Star & Galaxies flashcards

Speed of Light

The constant speed at which light travels in space (and air), approximately 299,800 km/s (or 3.0 x 10^5 km/s), used to define the light year.

Scale Model (Stars in Galaxy)

Using grains of sand to represent stars, 2 billion stars would fill about 500 cubic meters or over 130,000 gallons, enough to fill a classroom to the ceiling.

Scale Model (Distance between Solar Systems)

If our solar system is represented by a quarter, the next closest solar system would be located two football fields away.

Scale Model (Size of our Galaxy)

On the scale where a solar system is a quarter, our Galaxy would be as large as the United States.

Astronomical Time Scales

Very long durations of time where events that seem very long to humans may in fact be very short.

Age of the Universe

Approximately 13.7 billion years old.

Age of our Solar System (compared to Universe)

4.6 billion years old. In a scale model where the universe is one calendar year, our Solar System was created on September 2.

Human Lifespan (compared to Universe)

For a 20-year-old, their life is approximately 5/100ths of a second in a scale model where the universe is one calendar year.

Electromagnetic Radiation

A kind of radiation in which electric and magnetic fields vary simultaneously; more commonly known as light.

Frequency (f)

How often a wave repeats itself, measured in Hertz (cycles per second).

Wavelength (l)

The length over which a wave repeats in pattern, measured in meters.

Speed of light (c)

The constant speed of light in a vacuum, approximately 3 x 10^8 m/s, calculated as wavelength multiplied by frequency.

Transverse Wave

A wave in which the oscillating electric and magnetic fields are perpendicular to the direction of travel.

Photon

A particle representing a quantum or bundle of light energy.

Plancks Constant (h)

A physical constant (6.626 x 1034 Js) used in the equation for photon energy (E = hf).

Electromagnetic Spectrum

The full range of all types of light, which differ in terms of wavelength and frequency.

Visible Light

The portion of the electromagnetic spectrum that human eyes can perceive, ranging from approximately 400 to 750 nanometers.

Nanometer (nm)

A unit of length used to measure light wavelengths, equal to one billionth of a meter.

Opaque

A property of a medium that blocks or prevents the passage of a specified form of radiation.

Transparent

A property of a medium that allows the passage of a specified form of radiation.

Wavelength and Frequency Relationship

For light in a vacuum, wavelength and frequency are inversely proportional; as one increases, the other decreases.

Photon Energy and Frequency Relationship

The energy of a photon is directly related to its frequency; higher frequency means higher energy.

Photon Energy and Wavelength Relationship

The energy of a photon is inversely related to its wavelength; shorter wavelength means higher energy.

Spectroscopy

The study of light by spreading it out to see the various wavelengths being emitted.

Reason for using narrow slits in spectroscopy

To prevent various images at different wavelengths from overlapping and blurring when light is spread out, allowing for clean separation of wavelengths.

Continuous Spectra

A type of spectrum that covers a full range of wavelengths, typically emitted by dense objects (e.g., blackbody radiation).

Emission Spectra

A spectrum emitted by a hot, low density gas, appearing as a series of lines representing emission at only certain wavelengths.

Absorption Spectra

A spectrum where a continuous spectrum of light passes through a cool, low density gas, showing the continuous spectrum with certain wavelengths "missing".

Line Spectra

The collective term for emission and absorption spectra, originating from low density gases and providing information on the composition of an object.

Blackbody object

A theoretical body that absorbs all electromagnetic radiation falling on it; it is a perfect absorber and a perfect emitter of electromagnetic radiation. Dense objects (solids, liquids, dense gases) behave like blackbody objects.

Blackbody radiation

The thermal radiation emitted by a blackbody object, which covers a range of wavelengths, is dependent on the temperature of the object, and obeys blackbody radiation laws.

Stefan-Boltzmann law

A law stating that the intensity of light (energy/sec per unit area) emitted by a blackbody object is directly related to the temperature of the object raised to the fourth power (Intensity ~ T^4).

Wien's law

A law stating that a blackbody object gives off most of its light at one particular wavelength (its peak wavelength), and this wavelength is inversely proportional to the temperature of the object (λmax ~ 1/T).

Intensity (of light)

The luminosity radiated by a unit area of an object, measured as energy per second per unit area.

