AST101: Solar System, Universe, and Celestial Mechanics

What is the composition of the Solar System?

The Solar System includes the Sun, eight planets, their moons, dwarf planets, asteroids, and comets.

What is the radius of the Sun compared to Earth's radius?

The Sun's radius is approximately 696,000 km, about 109 times Earth's radius.

What is the distance of Earth from the Sun in astronomical units (AU)?

Earth is 1 AU from the Sun, which is 150 million km.

What are the characteristics of terrestrial planets?

Terrestrial planets (Mercury, Venus, Earth, Mars) are small, dense, rocky, and have few moons.

What distinguishes Jovian planets from terrestrial planets?

Jovian planets (Jupiter, Saturn, Uranus, Neptune) are large, gaseous, have many moons, and often have rings.

What is the nearest star to Earth beyond the Sun?

The nearest star is Proxima Centauri, located 4.24 light-years away.

How does light travel in space, and what is a light-year?

Light travels at 300,000 km/s, and a light-year is the distance light travels in one year.

What does looking into space imply about time?

Looking into space means looking back in time; light from distant objects takes time to reach us.

What is the significance of the Big Bang in the universe's history?

The universe began with the Big Bang approximately 13.7 billion years ago, leading to the formation of galaxies, stars, and planets.

What is the role of gravity and dark matter in galaxy formation?

Gravity and dark matter shape the cosmic web, forming filaments and voids in the universe.

What are the features of planetary orbits in the Solar System?

Planetary orbits are nearly coplanar, elliptical, and counterclockwise when viewed from above the North Pole.

What are the characteristics of Venus?

Venus has a thick CO₂ atmosphere, uniform surface temperature of ~460 °C, and is volcanically active.

How does Earth's axial tilt affect seasons?

Earth's axial tilt of 23.5° causes seasonal changes by altering the Sun's path and angle.

What is the Moon's orbital period around Earth?

The Moon orbits Earth every 27.3 days (sidereal period) and has a phase cycle of 29.5 days (synodic month).

What causes solar and lunar eclipses?

A solar eclipse occurs at New Moon when the Moon blocks the Sun; a lunar eclipse occurs at Full Moon when Earth's shadow falls on the Moon.

What did Copernicus propose about the structure of the Solar System?

Copernicus proposed the heliocentric model, placing the Sun at the center with planets orbiting around it.

What are Kepler's three laws of planetary motion?

1. Orbits are elliptical with the Sun at one focus. 2. A line joining a planet and the Sun sweeps equal areas in equal times. 3. The square of the orbital period is proportional to the cube of the semi-major axis.

What are the main features of Jupiter?

Jupiter is the largest planet, mostly hydrogen and helium, has a metallic hydrogen interior, faint rings, and over 60 moons.

What is the significance of the Oort Cloud?

The Oort Cloud is a distant spherical shell of icy bodies, believed to be the source of long-period comets.

What is the difference between the Kuiper Belt and the Oort Cloud?

The Kuiper Belt contains icy objects and is the source of short-period comets, while the Oort Cloud is a distant shell of icy bodies for long-period comets.

What happens to comets as they approach the Sun?

Comets develop tails due to the sublimation of ices when they are near the Sun.

What are the characteristics of Earth's Moon?

Earth's Moon is large relative to the planet and has a cratered surface.

What is the temperature range on Mercury?

Mercury's temperature ranges from −170 °C to +425 °C and it lacks a significant atmosphere.

What is unique about Uranus's rotation?

Uranus is tilted at 98°, producing extreme seasonal variations.

What is the Great Dark Spot on Neptune?

The Great Dark Spot is a storm system on Neptune, similar to Jupiter's Great Red Spot.

What did Galileo observe with his telescope that challenged the perfection of the heavens?

He observed the Moon's craters and mountains, Jupiter's four large moons, Venus' phases, and sunspots.

What is the significance of Galileo's observations?

They provided strong evidence for the heliocentric model of the solar system.

What are Newton's three laws of motion?

1. An object remains at rest or in uniform motion unless acted upon by a force. 2. F = ma (force causes acceleration proportional to mass). 3. For every action, there is an equal and opposite reaction.

What is the formula for momentum and how is it conserved?

Momentum is given by p = mv and is conserved in closed systems.

What does the universal law of gravitation state?

The force between two masses is F = G m₁ m₂ / r², where it is attractive and acts at a distance.

How does distance affect gravitational force according to Newton's law?

Doubling the distance reduces the gravitational force by a factor of four.

What is escape velocity?

The speed required to leave a planet's gravitational influence without further propulsion, dependent on the planet's mass and distance from its center.

What causes tides on Earth?

Tides result from the differential gravitational pull of the Moon and the Sun on Earth.

What are spring tides and when do they occur?

Spring tides are the largest tides that occur when the Sun and Moon are aligned (during new and full moons).

What is the structure of the Sun?

The Sun has a core (where fusion occurs), a radiative zone, a convective zone, and outer layers including the photosphere, chromosphere, and corona.

What is the process of energy generation in the Sun?

Energy is generated through nuclear fusion of hydrogen into helium via the proton-proton chain.

What is hydrostatic equilibrium in the context of the Sun?

It is the balance between the inward gravitational force and the outward pressure from fusion energy.

What are sunspots?

Sunspots are cooler, magnetically active regions on the Sun's surface.

What is the effect of the Sun's temperature on its spectrum?

The Sun's temperature (~6000 K) corresponds to its peak spectrum in visible light.

What happens during a solar eclipse?

A solar eclipse occurs when the Moon crosses the ecliptic plane at New Moon, blocking the Sun.

What is the definition of a planet?

A planet must orbit the Sun, be spherical, and clear its orbit; dwarf planets fail the last criterion.

What is the ecliptic?

The ecliptic is the path of the Sun on the celestial sphere, which is the projection of Earth's orbital plane.

What is the significance of Kepler's second law?

It states that planets move at variable speeds, faster near the Sun and slower farther away, covering equal areas in equal times.

What is the role of the Moon in Earth's tides?

The Moon's gravitational pull creates tidal bulges on Earth, resulting in two high tides and two low tides per day.

What is the relationship between angular momentum and planetary motion?

Angular momentum is conserved, meaning a planet's speed increases as it gets closer to the Sun (perihelion).

What is the effect of tidal friction on Earth's rotation?

Tidal friction slows Earth's rotation, lengthening the day over geological time.

What is the greenhouse effect on Venus?

Venus is hotter than Mercury not because of proximity to the Sun, but due to its thick CO₂ atmosphere causing a runaway greenhouse effect.