Astronomy

Astronomy  The scientific study of matter in

outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena.

Forget the big bang, tune in to the big hum

THE big bang sounded more like a deep hum than a bang, according to an analysis of the radiation left over from the cataclysm. Physicist John Cramer of the University of Washington in Seattle has created audio files of the event which can be played on a PC. "The sound is rather like a large jet plane flying 100 feet above your house in the middle of the night," he says. Giant sound waves propagated through the blazing hot matter that filled the universe shortly after the big bang.

These squeezed and stretched matter, heating the compressed regions and cooling the rarefied ones. Even though the universe has been expanding and cooling ever since, the sound waves have left their imprint as temperature variations on the afterglow of the big bang fireball, the so-called cosmic microwave background. Cramer was prompted to recreate the din- last heard13.7 billion years ago- by an11-year-old boy who wanted to know what the big bang sounded like for a school project.

To produce the sound, Cramer took data from NASA's Wilkinson Microwave Anisotropy Probe. Launched in 2001, the probe has been measuring tiny differences in the temperature between different parts of the sky. From these variations, he could calculate the frequencies of the sound waves propagating through the universe during its first 760,000 years, when it was just 18 million light years across. At that time the sound waves were too low in frequency to be audible. To hear them, Cramer had to scale the frequencies 100,000 billion billion times.

Nevertheless, the loudness and pitch of the sound waves reflect what happened in the early universe. During the 100-second recording (http://www.npl.washington.edu/AV/BigBangSound_2.wav), the frequencies fall because the sound waves get stretched as the universe expands. "It becomes more of a bass instrument," says Cramer.

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Author: Marcus Chown

The universe started as a single point. That point was extremely dense. It became unstable and exploded outward. Today the universe continues to expand.

The Universe  A massive explosion occurred, between 12 –15 billion years ago, and the universe has been expanding ever since

Evidence for Expansion

 The Doppler Effect is used as evidence that galaxies are moving away from us.

 When light moves away, it’s wavelength is expanded (gets longer), meaning it becomes redder.

 This is called the redshift.

Doppler Effect

  All galaxies show redshift in their spectra, meaning they are moving away from us.

Measuring Distance

  Distances between celestial objects are extremely large.

  Rather than miles, astronomers refer to a light-year as a standard unit of distance.

  One light-year is the distance light travels in one year.

  The speed of light is 186,000 mps (300,000 kps).   Thus, one light-year is about 6 trillion miles.   The nearest star to us (Proxima Centauri) is 4.2

light-years away.

Astronomical unit

 Another unit of distance is the Astronomical Unit (AU).

 One AU is the distance from the Earth to the Sun (93 million miles)

 Distances to other objects are given in multiples of AU.

1.  384,000 km 2.  1 AU 3.  100 AU 4.  1 light year 5.  75,000 light years

What is (approximately) the size of the solar system?

Remember:

1 AU = distance Sun – Earth = 150 million km

Galaxies

Galaxies

 A galaxy is a collection of millions or billions of stars.

 Galaxies can be spiral, elliptical, spherical or irregular in shape.

 The Sun is part of the Milky Way galaxy, which is a spiral galaxy.

 The Sun is located on one of the spiral arms, far from the galactic center.

Put these in order of size:

galaxy solar system universe

universe galaxy solar system

Regents Question Which sequence correctly lists the relative

sizes from smallest to largest?

(1)our solar system, universe, Milky Way Galaxy

(2)our solar system, Milky Way Galaxy, universe

(3)Milky Way Galaxy, our solar system, universe

(4)Milky Way Galaxy, universe, our solar system

Regents Answer

(2)our solar system, Milky Way Galaxy, universe

  Astarisahuge,shiningballinspacethatproducesalargeamountoflightandenergy.

  Starscomeinmanysizes.  About75%areapartofgroupsthatorbiteachother.  Theyaregroupedinlargestructurescalledgalaxies.(MilkyWay).

  Starshavelife-cycleslikehumans.  Astarscolordependsonsurfacetemperature.

Stars

 Stars are burning masses of gas.  Their energy is the result of nuclear

fusion, in which Hydrogen atoms combine to form Helium atoms, releasing energy.

