1. History of Astronomy
Key Figures and Their Contributions:
• Ptolemy: Proposed the Geocentric Model (Earth-centered universe).
• Copernicus: Suggested the Heliocentric Model (Sun-centered solar system).
• Galileo Galilei: Used telescopes to observe celestial objects; supported Heliocentrism.
• Tycho Brahe: Made detailed planetary observations.
• Johannes Kepler: Formulated the Laws of Planetary Motion.
• Isaac Newton: Developed the Law of Universal Gravitation.
Key Concepts:
• Geocentric Model: Earth is at the center of the universe.
• Heliocentric Model: The Sun is at the center of the solar system.
2. Telescopes
Types of Telescopes:
• Refracting Telescopes: Use lenses to gather and focus light.
• Reflecting Telescopes: Use mirrors to gather and focus light.
• Radio Telescopes: Detect radio waves from space.
• Space Telescopes: Operate outside Earth’s atmosphere (e.g., Hubble Space Telescope).
Important Terms:
• Aperture: Diameter of the primary lens or mirror; aMects light-gathering power.
• Magnification: Enlargement of an image.Celestial Sphere
Key Terms:
• Celestial Sphere: Imaginary sphere surrounding Earth where celestial objects appear.
• Zenith: Point directly overhead for an observer.
• Horizon: Where the sky meets the Earth.
• Celestial Equator: Projection of Earth's equator onto the celestial sphere.
• Ecliptic: Path of the Sun across the celestial sphere throughout the year.
Important Lines and Points:
• Meridian: Line running from North to South through the zenith.
• North Celestial Pole: Near Polaris (North Star).
• South Celestial Pole: Point directly opposite the North Celestial Pole.
4. Celestial Coordinates
Right Ascension (RA):
• Similar to longitude on Earth.
• Measured in hours, minutes, and seconds along the celestial equator.
• 24h of RA = 360° around the celestial sphere.
Declination (Dec):
• Similar to latitude on Earth.
• Measured in degrees north (+) or south (−) of the celestial equator.
• Ranges from +90° (North Celestial Pole) to -90° (South Celestial Pole).
How to Use Celestial Coordinates:
• Right Ascension determines when an object will cross the meridian.
• Declination determines how far north or south an object is from the celestial equator.Star Movements
Daily Motion:
• Caused by Earth's rotation.
• Stars appear to rise in the East and set in the West.
• Circumpolar Stars: Never set and move around the celestial pole.
Annual Motion:
• Caused by Earth's orbit around the Sun.
• Seasonal constellations change due to Earth’s changing position.
Special Movements:
• Parallax: Apparent shift in a star's position due to Earth's movement, used to measure
distances to nearby stars.
6. Constellations
Types of Constellations:
• Circumpolar Constellations: Always visible in the night sky (e.g., Ursa Major).
• Seasonal Constellations: Visible only during certain seasons.
• Zodiac Constellations: Lie along the ecliptic path.
Be able to identify constellations
• Orion: Visible in winter; contains bright stars Betelgeuse and Rigel.
• Ursa Major: Contains the Big Dipper, used to find Polaris.
• Cassiopeia: W-shaped, near the North Celestial Pole.
• Seasonal Changes: Constellations visible depend on the time of year. Right Ascension and Declination:
o If a star is at RA 6h and Dec +30°, when would it be highest in the sky? yes it would be
o Which stars would be circumpolar from a latitude of 45° N?stars with decliantion greater thean 45 N
• Constellation Identification:
o Where would you look to find Orion in January at 9:00 PM? Orion would be visible in the southern sky.
o Which constellation points to Polaris? Ursa Major .
o How do RA and Dec help in locating celestial objects? helps pinpoint the location of clestial objects in sky, RA is similar to longititude on Earth and measures East- West postion, while Dec is similar to lantitude and measures north-south postion,
o Why do constellations appear to shift throughout the year? due to earths revloution around the sun.
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