the solar system 

and 

stars and galaxies


Astronomy!

Astronomy is a natural science that deals with the study of celestial objects (such as moons, planets, stars, nebulae, and galaxies)

It used to be that astronomy was studied with the naked eye, and then during Galileo's time visible light-based telescopes were used.  We still use  visible light on many telescopes (e.g., The Hubble Telescope, which also uses UV and IR light).


These days, we also use other electromagnetic radiation, including X-Rays, radio waves, gamma rays, and we even use neutrinos to learn about the universe.


Astronomy

We will begin with the Solar System, which consists of the Sun and its eight planets (poor Pluto), the planets' moons, and other non-stellar objects, such as asteroids, comets, and planetoids.

We will then branch out past our solar system into the rest of our galaxy, and then on to other galaxies and the rest of the universe.




the solar system and its formation


Let's see a size comparison in our galaxy: http://goo.gl/zeRsM

Distances in our solar system

The distance from the Sun to the Earth is defined as one astronomical unit (AU).  In order of distance from the Sun:

What would this look like on a model? http://goo.gl/JsU92

the solar system and its formation

The Nebular theory:
Theory that the Sun and planets formed together from a cloud of gas and dust—a nebula.

the solar system and its formation

Nebular theory formation:
  • Gravitation between materials in the cloud pulled it inward.
  • When pulled inward, spin increased in accord with the conservation of angular momentum.
  • The spinning cloud conformed to the shape of a spinning disk.

The Solar System and Its Formation

Nebular theory formation:
  • The center of the disk is the protosun.
  • Away from the center, planetesimals formed.
  • Planetesimals accreted more matter to become planets.



Check question

As a nebula shrinks under the influence of gravity, it


  1. spins slower.
  2. spins faster. 
  3. loses its spin.
  4. spins into a protosun.

CHECK QUESTION

As a nebula shrinks under the influence of gravity, it


  1. spins slower.
  2. spins faster. 
  3. loses its spin.
  4. spins into a protosun.

Explanation:
In accordance with the conservation of angular momentum, as the radius of the nebula decreases, its spin rate increases (like a skater who pulls her arms inward in a spin).

the sun


the sun

  • nearest star to Earth (out of 100 billion in the galaxy)
  • composed of mostly hydrogen in the plasma phase
  • hydrogen is fused to helium by thermonuclear fusion in its core
  • 4.5 million tons of mass are converted to energy each second
  • a tiny fraction of this energy reaches and sustains Earth

Sun Facts

  • The solar core is 15 million degrees, and 12 times as dense as lead
  • Pressure in the core is 340 billion times the air pressure on earth, causing nuclear fusion of hydrogen to helium
  • The Sun slowly spins on its axis
  • It's a fluid, and equatorial regions spin once in 25 days, while higher latitudes spin once in 36 days (this causes sunspots)
  • The surface of the sun (the "photosphere) is 5700 degrees, and about 500km deep.
  • Above the photosphere is the 10,000km thick chromosphere, at 10,000 degrees
  • The outermost region is the corona, extending many millions of kilometers.


the sun

Chromosphere:


the sun

The corona, as seen during an eclipse:


check question

Strictly speaking, in every second that passes, the mass of the Sun

  1. decreases.
  2. remains constant. 
  3. increases.
  4. reinvents itself.

CHECK QUESTION

Strictly speaking, in every second that passes, the mass of the Sun

  1. decreases.
  2. remains constant. 
  3. increases.
  4. reinvents itself.

the inner planets


Mercury, Venus, Earth, Mars
The four planets nearest the Sun and composed of high-density solid rock.
Orbital speeds of planets around the Sun decrease with increasing distance from the Sun.

Mercury

  • closest to the Sun (and has a weird day)
  • slightly larger than our Moon
  • almost no atmosphere due to small size
  • daytime is long and hot (up to 430ºC)
  • nighttime is long and cold (about -170ºC)

Venus

  • next closest to the Sun
  • diameter about 0.95 that of Earth
  • very dense atmosphere, mostly carbon dioxide
  • volcanically active
  • very harsh place (e.g., sulfuric acid rain)

Earth

  • third planet from the Sun—our home
  • at a distance where most of its water is neither solid nor gas, but liquid

The only other planet in the habitable zone is...Mars!

