AST 102 UNIT 1 SLIDES SET

Cosmic Calendar

Compresses universe history into one year.

Milky Way Galaxy

A galaxy containing billions of stars.

Nebula

Interstellar cloud of gas and dust.

Solar System

Includes a star and its orbiting bodies.

Star

Large gas ball generating heat via fusion.

Planet

Moderately large object orbiting a star.

Dwarf Planet

Small celestial body orbiting a star, not a planet.

Moon

Natural satellite orbiting a planet.

Asteroids

Small rocky objects orbiting the Sun.

Comet

Icy body orbiting a star, often with a tail.

Weightlessness

Condition experienced by astronauts in space.

Total Solar Eclipse

Rare event where the Moon blocks the Sun.

North Star

Brightest star in the northern sky.

Light Year

Distance light travels in one year.

Gravity

Force that attracts objects toward each other.

Nuclear Fusion

Process powering stars, converting hydrogen to helium.

Visible Light

Electromagnetic radiation visible to the human eye.

Ultraviolet Light

Electromagnetic radiation beyond visible light spectrum.

Astronomical Unit (AU)

Average distance from Earth to the Sun.

Galaxies

Massive systems of stars, gas, and dust.

Observational Science

Science based on observing and experimenting.

Eternal Students

Concept of lifelong learning in science.

Curiosity in Science

Encouragement to ask questions and seek answers.

Observable Universe

Contains ~200-100 billion galaxies.

Milky Way Galaxy

One of ~100 billion galaxies.

Stars per Galaxy

About ~400-100 billion stars.

Order of Magnitude

Calculation: 10^11 stars x 10^11 galaxies.

Total Stars

Estimated at 10^22 stars.

Mass Composition

98% hydrogen and helium, 2% other elements.

Astronomical Unit (AU)

Average distance from Earth to Sun.

1 AU

Equals 150 million kilometers.

Light-Year (ly)

Distance light travels in one year.

1 Light-Year

About 9.5 trillion kilometers.

Planetary Distances

Mercury: 0.4 AU, Mars: 1.5 AU.

Sun to Earth

Approximately 8 light minutes.

Earth to Moon

About 1 light second.

Earth to Mars

Ranges from 22 to 3 light minutes.

Sun to Neptune

Approximately 4 light hours.

Nearest Star

Proxima Centauri, 4.2 light years away.

Galactic Movement

Earth orbits Sun once every year.

Earth's Rotation Speed

Rotates at ~1000 km/h.

Solar System Speed

Moves at ~70,000 km/h among stars.

Milky Way Rotation Speed

Rotates at ~800,000 km/h.

Constellation

Region of the sky with defined patterns.

Number of Constellations

88 internationally recognized constellations.

Asterism

Popular star patterns not officially constellations.

Celestial Sphere

Imaginary sphere where stars appear to lie.

Ecliptic

Sun's apparent path through constellations yearly.

Ecliptic

The apparent path of the Sun across the sky.

Zodiac

Twelve constellations the Sun moves through yearly.

Zenith

Point directly overhead an observer.

Nadir

Point directly opposite of the zenith.

Horizon

All points 90° from zenith.

Meridian

Line connecting zenith with N and S horizon.

Altitude-Azimuth System

Coordinate system based on observer's perspective.

Altitude (h)

Angle above the horizon to an object.

Azimuth

Angle from North, moving clockwise.

Angular Measurements

Quantitative angles used in celestial observations.

Full Circle

Total angular measurement of 360°.

Arcminute

1/60 of a degree, ~fingernail thickness.

Arcsecond

1/3600 of a degree, ~hair strand thickness.

Luminosity

Total energy output of a star per second.

Apparent Brightness

Starlight reaching Earth, varies with distance.

Brightness Formula

Brightness = Luminosity / (4π × distance²).

Magnitude Scale

Logarithmic scale for measuring star brightness.

First-Magnitude Stars

Brightest stars in ancient brightness classification.

Sixth-Magnitude Stars

Faintest stars visible to the human eye.

Absolute Magnitude

Intrinsic brightness of a star at standard distance.

Apparent Magnitude (m)

Observed brightness of a star from Earth.

Celestial Sphere

Imaginary sphere where celestial objects appear.

North Celestial Pole

Point in the sky directly above Earth's North Pole.

Circumpolar Stars

Stars that never set, visible year-round.

Celestial Equator

Imaginary line dividing the celestial sphere.

Latitude

Position north or south of the equator.

Longitude

Position east or west of the prime meridian.

Polaris

North Star, located near the North Celestial Pole.

Altitude of Polaris

Equal to observer's latitude in the Northern Hemisphere.

Earth's Axis Tilt

Earth's axis is tilted at 23.5° from vertical.

Precession

Slow circular motion of Earth's rotation axis.

Seasons

Caused by Earth's axial tilt, not distance from Sun.

Summer Solstice

Highest solar path, longest day of the year.

Equinox

Day when day and night are of equal length.

Northern Solstice

Occurs in June, marks summer in Northern Hemisphere.

Southern Solstice

Occurs in December, marks summer in Southern Hemisphere.

Zenith

Point directly above an observer in the sky.

Your Horizon

The line where the sky meets the ground.

Bright Stars

Stars that are prominent near the celestial poles.

Earth's Orbit

Path Earth takes around the Sun, affecting visibility.

Constellations

Patterns of stars that change with seasons.

Time of Year

Affects which constellations are visible at night.

Latitude Example

40° 50' 56" N indicates specific northern position.

Longitude Example

73° 3' 33" W indicates specific western position.

Summer Solstice

Sun is highest in the sky, Northern Hemisphere.

Winter Solstice

Sun is lowest in the sky, Northern Hemisphere.

Vernal Equinox

Sun crosses celestial equator in spring.

Autumnal Equinox

Sun crosses celestial equator in fall.

Tropic of Cancer

Latitude 23.5° N, direct overhead sun in June.

Tropic of Capricorn

Latitude 23.5° S, direct overhead sun in December.

Sun's Altitude

Changes with seasons, affects sunlight intensity.

Analemma

Figure-8 pattern of the Sun's position over time.