Luminosity

The total energy radiated per second by an object.

Bohr model of an atom

A model used to understand why atoms emit and absorb light, explaining observations even though it's not entirely correct.

Nucleus

The core of an atom where almost all of its mass resides, containing protons and neutrons.

Protons

Positively charged particles located in the nucleus, whose number determines the element.

Neutrons

Neutrally charged particles located in the nucleus, whose number determines the isotope of an element.

Electrons

Negatively charged particles that orbit the nucleus; their movement causes atoms to absorb or emit energy.

Ground state

The lowest allowed energy state of an atom, where electrons are as close to the nucleus as quantum mechanics allows.

Discrete energy levels

Specific distances or energy amounts at which electrons are allowed to orbit the nucleus, similar to rungs on a ladder.

Ionized atom / Ion

An atom that has absorbed enough energy to lose an electron, resulting in a net electrical charge.

Photon

A particle of light; its energy determines its wavelength.

Electron absorption of energy

When an electron absorbs a photon of just the right energy, causing it to jump to a higher permitted energy level.

Electron emission of energy

When an electron jumps from a higher energy level to a lower one, releasing a photon of energy.

Lyman series

A group of UV wavelengths (91nm - 122nm) associated with electron jumps to and from the n=1 energy level in hydrogen.

Balmer series

A group of visible and UV wavelengths (365nm - 656nm) associated with electron jumps to and from the n=2 energy level in hydrogen.

Paschen series

A group of IR wavelengths (820nm - 1875nm) associated with electron jumps to and from the n=3 energy level in hydrogen.

Hydrogen spectra

The unique pattern of wavelengths of light emitted or absorbed by hydrogen, crucial for understanding the universe's most abundant element.

Ha (Hydrogen Alpha)

A red hydrogen Balmer line at 656 nm.

Hb (Hydrogen Beta)

A blue-green hydrogen Balmer line at 486 nm.

Hg (Hydrogen Gamma)

A blue hydrogen Balmer line at 434 nm.

Hd (Hydrogen Delta)

A violet hydrogen Balmer line at 410 nm.

Spectra as identification

Unique patterns of spectral lines for different elements, used by astronomers like a fingerprint to determine chemical composition.

Continuous spectrum

Light from a hot, dense source that shows all wavelengths without interruption.

Absorption spectrum

Light that has passed through a low-density gas, showing specific dark lines where wavelengths were absorbed by the gas.

Emission spectrum

Light emitted by a low-density gas itself, showing specific bright lines at the wavelengths it re-emits.

Line spectra

The characteristic patterns of bright or dark lines in emission or absorption spectra that reveal the chemical composition of a gas.

Doppler Effect

A shifting of observed wavelengths due to a relative motion between the observer and the source.

Stationary Object Light Emission

When an object is sitting still emitting a wavelength of light in all directions, observers will measure the same wavelength of light regardless of their position.

Observer on Approaching Side (Doppler Effect)

Measures a wavelength shorter than the one emitted by a moving object.

Observer on Receding Side (Doppler Effect)

Measures a wavelength longer than the one emitted by a moving object.

Redshift

A shift of wavelength towards longer wavelengths (characterized by the red end of the visible spectrum), occurring when an object is moving away from the observer.

Blueshift

A shift towards shorter wavelengths (characterized by the blue end of the visible spectrum), occurring when an object is moving towards the observer.

Radial Motion

Motion towards or away, based on the perspective of the observer, which is the only type of motion given by the Doppler Effect.

Transverse Motion

Motion across your line-of-sight, based on the perspective of the observer.

Radial Velocity

The speed of an object moving towards or away from an observer, which can be measured using the Doppler shift, where faster motion leads to a greater shift.

Doppler Effect (Wave Type)

Affects all waves, including light and sound, not just light waves.

Astronomical Doppler Shift Detection

Astronomers detect Doppler shifts by observing the spectrum of light, noting that all characteristic lines are shifted in pattern but retain their relative positions, allowing determination of composition and radial speed.

Doppler Shift on Object Appearance

Does not typically change the apparent color of an object, as the shifting of wavelengths is usually too small to cause a noticeable change.

