This document is a 10-page summary of the Astrophysics Chapter of the IB Oxford Textbook. It includes detailed notes, graphs, images, definitions, and formulas. I obtained a predicted 7 in this class, and my average grade was a 97.
Astrophysics
Definitions
Astrophysics: study of physical astronomy.
Astronomy: study of celestial objects and phenomena.
Cosmology: study of the origin and evolution of the universe.
Light-year: distance light travels in 1 year. 1 ly=9.46× 1015 m
Light-minute: distance light travels in 1 minute. 1 lm=1.79 ×1010 m
Light-second: distance light travels in one second. 1 ls=2.99 ×108 m
Nebula: cloud of gas and dust in space. Born from “matter era” dust and
gas clouds formed when nuclei captured electrons and produced H. Also
born from ejected matter from a supernova explosion. Or, from the final
stage of a low mass red giant.
Precession: change in orientation of the rotational axis of a rotating object.
Standard candle: A standard candle is a star of known luminosity.
Apparent brightness: how a star appears on Earth–intensity.
Luminosity: power emitted from star.
Parsec: distance at which the mean radius of Earth’s orbit subtends an
angle of one second of arc. 1 pc=3.26 ly . Each degree is divided into 60 (1
arcminute), and each arcminute divided into 60 pieces is 1 arcsecond.
Astronomical unit: average distance from Earth to Sun. 1.50 ×1011 m
Planet: moderately large object that orbits a star; it shines by reflected
light. Terrestrial and Jovian.
Comet: irregular cosmic snowballs of frozen gases, rock, and dust that orbit
the Sun in an elliptical way. They have a tail.
Asteroid: a small and rocky object that orbits a star.
Star: a large, glowing ball of gas that generates heat and light through
nuclear fusion.
,Planetary system: consists of 1 or 2 stars, planets, satellites, asteroids,
meteors, and comets.
Constellations: pattern formed by stars that are generally in the same
direction when viewed from Earth. Not held together by gravity.
Stellar cluster: large groups of stars which are gravitationally bound.
Formed at the same time from the same nebula. Open clusters: younger
than 10 billion years, few stars, may contain gas and dust. Globular
clusters: older than 10 billion years, many stars, spherically shaped.
Galaxy: collection of gas, dust, and billions of stars and planetary systems
held together by gravity.
Galaxy clusters: collection of galaxies held together by gravity.
Spiral galaxy: disc-shape with spiral arms from a central galactic bulge. E.g.
Milky Way.
Universe: estimated 50 billion galaxies.
Star: born from nebulae.
Protostar: contracting mass of gas that represents an early stage in the
formation of a star, before nucleosynthesis.
Fusion ignition: when nuclear fusion becomes self-sustaining. Energy given
by fusion heats the fuel mass more rapidly than loss mechanism cools it.
Concepts – Slides and Video
What nuclear process powers stars? How does it relate to Einstein’s
famous equation?
Fusion. When converting from hydrogen to helium, some mass goes
missing. It is called mass defect. It goes into E=mc 2 . Energy can take the
form of light, so that is why stars shine. It can also be heat, so that is why
stars are hot.
L
To find the apparent brightness of a star: b= , where b is apparent
4 π d2
brightness, L is luminosity, and d is distance from star.
To represent Sun stuff: L⊙, M⊙, R⊙, etc.
26 30 5
L⊙=3.83 ×10 W ; M ⊙=1.99 ×10 kg ; R⊙ =6.95× 10 m
, 3 kinds of nebula:
Emission nebula: nebula formed by ionized gases that emit light of various
wavelengths.
A hot star illuminates a gas cloud, exciting and/or ionizing the gas, so
electrons recombining falling back to ground state produce emission lines.
Reflection nebula: nebula which might reflect light of nearby stars. Star
illuminates gas and dust clouds, so star light is reflected by dust. Reflection
nebula appear blue since blue light is scattered by larger angles than red
light (same with sky).
Dark nebula: AKA absorption nebula. Dense, non-luminous nebula that
obscures the visible wavelengths of light from other stellar objects.
D.1 Stellar Concepts
Universe components
Solar system is a collection of planets, moons, asteroids, comets, and rocky
objects traveling in elliptical orbits around the Sun under gravity. High
temperature close to the Sun allowed compounds with high condensation
temperatures to remain solid, accreting particles to form terrestrial planets.
Jovian (gaseous) planets are formed from cores of rock, metal, and ice.
Large quantity of icelarge planets large gravitational field that capture H
and He.
Some moons are asteroids captured by the gravitational field. Small
asteroids have an irregular shape since gravity is too weak. Asteroids of
6
10 m can be considered minor planets.
Stars form when gravity causes a gas in a nebula to condense. As atoms
move towards each other, GPE decreases and it is converted to KE
temperature increases, and atoms form a Protostar. It becomes denser, and
when the Protostar has sufficient mass, it becomes hot enough for nuclear
fusion. In a large Protostar, temperature and pressure in the center allow H
to fuse into He by releasing energy, creating ignition. Ignition produces
radiation from the core, whose pressure opposes gravity. The star achieves
hydrostatic equilibrium (becomes stable and is on the main sequence as
long as H is turned into He.
Los beneficios de comprar resúmenes en Stuvia estan en línea:
Garantiza la calidad de los comentarios
Compradores de Stuvia evaluaron más de 700.000 resúmenes. Así estas seguro que compras los mejores documentos!
Compra fácil y rápido
Puedes pagar rápidamente y en una vez con iDeal, tarjeta de crédito o con tu crédito de Stuvia. Sin tener que hacerte miembro.
Enfócate en lo más importante
Tus compañeros escriben los resúmenes. Por eso tienes la seguridad que tienes un resumen actual y confiable.
Así llegas a la conclusión rapidamente!
Preguntas frecuentes
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
100% de satisfacción garantizada: ¿Cómo funciona?
Nuestra garantía de satisfacción le asegura que siempre encontrará un documento de estudio a tu medida. Tu rellenas un formulario y nuestro equipo de atención al cliente se encarga del resto.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller Philippe21. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for 6,38 €. You're not tied to anything after your purchase.
