unit 1 and 2

Unit 1: Lecture Notes Part 1

Introduction to Astronomy

  • Astronomy is one of the oldest sciences.

  • Prehistoric artifacts include Egyptian monuments and Stonehenge.

  • Early civilizations (Babylonians, Greeks, Chinese, Indians, Maya) made systematic observations of the night sky.

  • The invention of the telescope marked the development of modern astronomy.

Branches of Astronomy

  1. Observational Astronomy

    • Collects data from celestial observations.

    • Analyzes data using physics principles.

  2. Theoretical Astronomy

    • Develops analytical or computational models to describe astronomical phenomena.

Amateur Astronomy

  • Amateurs significantly contribute to astronomical discoveries.

  • Particularly active in observing transient events, like supernovae and comets.

  • Unlike many sciences, astronomy allows non-professionals to contribute meaningfully.

Lexicology of Astronomy and Astrology

  • Astronomy (Greek: astron = "star", nomos = "law"): "Law of the stars".

  • Astrology (Greek: astron = "star", logia = "study"): "Study of the stars".

Patterns in the Night Sky

  • Over 2,000 stars and the Milky Way are visible to the naked eye from Earth.

Unit 1: Lecture Notes Part 2

Constellations and Their Characteristics

  • Constellations visible from Earth depend on location (latitude) and time of year.

Why Do Stars Twinkle?

  • Stars appear to twinkle due to light passing through the Earth's atmosphere.

  • Variable density and humidity in air pockets cause this effect.

  • Planets twinkle less because they appear larger.

  • This phenomenon is referred to as seeing.

Constellations and Zodiac Signs

  • Ancient constellations were named after mythological figures.

  • Today, constellations are officially defined regions of the sky (88 total).

  • Zodiac constellations follow the ecliptic; originally comprising of 12 but now recognized as 13 (including Ophiuchus).

Brightest Stars in Orion

  1. Betelgeuse (α Orionis)

    • Red supergiant, 900 times the Sun's radius, 150,000 times brighter, 640 light-years away.

  2. Rigel (β Orionis)

    • Blue supergiant, 100 times the Sun’s radius, 100,000 times brighter, 900 light-years away.

The Magnitude Scale

  • Introduced by Hipparchus (160-127 BCE).

  • Brightest stars = 1st magnitude, faintest visible stars = 6th magnitude.

  • Each magnitude difference corresponds to a 2.512 times difference in brightness.

  • Negative magnitudes denote extremely bright objects (e.g., Sun = -26.5, Sirius = -1.42).

Unit 1: Lecture Notes Part 3

The Celestial Sphere

  • North Celestial Pole (NCP): Above Earth's North Pole.

  • South Celestial Pole (SCP): Above Earth's South Pole.

  • Celestial Equator: Projection of Earth's equator onto the sky.

  • Ecliptic: Sun’s apparent annual path through the celestial sphere.

Earth Coordinates & The Local Sky

  • Latitude: Position north or south of the equator.

  • Longitude: Position east or west of the Prime Meridian.

Zenith & Horizon

  • Zenith: Point directly overhead.

  • Meridian: Line connecting zenith with North and South.

  • Horizon: All points 90° from zenith.

Apparent Motion of the Celestial Sphere

  • The rotation of Earth causes the Sun, Moon, and stars to appear to move from East to West.

  • The motion appears clockwise when facing North and counterclockwise when facing South.

Sun's Motion

  1. Daily Motion: The Sun moves westward due to Earth's rotation.

  2. Yearly Motion: The Sun appears to move eastward as Earth orbits around it (1 AU ~ 150 million km).

Precession

  • Earth's axis wobbles due to gravitational forces.

  • A precession cycle takes about 26,000 years.

  • The North Celestial Pole's position changes over millennia (currently near Polaris).

Unit 1: Lecture Notes Part 4

The Moon

Phases of the Moon

  • The Moon orbits Earth in 27.3 days.

  • A full cycle of phases (synodic month) takes 29.5 days due to Earth's motion.

Lunar Phases

  • Waxing: Moon visible in the afternoon/evening, rises later each day.

  • Waning: Moon visible in late night/morning, sets later each day.

  • Sidereal month: 27.32 days (orbit relative to distant stars).

  • Synodic month: 29.53 days (orbit relative to the Sun).

Eclipses

  1. Solar Eclipse: Happens when the Moon is between the Sun and Earth (new moon).

  2. Lunar Eclipse: Happens when Earth is between the Sun and Moon (full moon).

    • Can be penumbral, partial, or total.

Unit 1: Lecture Notes Part 5

Tides

  • Caused by the gravitational pull of the Moon and the Sun and Earth's rotation.

  • There are usually two high tides each day, approximately 12 hours apart.

Key Questions and Practice Questions

  1. Q: Which is the faintest star?

    • A: Magnitude 23.5.

  2. Q: The stars in a constellation may actually be far apart.

    • A: Answer C.

Unit 2: Lecture Notes Part 2

Introduction to Archeoastronomy

  • Interdisciplinary study of historical understanding of sky phenomena.

Cosmic Origins: The Big Bang

  • Occurred approximately 14 billion years ago from an extremely hot and dense state.

Early Universe Composition

  • Primary elements: Hydrogen (75%), Helium (25%), trace Lithium.

Element Formation Processes

  • Light elements formed during the Big Bang; heavier elements during stellar processes.

Solar System Formation

  • Began around 4.5 billion years ago from a molecular gas cloud.

Early Life on Earth

  • Emerged around 3.8 billion years ago.