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Stellar Evolution

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The process by which a star changes in its lifetime.

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Star Formation

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The process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions" collapse to form stars.

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Exoplanets

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A planet that orbits a star other than the sun

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Hertzsprung-Russell Diagram

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A scatter graph of stars showing the relationship between the stars' absolute magnitude of luminosities versus their spectral classification or effective temperatures

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Black-body Radiation

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The type of electromagnetic radiation within or surrounding a body in thermodynamic equilibrium with its environment, or emitted by a black body held at constant, uniform temperature.

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Hot Jupiter

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A class of extrasolar planets whose characteristics are similar to Jupiter, but that have a high surface temperature because they orbit very close-between approximately 0.015 and 0.5 astronomical units-to their parent stars, whereas Jupiter orbits its parent star at 5.2 astronomical units, causing low surface temperature.

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Ionization

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The process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes.

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Nebula

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An interstellar cloud of dust, hydrogen, helium and other ionized gases

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Emission nebulas

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A nebula formed ionized gases that emit light of various colors

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Supernovae

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Stellar explosion that briefly outshines an entire galaxy, radiating as much energy as the Sun or any ordinary star is expected to emit over its entire life span, before fading from view over several weeks or months.

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Protoplanetary Disk

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A rotating circumstellar disk of dense gas surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star.

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Planetesimals

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solid objects thought to exist in protoplanetary disks and in debris disks

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Nebular Hypothesis

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The most widely accepted model in the field of cosmogony to explain the formation and evolution of the solar system

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Cosmogony

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Any model concerning the coming-into-existence (i.e. origin) of either the cosmos (i.e. universe) or the so-called reality of sentient beings

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Brown dwarfs

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Substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their cores, unlike main sequence stars

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Kelvin-Helmhotts mechanism

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An astronomical process taht occurs when the surface of a star or planet cools

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Bok globule

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Dark clouds of dense cosmic dust and gas

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Thermodynamic equilibrium

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An axiomatic concept of classical thermodynamics

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Astronomical Unit

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A unit of length roughly the distance from the Earth to the Sun. However, that distance varies as the Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year.

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Galaxy

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A gravitationally bound group of stars, dust and stellar remnants

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Edwin Hubble/Hubble's Law

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This man found that the recessional velocity is proportional to the distance away an object is and created an equation v=HoD, where "v" is the recessional velocity, "Ho" is Hubble's constant, and "D" is the distance.

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Kepler's First Law

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All of the orbits of the planets are elliptical with the Sun at one focus. In terms of ellipses, the foci are two points along the semi-major axis of the ellipse around the planet orbits. This can be represented by the formula e=c/a.

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Kepler's Second Law

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A planet traces out equal areas in equal time. Since the satellite does note trace out as much when it is closer to the Sun, it has to move faster in order for this law to be true, so this law basically proves that objects move faster the closer they are to the central object.

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Binary Systems

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One of the most important things to note is that the two bodies orbit in direct opposition to each other with the same period. The more massive body is always closer to the center of mass, while the less massive object orbits further from the barycenter. These are related such that for an object with a mass ma and a distance from the barycenter ra and a second object with a mass mb and a distance rb: ma/mb=rb/ra.

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Barycenter

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As the period is constant, the object must travel the full circumference in one period. Therefore as circumference is proportion to radius so also the orbital velocity is directly proportional to the distance from the barycenter va/ra=vb/rb

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Arcsecond (second of an arc)

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Unit of measurement that amounts to one sixtieth of an arcminute. Simply put, it is equal to 1/3600 degrees of an arc

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Arcminute (minute of an arc)

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Unit of angular distance that is equal to a 60th of a degree

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Coronagraph

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An instrument that blocks out light emitted by the Sun's actual surface so that corona can be observed

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Kepler's Third Law

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The square of the satellite's period is directly proportional to the cube of the length of its semi-major axis. This law can be represented by p^2 = a^3

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Parallax

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Displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines

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Spectroscopic Parallax

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An astronomical method for measuring the distances to stars. Despite its name, it does not reply on the apparent change in the position of the star.

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Spectra (plural spectrum)

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A Condition that is not limited to a specific set of values but can vary infinitely within a continuum.

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Continuum

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Theories of models that explain variation as involving gradual quantitative transitions without abrupt changes or discontinuities

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Spacetime

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Any mathematical model that combines space and time into a single interwoven continuum.

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Euclidean space

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Figure that encompasses the two dimensional Euclidean plane, the three dimensional space of Euclidean geometry and certain other spaces.

