ASTR 1102 Exam 2 Study Guide

What are the three main components of an atom?

Protons, neutrons, and electrons. Protons are positive, neutrons have no charge, and electrons are negative.

What determines which element an atom is?

The number of protons in its nucleus. For example, hydrogen has 1 proton and helium has 2.

What are the three kinds of spectra?

Continuous spectrum, emission-line spectrum, and absorption-line spectrum.

What produces a continuous spectrum?

A hot, opaque object produces a continuous spectrum containing a broad range of wavelengths.

What produces an emission-line spectrum?

A hot, thin, transparent gas produces bright emission lines.

What produces an absorption-line spectrum?

Cooler gas in front of a hot, opaque source absorbs certain wavelengths, producing dark lines.

Why does the Sun have an absorption-line spectrum?

The hot photosphere produces a continuous spectrum, and cooler gas above it absorbs specific wavelengths, creating dark absorption lines.

What are the layers of the Sun's atmosphere from lowest to highest?

Photosphere → Chromosphere → Corona.

Which layer of the Sun's atmosphere is hottest?

The corona, which can reach temperatures around 2,000,000 K.

Which layer of the Sun's atmosphere is densest?

The photosphere.

Which layer of the Sun's atmosphere is brightest in visible light?

The photosphere. It is the visible surface from which most of the light we normally see comes.

Where does the solar wind come from?

The corona. Some particles in the extremely hot corona move fast enough to escape the Sun's gravity.

What causes a sunspot?

Strong magnetic fields restrict convection, so less hot gas reaches the surface. The region cools and appears darker than its surroundings.

Why do sunspots look dark?

They are cooler than the surrounding photosphere, although they are still very hot.

What is differential rotation?

Different parts of the Sun rotate at different speeds. The equator rotates faster than regions near the poles.

How does differential rotation help produce the solar cycle?

Different rotation speeds twist and wind the Sun's magnetic field lines, increasing magnetic activity and helping produce the approximately 11-year solar cycle.

How long is the solar activity cycle?

About 11 years.

What is a solar prominence?

A large loop of hot gas held above the Sun's surface by magnetic fields.

What is the difference between a prominence and a filament?

They are the same type of structure. It looks bright against space as a prominence and dark against the bright face of the Sun as a filament.

What is a solar flare?

A sudden release of magnetic energy in the Sun's atmosphere.

What is a coronal mass ejection or CME?

A huge eruption in which a large amount of solar material is blasted into space.

What is the basic difference between a solar flare and a CME?

A solar flare is mainly a sudden release of energy, while a CME is a large ejection of matter into space.

How can solar storms affect Earth?

They can disturb satellites, communications, electrical power grids, spacecraft, and produce unusually widespread aurorae.

What is an aurora?

Light produced when charged particles from the Sun interact with Earth's magnetic field and upper atmosphere.

How does the Sun generate its energy?

Through thermonuclear fusion in its core, where hydrogen is converted into helium.

What are the two components of an atomic nucleus?

Protons and neutrons.

What is an isotope?

A version of an element with the same number of protons but a different number of neutrons.

What is the difference between an element and an isotope?

The proton number determines the element. The neutron number determines which isotope of that element it is.

What are the main elements in the Sun?

About 74% hydrogen, 25% helium, and roughly 1% heavier elements.

What are important hydrogen isotopes?

Hydrogen-1 has 1 proton and 0 neutrons, deuterium or hydrogen-2 has 1 proton and 1 neutron, and tritium or hydrogen-3 has 1 proton and 2 neutrons.

What are important helium isotopes?

Helium-3 and helium-4.

What is the proton-proton chain?

A series of nuclear fusion reactions in the Sun's core that ultimately converts hydrogen into helium and releases energy, neutrinos, and gamma rays.

Why does nuclear fusion require extremely high temperatures?

Hydrogen nuclei are positively charged and repel each other. Very high temperatures make them move fast enough to get close enough for fusion to occur.

Why does fusion release energy?

The helium produced has slightly less mass than the original hydrogen. The missing mass is converted into energy according to E = mc².

What does E = mc² mean in this unit?

Mass can be converted into energy. Because the speed of light squared is enormous, a tiny amount of mass can produce a huge amount of energy.

Where are solar neutrinos produced?

In the Sun's core during nuclear fusion.

Why are neutrinos useful for studying the Sun's core?

They interact very weakly with matter, so they can escape directly from the core and give astronomers information about the fusion happening there.

What was the solar neutrino problem?

Early experiments detected only about one-third of the expected electron neutrinos from the Sun.

How was the solar neutrino problem solved?

