Astronomy Exam revision 1/3

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What is an Astronomical Unit (AU)?

The average distance between the Earth and the Sun, used for measurements within solar systems. [1]

Define a Lightyear (ly).

The distance light travels in one year; it is used to measure vast distances between stars and galaxies. [1]

What is a Parsec (pc)?

A unit for very large distances corresponding to the distance at which the mean radius of Earth's orbit subtends an angle of 1/3600 of a degree. [2]

How does the Parallax Method measure distance?

It uses trigonometry to calculate distances to nearby stars by measuring their apparent shift in position relative to distant stars over six months. [3]

What is the Inverse Square Law for luminosity?

Luminosity decreases with the square of the distance; doubling the distance makes a star appear four times ($2^2$) dimmer. [4]

Why are Cephid Variables called "standard candles"?

Their frequency of oscillation in brightness provides an accurate measurement of absolute luminosity, which helps determine their distance. [5, 6]

What does the Redshift Method indicate?

It shows that light from distant galaxies stretches toward the red end of the spectrum as the universe expands; further objects appear more shifted. [7]

What are the three requirements to be a planet?

An object must 1) orbit a star, 2) have enough mass for a nearly round shape, and 3) have cleared its orbital neighborhood of other objects. [8]

Difference between a Solar Day and a Sidereal Day?

A solar day is the average time from sunrise to sunrise (24 hours), while a sidereal day is the time for one actual rotation relative to stars (23h 56m). [9]

Define Periapsis and Apoapsis.

Periapsis is the point in an orbit closest to the central body, while Apoapsis is the point farthest away. [10, 11]

What is Obliquity (Axial Tilt)?

The angle between a planet's orbital plane and its equator; it determines seasonal patterns and the distribution of solar radiation. [12, 13]

What is the function of a Magnetosphere?

It is a magnetic field region that acts as a shield, deflecting charged particles from solar winds to protect a planet's atmosphere and surface. [14]

What two factors determine surface gravity?

An object's mass (more mass = more gravity) and its radius (smaller radius for the same mass = higher surface gravity). [15]

Why is Pluto classified as a Dwarf Planet?

It meets the first two planetary criteria but has failed to clear its orbital neighborhood of other objects, such as those in the Kuiper Belt. [8, 16]

Why is Venus hotter than Mercury?

Venus has a thick atmosphere (96.5% CO2) that creates a runaway greenhouse effect, trapping heat and reaching temperatures of about 465°C. [17, 18]

Describe the atmosphere of Mars.

It is very thin (0.006 atm) and composed mostly of carbon dioxide (95%), resulting in wide temperature ranges and frequent dust storms. [19]

How do Auroras form?

Charged particles from solar winds interact with a planet's magnetic field and excite atmospheric gases, causing them to emit light near the poles. [20]

How is the Sun classified and composed?

It is primarily composed of hydrogen and helium and is classified as a G-type main-sequence star (G dwarf). [21]

What process powers the Sun’s energy?

Nuclear fusion, which occurs in the Sun's core when hydrogen atoms fuse into helium. [22]

List the layers of the Sun from core to exterior.

The Core, Radiative Zone, Convective Zone, Photosphere, Chromosphere, and Corona. [21, 23]

What is the Life Cycle of the Sun?

It began as a nebula, is currently a main-sequence star, will expand into a red giant, and finally become a white dwarf. [24]

What is the Giant-Impact Model for the Moon?

A Mars-sized protoplanet (Theia) collided with early Earth, and the resulting debris collapsed under gravity to form the Moon. [25, 26]

Define Tidal Locking in the Earth-Moon system.

The Moon's rotational speed matches its orbital speed, meaning the same "near side" always faces Earth. [27, 28]

Contrast Moon Maria and Highlands.

Maria are dark, smooth frozen lava plains (basalt); Highlands are lighter, rugged areas dominated by mountains and impact craters. [29, 30]

How does the Moon influence Earth's core?

Tidal effects deform Earth's mantle, creating friction that produces heat to help keep the core active and molten. [31, 32]