Studying Space

Chapter 26, Section 1 - Viewing the Universe                                                                                                                                        

Astronomy - The scientific study of the universe.
Cosmology - The study of the origins, properties, processes and evolution of the universe.


  • Planet - a round body that orbits the Sun and has cleared out any material from its orbit (ex - the Earth).
  • Star - a celestial body that is composed of gas and that emits light (ex. - the Sun).
  • Solar System - the Sun and all of the planets and other bodies that orbit it.
  • Galaxy - A collection of stars, dust, and gas held together by gravity (ex - the Milky Way).
  • Galaxy Clusters, Superclusters, and the Universe
    • A group of galaxies held together by gravity is called a galaxy cluster.  The one to which our galaxy belongs is called the Local Group, which contains about 40 galaxies and is about 10 million ly across.
    • A group of galaxy clusters held together by their gravity is called a supercluster.  Ours is called the Local Supercluster, which contains a few dozen galaxy clusters and is about 150 million ly across.
    • The Great Attractor appears to be a cluster of superclusters, and is about 300 million ly across. 
    • The Universe contains everything.  We can see about 14 billion ly in any direction - although the universe may be larger than this.
  • See Astronomy: Preview notes for information on the organization of the cosmos.

Units of Measure

  • An Astronomical Unit (AU) is the distance between the Earth and the Sun.  ~93 million miles (150 million km).  
  • Light Year (ly) is the distance that light can travel in one year.  ~6 trillion miles (10 trillion km).  
  • See Astronomy: Preview notes for information on units or measure.
  • Electromagnetic Spectrum - All of the frequencies or wavelengths of electromagnetic radiation.
  • See Astronomy: Chapter 3 notes for information on light.

Telescope - An instrument that collects electromagnetic radiation from the sky and concentrates it for better observation.

  • Refracting Telescope - A telescope that uses a set of lenses to gather and focus light from distant objects.
  • Reflecting Telescope - A telescope that uses a curved mirror to gather and focus light from distant objects. 
  • See Astronomy: Chapter 4 notes for information on telescopes.

Chapter 26, Section 2 - Movements of the Earth                                                                                                                                   

Rotation - The spin of a body on its axis.
  • Evidence for Earth's Rotation
    • Foucault's Pendulum
      • The path of the pendulum follows the rotation of the Earth.
    • Coriolis Effect
      • Ocean and wind currents are deflected to the right in the Northern Hemisphere, left in the Southern Hemisphere.
      • This is caused by the Earth's rotation.
    • Movement of stars across the sky.
Revolution - The motion of a body that travels around another body in space; one complete trip along an orbit.
Perihelion - In the orbit of a planet (or other body) in the solar system, the point that is closest to the Sun.
AphelionIn the orbit of a planet (or other body) in the solar system, the point that is farthest from the Sun.
  • Evidence of Earth's Revolution
    • Changes in positions of constellations at different times of year.

Measuring Time
  • Day - Determined by the Earth's rotation.
  • Week - Days are named after the Sun, Moon, and the five planets visible without a telescope.
  • Month - Determined by the Moon's phases.
  • Year - Determined by the Earth's revolution.
  • See Astronomy: Essay 2 notes for more information on how our measurement of time relates to Astronomy.

The Seasons
  • Earth's axis is tilted 23.5o to the plane of its orbit.
  • When we (Northern Hemisphere) are tilted towards the Sun, we receive more direct sunlight and experience Summer.
  • When we are tilted away from the Sun, we receive less direct sunlight and experience Winter.
    • Note: The Southern Hemisphere is pointed the opposite way, so experience Summer during our Winter and vice versa.
Solstice - The point at which the Sun is as far North/South of the equator as possible.
Summer Solstice - The longest day of the year.  (The Sun follows its highest path across the sky.)
Winter Solstice - The shortest day of the year.  (The Sun follows its lowest path across the sky.)
Equinox - The time when the Sun appears to cross the celestial equator.  (Day and night are of equal length.)


Chapter Assignment
  • Read Chapter 26.
  • Pg. 742-743, #5-22, 32-35.