AST1002 Midterm FRQ Study Guide

Importance of Studying Asteroids

Asteroids are remnants of early Solar System formation and can provide clues about its composition and evolution. Studying them also helps assess impact risks to Earth and develop mitigation strategies.

Locations of Icy Bodies

Two key reservoirs of icy bodies are the Kuiper Belt, just beyond Neptune, and the Oort Cloud, a distant spherical shell surrounding the Solar System. Both regions harbor comets and other volatile-rich objects.

Three Asteroid Locations

Asteroids primarily reside in the Main Belt between Mars and Jupiter, where gravitational interactions prevented planet formation. They are also found as Near‑Earth Objects (NEOs) crossing Earth’s orbit, and as Trojans sharing Jupiter’s orbit at its L4 and L5 Lagrange points.

Solar Nebula Theory Evidence

The flat, disk‑like arrangement of planetary orbits reflects the original protoplanetary disk predicted by the Solar Nebula theory. Additionally, the elemental gradient—rocky inner planets and icy outer worlds—matches temperature‑driven condensation in a cooling nebula.

Comet Changes Near the Sun

As a comet approaches the Sun, solar heating sublimates its icy nucleus, forming a glowing coma of gas and dust. Solar radiation and the solar wind then shape this material into distinct dust and ion tails that point away from the Sun.

Effects of Earth's Revolution

Earth’s annual orbit around the Sun causes the seasonal shift in constellations visible at night. It also leads to the gradual change in sunrise and sunset times throughout the year.

Challenges of Venus Landers

Venus’s surface conditions—temperatures around 467 °C and pressures about 90 atmospheres—destroy most spacecraft quickly. Its corrosive sulfuric acid clouds and dense atmosphere add further technical difficulties.

Early Solar System Temperature and Chemistry

High temperatures close to the young Sun allowed only refractory materials like metals and silicates to condense, forming terrestrial planets. Farther out, cooler conditions enabled volatile ices and gases to solidify, creating gas and ice giants.

Leading Moon Formation Theory

The Giant Impact hypothesis proposes a Mars‑sized body collided with early Earth, ejecting material that coalesced into the Moon. This model explains the Moon’s composition and angular momentum of the Earth–Moon system.

Convection and Examples

Convection is the heat‑driven movement of fluid or gas, where warmer, less dense material rises and cooler, denser material sinks. Mantle convection in Earth drives plate tectonics, and in the Sun, plasma convection produces granulation on its surface.

Causes of Lunar Phases

Lunar phases result from the Moon’s orbit around Earth, altering the Sun‑lit portion we see. The relative positions of the Sun, Earth, and Moon dictate whether we observe new, crescent, quarter, gibbous, or full phases.

Copernicus’ Key Improvement

Copernicus introduced uniform circular orbits around the Sun but retained epicycles to match observed planetary motions. Removing Earth from the center corrected the apparent retrograde motion and improved predictive accuracy.

Planetary Magnetic Field Generation

A planet generates a magnetic field through the dynamo effect: the motion of conducting fluid in its interior, combined with rotation, induces electric currents. These currents produce a magnetic field aligned roughly with the planet’s rotation axis.

Carbon Dioxide Sources and Sinks

Volcanic outgassing and respiration from life add CO₂ to a terrestrial atmosphere, while rock weathering and photosynthesis remove it. In some cases, carbonate precipitation and burial in sediments serve as long‑term carbon sinks.

Lunar Eclipse Geometry and Phase

During a lunar eclipse, Earth lies directly between the Sun and Moon, casting its shadow on the lunar surface. The Moon is in the full phase when it enters the Earth’s umbra.

Venus vs. Mars Atmospheres

Both Venus and Mars atmospheres are dominated by CO₂ and have negligible water vapor compared to Earth. However, Venus has an extremely dense, high‑pressure atmosphere, whereas Mars’s atmosphere is thin, with surface pressures under one percent of Earth’s.

Volcanic Features on Venus

Venus’s surface showcases volcanic plains formed by extensive lava flows and large shield volcanoes with broad profiles. It also has pancake domes—flat, circular volcanic features created by viscous lava.

Solar Eclipse Geometry and Phase

In a solar eclipse, the Moon passes between the Sun and Earth, casting its shadow on Earth’s surface. The Moon is in the new phase at the time of the eclipse.

Mars Rover Example

One notable Mars rover is Curiosity, which landed in Gale Crater in 2012 to study past habitability. Its successor, Perseverance, touched down in Jezero Crater in 2021, seeking signs of ancient microbial life.

Evidence for Martian Water

Features like dried river valleys and sedimentary layers indicate past liquid water flowed on Mars. Observations of recurring slope lineae suggest transient briny flows may occur seasonally.

Jovian Planet Spots Formation

Spots on gas giants like Jupiter’s Great Red Spot arise from long‑lived high‑pressure systems in their atmospheres. These vortices form at the boundaries of adjacent jet streams where wind shear creates storm systems.

