Astronomy

Supporting files for this material can be found here.

Constellation Project Information


Solar System Basics

Solar System - The Sun and all of the planets, moons, and smaller bodies that orbit it.  Our solar system contains eight planets...

We can remember the order of the planets with the sentence:

Mary Visits Every Monday and Just Stays Until Noon.

Each of the capitalized words stands for a planet that begins with the same letter.  The "and" represents the asteroid belt.  The period at the end represents Pluto, which used to be a planet but was reclassified as a Dwarf Planet in 2006.


Dust Cloud Hypothesis - The idea that the solar system formed from a huge cloud of gas and dust in space.  Gravity caused the cloud to collapse, spinning and flattening out.  It eventually formed a spinning disk of material with a huge bulge in the middle.  The bulge became the Sun, the disk formed into the planets, moons, asteroid belt, etc.

Rotation - When a planet spins on its axis (an imaginary line that runs from North Pole to South Pole).  Rotation causes day and night.

Revolution - When a planet travels around the Sun.  A planet's revolution is its year.  (1 revolution of Earth around the Sun = 365.25 days)

Orbit - The path of a smaller body around a larger one.  (The Earth orbits around the Sun.  The Moon orbits around the Earth.)

Ellipse - An oval shape.  This is the shape of the planets' orbits around the Sun.  (We would say that the shape is an ellipse, but that the orbit is elliptical - in the shape of an ellipse.)

 

The Earth

The Earth has four main layers...

  • Crust - Outer layer, made of solid rock.
  • Mantle - Below the crust, made of molten rock (magma).
  • Outer Core - Below the mantle, made of liquid iron & nickel.
  • Inner Core - Center of the Earth, made of solid iron & nickel.

Latitude - Imaginary horizontal lines on the Earth.  The equator is 0o latitude.  Other lines are measures as degrees north or south of the equator.

Longitude - Imaginary lines on the Earth that run from pole to pole.  The prime meridian is 0o longitude.  Other lines are measured as degrees east or west of the prime meridian.

Seasons.  Earth rotates on its axis.  The axis is tilted 23.5o, which means that the Earth is tilted slightly. 

  • During part of the year, the North Pole is tilted towards the Sun - we call this summer. 
  • When the North Pole is tilted away from the Sun, we are having winter.
  • During spring and autumn, the North Pole is tilted sideways - not towards or away from the Sun.

Summer solstice - The longest day of the year (around June 21st).

Winter Solstice - The shortest day of the year (around Dec. 21st).

Equinox - Two days each year when the day and night are even in length.  The Vernal Equinox is around March 21st, the Autumnal Equinox is around Sept 21st.

For a better description and pictures, check out the attached "Earth and Seasons" PowerPoint attached below.


The Sun

Our Sun is a small, yellow star.  It is more than 1 million times the size of Earth, and is 93 million miles away from Earth.  Click here for a song about the Sun.

Distance of the Earth from the Sun...

  • 93 million miles
  • 1 AU (astronomical unit) - An AU is defined as the distance from the Earth to the Sun.
  • 8 light minutes - it takes light eight minutes to travel from the Sun to the Earth. 

The Sun has four main layers...

  • Core - Nuclear fusion happens here to make the Sun shine.  (Temp = 15,000,000 oC)
  • Photosphere - The surface of the Sun, this makes the light that we see.  (Temp = 6,000 oC)
  • Chromosphere - The Sun's lower atmosphere, it makes a reddish glow, but is drowned out by the light from the photosphere.  (Temp = 15,000 oC)
  • Corona - The Sun's outer atmosphere, it extends past the Earth and gradually fades out into space.  (Temp = 2,000,000 oC)

There are also several types of surface features on the Sun...

  • Sunspots - darker, cooler areas on the Sun's surface.
  • Promincences - huge arcs of glowing gas that form above sunspots.
  • Solar Flares - huge eruptions of gasses that shoort out from the Sun's surface.  These cause a surge in the solar wind (a constant stream of charged particles that come out of the Sun).
    • Solar flares interfere with radio and TV broadcasts and satellites.  They can cause blackouts and brownouts.
    • Auroras (the Northern and Southern Lights) are caused by solar wind interacting with gases in our atmosphere.

Cool video of a solar flare (seen in various wavelengths of light) - click here.  An explanation of what causes auroras - click here.

Nuclear fusion is the process where hydrogen atoms are crushed together to form helium atoms.  This happens in the Sun's core, and gives off a LOT of energy.  Fusion is what makes the Sun shine!

Radiant energy is energy that travels through space in waves.  It is given off by the Sun.  Types of radiant energy include...

  • Gamma Rays
  • X-Rays
  • Ultraviolet Light
  • Visible Light (the light that we can see)
    • Red  Orange  Yellow  Green  Blue  Indigo  Violet
  • Infrared Light
  • Microwaves
  • Radio Waves

The Planets

To be a planet, an object in our solar system must...