Interstellar Medium (ISM)

Composed of gas and dust located in the regions between the stars; roughly 75% Hydrogen, 25% Helium for gas, and microscopic carbon and silicates for dust.

Gas (in ISM)

Roughly 75% Hydrogen and 25% Helium, with trace amounts of metals.

Dust (in ISM)

Microscopic (10^-6 meters) in size, composed mostly of carbon and silicates.

Metals (in astronomy)

Any element other than hydrogen and helium.

Nebula

An enormous cloud of dust and gas occupying the space between stars, often acting as a nursery for new stars.

Dark Nebula

A cloud that is dense enough to block background light, appearing dark due to obscured visible light.

Emission Nebula

A cloud that is ionized by nearby hot stars (hotter than 25,000 K) and emits an emission spectrum, typically appearing reddish-pink due to hydrogen Balmer-line emission.

H II Region

Another name for an emission nebula, referring to ionized hydrogen (hydrogen with its electron stripped away).

Reflection Nebula

A cloud that scatters light from nearby cooler stars, appearing blue because dust scatters blue light more than red light.

Interstellar Reddening

The phenomenon where visible light, especially blue light, is absorbed and scattered more by small dust particles in nebulae, causing the transmitted light to appear not only dimmed but also redder.

Dust Emission

The process where cosmic dust re-radiates energy it absorbs, but at infrared wavelengths, causing optically dark nebulae to appear bright in infrared images.

21-cm Radiation

A long-wavelength radio emission (21 cm) produced when an electron in an atomic hydrogen atom flips its spin from a slightly higher energy state to a lower one. It is important because it is not obscured by dust, allowing detection of atomic hydrogen clouds over long distances.

Molecular Hydrogen (H2)

The form in which most hydrogen exists in the coldest regions of space (~10 K), which does not emit 21-cm radiation.

Tracers

Other molecules, significantly less abundant than hydrogen, which emit their own radiation and are therefore easier to detect, used to map out the locations of molecular hydrogen.

Molecular Clouds

Dense regions of space (approximately 1000 atoms/cm³) primarily composed of molecular hydrogen, containing 100,000 to a few million solar masses of material, and are sites of future star formation.

Interstellar Cloud

A large cloud of gas and dust in space where star formation begins, initially balanced by random particle motions and gravity.

Gravitational Collapse

The process where a cloud of gas and dust contracts due to the force of gravity continually pulling material inward.

Fragmentation

The process where an interstellar cloud, due to non-uniform density and gravitational collapse, breaks into smaller cloudlets centered around denser regions.

Molecular Cloud (Sun'sOrigin)

The original cloud from which our Sun formed, roughly 10,000 times bigger than our solar system (or 10^14 km) with a temperature of only 10 K.

Evaporating Gaseous Globules (EGGs)

Denser regions of gas and dust that are contracting under their own gravity and will eventually form stars, protected from high-energy UV rays by their density.

Protostar

A collapsing cloud of gas and dust where the central temperature has risen to around 10,000 K and it has collapsed to the size of our solar system, destined to become a star.

Orion Nebula

A site of current star formation that contains an immense cloud of gas and dust, showing evidence of forming protostars and planets.

Conservation of Angular Momentum

A law stating that the total angular momentum of an isolated physical system remains constant; as a cloud collapses and particle distances from the rotation axis decrease, their velocity must increase.

Angular Momentum

A physical property describing the movement of mass about a rotation axis, calculated as L = mvr for a single particle.

Disk Formation

The process by which a collapsing cloud of gas and dust flattens into a disk perpendicular to its rotation axis due to the conservation of angular momentum.

Dust Disks Around Young Stars

Dense disks of gas and dust observed in visible and radio wavelengths orbiting young stars, serving as probable sites of ongoing planetary formation.

Infrared-emitting Disks

Very cold, low-density disks around stars observed at infrared wavelengths, representing debris from comets or collisions and evidence of already formed planetary systems.

T Tauri Stars

Protostars (technically not stars) that exhibit violent surface activity and strong stellar winds, appearing bright in the infrared due to surrounding dust, representing an active stage of star formation.

Herbig-Haro (HH) Objects

Formations caused when energetic jets ejected perpendicular to a protostar's disk (along its magnetic field axis) encounter and energize nearby interstellar gas and dust.