Saturn’s Muted Colors

Saturn’s upper atmosphere has a thicker haze of photochemical smog, which mutes and diffuses sunlight more than Jupiter’s clearer atmosphere. Additionally, its colder temperatures slow chemical reactions that produce vibrant colors.

Blue Atmospheres of Uranus and Neptune

Methane in the atmospheres of Uranus and Neptune absorbs red light, scattering more blue wavelengths and giving them their distinctive hue. Jupiter and Saturn have less methane and more complex hydrocarbons that produce red and green coloring.

Convection and Jupiter’s Bands

Convection in Jupiter’s deep atmosphere brings materials of different composition and temperature to the surface. Variations in cloud thickness, composition, and altitude cause the light‑scattering differences that create distinct colored bands.

Io’s Volcanic Activity

Io is the most volcanic body due to intense tidal heating from gravitational interaction with Jupiter and other Galilean moons. Flexing of its interior generates enough heat to drive continuous volcanic eruptions.

Outer Moons with Liquid Water

Europa and Enceladus are believed to host subsurface oceans beneath icy crusts, potentially providing habitats for life. Both moons exhibit geysers or surface features consistent with liquid water reservoirs.

Saturn’s Rings Composition and Size

Saturn’s rings consist of countless icy particles ranging from micrometers to meters across, primarily composed of water ice with traces of rock and dust. Their total mass is about one‑tenth that of Saturn’s moon Mimas.

Unique Feature of Titan

Titan is the only moon with a dense nitrogen‑rich atmosphere and stable liquid bodies—lakes and seas of methane and ethane—on its surface. This active hydrocarbon cycle parallels Earth’s hydrologic cycle.

Unusual Triton

Triton orbits Neptune in a retrograde direction, suggesting it is a captured Kuiper Belt object. Its surface features include nitrogen geysers and a young, geologically active crust.

Electromagnetic Spectrum Commonality and Differences

All these forms of light are electromagnetic waves traveling at the speed of light in vacuum. They differ in wavelength and frequency, with gamma rays having the shortest wavelengths and highest energies, and radio waves the longest wavelengths and lowest energies.

Hot Blackbody Spectrum

A hot blackbody emits a continuous thermal spectrum whose peak wavelength shifts inversely with temperature, following Wien’s law. The curve’s shape is smooth with intensity falling off at both longer and shorter wavelengths.

Information from Continuous Spectrum

A continuous spectrum reveals an object’s temperature by the peak wavelength and overall shape. It also provides the total energy output across wavelengths, indicating luminosity.

Spectroscope with Cool Hydrogen Cloud

The spectrum displays an absorption line spectrum: a continuous background with dark hydrogen absorption lines superimposed. These lines correspond to specific electronic transitions in hydrogen.

Ionized Gas Emission Spectrum

An emission spectrum shows bright spectral lines at wavelengths where ionized gas emits photons. The pattern reveals the elements present and gas conditions like temperature and density.

Nuclear Fusion Process

Fusion in stars starts with hydrogen nuclei combining at temperatures above 10 million kelvins. Protons fuse through the proton–proton chain or CNO cycle to form helium, releasing energy and neutrinos.

Sunspots and Prominences Link

Both sunspots and prominences are manifestations of the Sun’s magnetic field. Sunspots are cooler, darker regions where magnetic fields emerge, and prominences are plasma loops supported by these fields.

Sunspot Cycle Variation

Sunspot numbers follow an approximately 11‑year cycle, rising from a minimum to maximum before declining again. This solar activity cycle affects space weather and Earth’s upper atmosphere.

Solar Wind Definition

The solar wind is a continuous flow of charged particles—mainly electrons and protons—streaming outward from the Sun’s corona. It shapes planetary magnetospheres and drives space weather phenomena.

Layers of the Sun’s Atmosphere

The three layers are the photosphere (visible surface), chromosphere (thin intermediate layer), and corona (extensive, hot outer atmosphere). Each layer has distinct temperatures and densities.

Parallax Determination

Stellar parallax is measured by observing a star’s apparent shift against background stars from opposite points in Earth’s orbit. The angle of this shift, divided by two, gives the parallax angle used to calculate distance via the inverse relation.

Upper-Right HR Diagram Star Properties

Stars in the upper-right are cool and luminous, indicating they are large, evolved red giants or supergiants. Their low surface temperatures produce red colors, while their size accounts for high luminosity.

Sun’s Size in Stellar Context

The Sun is considered an average-sized main sequence star (G‑type). Many stars are smaller (M dwarfs), but it is not large enough to be a subgiant or giant.

Mass of Common Stars

Most stars are red dwarfs with masses between 0.1 and 0.5 solar masses. Their low mass yields low luminosity and long lifetimes.

Emission Nebula Formation

An emission nebula forms when ultraviolet radiation from hot young stars ionizes surrounding gas. Recombination of electrons with ions produces characteristic emission lines.

New Star Birth Indicators

Telescope images of star-forming regions show protostellar jets and bipolar outflows carving cavities in molecular clouds, along with dense dust cocoons. These features signal active accretion onto young stellar objects.