  • Orbit the Sun.
  • Have enough mass that its gravity pulls it into a round shape.
  • Clear out any debris from its orbit.

The eight planets of our solar system are classified into two groups:

  Inner Planets - Small, rocky planets that are inside the asteroid belt.

  • Mercury
  • Venus
  • Earth
  • Mars

  Outer Planets - Large, gas planets that are outside the asteroid belt.

  • Jupiter
  • Saturn
  • Uranus
  • Neptune

 

Dwarf Planets are similar to planets, but much smaller.  Dwarf Planets...

  • Orbit the Sun.
  • Have enough mass for their gravity to pull them into a round shape.
  • Do not clear out the debris from their orbits.
  • Are not satellites.

So the moral is: if you don't clean your room, you'll never be a planet!

More information about Dwarf Planets here!

 

Smaller Members of the Solar System

Asteroids - Smaller bodies, made of rock, that orbit the Sun.  Most of these are in the Asteroid Belt, between Mars and Jupiter.  (Some have been re-classified as dwarf planets.)

Meteor - A rock that is falling through our atmosphere.  Meteors burn up as they go through the atmosphere, creating a bright streak of light in the sky.

Meteorite - A meteor that hits the ground.

Comet - An icy body that has a long, oval orbit around the Sun.  Comets come from the Kuiper Belt or the Oort Cloud - outside the orbit of Neptune.

 

The Moon

The Moon is Earth's only natural satellite (an object that orbits a larger object).

  • It is about 1/4 the size of the Earth.
  • It has about 1/6 of Earth's gravity.
  • It is about 380,000km (228,000mi) from the Earth.
  • The Moon takes about 271/3 days to make one orbit around the Earth.  (But about 291/2 days to go from one full moon to the next!)
  • The Moon rises about 50 minutes later each day.  This is because the Earth is spinning as the Moon goes around it, so the Moon takes this extra time to "catch up".

The Moon has no atmosphere or magnetosphere.  There are two types of landscape there...

  • Highlands - Brighter, older areas that are covered with craters from meteor impacts.  There is no weather to wipe out the craters, so they last for millions of years.
  • Maria - Darker, smoother areas.  These are lava plains.  Millions of years ago, huge meteorites hit the Moon and broke through its crust.  Lava filled in the craters, and hardened into rock to form the maria.  (Maria is Latin for "seas".)

Origin of the Moon - There are several theories of where the Moon came from, but the one that is most widely accepted by scientists is the collision theory.  According to this theory, a planet-sized object crashed into the Earth (billions of years ago).  The material that got blasted out of the Earth eventually formed the Moon.

 

Moon Phases - The changing appearance of the Moon as seen from Earth.

  • New Moon - The Moon looks completely dark.
  • Crescent - The Moon is less than half lit up.  It looks like a fingernail clipping.
  • Quarter Moon - We see half of the lit-up side of the Moon.  It looks like a half-Moon.
    • First Quarter - The quarter that follows a New Moon.
    • Last Quarter - The quarter after a Full Moon (before New Moon).
  • Gibbous - The Moon is more than half lit up.
  • Full Moon - The Moon is completely lit up.

The Moon phases go in this order: New Moon, Crescent, First Quarter, Gibbous, Full Moon, Gibbous, Last Quarter, Crescent, New Moon.

Waxing - When the Moon is becoming more full.  (Waxing crescent, waxing gibbous)

Waning - When the Moon is becoming less full.  (Waning crescent, waning gibbous)

 

Eclipses happen when the Sun, Earth, and Moon all line up.  There are two kinds...

  • Solar Eclipse - The Moon is between the Sun and Earth.
    • Moon's shadow falls on the Earth.
    • The Moon appears to block out the Sun in the sky.
  • Lunar Eclipse - The Earth is between the Sun and Moon.
    • Earth's shadow falls on the Moon.
    • The Moon appears to get darker as it goes through Earth's shadow.

Eclipses don't happen every month because the Moon's orbit is tilted slightly compared to the Earth's orbit around the Sun. 

NASA's eclipse site.

 

Stars

Constellation - A group of stars that forms a particular pattern.

  • Used since ancient times for navigation and as a calendar.
  • Some are seen year-round (Ursa Major, Ursa Minor).
  • Some are only seen at certain times of the year (Orion, Gemini).

Polaris - The North Star.  Located directly above the North Pole.

    - Polaris is at the end of the handle of the Little Dipper (Ursa Minor).

    - The two stars forming the bowl of the Big Dipper point to it.

Distance to the stars...

  • Measured in light years (the distance that light travels in a year).
    • 1 ly = 9,000,000,000,000 km  (5,400,000,000,000 miles)
  • Measured by using...
    • Absolute Magnitude - the actual brightness of a star.
    • Parallax - The apparent shift in a star's position when seen from different points in the Earth's orbit.