 Electromagnetic energy is radiated by stars.

Star Characteristics

 Stars vary in their size, mass, density, temperature and composition.

 Luminosity – the actual brightness of a star

 Luminosity depends only a star’s size and temperature

Composition

 Stars are primarily made of Hydrogen and Helium

 Many other elements are present in stars in small amounts

 A star’s composition can be determined by spectral analysis.

Spectral Analysis

 Spectral analysis is the study of the electromagnetic spectrum emitted by a star, using a spectroscope.

 Each element emits radiation is a specific set of wavelengths

Electromagnetic Spectrum

Color and Temperature

ESRTs p15

ESRTs p15

What type of star is our Sun classified as? ESRT p15

Circle where it is on the chart

The H-R Diagram

 The Hertzsprung-Russell (H-R) Diagram is a graph of stars, comparing luminosity and temperature.

 Stars are categorized according to these two properties

The H-R Diagram

 Main Sequence – band into which most stars fall – High temperature, high luminosity –  Low temperature, low luminosity

 Red Giants and Supergiants – cooler, very luminous stars that are very large

 White Dwarfs – hotter, low luminosity stars that are small

Shade the chart where all of the stars are hotter than our sun.

Draw a line on the chart which separates those stars brighter

than our sun and those less bright.

ESRTs p15

The H-R Diagram

Regents Question Which statement describes the general

relationship between the temperature and the luminosity of main sequence stars?

(1) As temperature decreases, luminosity increases.

(2) As temperature decreases, luminosity remains the same.

(3) As temperature increases, luminosity increases.

(4) As temperature increases, luminosity remains the same.

Regents Answer

(2) As temperature increases, luminosity increases.

Regents Question

Compared to other groups of stars, the group that has relatively low luminosities and relatively low temperatures is the

(1)Red Dwarfs (3)Red Giants (2)White Dwarfs (4)Blue Supergiants

Regents Answer

(1)Red Dwarfs

Regents Question Which list shows stars in order of

increasing temperature?

(1)Barnard’s Star, Polaris, Sirius, Rigel. (2)Aldebaran, the Sun, Rigel, Procyon

B. (3)Rigel, Polaris, Aldebaran, Barnard’s

Star. (4)Procyon B, Alpha Centauri, Polaris,

Betelgeuse.

Regents Answer

(1)Barnard’s Star, Polaris, Sirius, Rigel.

Star Life Cycles

  Stars are born in a cloud of gas and dust, called a nebula.

  Most stars remain as main sequence stars, until their hydrogen fuel is depleted

  An average star, like the sun, would go through the Red Giant phase, eventually becoming a White Dwarf.

  A large star would become a Supergiant, then explode as a supernova. The result may be a neutron star, pulsar or black hole.

Sun

http://en.wikipedia.org/wiki/Image:Sun920607.jpg

Mythology The Sun God. Greeks Called it Hellos

Mass 333 400 times the mass of the Earth

Diameter 1 392 000 km (109 x Earth’s

diameter)

Gravity 28 times that on Earth

Surface Temperature 6000°C (average). From 4500 to

2000000°C up to 15000000°C in the core.

Period of rotation (day)

Equator 26 Earth days, poles 37 Earth days

Tilt of axis 122°

Solar System Components

 The Solar System includes: •  The Sun, a medium size, middle-aged

star •  The eight planets and associated moons •  Asteroids – chunks of rock found mostly

in a belt between Mars and Jupiter •  Comets – mass of frozen gas and rock •  These are considered celestial objects

which appear in the sky during day and night.

Formation of the Solar System   4.6 Billion years ago a large cloud of gas, ice & dust

existed   Began to contract & slowly rotate

–  Contraction increased density & rotation –  Gravity began to pull material toward the center –  Density increases = increased rotation & gravity –  Begins to form disk with large center –  Central mass begins to heat up due to contraction

•  Temperatures reach 10 million 0K •  Hydrogen atoms begin to fuse together forming

Helium •  Fusion occurs, driving the formation of our Sun

–  The material outside the central mass forms planets

The Parts of Our Solar System   The sun is the center of the Solar System

–  Inner Planets: Also called Terrestrial planets: first four planets. They are solid, rock like structures

