Unit E: Space Exploration Study Guide

Early Views of the Cosmos and Tracking the Universe

• Ancient Observations and Seasonal Prediction:

  • Ancient peoples observed the skies to predict the onset of summer and winter.

  • Solstices:

    • Summer Solstice: Occurs on June $21$ in the Northern Hemisphere; it is the longest day of the year.

    • Winter Solstice: Occurs on December $21$ in the Northern Hemisphere; it is the shortest day of the year.

  • Equinoxes: These occur two times a year when daylight and nighttime are equal in length, occurring on March $21$ and September $21$.

  • Ancient Structures: Many structures were built to predict solstices and equinoxes; a primary example is Stonehenge.

• Planetary Motion and Constellations:

  • Ancient peoples sought to understand the constant movement of objects in the sky.

  • Models of planetary and star movement emerged as constant observers noticed repeating patterns.

  • Constellations: These are patterns assigned to specific groups of stars in the night sky.

Development of Astronomical Models

• The Geocentric Model:

  • Proposed by Aristotle approximately $2000$ years ago.

  • This is an Earth-centered model of the universe.

  • In this view, the Sun, Moon, Mercury, Venus, Mars, Saturn, and Jupiter orbit the Earth.

  • Early astronomers used this to calculate moon phases but were unable to explain all celestial events.

• The Heliocentric Model:

  • In $1530$, Copernicus suggested a sun-centered model.

  • This model posits that Earth and other planets orbit the Sun.

  • In the $1600s$, Galileo became the first scientist to use a telescope to support or explore these ideas.

• Refining the Model:

  • Tycho Brahe studied and recorded the precise movement of the planets.

  • Johannes Kepler later added that the orbits of planets are elliptical (oval-shaped) rather than perfectly circular.

Astronomical Tools and Measurement Units

• Historical Observation Tools:

  • Egyptians: Used merkhets and quadrants to chart the stars.

  • Arabians: Utilized astrolabes and cross-staffs.

  • Galileo: Used telescopes containing combinations of different lenses.

• Measuring Distance in Space:

  • Standard units like metres ($m$) and centimetres ($cm$) are too small for cosmic distances.

  • Astronomical Unit (AU): Defined as the distance from the center of the Earth to the center of the Sun.

    • $1\,AU = 149,599,000\,km$

    • Used to describe positions within our solar system.

  • Light-Year (LY): The distance traveled by light in one year.

    • In $1\,second$, light travels $300,000\,km$.

    • Sunlight takes $8.5\,minutes$ to reach Earth.

    • $1\,LY = 9,500,000,000,000\,km$ (approximately $9.5\,trillion\,km$).

    • Used to measure vast distances between stars and galaxies.

Distribution of Matter in the Universe

• Key Definitions and Hierarchy (Largest to Smallest):

  1. Galaxy: A vast collection of many stars, planets, dust, and other objects held together by gravity (e.g., Milky Way).

  2. Nebula: Accumulations of gas and dust that form new solar systems (e.g., Cat’s Eye).

  3. Star System: A group of planets and other objects orbiting a central star (e.g., Solar System).

  4. Star: A vast sphere of plasma gas transforming nuclear energy into solar energy (e.g., the Sun).

  5. Planet: A large rocky or gaseous object moving in an elliptical orbit around a star (e.g., Earth).

  6. Satellite: Any object orbiting a planet, whether natural (Moon) or artificial.

Characteristics and Life Cycle of Stars

• Star Properties:

  • A star is a hot, glowing ball of gas consisting mainly of hydrogen and helium.

  • Stars vary in color, size, and density.

  • Color indicates temperature: Blue stars are hot, while Red stars are cool.

  • Hertzsprung-Russell (H-R) Diagram: A chart that shows stars falling into distinct groupings based on luminosity and temperature.

• Star Birth (Nebula to Protostar):

  1. Swirling dust and gas in a nebula collapse under gravity.

  2. The core mass and temperature increase.

  3. The core material begins to glow, forming a protostar.

  4. When the core temperature reaches $10,000,000\,{^\circ}C$ ($10\,million\,degrees$), nuclear fusion begins, and a star is born.

• Life and Death of a Star:

  • The mass of a star determines its life cycle.

  • Most stars begin in the Main Sequence.

  • Sun-like Stars: Transition from Main Sequence to Red Giant, then to White Dwarf, and finally to Black Dwarf.