Importance of O Stars

O‑type stars produce intense ultraviolet radiation that ionizes nearby gas, triggering and illuminating emission nebulae. Their strong stellar winds compress surrounding clouds, potentially inducing further star formation.

Locations of Emission Nebulae

Emission nebulae form in regions of active star formation within molecular clouds, often in spiral arms of galaxies. They cluster around hot, massive stars whose radiation energizes the gas.

Trigger for Red Giant Evolution

A main sequence star evolves into a red giant when core hydrogen is exhausted and fusion moves to a shell around the helium core. The core contracts and heats the envelope, causing it to expand and cool.

Stellar Death and Earth’s Life

The death of stars disperses heavy elements synthesized by fusion into the interstellar medium. These elements, including carbon and oxygen, are essential building blocks for planets and life.

Iron’s Role in High-Mass Stars

Iron is the end point of exothermic fusion; once a star’s core accumulates iron, fusion no longer releases energy. Core collapse follows, triggering a supernova that disperses elements.

Definition of White Dwarf

A white dwarf is the dense, degenerate remnant of a low‑ to intermediate‑mass star after it sheds its outer layers. It is supported by electron degeneracy pressure and gradually cools over time.

Planetary Nebula Formation

A planetary nebula forms when an aging star expels its outer envelope as fusion ceases. Ultraviolet radiation from the hot central core ionizes the ejected gas, causing it to glow.

Cause of Type I Supernova

A Type I supernova occurs when a white dwarf in a binary accretes enough mass from its companion to exceed the Chandrasekhar limit, igniting runaway carbon fusion. This explosion completely disrupts the white dwarf.

Neutron Star Properties

Neutron stars are extremely dense objects with masses around 1.4–2 solar masses packed into a ~20 km radius. They have strong magnetic fields and rapid rotation rates.

Pulsar Explanation

A pulsar is a rotating neutron star emitting beams of radiation from its magnetic poles. Observed as periodic pulses when the beam sweeps across Earth, they serve as highly precise cosmic clocks.

X-ray Burst Mechanism

X‑ray bursts occur on neutron stars in binaries when accreted material from a companion accumulates and ignites thermonuclear runaway on the surface. The sudden fusion releases intense X‑rays.

Gamma Ray Burst Locations

Gamma ray bursts are observed at cosmological distances, originating from random directions across the sky. Their isotropic distribution implies they occur in distant galaxies throughout the universe.

Gamma Ray Burst Model

One model for long gamma ray bursts posits the collapse of a massive star's core into a black hole, launching relativistic jets that produce gamma rays as they interact with surrounding material.

Black Hole Binary Conditions

To identify a black hole binary, astronomers look for rapid orbital motion of a visible companion without detectable light from the unseen object and high X‑ray emissions from accretion. These conditions indicate a compact, massive companion.

Halo vs. Disk Differences

The galactic halo is a spherical region containing old stars and globular clusters with random orbits, while the disk is a flattened plane with younger stars, gas, and spiral structure moving in orderly orbits. The halo lacks significant star formation compared to the active disk.

Dark Matter Evidence

Galaxy rotation curves remain flat at large radii instead of declining, implying unseen mass in the halo. Gravitational lensing of background objects also reveals more mass than visible matter provides.

Supermassive Black Hole Indicators

Observations of stars orbiting rapidly around Sagittarius A* suggest a central mass of ~4 million solar masses in a very small volume. Bright X‑ray and radio flares from the galactic center further support an accreting black hole.

Definition of Globular Cluster

A globular cluster is a dense, spherical collection of up to millions of old stars bound by gravity, orbiting in a galaxy’s halo. These clusters are among the oldest structures in galaxies.

Cepheid Distance Measurement

By measuring a Cepheid variable’s pulsation period, astronomers use the period–luminosity relation to determine its absolute brightness. Comparing that to its observed brightness yields the distance.

Properties of the Galactic Disk

The disk contains significant amounts of gas and dust fueling star formation, hosts spiral arms with young, massive stars, and has stars orbiting in a relatively thin, flat plane. Its metallicity is higher than the halo’s, reflecting ongoing chemical enrichment.

Hubble’s Galaxy Types

Three of Hubble’s morphological types are spiral galaxies, elliptical galaxies, and barred spiral galaxies. (The fourth is irregular galaxies.)

Spiral vs. Elliptical Differences

Spiral galaxies have well‑defined arms, ongoing star formation, and abundant gas and dust, whereas ellipticals are smoother, ellipsoidal, and contain older stars with little interstellar matter. Ellipticals lack significant rotation compared to the disk‑dominated rotation of spirals.

Active Galaxy Common Traits

Active galaxies exhibit extremely luminous cores powered by accretion onto supermassive black holes and often show strong emission lines from high‑energy regions. They also emit across the electromagnetic spectrum, including radio and X‑rays.

Hubble’s Law

Hubble’s Law states that a galaxy’s recessional velocity is proportional to its distance from us, implying the universe is expanding. The relation is given by v = H₀ × d, where H₀ is the Hubble constant.