Scientists discovered that neutrinos can change flavor as they travel. When electron, muon, and tau neutrinos were all counted, the total matched solar-model predictions.

What are the three neutrino flavors?

Electron neutrino, muon neutrino, and tau neutrino.

What is thermal equilibrium in the Sun?

The rate at which the Sun produces energy is approximately equal to the rate at which it loses energy from its surface.

What does thermal equilibrium prevent?

It prevents the Sun from rapidly getting hotter or cooler.

What are the main interior layers of the Sun from the center outward?

Core → Radiative zone → Convection zone.

Where is the Sun's energy produced?

In the core through nuclear fusion.

How is energy transported through the radiative zone?

By radiation, with photons carrying energy outward.

How is energy transported through the convection zone?

By convection. Hot gas rises while cooler gas sinks.

Is conduction an important way energy moves through the Sun?

No. Conduction is not an important energy-transport process in the Sun.

What is hydrostatic equilibrium?

The inward pull of gravity is balanced by outward pressure inside the Sun.

What is the difference between thermal equilibrium and hydrostatic equilibrium?

Thermal equilibrium is an ENERGY balance: energy produced equals energy lost. Hydrostatic equilibrium is a FORCE balance: gravity inward equals pressure outward.

What is the interstellar medium?

The gas and dust found in the space between stars.

What is a nebula?

A concentration or cloud of interstellar gas and/or dust.

What is an H II region?

A region of ionized hydrogen, usually created when ultraviolet radiation from hot young stars knocks electrons off hydrogen atoms.

What is the difference between H I and H II hydrogen?

H I is neutral hydrogen. H II is ionized hydrogen.

What are the three major types of nebulae?

Emission nebulae, dark nebulae, and reflection nebulae.

What is an emission nebula?

A cloud of excited gas that produces its own light and emission lines.

What is a dark nebula?

A dusty cloud that blocks or scatters background light, making it appear dark.

What is a reflection nebula?

A dusty nebula that is visible because dust scatters light from nearby stars toward us, often making the nebula look blue.

Why do reflection nebulae often look blue?

Dust scatters shorter blue wavelengths more strongly than longer red wavelengths.

What does interstellar dust do to stars seen behind it?

It makes them appear fainter and redder.

What is interstellar reddening?

The effect in which dust scatters shorter wavelengths more strongly, causing objects behind the dust to appear redder.

What kind of telescope is especially useful for studying dusty star-forming regions?

An infrared telescope.

Why is infrared useful for studying star-forming regions?

Infrared is scattered less by dust than visible or ultraviolet light and is also well suited for observing cool protostars.

What are giant molecular clouds?

Large, cold, dense clouds of gas and dust where stars can form.

What causes a gas cloud to begin collapsing into a protostar?

Gravity becomes stronger than the internal gas pressure supporting the cloud.

What kind of gas cloud is most likely to collapse?

A cold, dense gas cloud.

Why does high density help a gas cloud collapse?

Higher density gives the cloud stronger self-gravity.

Why does low temperature help a gas cloud collapse?

Lower temperature means lower gas pressure, making it easier for gravity to overcome pressure.

What is a protostar?

A forming star created by the gravitational collapse of a gas cloud before sustained hydrogen fusion begins.

What powers a protostar before nuclear fusion begins?

Gravitational contraction.

How does gravitational contraction heat a protostar?

As the cloud contracts, gravitational potential energy is converted into heat.

Why can't gravitational contraction support a star indefinitely?

It provides energy only while the star continues collapsing. A long-term energy source such as nuclear fusion is needed to stabilize the star.

Where does a protostar enter the H-R diagram in the simplified course model?

Near the upper-right region because it begins relatively cool but can be large and luminous.

What happens to a protostar as it contracts?

It becomes smaller and hotter as gravitational contraction releases energy.

Why does a protostellar disk form?

A collapsing gas cloud usually rotates. Conservation of angular momentum causes it to spin faster and flatten into a disk.

What is an accretion or protostellar disk?

A rotating flattened disk of gas and dust surrounding a forming star.

Where can planets eventually form around a young star?

From material in the protostellar or accretion disk.

What structures can be seen around or near a protostar?

A protostellar/accretion disk, jets, and strong stellar winds.

What are protostellar jets?

Narrow streams of gas flowing outward from a young star and its disk, probably guided by magnetic fields.

What is the overall sequence of star formation?

Cold dense gas cloud → gravity overcomes pressure → cloud collapses → protostar forms → gravitational contraction heats it → disk and jets may form → core becomes hot enough for fusion → main-sequence star.