Introduction to Astronomy The Universe

Cosmology

• the branch of astronomy that deals with the origin, large-scale properties, and the evolution of the observable universe

The Universe

• in astronomy, the sum total of all things which can be directly observed or whose physical effects on other things can be detected

• in simpler terms, space and all the matter and energy in it

• major components: – galaxies

– solar systems

– planets

Can you think of something in the universe that cannot be

seen, but its effects on other things can be detected?

Telescope

• a device that gathers electromagnetic radiation

• Types: – Visible, infrared, ultraviolet – pick up visible,

infrared, and ultraviolet waves • Reflecting - use mirrors that reflect the image being

viewed

• Refracting – using lenses, gathers light and focuses it near the opposite end of the tube; works like a magnifying glass

– Radio - pick up radio waves emitted from space; not effected by variables like weather or clouds

Internet Telescope

Hubble Space Telescope • a reflecting telescope

that was placed into orbit in 1990

• sends images and measurements back to Earth electronically

• Hubble does not have the

interference of Earth’s

atmosphere when viewing

space

What is one of the main benefits of having the Hubble Space

Telescope in orbit, as opposed to it being here on Earth?

Image taken from: http://hubblesite.org/gallery/

“Big Bang” Theory

• the primeval expansion of space, time, matter and energy that most astronomers think gave rise to the universe as we see it today.

• occurred about 13.7 billion years ago • thought to have expanded within a second from

something the size of a spec of dust to the size of our solar system

Time begins • The universe begins

~13.7 Billion years ago

• The universe begins as the size of a single atom

• The universe began as a violent expansion – All matter and space

were created from a single point of pure energy in an instant

~ 3 minutes after big bang • The universe has grown from

the size of an atom to larger than the size a grapefruit

• E=mc2

• energy froze into matter according to Albert Einstein’s equation.

• This basically says that like snowflakes freezing, energy forms matter into clumps that today we call protons, neutrons and electrons.

• These parts later form into atoms

~ Several hundred thousand

years after Big Bang

• ATOMS form (specifically Hydrogen and its isotopes with a small amount of Helium.)

• The early Universe was about 75% Hydrogen and 25% Helium. It is still almost the same today.

~200 to 400 million

years after Big Bang • 1st stars

and

galaxies

form

~ 4.6 billion years ago

• Our

Solar

system

forms

Misconceptions about the Big

Bang • there was no explosion; there was (and

continues to be) an expansion

– Rather than imagining a balloon popping and releasing its contents, imagine a balloon expanding: an infinitesimally small balloon expanding to the size of our current universe

• we tend to image the singularity as a little fireball appearing somewhere in space

– space began inside of the singularity. Prior to the singularity, nothing existed, not space, time, matter, or energy - nothing.

Edwin Hubble

• determined that other galaxies exist, besides the Milky Way

• observed that galaxies were moving away from each other – Hubble Law – the farther

away a galaxy is, the faster it is moving away from us; supports the Big Bang Theory

Image taken from: http://apod.nasa.gov/apod/ap960217.html

Arno Penzias & Robert Wilson

• accidentally detected faint radiation on a radio telescope in 1965

• determined that the radiation was leftover thermal energy from the “big bang”

• Background radiation from all of objects in the universe which is hypothesized to have originated during the Big Bang

Image taken from:

http://www.einstein-online.info/en/elementary/cosmology/early_universe/index.html

15

Doppler Effect

• Shifting of wavelengths can occur with both

sound and light

• Doppler effect is easier to observe with sound

– With sound you will hear a change in pitch

– Imagine an ambulance approaching a person standing

on a sidewalk:

• As the ambulance moves closer the pitch becomes higher

• As the ambulance moves away the pitch becomes lower

Ambulance Doppler

16

Come and ride the Doppler Train Higher

pitch

Lower

pitch

17

Doppler effect with light

• Remember each element has its own

spectra that we can identify

• We can notice changes or shifts in

wavelengths of the spectra

– blue shift – spectra shifted to the blue end of

the spectra, the object is moving closer

– red shift – spectra shifted to the red end of

the spectra, the object is moving away

18

19

Blue Red

Blue Red

Blue shift – object is moving closer

20

Blue Red

Blue Red

Red Shift – object is moving away

21

Blue Red

Blue Red

No shift – object is moving same speed

22

The Universe is still expanding

• Most objects in the universe show a red

shift so the universe is still expanding

since the Big Bang

• The objects furthest away show the

greatest red shift, so moving away fastest

Section 2

Parts of the Universe • Organization of Universe

– Universe

– Galaxies

– Solar Systems

– Planets

– Smaller satellites

• Objects that orbit a larger object, ex: moon orbits

the earth so the moon is one of Earth’s satellites

Galaxy

• Gravitationally bound system of stars, stellar remnants, interstellar gas and dust, dark matter

