Angular Momentum, Matter, and Light in Astronomy

Flashcards covering key concepts from the lecture on angular momentum, properties of matter (atoms, phases, phase changes), and the nature and properties of light (electromagnetic waves, photons, spectrum) as tools for astronomy.

Angular Momentum (L)

The quantity of motion of a spinning (rotating) object, calculated as L = m
. v
. r or P
. r, with units kg m
2 s
-1. It depends on the geometry, mass, and rotational velocity of an object.

Conservation of Angular Momentum

The tendency of a spinning object to keep spinning with its rotation axis in a constant direction. Its value cannot change unless an external twisting force (torque) acts on it.

Vector Quantity (Angular Momentum)

Angular momentum is a vector quantity, meaning the direction of its axis of rotation is resistant to change.

Torque

An external twisting force that causes the angular momentum of an object to change.

Kepler
’s Second Law of Orbits

As a planet moves around its orbit, the closer the planet is to the Sun, the higher its speed, due to the conservation of angular momentum (L = m
.v
.r = constant).

Mass-Energy Equivalence

Describes that mass itself is a form of potential energy, represented by the equation E = mc
2.

E = mc
2

Einstein's formula showing that mass can produce energy (a small amount of mass can release a great amount of energy) and energy can be used to produce mass.

Matter

Comes in different forms (phases) depending on temperature and type, but is composed of atoms.

Phases of Matter

The different forms matter can take: Solid, Liquid, Gas, and Plasma.

Atom

The fundamental building block of matter, made of electrons, protons, and neutrons.

Electrons

Negatively charged particles that swarm around the nucleus of an atom.

Protons

Positively charged particles located in the nucleus of an atom.

Neutrons

Neutral particles (no charge) located in the nucleus of an atom.

Nucleus

The central part of an atom, containing protons and neutrons, and nearly all of the atom
’s mass, held together by the nuclear force.

Coulomb (Electrical) Force

The attractive force between the positively charged nucleus and the negatively charged electrons, binding the atom together.

Nuclear Force

A strong force that holds the protons and neutrons together in the nucleus, working only over extremely short separations.

Element

A kind of atom, determined by the number of protons in its nucleus.

Atomic Mass

The sum of both protons and neutrons in an atom
’s nucleus.

Hydrogen (H)

The most abundant element, with one proton (+ one electron).

Helium (He)

The next most abundant element after hydrogen, with two protons (and two neutrons + two electrons).

Molecules

Electrically neutral groups of atoms held together by chemical bonds.

Chemical Bonds

Forces that hold atoms together to form molecules.

Isotope

An atom of an element that has a different number of neutrons in its nucleus (but the same number of protons).

Solid Phase

A phase of matter where molecules are pretty much fixed together.

Liquid Phase

A phase of matter where molecules move around a bit.

Gas Phase

A phase of matter where molecules move about freely.

Ionization

A phase change involving the stripping of electrons, changing atoms into plasma.

Dissociation

A phase change involving the breaking of molecules into atoms.

Evaporation

A phase change involving the breaking of flexible chemical bonds, changing liquid into gas.

Melting

A phase change involving the breaking of rigid chemical bonds, changing solid into liquid.

Plasma

A phase of matter consisting of a gas of elementary particles, formed when atoms are ionized.

Light

A form of energy (radiant energy) and information that can travel through empty space, acting as both a wave and a particle.

Radiant Energy

Another term for light, emphasizing its nature as a form of energy.

Electromagnetic Wave

Light described as a wave, specifically a vibration of electric and magnetic fields moving through space at the speed 'c'.

Photon

A particle of light, also called a quantum, which is a massless 'bundle of energy' that carries energy and reacts to gravitational fields.

Watts

Units used to measure the power (flow of energy) of light, where 1 watt = 1 joule/s.

Speed of Light (c)

The constant rate at which electromagnetic waves (light) move through empty space, approximately 2.99792458

10
8 m/sec.

Wavelength (λ)

The distance between two consecutive crests (or troughs) of a wave.

Frequency (ν)

The number of crests (or troughs) of a wave that pass by each second.

Visible Light

A small part of the electromagnetic spectrum that our eyes can perceive, ranging from blue (shorter wavelength) to red (longer wavelength).

White Light

Light that is made up of nearly equal amounts of all frequencies in the visible portion of the spectrum.

Electromagnetic Spectrum

The entire range of electromagnetic radiation, encompassing various forms of light with different wavelengths, frequencies, and energies.

Energy of a Photon (E)

The energy carried by a photon, which depends on its frequency, given by the formula E = h

(where h is Planck's constant).

Planck
’s Constant (h)

A fundamental constant relating the energy of a photon to its frequency, with a value of approximately 6.626

10
-34 m
2 kg / s.

Wave-Particle Duality

The concept that all types of electromagnetic radiation act as both waves and particles, connected by the relation E = h

= hc /
λ.

Light Intensity

Determined by the number of photons; a more intense (brighter) light means more photons of the same frequency.

UV Radiation and Sunburn

Sunburn is caused by the high energy of UV radiation from the Sun,だけでなくその強度.