  • Massive Stars: Transition from Main Sequence to Red Supergiant, followed by a Supernova explosion. The remnant becomes either a Neutron Star (Pulsar) or a Black Hole.

• Galaxies:

  • Groupings of millions or billions of stars, gas, and dust held by gravity.

  • Shapes include Spiral (like the Milky Way), Elliptical, or Irregular.

Our Solar Neighbourhood

• Protoplanet Hypothesis:

  1. A cloud of gas and dust begins swirling.

  2. Greater than $90\,$ of material gathers in the center to form the Sun.

  3. Remaining material clumps together into planets and moons.

• The Sun:

  • Surface Temperature: $5500\,{^\circ}C$.

  • Core Temperature: $15,000,000\,{^\circ}C$.

  • Solar Wind: Emitted charged particles. Earth is protected from these by its magnetic field.

• The Planets:

  • Inner "Terrestrial" Planets: Small and rocky (Mercury, Venus, Earth, Mars).

  • Outer "Jovian" Planets: Large and gaseous (Jupiter, Saturn, Uranus, Neptune).

  • Pluto: Was the farthest planet until $2003$; now there is discussion of a potential tenth planet with its own moon.

• Asteroids, Comets, and Meteors:

  • Asteroids: Range from a few metres to a few hundred metres; found in the asteroid belt between Mars and Jupiter (e.g., Gaspra).

  • Comets: Composed of dust, rock, and ice. They release gas when near the sun, forming tails millions of km long (e.g., Halley’s Comet, Hale-Bopp, Shoemaker-Levy).

  • Meteoroids: Pieces of rock floating in space.

  • Meteors: Meteoroids that glow in Earth's atmosphere due to friction heat.

  • Meteorites: Meteors that successfully impact Earth's surface.

Describing the Position of Objects in Space

• Locating Objects:

  1. Azimuth: Compass direction in degrees from North ($0^\circ = North$, $180^\circ = South$).

  2. Altitude: Height in the sky above the horizon ($0^\circ = horizon$, $90^\circ = straight\,up$).

  • Zenith: The point directly overhead at an altitude of $90^\circ$.

• Motion and the Ecliptic:

  • Stars appear relatively motionless, while planets change positions significantly throughout the year.

  • Ecliptic: The path through the sky that the Sun follows.

Space Transport and Technology

• History of Rockets:

  • Ancient Greeks used steam to make rocket-propelled objects.

  • To enter space, objects must reach escape velocity, which is $40,000\,km/h$.

  • Sputnik: Launched by Russia in $1957$; the first artificial satellite.

• Rocket Science and Design:

  • Propelled by the principle: For every action, there is an equal and opposite reaction.

  • Basic Parts:

    1. Structure and Mechanical: Body, fins, engines.

    2. Fuel: Liquid oxygen, hydrogen, and gasoline (comprises most of the mass).

    3. Payload: Crew cabin, personnel, air, water.

• Future Propulsion:

  • Ion Drives: Engines using electrically charged Xenon gas. They have weaker thrust than chemical fuel but last an extremely long time.

  • Solar Sails: Thin carbon fiber sheets that capture energy from photons emitted by the sun.

• Spacecraft Types:

  • Shuttles: Transport personnel and equipment.

  • Probes: Robotic exploration (e.g., Voyager, Hubble Space Telescope).

  • International Space Station (ISS): Orbiting laboratory allowing long-term human habitation.

Life Support and Living in Space

• Hazards:

  • Outer space is a vacuum (no air or water).

  • Exposure to cosmic and solar radiation.

  • Extreme temperatures and meteoroid impacts.

  • Microgravity: Constant "weightlessness" leads to muscle weakening, reduced depth perception, brittle bones (calcium loss), and weakened heart muscle.

• Surviving the Environment:

  • Space Suits: Provide air, water, heating/cooling, and waste management.

  • Water Management: The ISS recycles $100\,$ of water, including urine, through filtration and purification.

  • Air Management: Oxygen is produced via electrolysis of recycled water. Carbon dioxide ($CO_2$), dust, and microbes are filtered out.

Satellite Applications

• Communication Satellites: Use digital systems and wireless technology for cell phones and satellite TV.

  • Geosynchronous Orbit: Satellites that stay in a fixed position above Earth by matching its rotation rate.

