Introduction to Astronomy

I know nothing with any certainty but the sight of stars makes me dream.

- Vincent Van Gogh

This is big to us.

Diameter of the Earth = 12,756 km

The sun is much bigger.

Diameter of the sun = 1,391,960 km

( 109 Earths across )

The farthest a human has traveled from the Earth is the moon, 283,000 miles (452,000 km) during the Apollo missions in the 1960’s and 70’s. This is 35 Earth diameters away.

The difference between a planet and a star involves their size. A planet is much smaller and shines only by reflecting starlight. A star is huge and produces its own light through a nuclear fusion reaction.

However…

Distance from the Earth to the sun = 93,000,000 miles( about 100 solar diameters)

1 Astronomical Unit ( 1 A.U.)

150,000,000 km = 1 Earth-Sun Distance

Pluto is 3,673,500,000 km from the sun.

( 39.5 A.U.)

Pluto

The farthest distance traveled by an Earth spaceship (unmanned) is Voyager 1, which is now about 105 A.U. It was launched in 1970 and covers about 3.6 A.U. per year.

Astronomical units (A.U.s) are used to measure distances between planets and their parent stars or other distances within the local neighborhood of a solar system.

Light yearsA light year is the distance light will travel in 1 year.

A light year is a unit used to describe the immense distance between stars or galaxies. Stars are usually trillions of miles apart. Galaxies are millions of times further than that. Since light travels very quickly it can be used to measure the huge distances.

Our sun is just another star. It is a little less than 8 light minutes away the Earth. The stars we see at night only look different to us because they are so much further away. Most of them are many light years away.

Light yearsA light year is the distance light will travel in 1 year.

The speed of light is 300,000 kilometers per second.

So…...

1 light year is 9,460,000,000,000 kilometers (approximately 1016 meters)

Our nearest neighboring star is 4 light years away.

37.8 trillion kilometers.

1 Light year = 63,133 A.U.

1 year = 365 days x 24 hours x 60 minutes x 60 seconds= 31,536,000 seconds

This would take 17,500 years in Voyager 1.

Our home galaxy, the Milky Way, is over 100,000 light years across. This spiral galaxy looks similar to our own.

It is home to over 200 billion stars… many are larger than our sun. Each star represents its own solar system.

You are here.

Our galaxy is called the Milky Way because on a dark night, far away from city lights, you can see a band of stars

(and dust) stretching across the sky. Some think it resembles a river of milk across the sky.

This is a picture of our galaxy (from the inside, of course) looking toward the center.

We cannot see our own galaxy from the outside because it would take millions years in our fastest spaceship to leave

our galaxy so we could turn around and look back at it.

Galaxies come in many different shapes and sizes but they are all huge collections of billions of stars held together by

gravity.

Elliptical galaxySpiral galaxy

Irregular galaxy

From an edge-on view a galaxy would appear very thin with a central bulge and lanes of dust cutting across the middle. Clusters of stars form a halo surrounding the central bulge.

There are billions of other galaxies visible from Earth. This photo contains 10,000 of them and represents only a tiny fraction of the sky.

A galaxy is a massive collection of billions of stars and clouds of gas and dust held together by gravity.

A nebula is a huge cloud of gas and dust that may be lit

up by nearby stars. It is where new stars may form.

Stars may form in massive clusters containing thousands

or millions of stars.

As nebulas collapse due to gravity new stars are created.

Stars come in many sizes and colors. The color of the star depends on its temperature.

Small, dim stars are the hard-to-see red stars.

The bright blue and white stars we see at night are the largest and hottest stars in the galaxy.

Each star represents its own solar system.

Our sun is a medium-sized star. That means its brightness and surface temperature is average giving the sun its yellow color.

Stars verses Planets

• A star produces its own light and generates power by the process of fusion

• A planet cannot produce its own light (it shines only reflected light) and it orbits another object.

Planets are much smaller than stars. The main difference between them is their size. Bigger means hotter.

Mer

cury

Venus

Earth

Mar

s

Jupit

er

Satur

nUra

nus

Neptu

ne

Pluto

Sun

M V E M J S U N P

My Very Eager Mother Just Sent Us Nine Pizzas

A solar system consists of a star (like our sun) and the objects that orbit around it (planets and their moons, comets, asteroids). Moons orbit planets and everything is held by the

sun’s gravity.

Asteroids are large leftover rocks (from boulder-sized to

mountain-sized) that orbit the sun.

Comets are dirty snowballs the size of mountains that melt as

they fall toward the sun creating long tails lit up by sunlight.

Some planets are small and rocky, called terrestrial. These are like our home planet, Earth.

Other planets are huge and made mostly of layers of gases, called gas giants. These, like Jupiter, were not big or hot enough to become stars, but they are still many time larger than the Earth.

Sizes

Comets

AsteroidsMoonsPlanetsStars

Galaxies

All energy travels in waves.

