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.