Astronomy 3 — In-Depth Study Guide

A set of flashcards covering key concepts and terms from the Astronomy 3 lecture notes to prepare for exams.

What is astronomy?

The study of the universe and everything in it, including planets, stars, galaxies, space, time, and energy.

Why do astronomers study the universe?

To understand natural phenomena, learn the origins of celestial objects, study extreme objects, develop technology, and protect Earth.

What is a star?

A huge glowing ball of hydrogen gas that produces energy through nuclear fusion.

What is a planet?

An object that orbits a star, shines by reflected light, and can be rocky or gaseous.

What is a moon?

A natural satellite that orbits a planet.

What is an asteroid?

A small, rocky object orbiting a star.

What is a solar system?

A star and everything orbiting it, including planets, moons, and asteroids.

What is a nebula?

A huge cloud of gas and dust that is the birthplace of stars.

What is a black hole?

An extremely dense region of space from which nothing can escape, not even light.

What is a galaxy?

A massive system of stars held together by gravity.

What is the universe?

Everything that exists, encompassing all matter and energy.

What is an Astronomical Unit (AU)?

The distance from Earth to the Sun, approximately 1.49 × 10¹¹ meters.

What is a light-year?

The distance light travels in one year, approximately 10 trillion kilometers.

What causes day and night on Earth?

The rotation of the Earth, which spins once per day.

What is the speed of Earth's revolution around the Sun?

Approximately 67,000 miles per hour.

What are constellations?

Official sky regions with no physical meaning, consisting of stars that may appear close but are actually far apart.

What is the celestial sphere?

An imaginary sphere surrounding Earth used to map star positions.

What is the order of the Moon phases?

New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, Waning Crescent.

What is a lunar eclipse?

An eclipse that occurs when Earth blocks sunlight from reaching the Moon.

What is a solar eclipse?

An eclipse that occurs when the Moon blocks sunlight from reaching Earth.

What is the geocentric model?

An astronomical model with Earth at the center, supported by Plato and Aristotle.

What is the heliocentric model?

An astronomical model with the Sun at the center, proposed by Aristarchus and supported by Copernicus.

What is retrograde motion?

The apparent backward movement of a planet as observed from Earth.

What is parallax?

The apparent shift of a nearby star as Earth orbits the Sun.

Who were the key figures in the Copernican Revolution?

Copernicus, Tycho Brahe, Kepler, Galileo, and Newton.

What does it mean when the universe is expanding?

The farther away galaxies are, the faster they are moving.

How old is the universe?

about 14 billion years

What is the celestial equator?

An imaginary extension of the Earth’s equator onto the celestial sphere

What are the North & South celestial poles?

Points in the sky directly above Earth’s most top north and south points/poles.

What is the latitude?

Horizontal lines, going up and down measuring north and south

What is the longitude?

Vertical lines, going left and right measuring West and East

What is zenith?

the point directly above you

What is the horizon?

The line where the earth's surface and the sky appear to meet, marking the limit of your view; all points 90 degree from zenith

What is elevation?

The angle above the horizon?

What is meridian in the sky?

An imaginary line running from the North to South Pole, representing the highest point a celestial object reaches in the sky.

What is azimuth?

The angular measurement in the horizontal plane, typically defined as the angle from the north point in a clockwise direction.

What is declination?

The angular measurement in the vertical plane, representing the angle of a celestial object above or below the celestial equator.

what is right ascension?

The celestial equivalent of longitude, measured in hours, minutes, and seconds, indicating the position of a celestial object eastward along the celestial equator.

What is ecliptic?

The apparant path of the sun through the celestial sphere

What is the equinox?

Where the ecliptic (path of sun) intersects with the celestial equator during the spring and autumn, resulting in nearly equal day and night lengths.

What is solstice?

The points in the year where the ecliptic is farthest from the celestial equator, resulting in longest and shortest days of the year.

What is umbra?

The darkest part of a shadow during an eclipse, where the light source is completely blocked.

What is penumbra?

The lighter part of a shadow during an eclipse, where only a portion of the light source is blocked, resulting in a partial shadow.

What phase is the moon in during a solar eclipse?

the new moon phase

positions in solar eclipse?

The specific alignments of the Earth, Moon, and Sun, where the Moon is directly between the Earth and the Sun, blocking sunlight.

What phase is the moon in during a lunar eclipse?

the full moon phase

positions in a lunar eclipse?

The specific alignments of the Earth, Moon, and Sun, where the Earth is directly between the Moon and the Sun, casting a shadow on the Moon.

what is the formula for kepler’s third law of planetary motion?

p² = a³

What is Kepler’s First Law (Law of Orbit)?

Each planet's orbit about the Sun is an ellipse, not a perfect circle, with the Sun located at one of the two foci.

What is Kepler’s Second Law (Law of Areas)?

A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, meaning that a planet travels faster when it is closer to the Sun (perihelion) and slower when it is farther away (aphelion)

What is Kepler’s Third Law (Law of Periods)?

More distance planets orbit the Sun at slower average speeds: p² = a³

How did Copernicus, Tycho and Kepler challenge the Earth-centered idea?

Copernicus created a sun-centered (heliocentric) model;

Tycho provided the quantitative data needed to improve this model;

Kepler found a model that fit Tycho’s data