1 wavelength

Since the human eye can only see a tiny fraction of these different wavelengths of electromagnetic energy, scientists must create different tools to observe different forms of energy traveling through the universe.

Types of Spectrumcan be used to identify elements in stars and nebula from across the

galaxy.

• Absorption spectrum has certain wavelengths of light absorbed leaving black lines which act as a fingerprint. Each element will absorb a specific pattern of colors.

• Emission spectrum is created when an element is heated to the point it emits a certain wavelength of light. Each element emits a different wavelength.

Spitzer Space Telescope

Hubble Space Telescope

Neutrino detector

This Neutrino detector is located deep underground where all other wavelengths of energy would be blocked. Neutrinos are tiny particles created by stars. They are so small they can travel right through normal matter, even through our entire planet.

By studying different wavelengths of energy we can learn different things about the universe around us.

Infra red (IR) X-ray Sonar

Ultrasound

Ultraviolet (UV)

Magnetic Resonance Image (MRI)

By combining images from different wavelengths of energy scientists can get a

more complete picture.

Space Exploration• Space exploration began with the launch of the Soviet spacecraft Sputnik Oct. 4,

1957.• Since then humans have orbited the Earth and walked on the moon (Apollo

missions). Now, the space shuttle is the primary spacecraft used to carry humans into Earth orbit and bring satellites into space. The Space shuttle fleet of seven spacecraft has conducted 120 missions, with two deadly accidents, and will be retired in 2011 to make way for the next generation.

• Hundreds of robotic spacecraft have been launched for many missions around our solar system. Most of these do not return to the Earth.

• Typically, spacecraft will use the gravity of the Earth or other planets to send them farther out into space. The method is called “gravity assist” or “sling-shot”. Otherwise, spacecraft would have to be much larger to carry enough fuel and more powerful engines to get anywhere. Sling-shotting through space requires very precise math calculations.

• Within our solar system, spacecraft have explored all planets (except Pluto, although one is on its way there), as well several comets and asteroids, the sun and our moon.

Important Robotic Spacecraft

• Mariner 10 (USA)– Launched 11/3/1973 to explore Venus and Mercury– First (only) spacecraft to explore Mercury. Only one side

of Mercury was visible.– Mariner 10 still orbits the sun though all of its instruments

are dead.

• Magellan Space Probe (USA)– Launched from the Space Shuttle 8/10/90 to explore

Venus– Conducted extensive radar mapping of Venus surface

until it was deliberately crashed into the atmosphere of Venus in 1994

• Galileo Spacecraft (USA)– Launched 10/18/89 to explore Jupiter system– Discovered an asteroid with a moon (Ida and

Dactyl) on its way– Studied Jupiter, its moon and rings, witnessed a

comet, Shoemaker-Levi, colliding with Jupiter– Mission ended when it was deliberately crashed

into Jupiter in 2003 (it reached a speed of 50 km/sec on its way down).

• Voyager 2 (USA)– Launched 8/20/77 to explore all four gas giants

(Jupiter, Saturn, Uranus and Neptune)– First (only) spacecraft to pass Uranus, 1986– First (only) spacecraft to pass Neptune, 1989– Still flying away, near the edge of the solar

system, it will run out of power by 2025, will pass star Sirius in 295,000 years

• Cassini Spacecraft (joint USA and European Mission)

– Launched 10/15/97 to explore Saturn system– Tested Einstein’s Theory General Relativity, seeing

how time was altered by the gravity of the sun– Arrived at Saturn 2004– Huygens probe landed on moon Titan (only moon

besides the Earth that we have ever landed on)– Cassini is still orbiting Saturn making close passes of

all of Saturn’s many moons and sending back high resolution pictures

• Spitzer Space Telescope– Launched 8/25/2003 to observe the universe at

infrared wavelengths– Still orbiting the sun (heliocentric orbit) as it studies

distant objects.

• Hubble Space Telescope– Launched from the space shuttle 4/24/90 to

observe the universe– 10 year mission has lasted 19 years and still

working– Primary mirror was seriously flawed and needed to

be repaired by a space shuttle mission. 3 other servicing shuttle missions have kept the telescope working and improving as it aged. There will be no more missions to Hubble. Once it starts to break down it will be deliberately crashed into the ocean to prevent it from accidentally crashing somewhere people might be hurt.

• Lunar Prospector (NASA)

– Launched 1/7/1998– Polar orbit of the moon– It created a detailed map of the moon

and attempted to look for signs of water ice in the rims of craters

– It was deliberately crashed into the moon to try and throw ice crystals up in the cloud created on impact

Sacrifices

• 3 astronauts died in fire during a prelaunch test of Apollo 1 on Jan 27, 1967.

• 14 astronauts have died in two separate accidents involving shuttle missions causing NASA to be much more cautious about the reasons for launching the shuttle. Challenger Shuttle

explodes after launch, Jan. 28, 1986

Columbia Shuttle disintegrates during reentry of the atmosphere, Feb. 1, 2003