–  Asteroid belt: band of rocks orbiting the sun –  Outer Planets: Also called Jovian planets: The 4

planets farthest from the sun •  4 are made up of mainly lighter element gases •  Last two are frozen materials

Two Kinds of Planets Planets of our solar system can be divided into

two very different kinds:

Terrestrial (earthlike) planets: Mercury, Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter,

Saturn, Uranus, Neptune

Size of Terrestrial Planets Compared to Jovian Planets

Terrestrial Planets

Four inner planets of the solar system

Relatively small in size and mass (Earth

is the largest and most massive)

Rocky surface

Surface of Venus can not be seen directly from Earth because of its

dense cloud cover.

The Jovian Planets Much larger in mass

and size than terrestrial planets

Much lower average density

All have rings (not only Saturn!)

Mostly gas; no solid surface

Asteroids

The total mass of all the asteroids is less than that of the Moon.

-rocky objects with round or irregular shapes

lie in a belt between Mars and Jupiter

The Asteroid Belt

Plut

o

(Distances and times reproduced to scale)

Most asteroids orbit the sun in a

wide zone between the orbits of Mars

and Jupiter.

Asteroids –  Believed to be a planet that never formed –  Range in size from dust to almost Moon size –  Photographed by Galileo probe

•  Some Named Asteroids: –  Ceres: 940 km (Largest known) –  Pallas: 523 km –  Vesta: 501 km –  Juno: 244 km –  Gaspra & Ida

only visible when they are close to

the sun

Comets

Mostly objects in highly elliptical orbits, occasionally coming close to the sun.

Icy nucleus, which evaporates and gets blown into space by

solar wind pressure.

Comet Information:   Comet Composition:

–  Dust, rock, frozen methane, ammonia, and water –  Comets normally look like dirty snowballs –  When they get close to stars, they change

•  They begin to vaporize & Glow •  Forms a coma (tail) from the nucleus (head)

–  Coma: glowing trail of particles –  Always points away from the star

–  Comets eventually break up into space debris   Oort Cloud: large collection of comets beyond

Pluto

Meteoroids Small (µm – mm sized)

dust grains throughout the solar system

If they collide with Earth, they evaporate in the

atmosphere.

Visible as streaks of light (“shooting stars”):

meteors.

LARGEST METEORITE TO HIT EARTH – Namibia, Africa

Meteoroids, Meteors, & Meteorites   Meteoroids: chunks of rock

–  Randomly moving through space –  Usually leftover comet or asteroid debris

  Meteor: Meteoroid that enters Earth’s atmosphere –  Heat up & begin to glow = shooting star –  Most burn up before reaching the surface –  Many meteors at one time = meteor shower

  Meteorite: Meteor that does not totally burn up, & strikes the Earth’s surface –  Impact creates a crater

Cosmic Collision Video Clip

http://solarsystem.jpl.nasa.gov/multimedia/gallery/solarsys_scale.jpg (Distance between objects not to scale)

How small are we?

source: Celestia (application) (Distance between objects not to scale)

Earth

Earth

How small are we?

source: Celestia (application) (Distance between objects not to scale)

Relative distance of planets   Sun = 1300mm

diameter (blown up garbage bag)

  Mercury = 4.5mm (coffee bean) 54m from Sun

  Venus = 11.3mm (small blueberry) 101m from Sun

  Earth = 11.9mm (small blueberry) 139m from Sun

  Mars = 6mm (pea) 213m from Sun

image source: Google Earth

Relative distance of planets   Jupiter = 133.5mm

(large grapefruit) 727m from Sun

  Saturn = 112.5mm (large orange) 1332m from Sun

  Uranus = 47.7mm (Kiwi) 2681m from the Sun

  Neptune = 46.2mm (nectarine) 4200m from the Sun

  Pluto = 2mm (grain of rice) 5522m from the Sun

image source: Google Earth

Relative distance of planets   Jupiter = 133.5mm

(large grapefruit) 727m from Sun

  Saturn = 112.5mm (large orange) 1332m from Sun

  Uranus = 47.7mm (Kiwi) 2681m from the Sun

  Neptune = 46.2mm (nectarine) 4200m from the Sun

  Pluto = 2mm (grain of rice) 5522m from the Sun

image source: Google Earth

  A planet is a body that is in orbit around the Sun, has enough mass for its self-gravity to overcome forces (nearly round) shape, and clears the neighborhood around its orbit.