• typically containing millions to hundreds of billions of stars – Star - a large hot ball of gas which generates energy in its core by nuclear

reactions

• around 100 billion in the universe • held together by the gravitational attraction of all its member

stars on one another • formed around 200 million years after the “Big Bang” • most large ones seem to have super-massive black holes at their

centers • sometimes contain very bright centers called quasars • 3 major types:

– Spiral – Elliptical – Irregular

What is the name of the galaxy we reside in?

3 Types of Galaxies

Spiral have arms of stars, gas , and dust that curve away from the center of the

galaxy in a spiral pattern Ex. – Milky Way

Elliptical shaped like

spheres or eggs; have almost no

dust or gas between stars;

contain old stars

Irregular faint galaxies without

a definite shape; smaller than the other

types of galaxies; contain fewer stars

The process of galaxies colliding to create a larger galaxy is known as “galactic cannibalism.”

Images taken from: http://school.discoveryeducation.com/schooladventures/universe/galaxytour/toknow.html

Constellation

• a group of stars that form a pattern in the sky • stars of a constellation are often far apart from each

other, but they appear grouped together when viewed from Earth

• one of 88 sectors into which astronomers divide the sphere of the sky – named after a traditional constellation in that sector

• patterns of constellations are dynamic; therefore, the constellations of 100,000 years ago are quite different from today’s

• a part of a constellation that forms its own pattern in the sky is known as an asterism (ex. – The Big Dipper)

Why is it not possible to see all constellations at once?

Solar System

• A star and all the objects that orbit around it

• Our Solar System: the sun and all things orbiting around it, including the eight major planets, their satellites, and all the smaller pieces such as asteroids and comets

• formed around 4.6 billion years ago

Image taken from: http://asm.arc.nasa.gov/Gallery/images/generic/LG_Capableofeverything.jpg

Planet

• derived from a Greek word that means “wanderer”

• a major object which orbits around a star

• in our solar system, there are eight such objects which are traditionally called “planets”

Satellite

• an object that orbits a more massive object (i.e. – moons)

• probes we launch into orbit around the Earth are called “artificial satellites”

The Earth animation is not rotating

in the correct

direction; it should be

rotating from west to

east

Asteroids

• small, solid, rocky bodies that orbit close to the Sun

• most found between the orbits of Mars and Jupiter in the “Asteroid Belt”

• thought to be leftover material from the formation of the solar system

• range in size from 1000 km or 621 miles (Ceres) to the size of pebbles Image taken from:

http://www.windows.ucar.edu/tour/link=/our_solar_system/asteroids.html

Meteoroid, Meteor, Meteorite • Meteoroid – solid debris from space

(asteroids) that are moving towards Earth

• Meteor – a brief streak of light produced by

a small particle entering Earth’s atmosphere at high speed

– often referred to as “shooting stars” or “falling stars”

– travel at speeds between 11-72 kilometers per second (6.8 – 44.7 miles per second)

• Meteorite – a small object from outer space that passes through Earth’s atmosphere and reaches the surface

Meteoroid (asteroid)

Meteor

Meteorite

The Earth animation is not rotating

in the correct

direction; it should be

rotating from west to

east

What causes a meteor shower to occur?

Comet

• a small body of ice and dust (“dirty snowball”) that orbits the Sun

• contain a head (coma) followed by a tail(s) of gas and dust

• the tail always points away from the sun and can be millions of kilometers long (but the amount of matter it contains can be very small)

Image taken from: http://www.space.com/bestimg/index.php?guid=45b0fd31f065d&cat=bestcomet

Astronomical Unit (AU)

• unit of distance equal to the average spacing between the Earth and the Sun

• equal to about 150 million kilometers (93 million miles)

• light takes about eight minutes to cover this distance

150 million km (93 million mi.)