• Observation/Research Satellites: Used for tracking forest fires, weather patterns, and environmental changes (e.g., LANDSAT, RADARSAT).

• Remote Sensing: Satellites in low orbit ($200\,km$ to $1000\,km$) that sense heat and radiation or take photographs.

• Global Positioning System (GPS): A network of $24$ satellites; a receiver requires signals from at least $3$ satellites to determine precise location.

Tools for Observation: Optical and Beyond

• Optical Telescopes:

  • Refracting Telescopes: Use $2$ lenses to focus images; limited to roughly $1\,m$ in diameter.

  • Reflecting Telescopes: Use mirrors; can be much larger (e.g., $6\,m$).

  • Segmented Mirrors: Used to create enormous light-gathering surfaces.

  • Interferometry: Combining $2$ or more telescopes to improve resolution (e.g., Keck I and II in Hawaii, Very Large Telescope (VLT) in Chile).

  • Hubble Space Telescope: A reflecting telescope orbiting at $600\,km$ to avoid atmospheric pollution.

• The Electromagnetic Spectrum:

  • Objects emit energy beyond visible light: radio waves, X-rays, infrared, and gamma rays.

  • Wavelength is the distance between peaks; frequency is the number of waves per second.

• Radio Telescopes:

  • Used to study radio waves from space.

  • Unaffected by weather, clouds, or the atmosphere.

  • Requires large dishes (e.g., $300\,m$ diameter) due to long wavelengths.

  • Radio Interferometry: Combining multiple radio telescopes into arrays to increase measurement accuracy.

Triangulation, Parallax, and Spectroscopy

• Measuring Distance:

  • Triangulation: Based on geometric properties using two angles and a known baseline.

  • Parallax: The apparent shift in an object's position when viewed from two different places. For stellar measurements, the diameter of Earth’s orbit is used as the baseline, with measurements taken $6\,months$ apart.

• Analyzing Star Composition:

  • Spectroscopes: Separate star light into spectrum bands.

  • Every element creates a unique spectral signature. Comparing star spectra to known elements determines composition (e.g., identifying Hydrogen).

• Determining Motion (Doppler Effect):

  • A change in wave frequency due to the movement of the source.

  • Blue-shifted: Light wavelengths compress as a star moves toward Earth.

  • Red-shifted: Light wavelengths stretch as a star moves away.

  • Most distant galaxies show a red-shift, indicating the universe is expanding.

Risks, Contributions, and Societal Issues

• Accidents and Dangers:

  • Apollo 1 (1967): Fire during training, $3$ deaths.

  • Challenger (1986): Exploded on lift-off, $7$ deaths.

  • Columbia (2003): Exploded on re-entry, $7$ deaths.

  • Re-entry Hazards: A shallow angle causes the craft to bounce off the atmosphere; a steep angle causes it to burn up.

  • Space Junk: Debris moving at $20,000\,km/h$ poses catastrophic risks.

• Canadian Contributions:

  • Canadarm 1 & 2: Robotic arms for the shuttle and ISS; Canadarm 2 features computer-controlled fingers.

  • Key Astronauts:

    • Marc Garneau: First Canadian in space ($1984$).

    • Roberta Bondar: First Canadian woman in space ($1992$).

    • Chris Hadfield: First Canadian to walk in space ($2001$).

• Exploration Issues:

  • Political: Ownership rights and space laws.

  • Ethical: Determining beneficial uses and fairness.

  • Environmental: Conservation of space and Earth.

  • Economic: High costs versus solving issues on Earth like poverty and disease.

Questions & Discussion

• Celestial Classification Query: Which planet is terrestrial? (Answer: Mercury).

• Size Ordering Exercise: Earth ($1$), Galaxy ($2$), Solar System ($3$), Sun ($4$). Smallest to largest: Earth ($1$) -> Sun ($4$) -> Solar System ($3$) -> Galaxy ($2$).

• Stellar Property Query: Spectral analysis determines a star's composition.

• Orbital Mechanics Query: A geosynchronous orbit allows a satellite to send signals continuously to a specified area on Earth.

• Economic Perspectives: Discussion on the cost of a Moon base and ownership of Moon resources are economic and political perspectives (Speakers I and II).

• Space Junk Concern: The most significant concern for an astronaut is damage to the spacecraft or International Space Station.