Astro 5 - UCLA ( Midterm)

Week 8 Midterm,

Star

Generates its own energy and light

Planet

Orbits a star and shines by reflection

Asteroid

A rocky or metallic body that orbits a star and is smaller than a planet

Comet

An icy body that orbits a star and can form a visible tail when near the Sun

Moon

A natural satellite that orbits a planet

Light-year

The distance that light travels in 1 year

Speed of Light

Approximately 300,000 km/s or 670 million mph

Cosmic Calendar

A scale model where the 13.8 billion-year age of the Universe is compressed into 1 single calendar year

Big Bang (Cosmic Calendar)

Occurs on January 1 at the very beginning of the Cosmic Calendar year

Milky Way Formation (Cosmic Calendar)

Formed in February on the Cosmic Calendar scale

Earth's Formation (Cosmic Calendar)

Formed on September 3 on the Cosmic Calendar scale

Early Life on Earth (Cosmic Calendar)

Arises on September 22 on the Cosmic Calendar scale

Modern Humans Evolve (Cosmic Calendar)

Evolved about 2 minutes before midnight on December 31 (11:58 pm)

Model (Scientific)

A simplified but significant conceptual description of nature

Geocentric Model

A model of the universe that assumes the Earth is stationary at the center

Ptolemy

A Greek scholar (A.D. 100-170) who created the most sophisticated geocentric model

Copernicus

Proposed a Sun-centered (heliocentric) model of the solar system, but incorrectly assumed perfectly circular orbits

Johannes Kepler

Discovered that planets move in elliptical orbits rather than circles, formulating three laws of planetary motion

Kepler's First Law

Planets move in elliptical orbits with the Sun located at one focus

Kepler's Second Law

A line connecting a planet to the Sun sweeps out equal areas in equal times, meaning planetary velocity is not constant (faster when closer to the Sun)

Kepler's Third Law

The square of a planet's orbital period in years (p²) equals the cube of its semi-major axis in AU (a³)

Galileo Galilei

Used the telescope to observe sunspots, mountains/valleys on the Moon, moons of Jupiter, and phases of Venus, proving the heliocentric layout

Scientific Method

Process requiring that a model make testable predictions that force us to revise or abandon it if observations disagree

Acceleration

Any change in velocity, which can be a change in either speed or direction

Acceleration due to Gravity (g)

9.8 m/s² near Earth's surface; the constant rate at which all falling objects pick up speed regardless of mass when ignoring air resistance

Linear Momentum

The product of an object's mass and its velocity (p = mv)

Angular Momentum

The product of an object's mass, velocity, and distance from its axis of rotation (L = mvd)

Mass

The fundamental measurement of the amount of matter in an object, which does not change based on location

Weight

The force exerted on an object due to gravity (w = mg), which varies depending on the gravity of the local environment

Free-fall

The condition of motion experienced when gravity is the only force acting upon an object

Newton's First Law of Motion

An object moves at a constant velocity unless acted upon by a net outside force

Newton's Second Law of Motion

Force equals mass times acceleration (F = ma); for a constant force, a larger mass experiences a smaller acceleration

Newton's Third Law of Motion

For every force applied, there is an equal and opposite reaction force

Conservation Laws

Principles stating that energy, momentum, and angular momentum are conserved and cannot be created or destroyed

Kinetic Energy

The energy of motion, calculated as KE = 0.5 * m * v²

Radiative Energy

Energy carried by light or electromagnetic radiation

Potential Energy

Stored energy that can be converted into other forms, such as gravitational potential energy

Temperature

A measure of the average kinetic energy of the individual particles in a substance

Total Heat Energy Content

The sum of all the kinetic energies of all the individual particles within a substance

Absolute Zero

0 Kelvin (-273.15°C), representing a state of absolutely no atomic or particle motion

Law of Gravitation

Every mass attracts every other mass with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers [Fg = G * (M1 * M2) / d²]

Inverse-Square Law (Gravity)

A rule stating that doubling the distance (d) between two masses reduces the gravitational attraction force to 1/4 of its original strength

Newton's version of Kepler's Third Law

A formula that allows you to calculate the mass of a large central body if you measure the orbital period and average radius of a smaller object orbiting it

Atmospheric Drag

A form of friction from a planet's atmosphere that causes satellites to lose orbital energy

Gravitational Encounter

An orbital interaction where objects pass near each other and transfer gravitational energy, altering their paths (e.g., comets interacting with Jupiter)