Planet order (closest to the sun to furthest):  MERCURY  VENUS  EARTH  MARS  JUPITOR  SATURN  URANUS  NEPTUNE

  Position: Closest planet to the Sun.   Atmosphere: Like Earth’s moon, very little.   Landscape: Many craters, a little ice. Cliffs

and valleys present.   Temperatures: Super-heated by the sun in

the day. At night temperatures reach hundreds of degrees below freezing. (Not as warm as you would think).

  Year (Full rotation around the sun): 88 days.   Moons: 0   Rings: 0

Mercury

http://en.wikipedia.org/wiki/Image:Reprocessed_Mariner_10_image_of_Mercury.jpg

Mythology God of travel, commerce and

thieves

Mass 0.056 times that of Earth

Moons None

Diameter 4878 km ( = 0.38 x Earth’s

diameter)

Surface Similar to Earth’s moon

Gravity 0.38 times that on Earth

Surface Temperature –170°C to 430°C

Period of rotation (day) 59 Earth days

Tilt of axis 0°

Distance from Sun 0.39 AU (58 million kilometres)

Time to orbit Sun (year)

88 Earth days

 Position: 2nd planet from the sun.  Atmosphere: Thick enough to trap heat,

hurricane winds, lightning, and acid clouds.  Landscape: Volcanoes and deformed mountains.  Temperatures: Intense heat.  Year (Full rotation around the sun): 225 Earth

days.  Moons: 0  Rings: 0

Venus

Venus

http://en.wikipedia.org/wiki/Image:Venus-real.jpg

Mythology Goddess of love and beauty

Mass 0.815 times that of Earth

Moons None

Diameter 12 103 km ( = 0.95 x Earth’s

diameter)

Surface Extensive cratering, volcanic

activity.

Gravity 0.9 times that on Earth

Surface Temperature 460°C

Period of rotation (day) 243 Earth days

Tilt of axis 30°

Distance from Sun 0.72 AU (108 million kilometres)

Time to orbit Sun (year)

225 Earth days

 Position: 3rd planet from the sun.  Atmosphere: Suitable air pressure to

have life. Air is made of oxygen.  Landscape: The only planet that has

liquid on the surface, rocky, land formations.

 Temperatures: Suitable for life. Ranges from locations on Earth.

 Year (Full rotation around the sun): 365 Earth days.

 Moons: 1  Rings: 0

Earth

http://en.wikipedia.org/wiki/Image:The_Earth_seen_from_Apollo_17.jpg

Mythology Gaia—mother Earth

Mass 1.0 times that of Earth (5 980 000

000 000 000 000 000 000 kg)

Moons One (‘the Moon’)

Diameter 12 756 km

Surface Two-thirds water, one-third land

Gravity 1.0 times that on Earth

Surface Temperature average 22°C

Period of rotation (day) 1 Earth day

Tilt of axis 23.5°

Distance from Sun 1 AU (150 million kilometres)

Time for light to reach Earth

8 minutes

Time to orbit Sun (year)

365.25 Earth days

  Position: 4th planet from the sun.

  Atmosphere: Thinner air than Earth.

  Landscape: Frozen water below the surface, rocky, dusty, and has craters.

  Temperatures: Like Earth, but drier and colder

  Year (Full rotation around the sun): 687 Earth days.

  Moons: 2   Rings: 0

Mars

http://en.wikipedia.org/wiki/Image:2005-1103mars-full.jpg

Mythology God of war

Mass 0.107 times that of Earth

Moons 2 (Phobos—diameter 23 km,

Deimos—diameter 10 km)

Diameter 6794 km ( = 0.53 xEarth’s

diameter)

Surface

Soft red soil containing iron oxide (rust). Cratered regions, large volcanoes, a large canyon and

possible dried-up water channels.

Gravity 0.376 times that on Earth

Surface Temperature –120°C to 25°C

Period of rotation (day) 1.03 Earth days

Tilt of axis 25.2°

Distance from Sun 1.52 AU (228 million kilometres)

Time to orbit Sun (year)

687 Earth days

Time to reach Mars 9 months

  Position: 5th planet from the sun.

