Midterm 3 Astronomy

What is a telescope?

A device that gathers and focuses electromagnetic radiation from distant objects.

What are the three main functions of telescopes?

Collect more light, reveal finer detail (resolution), and magnify.

What is aperture?

The diameter of a telescope's primary light-gathering lens or mirror.

What does a larger telescope aperture improve?

Light-gathering power and angular resolution.

How does light-collecting area scale with aperture diameter?

With diameter squared: area ∝ diameter².

How much more light does a 3-m telescope gather than a 1-m telescope?

9 times as much (3² / 1² = 9).

Does a larger objective lens primarily make images bigger or brighter?

Brighter, not necessarily bigger.

How do reflecting telescopes focus light?

With mirrors; most modern research telescopes are reflecting.

How do refracting telescopes focus light?

With transparent lenses.

During refraction, what remains unchanged?

Frequency stays constant; wavelength changes with wave speed.

If light slows in a new medium, what happens to its wavelength?

It decreases while frequency stays constant.

Why are observatories often built on mountains or in deserts?

Clear skies, remote darkness, and often less atmospheric interference.

What causes stars to twinkle?

Atmospheric turbulence bends incoming light unpredictably.

What three obstacles does Earth's atmosphere create for astronomy?

Light pollution, atmospheric turbulence, and absorption.

Which wavelengths readily reach Earth's surface in these lectures?

Visible light and radio waves; a little ultraviolet also gets through.

Why must gamma-ray and X-ray telescopes observe from space?

Earth's atmosphere absorbs gamma rays and X-rays.

Why are space telescopes useful—not because they are closer to stars?

They avoid atmospheric absorption and distortion, and most light pollution.

What is adaptive optics?

Fast adjustments to telescope mirrors/images that compensate for atmospheric turbulence.

Why are radio telescopes often very large?

Radio waves have long wavelengths; large dishes improve collecting power and resolution.

Which location is better for an infrared supernova telescope: ground or orbit?

Orbit, because the atmosphere absorbs much infrared light.

What objects belong to our solar system?

The Sun and orbiting planets, asteroids, Kuiper Belt objects, and comets.

Where are most asteroids found?

In the region between Mars and Jupiter.

Where do many short-period comets come from?

The Kuiper Belt.

Where do long-period comets originate?

The Oort cloud.

Name the four terrestrial planets.

Mercury, Venus, Earth, and Mars.

How do terrestrial planets compare with Jovian planets?

Terrestrial: small, dense, rocky, inner; Jovian: large, low-density, gas/ice-rich, outer.

What is a nebula?

A cloud of gas and dust in which a star can form.

What causes a nebula to collapse?

Mutual gravitational attraction among its particles.

What happens to temperature as a forming nebula contracts?

It heats up; the inner disk is hotter than the outer disk.

Why does a collapsing nebula rotate faster?

Conservation of angular momentum.

What is a protoplanetary disk?

Flattened leftover material orbiting a young star, from which planets form.

Why do the planets tend to orbit in an orderly disk?

The rotating solar nebula flattened as it contracted and collided.

What is the frost line?

The dividing distance beyond which hydrogen compounds could condense as ice.

What could condense in the hot inner solar system?

Mostly solid rocks and metals, not abundant hydrogen-compound ices.

Why did small rocky planets form near the Sun?

Only relatively scarce rocks and metals could solidify there.

Why did larger planets form farther from the Sun?

Abundant ices could solidify with rocks and metals, making larger cores.

Why could outer planets capture huge H/He atmospheres?

Their massive cores exerted stronger gravity on gas.

What is a planetesimal?

A small solid body built from particles that can accrete into a planet.

Which planet type matches high density, small diameter, and rock?

Terrestrial.

Which planet type matches low density, large diameter, and gas?

Jovian.

Why does Venus retain so much COI compared with Earth?

Venus lacks Earth's oceans and plate-tectonic carbon storage; heavy COI is not easily stripped.

What are the main parts of an atom?

Protons and neutrons in the nucleus, with electrons outside it.

What does an element's atomic number tell you?

Its number of protons.

What does HIO indicate?

Two hydrogen atoms and one oxygen atom per molecule.

Name three hydrogen compounds important for giant-planet ices.

Water (HIO), methane (CHI), and ammonia (NHI).

What four processes shape planetary surfaces?

Impact cratering, erosion, volcanism, and tectonics.

What is an impact crater?

A bowl-shaped mark caused by an asteroid or comet striking a surface.

What does a heavily cratered surface usually indicate?

An old surface with little erosion, volcanism, or tectonic resurfacing.

What processes can erase older impact craters?

