source of bright and the source of much of the light we see on much of the light we see on earth.earth.

The ChromosphereThe Chromosphere

•ChromosphereChromosphere = is an = is an active layer of the sun that active layer of the sun that is where the magnificent is where the magnificent displays of prominence and displays of prominence and flares take place.flares take place.

Prominence / Solar Prominence / Solar FlaresFlares

• Prominence / Flares are bright spots on the sun formed as gas particles shoot outward from the sun.– These affect the magnetic fields on

earth (radio, television, communications).

– These also cause the Northern Lights or “Aurora Borealis”.

Aurora Borealis – “Northern Lights”

Northern Lights

Sun spots• Sun spot = a dark, cooler spot on

the surface of the sun.

What are Stars?• Star = a hot, glowing sphere of Star = a hot, glowing sphere of

gas that produces energy by gas that produces energy by fusion (of hydrogen molecules).fusion (of hydrogen molecules).

–Some stars produce more Some stars produce more energy therefore they are energy therefore they are hotter.hotter.

How Do Stars Form?

•Nebula = a cloud of dust and gas where stars are born. –Here gravity pulls particles together and fusion starts at 10,000,000 oC and a star is born.

The Horse Head Nebula

More Horse Head Nebula Shots

How Are Stars Classified?

•Stars are classified by:–Temperature–Color–Brightness

Stars are Classified by Temperature and Color.

• HOT COLD

BLUE WHITE YELLOW ORANGE RED BROWN

What is a Main Sequence What is a Main Sequence Star?Star?

Stars are Classified by Brightness

• Actual brightness is how bright a star really is.

• Actual brightness does not change, it is an absolute value.

• Example: a 40 watt light bulb is actually converting 40 watts of energy into light.

• Apparent brightness is how bright a star looks from earth.

• Apparent brightness changes depending on distance from earth and viewing conditions (atmosphere).

• Example: a 40 watt light bulb 10 feet away appears brighter than a 40 watt bulb 100 feet away.

…And After Stars are Born?

Life Cycle of a Star

What is a Supernova?

• Supernova is when the core of a star collapses and the outer portion explodes.– This is the “death of a star”.

• What remains when a star dies out depends on the mass of the star.– The most massive stars collapse into black

holes.

What is a Black Hole?

• Black Hole = the most dense thing known to exist in the universe. The gravity of a black hole is so great that even light can not escape the pull of a black hole.

The massive density of Black Holes creates a gravitational force that pulls in anything that comes within reach: the reach of this force is called the event horizon.

The fate of objects that enter a Black Hole is still uncertain.

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Other Objects in the Solar Other Objects in the Solar SystemSystem

•Other objects in the solar system include:–Comets–Asteroids–Meteoroids

What is a Comet?What is a Comet?

•A Comet is a large chunk of ice, dust, frozen gas and rock fragments that moves through space.

Comets form in an icy cloud, called the Oort Cloud, as the gravity of a passing star pulls

material out of the cloud.

Comets Have Two Tails

The Ion Tail always points away from the sun

The Dust Tail is left behind in the comets path

Halley’s Comet

Comet - Liner

Asteroids

• Asteroid = a large chunk of rock traveling through space.– Most, not all, are found in the asteroid belt

located between Mars and Jupiter.

Asteroid approaching EarthAsteroid approaching Earth

Asteroid ImpactAsteroid Impact

Meteoroid, Meteor, Meteorite

• Meteoroids = small pieces of rock moving through space.

• Meteors = small pieces of rock moving through space (a meteoroid) that enters Earth’s atmosphere.

• Meteorite = a small piece of rock moving through space that hits the Earth.

Perseid Meteor Shower

How are Distances Measured in Space?

• Astronomical Unit (AU) is the distance from the Earth to the Sun. 1 AU = ~92,000,000

miles

• Light Year (LY) is the distance that light travels in one year.1 LY = ~6 trillion

miles

Light Year = DistanceLight Year = Distance

1 light-second = 0.0020 AU = 186,322 miles

1 light-minute = 0.1202 AU = 11.18 mil. miles

1 light-hour = 7.2143 AU = 670.76 million miles

1 light-day = 173.14 AU = 16.098 billion miles

1 light-week = 1212.0 AU = 112.69 billion miles

1 light-month = 5194.3 AU = 482.95 billion miles

1 light-year = 63240.2 AU = 5.89 trillion miles

Our Planets in Light Years

OBJECT Light-travel Distance

Mercury 3.22 light-minutes

Venus 6.01 light-minutes

Earth 8.32 light-minutes

Mars 12.7 light-minutes

Jupiter 43.3 light-minutes

Saturn 1.32 light-hours

Uranus 2.66 light-hours

Neptune 4.16 light-hours

Farthest comets 1.58 light-years

Proxima Centauri 4.3 light-years

Orion Nebula 1,500 light-years

Center of Milky Way 26,000 light-years

Andromeda Galaxy 2.36 million light-years

What is a Galaxy?

• Galaxy = a large group of stars, gas and dust held together by gravity.

Three Types of Galaxies

Spiral Galaxy

Elliptical Galaxy

Irregular Galaxy

Elliptical Galaxies

• Elliptical galaxies = are groups of stars that appear to be shaped like an ellipse (football)

Irregular Galaxies

• Irregular galaxies = are groups of stars that appear to be together but have no regular shape.

Irregular Galaxy

Spiral Galaxies

• Spiral galaxies = are groups of stars that appear to have a dense concentration of stars in the center and arms that are made of stars and dust.

Barred Spiral Galaxy

– A “Barred” Spiral galaxy looks similar to a spiral galaxy with a “bar” of stars through the center and the arms extend outward from the ends of the “bar”.

Clusters

• As stars are grouped into galaxies, galaxies are grouped into clusters.

• Our cluster is called the “Local Group”

So Where in the Universe Are We?

• The astronomical address for Earth would be:– Earth is the 3rd planet in the solar

system of the star called the Sun, which is in the Milky Way Galaxy, of the Local Group of galaxies in the Universe.