  Atmosphere: Colorful clouds, until it is squished unto liquid. Cold and windy, giant storms.

  Landscape: Thick super hot soup.

  Temperatures: Extremely cold at clouds. Extremely hot and cold radiation.

Jupiter

http://en.wikipedia.org/wiki/Image:Jupiter.jpg

Mythology Ruler of the Gods

Mass 318 times that of Earth

Moons

At least 28 moons and four rings, including the four largest moons:

Io, Ganymede, Europa and Callisto. These are known as the ‘Galilean’

moons.

Diameter 142 984 km ( = 11.21 x Earth’s

diameter)

Surface Liquid hydrogen

Gravity 2.525 times that on Earth

Surface Temperature Cloud top –150°C

Period of rotation (day) 9 hours 55 minutes

Tilt of axis 3.1°

Distance from Sun 5.2 AU (778 million kilometres)

Time to orbit Sun (year)

11.8 Earth years

  Position: 6th planet from the sun.   Atmosphere: Composed mostly of gas

with no solid surface. Cloud strips.   Landscape: No solid surfaces, high

pressures turn gas into liquids.   Temperatures: Rings made out of water

ice, really cold.

Saturn

http://en.wikipedia.org/wiki/Image:Saturn_from_Cassini_Orbiter_%282007-01-19%29.jpg

Mythology God of agriculture

Mass 95.184 times that of Earth

Moons At least 30 moons and rings in

seven bands

Diameter 120 536 km (= 9.45 x Earth’s

diameter)

Surface Liquid hydrogen

Gravity 1.064 times that on Earth

Surface Temperature –180°C

Period of rotation (day) 10 hours 39 minutes

Tilt of axis 26.7°

Distance from Sun 9.6 AU (1400 million kilometres)

Time to orbit Sun (year)

29.5 Earth years

 Position: 7th planet from the sun.� Atmosphere: Gets thicker and

thicker, until it is squished unto liquid. Cold and windy.�

 Landscape: Layer of superheated water and gases that form bright clouds.�

 Temperatures: Extremely cold at cloud tops and superheated towards the center.�

Uranus

http://en.wikipedia.org/wiki/Image:Uranusandrings.jpg

Mythology Father of Saturn

Mass 14.54 times that of Earth

Moons At least 21 moons and 11 rings

Diameter 51 200 km (= 4.01 x Earth’s

diameter)

Surface Likely to be frozen hydrogen and

helium

Gravity 0.903 times that on Earth

Surface Temperature –220°C

Period of rotation (day) 17 hours 14 minutes

Tilt of axis 98°

Distance from Sun 19.2 AU (2875 million kilometres)

Time to orbit Sun (year)

84 Earth years

  Position: Furthest from the sun (Cannot see without a Telescope). 8th planet.

  Atmosphere: Very Windy, cold clouds, a layer of methane gas (giving it a blue color), storms as large Earth.

  Landscape: Scientist think it may have an ocean of super hot lava.

  Temperatures: Cold

Neptune

http://en.wikipedia.org/wiki/Image:Neptune.jpg

Mythology God of the sea

Mass 17.15 times that of Earth

Moons 8 moons and 5 rings

Diameter 49 528 km ( = 3.88 x Earth’s

diameter)

Surface Frozen hydrogen and helium

Gravity 1.135 times that on Earth

Surface Temperature –220°C

Period of rotation (day) 16 hours 7 minutes

Tilt of axis 29.3°

Distance from Sun 30.1 AU (4500 million kilometres)

Time to orbit Sun (year)

165 Earth years

  Pluto is NOT considered a planet anymore!

  It is classified as a dwarf planet.

  Temperatures: Extremely cold, covered with frost.

  Year (Full rotation around the sun): 248 Earth years.

  Moons: 3   Pluto is very hard to

see, if with a really powerful teloscope.

The planets to scale. The rings of the gas giants are not shown.

http://www.solarviews.com/cap/misc/obliquity.htm

Comparing tilt of axis

Draw a line across the table between the terrestrial and jovian planets and label.