Ocean Tides

Periodic rises and falls of large bodies of water on Earth caused by the gravitational pull of the Moon

Light Equation

Wavelength multiplied by frequency equals the speed of light (c)

Photons

Individual bundles or packets of radiant energy, each possessing a precise wavelength, frequency, and energy

Photon Energy Formula

Energy equals Planck's constant times frequency (E = h * f)

Atomic Number

The specific number of protons contained within an atom's nucleus

Atomic Mass Number

The combined total number of protons and neutrons located in an atom's nucleus

Isotope

Atoms that share the same number of protons but have a different number of neutrons

Emission

The process where photons are produced as an electron drops from a higher energy level to a lower one

Absorption

The process where incoming photons are captured by an atom, shifting an electron to a higher energy level or converting into thermal energy

Transmission

The process where photons pass freely through a transparent medium without interaction

Reflection

The process occurring when photons bounce off a polished or reflective surface, redirecting in the same direction

Refraction

The tendency of a wave to bend as it passes from one transparent medium to another

Scattering

The process where photons hit a substance and are redirected in random directions

Thermal Radiation Law 1 (Stefan-Boltzmann)

Law stating that a hotter object emits more radiation per unit of surface area at every single wavelength compared to a cooler object

Thermal Radiation Law 2 (Wien's Law)

Law stating that the peak wavelength of a hotter object is shifted to shorter wavelengths (higher energy/bluer light) compared to a cooler object

Thermal Radiation

Electromagnetic radiation emitted by an object that depends exclusively on its temperature

Spectral Lines

Distinct lines of emission or absorption that serve as a star's unique chemical "fingerprint" due to electron transitions between specific energy levels

Telescope Sensitivity

The light-collecting capability of a telescope, which scales directly with the square of the mirror's diameter (D²)

Telescope Resolution (Angular Resolution)

A telescope's ability to distinguish two adjacent objects that are close together in the sky

Hubble Space Telescope Advantage

Being in orbit above Earth's atmosphere allows it to avoid atmospheric blurring and operate at its diffraction limit for visible light

Greenhouse Effect

Atmospheric mechanism that traps outgoing infrared radiation emitted by the Earth's surface, warming the planet

Principal Greenhouse Gases

Water vapor (H2O) and carbon dioxide (CO2) in Earth's current atmosphere

Seismic Waves

Earthquake data waves used by scientists to determine the internal structure of the Earth's core

Earth's Interior Heating Processes

Funded by three core mechanisms: gravitational potential energy from accretion, planetary differentiation, and radioactive decay

Terrestrial Planets

Planets located in the inner solar system (Mercury, Venus, Earth, Mars) that are small, high-density, and rocky/solid

Jovian Planets

Planets located in the outer solar system (Jupiter, Saturn, Uranus, Neptune) that are large, low-density, gaseous, and have many moons and rings

Solar Nebula Contraction

When a solar nebula shrinks, conservation laws dictate that it flattens out, spins faster, and heats up

Nebular Composition Factor

The variation in temperature throughout the contracting solar nebula, determining what materials could solidify at different distances from the center

Radioactive Dating (25% Parent Left)

Indicates that exactly 2 half-lives have elapsed since the rock solidified (100% -> 50% -> 25%)

Half-Life Calculation (7 parts daughter to 1 part parent)

Means 3 half-lives have elapsed; if the half-life is 22 years, the sample's age is 66 years (22 * 3)

Wave Velocity

The physical property calculated as the product of a wave's frequency times its wavelength (v = f * lambda)

Radio Waves

The form of electromagnetic radiation (light) that possesses the longest wavelength in the entire spectrum

Doppler Effect (Approaching Source)

A phenomenon where a light source moving rapidly toward you has its light shifted to shorter wavelengths, appearing bluer

Ecliptic

The apparent annual path that the Sun traces across the celestial sphere over the course of a year

Celestial Equator

The projection of Earth's equator into space, which sits inclined at an angle of 23.5 degrees relative to the ecliptic due to Earth's axial tilt

Zodiac

The group of 12 specific constellations that lie directly along the path of the ecliptic line

Equinoxes

The two specific dates each year when the Sun's path on the ecliptic crosses directly over the celestial equator

Solstices

The physical points on the ecliptic path where the Sun reaches its northernmost and southernmost positions relative to the celestial equator