MARS

  • fourth planet from the Sun—a potential habitat 
  • thin atmosphere—95% carbon dioxide and 0.15%  oxygen  (A planet with a thin atmosphere is ineffective in lowering temperature difference between day and night!)
  • temperatures range from 30ºC in day to  –130ºC at night
  • presently the focus of planetary exploration

Mars rover landing videos


Mars Exploration Rover (2004 and still going):
http://www.youtube.com/watch?v=-_9BYSDtwRc


Curiosity Rover (2012-present):
http://www.nasa.gov/mission_pages/msl/news/msl20110624.html



the outer planets


Jupiter, Saturn, Uranus, Neptune
  • gaseous, low-density worlds
  • appreciably larger than Earth
  • more widely spaced than the inner planets

Jupiter

  • first of the outer planets, beyond Mars
  • more than 11 times Earth’s diameter—giant of the solar system
  • composition more liquid than gaseous or solid
  • atmospheric pressure more than a million times that of Earth’s


jupiter

  • atmosphere is 82% hydrogen, 17% helium, 1% methane, ammonia, and other molecules
  • no definite surface as occurs on the inner rocky planets
  • solid core of iron, nickel, and other minerals
  • Because of its thick atmospheric blanket, daytime and nighttime temperatures are about the same for equal altitudes above its “surface.”
  • Many moons, but four large "Galilean" moons.

jupiter's largest moons


Discovered by Galileo in 1609-1610
The largest of the Galilean satellites (and the largest moon in the solar system) is Ganymede. At 5262 km across, Ganymede is larger than Mercury, but is classified as a moon because it orbits a planet.

Europa

Jupiter’s moon Europa has an ice-capped ocean, which may hold extraterrestrial life


Saturn


News from this week (May 1, 2013):
Massive hurricane circles around Saturn’s north pole; pictures taken by NASA's Cassini spacecraft (which is still orbiting Saturn).

Saturn

Saturn is surrounded by rings—
hypothesized to be bits of a moon never formed, or remnants of a moon torn apart by tidal forces
inner part of rings, like any satellite, travels faster than outer part of the ring system

Rocks that make up the rings orbit independently of other rocks.

Huygens

Cassini launched a lander ("Huygens") that landed on Saturn's moon, Titan.

uranus


neptune


The planet Neptune was mathematically predicted before it was directly observed.

Pluto

  • since 2006, classified as a dwarf planet
  • very unlike other planets in composition, size, and orbit
  • highly elliptical orbit, like comets
  • spends most of its orbital time well beyond Neptune, in the Kuiper Belt
  • composition like that of Kuiper-Belt objects
  • look-alike neighbors not classified as planets
  • former planetary status was more historical than astronomical

Earth's Moon

  • more is known about the Moon than any other celestial body
  • diameter about one quarter that of Earth
  • no atmosphere—no weather and erosion to conceal past scarring of its surface

Earth's Moon

Twelve people have stood on the Moon. Here we see Buzz Aldrin, one of the three Apollo 11 astronauts.

Earth's Moon: Formation


Earth's Moon: Phases



Earth's Moon

The Moon spins about its polar axis as it revolves around Earth.

Earth's Moon

Eclipses occur when the Moon’s shadow falls on part of Earth.
This is a solar eclipse.

Earth's Moon

A lunar eclipse occurs when Earth’s shadow falls on the Moon.

What kind of eclipse happens when the Sun gets between the Earth and the Moon?

Lunar Eclipse

The red light of sunrises and sunsets all around Earth is refracted onto the Moon’s surface during a lunar eclipse.


Failed Planet Formation


Failed Planet Formation: Comets

Comets:
  • differ from asteroids in chemical composition
  • are masses of water, methane, and ice—dirty snowballs
  • most located in Kuiper Belt and Oort Cloud
  • highly elliptical (highly eccentric) orbital paths
  • tail of comets swept outward from Sun by solar wind

comets


failed planet formation


Kuiper Belt and Oort Cloud

Beyond Neptune at a distance of about 30-50AU is the Kuiper belt (pronounced "K-eye-per")

The Kuiper belt has many rock-covered planetoids and other objects, with Pluto being the prime example.

The Kuiper belt is responsible for many comets.

Even further out is the Oort Cloud, which also contains comets and may extend as far as 50,000AU from the Sun.  Some of these comets may have an orbital period of thousands or millions of years.

Stars


and


Galaxies

The Night Sky

Constellations are groups of stars named throughout human history

For example: Ursa Major ("the Great Bear")


observing the night sky

The monthly constellations seen in the night sky change as Earth’s path around the Sun progresses.


observing the night sky

The Big Dipper is a well-known constellation. The pairs of stars at the end of its bowl point to Polaris, the North Star.

observing the night sky

The seven stars of the Big Dipper are at very different distances from Earth.


ly = Light Year = distance, not time!