The Earth animation is not rotating

in the correct

direction; it should be

rotating from west to

east

Light Year

• the distance that light travels in one year in a vacuum, which is about 9.5 trillion kilometers (6 trillion miles) – The Milky Way Galaxy is about 100,000 light years

in diameter

• the speed at which light travels this distance is about 300,000 km/sec (186,000 mi/sec)

The second closest star to the Earth is a little over four light years away. How far

away (in miles) is the star?

Parsec

• unit of distance equal to about 3.26 light years (or 206,265 AU)

If one parsec equals 206, 265 AU, how many miles is it equal to?

Parallax

• the apparent shift in position of an object when viewed from different locations

• used by astronomers to measure distance

Parallax Simulation Parallax Simulation – 1 Parallax Simulation - 2

Find the Distance to HT Cas Using Parallax

Put your pointer finger in front of your face and begin opening and closing your eyes in an alternating manner. What

do you notice about the your finger’s position?

Early Models of the Solar

System Geocentric -an Earth-centered model of the solar system. • In this model, the sun, the stars, an the planets revolved

around Earth. • Suggested by Aristotle

• Ptolemy proposed changes to Aristotle’s model. • He thought that planets moved in small circles, called

epicycles, as they revolved in larger circles around Earth.

Heliocentric -a sun-centered model of the solar system. • In this model, the planets revolved around the sun in the

same direction, but different speeds and distances from the sun.

• Proposed by Copernicus

Isaac Newton

• Sir Isaac Newton was the first person to hypothesize that the force that pulls an apple to the ground also pulls the moon toward Earth, keeping it in orbit.

Force

• A force is a push or a pull. • Force gives an object the energy to move,

stop moving, or change direction. • When you write with a pen you exert a force.

When you peddle your bike, blow your nose, turn on a faucet, chew your gum, or swimming in a pool, you are exerting forces on other objects.

Friction

• Friction is a force that opposes motion. Friction

acts in a direction opposite to the objects

direction in motion.

• Without friction, the object would continue to

move at a constant speed forever.

• Example: sliding friction. This is when two

surfaces slide one over the other. A

snowboarder slides over the snow covered

slopes using sliding friction every day.

Gravity • Newton was the first person to seriously

study gravity • Gravity is a force that attracts all objects

toward each other. • The force of gravity is measured in units

called Newtons (N).

Gravity • The strength of gravity between two

objects depends on two factors:

• 1. masses of the objects (If mass increases, force also increases)

• 2. distance between the objects (If distance increases, force decreases)

Mass vs. Weight

• Mass- is the amount of matter in an object

• Weight- is the force of gravity on an object

• The greater the mass the greater the force (weight)

• Weightlessness – free from the effects of gravity

Newton’s First Law of Motion

• An object at rest will remain at rest unless acted on by an unbalanced force.

• An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

• This law is often called "the law of inertia".

Law of Inertia

• Inertia- the tendency of an object to resist a change in motion.

• This law is the same reason why you should always wear your seatbelt.

Why do Earth and the moon remain in their orbits?

• Inertia and gravity combine to keep Earth in orbit around the sun and the moon in orbit around the Earth.

• While gravity pulls an object towards the sun, inertia keeps the object moving forward in a straight line. This forms the ellipse of a stable orbit.

Kepler’s Laws

First Law: Law of Ellipses • States: an orbiting body travels in an elliptical path around a

central, massive body, which is located at one of the ellipse’s foci. – An ellipse is a closed curve, whose shape is determined by two points, or

foci, within the ellipse. – In planetary orbits, one focus is the sun.

• Elliptical orbits vary in shape. Its eccentricity (degree of elongation

of an elliptical orbit) is determined by dividing the distance between the foci of the ellipse by the length of the major axis.

Kepler’s Laws, continued Second Law: Law of Equal Areas • States that equal areas are covered in equal amounts of

time as an object orbits the sun. • Describes the speed at which objects travel at different

points in their orbit.

• When the object is near the sun, it moves relatively quick. When the object is far from the sun, it moves relatively slow.

Kepler’s Laws, continued The diagram below demonstrates Kepler’s Law of Equal Area.

Kepler’s Laws, continued Third Law: Law of Periods orbital period - time required for a body to complete a single

orbit • Describes the relationship between the average distance of a

planet from the sun and the orbital period of the planet.

• The mathematical equation, K x a3 = p2, where K is a constant, describes this relationship. The cube of the average distance (a) of a planet from the sun is always proportional to the square of the period (p).