Pre-Midterm 1 Material

Nuclear Fusion

The reaction of two light nuclei fusing to generate one heavier nucleus. In the Sun, four 1-hydrogen atoms fuse to form one 4-helium atom.

high temperatures

Nuclear fusion requires ________ in the core of the Sun.

hydrogen

The Sun is mostly _____, so most of its core is protons.

Gravitational Contraction

Gravitational potential energy is converted into heat, which is then radiated away in photons ad the star shrinks with time.

Mass-Energy

Energy obtained by converting mass into pure energy.

Mass-Energy Equation

E = mc^2

The Sun was formed out of a molecular cloud that underwent gravitational contraction until the centre was hot enough to ignite nuclear fusion reactions.

How was the Sun born?

Gravitational Equilibrium

Gravity is balanced by pressure forces.

Energy Balance

Energy produced by nuclear reactions is balanced by energy lost in radiation from the surface.

the energy per unit time leaving the surface in the form of photons.

The energy generated per unit time by fusion is equal to…

Photosphere

The visible surface of the Sun, from which most of the light escapes. The outside is transparent while the inside is opaque to radiation. This is where sunspots are visible.

Chromosphere

The layer just outside the photosphere; emits most of the UV light and is hotter than the photosphere.

Corona

The layer just outside the chromosphere; very low in density and is very hot, emits most of the Sun’s x-rays.

Convection Zone

Interior layer to the photosphere in which material transports energy by “boiling.”

Radiation Zone

The layer interior to the convection zone in which energy is transported by protons bouncing off one another.

Core

The innermost and hottest region of a star in which energy is produced via nuclear fusion.

produces more energy and thus more pressure, so the core expands. This decreases the temperature and the energy generation until the star returns to stability.

An increase in core temperature of a star…

produces less energy and thus less pressure, so the core shrinks. This increases the temperature and energy generation until the star returns to stabilty.

A decrease in the core temperature of a star…

Radiative Diffusion

Energy transport mechanism in which photons bounce around and collide with free electrons in the interior.

Convection

An energy transport mechanism in which matter circulates.

Solar Vibrations

Vibrations of the Sun’s surface. Can be used to study solar interiors as the vibration frequencies and amplitudes depend on interior quantities such as temperature and density.

Solar Neutrinos

Elementary particles generated during nuclear fusion which interact very weakly with matter and thus probe the solar core directly.

Sunspots

Darker, cooler regions of the Sun’s surface which emit less thermal radiation. They are colder because magnetic fields suppress convection in their vicinity and this hot material can not rise to the surface. They tend to occur in pairs.

Solar Flares

Short, intense bursts of high energy radiation and charged particles caused the the magnetic fields of the Sun changing their configuration.

the generation of aurorae, disruption of radio communications, and additional drag on satellites in low Earth orbits.

Coronal mass ejections from solar flares can cause…

Sunspot Cycle

The average number of sunspots on the Sun gradually rises and falls, with an average length of one cycle lasting 11 years.

Luminosity

Total power emitted by a star.

Apparent Brightness

Amount of power per unit surface area measured at a certain distance.

1

Brightest stars in the sky were assigned a magnitude of…

6

Faintest stars in the sky were assigned a magnitude of…

Spectral Sequence Mnemonic

Oh Be A Fine Girl, Kiss Me → O is the hottest temperature spectral type, M is the lowest temperature spectral type.

Binary Star Systems

Two stars orbiting one another around their common centre of mass.

Visual Binary

The binary system can be directly observed using a telescope .

Spectroscopic Binary

The binary system’s orbital motion can be determined through periodic Doppler shifts in the star’s spectral lines. If only one star is detectable it is a single-lined spectroscopic binary, if both stars are visible it is a double-lined spectroscopic binary.

Main Sequence Stars

Stars powered by the nuclear burning of hydrogen to helium.

Giants and Supergiants

Stars in the upper right corner of the H-R diagram which are more luminous than the main sequence stars of the same surface temperature.

White Dwarfs

Stars in the lower left H-R diagram which are less luminous than main sequence stars of the same surface temperature.

results in the supply being consumed much faster and thus massive stars live shorter lives.

More massive stars are born with more hydrogen to burn, but the higher luminosity…

Open Star Clusters

Stars found in the disk of the galaxy and are relatively young (<10 billion years).

Globular Star Clusters

Found in the halo of the galaxy and are very old (>10 billion years).

first.

Massive stars, which live the shortest, leave the main sequence…

Main Sequence Turnoff Point

Location at which stars leave the main sequence.

Emission

The generation of light via the conversion of energy.

Absorption

Matter absorbs light which causes the matter to be heated or changed.

Transmission

Light may pass through some types/colours of matter.

Reflection

Light bounces off matter in an organized way, i.e. it bounces off at the same angle it struck at.

Scattering

Light bounces off matter in random ways (which happens with most things).

Atomic Number

\# protons + # electrons

Isotopes

Atoms with different mass numbers than their normal state; atomic mass number is # protons + # neutrons

Plasma

Atoms which have had their electrons stripped from their nuclei.

Continuous Spectrum

Smooth, continuous spectrum given by a hot, uninterrupted light source.

Emission Spectrum

Bright emission lines at specific wavelengths are caused by the atoms in a warm gas emitting light only at specific wavelengths.

Absorption Spectrum

Dark absorption lines at specific wavelengths are caused the the light from a hot source passing through a cooler gas cloud in which some of the wavelengths are absorbed.

Light Collecting Area

Telescopes with a larger collecting area can gather a greater amount of light in a shorter time.

Angular Resolution

The ability to distinguish between different objects; telescopes that are larger are capable of taking images in greater detail.

the diffraction limit, which is caused by limitations due to the size of the light collecting area.

The limit on angular resolution is known as…

EMR Observable Below Earth’s Atmosphere

Radio waves and visible light waves.