Which are more dense? Jovian or terrestrial

Which have more moons ? Jovian or terrestrial

Which have longer periods of revolution? Jovian or terrestrial

Which are larger in size on average ? Jovian or terrestrial

Which planet has the longest day?

Which planet has the longest year?

Regents Question

Which object in our solar system has the greatest density?

(1) Jupiter (3) the Moon (2) Earth (4) the Sun

Regents Answer

(2) the Earth

1.  What is the solar system (what objects make up the Solar System?

2.  Draw a diagram of planet placement and list the planets in order from the closest to the furthest from the sun.

3.  When did the solar system form? 4.  When did the universe form? 5.  What is the difference between the Jovian and

Terrestrial planets? 6.  What is the difference between a meteor,

meteoroid, and meteorite? 7.  What is your favorite planet and why?

Planetary Orbits

Plut

o

Earth

Venus Mercury

Do Now:

Make 3 observations about this animation

(Distances and times reproduced to scale)

http://solarsystem.jpl.nasa.gov/multimedia/gallery/vis_orb.jpg

http://solarsystem.jpl.nasa.gov/multimedia/gallery/outer_orb.jpg

How the planets move  All planets move in the same

plane (a large imaginary flat surface)

Tipped over by more than 900

Mercury and Pluto: Unusually highly inclined orbits

Planetary Orbits

Planetary Orbits

Plut

o

Earth

Venus Mercury

All planets in almost circular (elliptical)

orbits around the sun, in approx. the same

plane (ecliptic).

Sense of revolution: counter-clockwise

Sense of rotation: counter-clockwise (with exception of Venus, Uranus, and

Pluto)

Orbits generally inclined by no more than 3.4o

Exceptions:

Mercury (7o)

Pluto (17.2o)

(Distances and times reproduced to scale)

Orbits

 Revolution – the movement of an object around another object

 Orbit – the path taken by a revolving object

 Celestial objects have elliptical orbits

Elliptical Orbit  A circle has one central point, called a

focus.  Ellipses have two points, called foci.

Eccentricity

Calculate the eccentricity of the ellipse below:

Formula: eccentricity = distance between foci length of major axis

length of major axis

Regents Question

Which object is located at one foci of the elliptical orbit of Mars?

(1)the Sun (3)Earth (2)Betelgeuse (4)Jupiter

Regents Answer

(1)the Sun

Regents Question The bar graph below shows one planetary characteristic,

identified as X, plotted for the planets of our solar system.

Which characteristic of the planets in our solar system is represented by X?

(1)mass (3)eccentricity of orbit (2)density (4)period of rotation

Regents Answer

(3)eccentricity of orbit

Regents Question

Which planet has the least distance between the two foci of its elliptical orbit?

(1)Venus (3)Mars (2)Earth (4)Jupiter

Regents Answer

(1)Venus

Laws of Planetary Motion   Devised by German

astronomerJohannes Kepler: 1.  The planets move in elliptical orbits,

with the Sun at one focus 2.  The line joining the Sun and a planet

sweeps equal areas in equal intervals of time

3.  The square of the time of revolution (T²) is proportional to the planet’s mean distance from the Sun (R³)

Kepler’s First Law

• Planets move around sun in elliptical orbits. • Sun is at one focus point. • Flatness called eccentricity • Formula in ESRT.

Focus points

Major axis

Eccentricity =

Distance between foci Length of major axis

Kepler’s Second Law

Area of orange section is equal.

Distance along orbit is not the same. But the time covered is equal. eccentricity website

Kepler's Third Law

Not drawn to scale.

Earth – 150 mill. Km, 365 days

Orbital Energy

 Gravitation – the force of attraction between 2 objects

 Inertia – the tendency of an object in motion to continue in motion along a straight path

 The interaction of gravity and inertia keep planets in orbit

Energy Transfer

 Energy is transferred between potential and kinetic as a planet orbits the Sun.

Orbital Velocity

 The Earth’s orbital velocity is highest when kinetic energy is the highest.

 This occurs when the Earth is nearest to the Sun in its orbit.

When furthest from Sun

When closest to Sun

eccentricity website

Which planet has the least perfectly circular orbit?

Which planet has the most perfectly circular orbit?