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Light Curve

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A graph of light intensity of celestial object or region as a function of time.

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Celestial Object (astronomical object)

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A naturally occurring physical entity, association, or structure that current science has demonstrated to exist in the observable universe.

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Motion

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Any movement of change in position or time

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Luminosity

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The total amount of energy emitted by a star, galaxy, or other astronomical object per unit time.

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Star

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A luminous sphere of plasma held together by its own gravity.

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Gravity

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A natural phenomenon by which all things with mass are brought towards one another including stars, planets, galaxies, and even light and subatomic particles.

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Color Index

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Simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The smaller the color index, the more blue (or hotter) the object is.

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Protostars

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A contracting mass of gas that represents an early stage in the formation of a star before nucleosynthesis has begun.

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Nucleosynthesis

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The process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons.

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Gas Giant

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A Giant planet composed mainly of hydrogen helium. Jupiter and Saturn are the Solar System's gas giants.

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Terrestrial planets

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A planet that is composed primarily of silicate rocks and metals

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Super-earth

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An extrasolar planet with a mass higher than Earth's, but substantially below the mass of the Solar System's ice giants Uranus and Neptune.

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Mini-Neptune

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A planet of up to 10 Earth masses, smaller than Uranus and Neptune, which have about 14.5 Earth masses and 17 Earth masses

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Habitability

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The conformance of a residence or abode to the implied warrant of habitability.

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Red supergiants

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Supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive.

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Black Hole

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A geometrically defined region of spacetime exhibiting such strong gravitational effects that nothing-including particles and electromagnetic radiation as light-can escape from inside it.

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White dwarf (degenerative dwarf)

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A stellar remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, and its volume is comparable to that of the Earth.

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Neutron Star

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A type of compact star that can result from the gravitational collapse of a massive star after a supernova.

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Photoevaporation

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denotes the process when a planet is stripped of its atmosphere (or parts of the atmosphere) due to high energy photons and other electromagnetic radiation. If a photon interacts with an atmospheric molecule, the molecule is accelerated and its temperature increased. If sufficient energy is provided, the molecule or atom may reach the escape velocity of the planet and "evaporate" into space. The lower the mass number of the gas, the higher the velocity obtained by interaction with a photon. Thus hydrogen is the gas which is most prone to photoevaporation.

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Parsec

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A unit of length used to measure large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond

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Light-year

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A unit of Length used informally to express astronomical distances. It is approximately 9 trillion kilometers (6 trillion miles.) The definition is "the distance that light travels in a vacuum in one Julian year"

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Julian Year

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A unit of measurement of time defined as exactly 365.25 days of 86,400 SI seconds each

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Vacuum

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A space void of all matter. AN approximation to such vacuums is a region with a aseous pressure much less than atmospheric pressure. The quality of a partial vacuum refers to how closely it approaches a perfect vaccum. Lower gas pressure means high-quality vacuu.

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Metallicity

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The fraction of mass of a star or other kind of astronomical object beyond hydrogen (X) and helium (Y). Most of the physical matter in the universe is in the form of hydrogen and helium, so astronomers conveniently use the blanket term "metals" to refer to all other elements.

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Spectral Classes

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Classification of Stars based upon groups based on color, mass, radius, and luminosity. They are mostly classified by the surface atmospheric temperature. Spectral classes are contained of OBAFGKM.

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Class O Stars

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-Very rare, Very massive Stars -Extremely short lifespans -0.00003% of local stars

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Class B Stars

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-Extremely luminous, short lifespans -Rarely found far from area of formation -0.125% of stars in solar neighborhood are of spectral class B

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Class A Stars

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-More common naked-eye stars with higher tendency to have massive planets -.625% of stars in solar neighborhood

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Class F stars

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-Technically a "dwarf star", may be referred as a yellow-white dwarf -3.03% of stars in the solar neighborhood

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Class G stars

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- Lifetime of 10 Billion years until hydrogen fusion ceases and transition to a red giant -7.5% of local stars, Most well known being the Sun

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Class K stars

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-Low mass and intermediate size lifespans of 15-30 billion years -12% of main sequence stars in the solar neighborhood

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Class M Stars

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-Low mass and Low surface temperature -Very dim stars

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Apparent Magnitude

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The brightness of a celestial object as seen from Earth.

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Absolute Magnitude

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Brightness of a celestial object at a distance of 10 parsecs away.

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Luminosity

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Measure of a brightness. SI units of joules per second or watts.

Penguin’s Science Olympiad Astronomy 2017 – Flashcards

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