Erosion, volcanic resurfacing, and tectonics.

Which lunar surface is generally younger: maria or highlands?

The dark maria.

What is erosion?

Wearing down or building up terrain by moving water, ice, wind, or other fluids.

What conditions favor erosion by wind?

A substantial atmosphere and faster planetary rotation.

Two equally atmospheric planets rotate in 120 vs 240 hours. More wind erosion?

The 120-hour planet, because it rotates faster.

Why does Venus have relatively little wind erosion in these lectures?

Its rotation is extremely slow, despite a dense atmosphere.

What is volcanism?

Molten rock erupting from a planet's interior onto its surface.

What is tectonics?

Breaking and moving the rigid outer layer as interior material moves.

What is the lithosphere?

The rigid outer rocky shell; on Earth, crust plus uppermost mantle.

How does lithosphere thickness affect geology?

Thicker lithosphere resists fracturing and lava penetration.

What happens to the lithosphere as a planet cools?

It thickens; volcanism and tectonic activity generally diminish.

Why does a larger rocky planet generally stay active longer?

Its interior cools more slowly.

Earth vs Moon: which cools more slowly and has a thinner lithosphere?

Earth cools more slowly; the Moon has the thicker relative lithosphere.

How would doubling Mars's size affect its geology, per the lecture model?

More volcanism and tectonics; fewer preserved craters.

What surface traits are typical of a larger terrestrial planet?

More ongoing resurfacing and a younger-looking surface.

What formed the lunar maria?

Ancient impacts fractured the crust; lava flooded the basins and cooled.

What are the lunar highlands?

Light-colored, raised, older terrain formed from buoyant silicate materials.

What distinguishes a complex impact crater?

A central peak; simple craters lack one.

What are the major features of an impact crater?

Floor, walls, rim, ejecta, rays, and sometimes a central peak.

What is crater ejecta?

Rock and debris thrown outward by an impact.

What are crater rays?

Bright streaks of ejecta radiating from the crater.

What makes an impact crater larger?

A larger and/or faster incoming object.

How does a low impact angle change crater shape?

It can produce a more elliptical crater and asymmetric ejecta.

What currently reshapes the Moon most, in the lectures?

Impact cratering.

How long is Mercury's orbital period?

About 88 Earth days.

How long is Mercury's rotation period?

About 58 Earth days.

What is Mercury's spin-orbit relationship?

Three rotations for every two orbits.

Why does Mercury experience extreme temperatures?

It has almost no atmosphere to redistribute or retain heat.

What is Mercury's major internal component?

A large iron-nickel core; about 60% of its mass is metal.

What is the Caloris Basin?

Mercury's largest impact basin; evidence of ancient impact and lava flooding.

What caused Mercury's huge scarps or cliffs?

Its cooling interior contracted and the crust fractured.

What do Mercury and the Moon have in common?

Old, heavily cratered surfaces and almost no atmosphere.

What is differentiation in planet formation?

Dense materials sink toward the center; less-dense materials rise.

List Earth's interior by decreasing density.

Core, mantle, crust.

How long does Venus take to rotate once?

About 243 Earth days.

Why is Venus's surface younger-looking than Mercury's?

Volcanic resurfacing erased many old craters.

What surface ages are listed for Venus?

Approximately 300-600 million years.

How do most Venusian volcanoes form, per these slides?

Through hot spots, rather than Earth-style plate boundaries.

Why does Venus lack Earth-like plate tectonics, according to the lectures?

Strong lithosphere, high temperatures, and lack of water.

What are coronae on Venus?

Crown-shaped concentric cracks linked to rising and sinking lava.

What are lava domes on Venus?

Broad pancake-shaped lava features with wrinkled or cracked surfaces.

What is Venus's surface pressure compared with Earth's?

Roughly 88 times Earth's surface pressure.

What is Venus's approximate surface temperature in the slides?

About 750 K, hot enough to melt lead.

How long does Mars take to orbit the Sun?

About 687 Earth days.

How long is a Martian day?

About 1.026 Earth days.

What is the Tharsis Bulge?

A high volcanic region shaped by upwelling magma.

What is Valles Marineris?

A huge Martian canyon system; its exact origin is uncertain in the slides.

What is Olympus Mons?

The largest known volcano in the solar system, on Mars.

Why could Olympus Mons grow so large?

Mars's relatively low surface gravity.

What do the slides say about dust storms on Mars?

Fast winds in a thin atmosphere can raise huge dust storms.

What gas dominates Mars's atmosphere today?

Carbon dioxide, about 95.3% in the lecture table.

What is a primary planetary atmosphere?

An early atmosphere captured from gases surrounding the young Sun.