The Brightness and Colors of Stars

A star’s color indicates its temperature: 
  • a red star is cooler than a blue star
  • a blue star is almost twice as hot as a red star (blue light has almost twice the frequency of red light in accord with f~ T)

the brightness and color of stars

We measure the brightness of a star in two ways:

  • apparent brightness—the brightness as it appears to us
  • luminosity—the intrinsic brightness, independent of how bright it appears

The luminosity of stars is compared to that of the Sun, which is noted LSun. 

check question

We measure the Sun’s luminosity as LSun. If we were on a spaceship twice as far away from the Sun, its apparent brightness would appear

  1. the same.
  2. half as much. 
  3. one quarter as much.
  4. four times as much.

CHECK QUESTION

We measure the Sun’s luminosity as LSun. If we were on a spaceship twice as far away from the Sun, its apparent brightness would appear

  1. the same.
  2. half as much. 
  3. one quarter as much.
  4. four times as much.

Remember the inverse-square law!

The Hertzsprung-Russell Diagram


The periodic table for astronomers!

check question

On the H-R diagram, the Sun is

  1. an average star.
  2. seen to be special. 
  3. a low-temperature star.
  4. especially bright.

CHECK QUESTION

On the H-R diagram, the Sun is

  1. an average star.
  2. seen to be special. 
  3. a low-temperature star.
  4. especially bright.

The Life Cycles of Stars

Life cycle of stars:
  • begins as a nebula
  • advances to a protostar
  • becomes a star when fusion in its core occurs
Depending on its mass, the star may become a red giant and then burn out to become a white dwarf.

THE LIFE CYCLES OF STARS

White dwarf:
  • cools for eons until it is too cold to emit light
  • if part of a binary, pulls matter from its partner, which can lead to a nuclear blast (nova)

The life cycles of stars

Final stage of more massive stars is collapse, then an explosion called a supernova.

Remnant of a supernova is the Crab Nebula.


Supernova videos...

black holes

Black hole:
  • what remains when a supergiant star collapses into itself
  • named because gravitation at its surface is so intense that even light cannot escape
Why gravitation at the surface of a star increases when it collapses

star shrinks to half its radius ⇒gravitation at its surface increases by 4 (inverse-square law)

check question

When a giant star collapses to become a black hole, gravity is greatly increased

  1. at it surface.
  2. at its center. 
  3. in all surrounding space.
  4. All of the above.

CHECK QUESTION

When a giant star collapses to become a black hole, gravity is greatly increased

  1. at it surface.
  2. at its center. 
  3. in all surrounding space.
  4. All of the above.

Explanation:
It is important to know that gravitation increases mainly at the surface of the collapsed star. Gravity at the surface before collapse is the same at that same distance from the center of the black hole after collapse. 

check question

If the Sun collapsed to become a black hole, the orbit of Earth would

  1. remain unchanged.
  2. be pulled inward toward the black hole. 
  3. spiral outward away from the black hole.
  4. be a straight-line path.

CHECK QUESTION

If the Sun collapsed to become a black hole, the orbit of Earth would

  1. remain unchanged.
  2. be pulled inward toward the black hole. 
  3. spiral outward away from the black hole.
  4. be a straight-line path.
Explanation:
F = G(m1×m2)/d2. Letting this equation guide our thinking, we see that none of its terms differ. Although the density of the black hole has greatly increased, its mass is the same before and after collapse. Because the mass of Earth and the solar black hole are the same, and distance between centers is the same, the force holding Earth in orbit wouldn’t change. Equations nicely guide thinking!

Galaxies

  • huge assemblage of stars, interstellar gas, and dust
  • most familiar—Milky Way


Galaxies

Three types of galaxies:
elliptical, irregular, and spiral

Galaxies

A pair of irregular galaxies—
the Large Magellanic Cloud and neighboring 
Small Magellanic Cloud


Galaxies

This is Spiral Galaxy NGC 6744, much like our Milky Way.

Galaxies are not the largest things in the universe. There are clusters of galaxies, and then galaxy superclusters—larger than can be imagined!

clusters and superclusters

The Milky Way Galaxy and its neighboring galaxies are known as the Local Group.

clusters and superclusters

Our local group is situated between the Virgo and Eridanus clusters, which all together make our Local Supercluster.

clusters and superclusters

Our Local Supercluster is part of a network of superclusters.

Clusters and superclusters

As far as we can see, superclusters hold together like a foam within which there are bubbles of super large voids. 

the solar system and stars and galaxies

By Chris Gregg

the solar system and stars and galaxies

  • 6,697

More from Chris Gregg