Star Life Cycles- For animations of these, click here.

0. Dust Cloud

  • The star begins as a huge cloud of dust and gas, called a nebula.
  • Gravity pulls the cloud into the center.  As it collapses, it spins and flattens into a disk with a bulge in the middle.
    • The bulge will become the star.
    • The disk will form planets, moons, asteroids, comets, etc.

1. Main Sequence Star

  • During this stage, the star is fusing hydrogen (H) to make helium (He).
    • Gravity pulls into the center, fusion pushes out from the center.  Since they are balanced, the star is stable.
  • Eventually the star runs low on H and fusion slows down.  Gravity crushes the core, which gets hotter and hotter until He starts being fused to make larger elements.
  • When He fusion begins, the surface of the star begins to expand.  This turns the star into a...

2. Red Giant

  • During this stage, the star is fusing helium (He) to make larger elements.
    • Gravity pulls into the center, fusion pushes out from the center.  Since they are balanced, the star is stable.
  • Eventually the star runs low on He and fusion slows down.  Gravity pulls into the center and the star collapses.
  • What happens next depends on the size and mass of the star...

3.a. White Dwarf

  • When an average-sized star runs low on He, gravity causes it to collapse down to a very small, hot star called a White Dwarf.
  • White Dwarfs continue to fuse any leftover H and He until they run out and fade to dark.

3.b. Supernova

  • When a very large star runs low on He, the star collapses with so much force that it creates a huge shock wave...
    • The shock wave crushes the core so much that all of the atoms are crushed into neutrons.  The star is now a neutron star.
      • Neutron stars are only about 15km (9mi) across.
      • 1 teaspoon of neutron star weighs more than 90,000,000,000,000 tons because it is so dense.
      • Neutron stars give off beams of light, radio, and X-rays, and they spin.  If their spin makes these beams of light shine towards Earth, the star seems to pulse, and it is called a pulsar.
    • As the shockwave bounces off the core, it blasts off the outer layers of the star in a huge explosion called a supernova.
      • This creates a new dust cloud (nebula) that can form new stars.

3.c. Black Hole

  • When a very, very large star collapses, it has so much force that it creates a Black Hole.
    • A Black Hole's gravity is so intense that not even light can escape it.  Since we see objects by the light that is reflected off of them, this means that Black Holes are invisible - we detect them by their effects.

Starlight

Stars give off radiant energy, including visible light.  However, the different elements and compounds that make up the star absorb some of the wavelengths, making a gap in the colors.  Each star has its own unique "fingerprint" of starlight.  More info here.

If a star (or galaxy) is moving away from us, the lines in its spectrum are shifted towards the red end - this is called Red Shift.

If a star (or galaxy) is moving towards us, the lines in its spectrum are shifted towards the blue end - this is called Blue Shift.

 

Galaxies

Galaxy - A huge system of stars held together by gravity.

Our galaxy is the Milky Way and has hundreds of billions of stars in it.

Galaxies are classified by their shapes...

  • Elliptical - Oval-shaped.
  • Spiral - Oval center with several "arms" coming out and spiraling around it.
  • Barred Spiral - Shaped like a spiral galaxy, but with a dark line or bar running across the center.
  • Irregular - No definite shape.

A cool video of galaxies colliding - click here.


Exoplanets

Exoplanets are planets in our galaxy that orbit other stars (outside of our solar system).  Information about them can be found here and here.

Some ways that we look for exoplanets...

  • Direct Observation (aka - Direct Imaging, Photometric Imaging)
    • New telescopes, such as the Kepler Space Telescope, are able to "see" exoplanets directly.  
    • We don't see much detail with these, and this has only been in recent years.
  • Star Wobble (using Doppler Shift)
    • As a planet orbits its star, the planet's gravity causes the start o wobble slightly.
    • We measure the star's movement by its light (we look for red shift and blue shift).
    • The amount of wobble lets us estimate the planet's mass.
  • Star Dimming (using the Transit Method)
    • As a planet orbits its star, it may pass between its star and the Earth.  This is called a transit (when a planet passes in front of its star).
    • During a transit, the planet blocks some of the star's light, causing a temporary drop in the star's brightness.
    • The amount of change in the star's brightness lets us estimate the planet's size.


The Drake Equation gives us an interesting way to think about the possibility of life and civilizations on other planets in our galaxy.  Try it out here - make sure to launch the interactive.

 

The Universe

The universe is everything - all the stars, planets, galaxies, space, etc.  There is evidence that it began in a huge explosion, 13 billion years ago.  This is called the Big Bang Theory.

Quasars are the farthest objects that we are able to see.  They are small, bright objects that produce much more energy than galaxies.  Some scientists think that these are young galaxies in the process of forming.  Video - click here.

 

Resources

Videos

Supporting files for this material can be found here.