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Astronomy Unit 1
NCC astronomy review question for unit 1 exam.
| Question | Answer |
|---|---|
| What is the celestial sphere? | An imaginary sphere surrounding Earth onto which celestial objects appear projected. |
| In what units do we measure objects on the celestial sphere? | Angular units such as degrees arcminutes and arcseconds. |
| Which are the fixed points on the celestial sphere? | The north celestial pole and south celestial pole are fixed points. |
| Which points on the celestial sphere depend on the observer? | The zenith nadir and horizon depend on the observer's location. |
| How do you determine your latitude on Earth? | Measure the altitude of the celestial pole above the horizon. Polaris altitude is approximately your latitude in the Northern Hemisphere. |
| How do you locate the celestial equator in the sky? | It is 90 degrees from the celestial poles and crosses the horizon due east and due west. |
| What is a smaller recognizable star pattern called? | An asterism such as the Big Dipper. |
| What is an AU? | An astronomical unit is the average Earth to Sun distance. About 149.6 million km. |
| What is a light year? | The distance light travels in one year. About 9.46 trillion km or 63241 AU. |
| How far away is the closest star beyond the Sun and what is its name? | Proxima Centauri is about 4.24 light years away. |
| Roughly how large is the Milky Way galaxy? | About 100000 light years across. |
| What is apparent brightness versus absolute brightness? | Apparent brightness is how bright an object looks from Earth. Absolute brightness describes its intrinsic brightness. |
| How does the astronomical magnitude scale work? | Lower or more negative magnitudes are brighter. A difference of 5 magnitudes equals a factor of 100 in brightness. |
| What do we call the plane in which the planets approximately orbit? | The ecliptic plane. |
| Which planet has the highest orbital inclination to the ecliptic? | Mercury at about 7 degrees. |
| What causes the seasons on Earth? | Earth's 23.5 degree axial tilt changes sunlight angle and day length as Earth orbits the Sun. |
| What is it called when Earth is closest to the Sun? | Perihelion. |
| What is it called when Earth is farthest from the Sun? | Aphelion. |
| What is it called when the Moon is closest to Earth? | Perigee. |
| What is it called when the Moon is farthest from Earth? | Apogee. |
| In what direction do the planets orbit the Sun? | Counterclockwise when viewed from above the Sun's north pole. This is prograde motion. |
| What is the difference between a sidereal and synodic period? | Sidereal is one orbit relative to the stars. Synodic is the time to repeat the same configuration relative to Earth and the Sun. |
| What is the Saros Cycle? | An eclipse repetition cycle of about 18 years 11 days and 8 hours. |
| What is precession? | The slow wobble of Earth's rotation axis. One cycle takes about 26000 years. |
| The tilt of Earth's rotation axis relative to its orbital plane. It is about 23.4 degrees and slowly changes. | |
| What is eccentricity? | A measure of how noncircular an orbit is. Zero is a circle and larger values are more elongated. |
| What makes the zodiac constellations significant? | They lie along the ecliptic which is the apparent path of the Sun Moon and planets across the sky. |
| What is elongation? | The angular separation between two objects in the sky measured in degrees. |
| What are the main Moon phases and their configurations? | New Moon is 0 degrees. First quarter is 90 degrees east. Full Moon is 180 degrees. Third quarter is 90 degrees west. |
| What phase must the Moon be in for a lunar eclipse to occur? | Full Moon. |
| What phase must the Moon be in for a solar eclipse to occur? | New Moon. |
| How often do solar and lunar eclipses occur? | Worldwide there are usually 2 to 5 solar eclipses and 2 to 5 lunar eclipses each calendar year. |
| What determines whether a lunar eclipse is partial or total? | It depends on how much of the Moon enters Earth's umbra. Part of the Moon means partial and the whole Moon means total. |
| Who were among the first people to make major systematic astronomical discoveries? | The Babylonians kept detailed observations and developed methods for predicting celestial events. |
| How did Aristotle differentiate Earth from the heavens? | Earth was considered changeable and imperfect while the heavens were considered perfect and unchanging. |
| What was Aristotle's fundamental argument for a geocentric universe? | No stellar parallax was visible and his physics placed heavy matter at the center of the universe. |
| How did ancient astronomers account for retrograde motion? | They used epicycles. Planets moved on small circles whose centers moved along larger circles called deferents. |
| Who developed the famous geocentric model using epicycles? | Claudius Ptolemy refined and popularized the epicycle based geocentric model. |
| What theory did Copernicus propose? | The heliocentric model in which Earth and the other planets orbit the Sun. |
| Was Copernicus's model completely correct? | No. The Sun centered arrangement was basically correct but he incorrectly used perfect circular orbits. |
| Who collected the data Kepler later used to develop his laws? | Tycho Brahe. |
| What did Kepler fix about Copernicus's model? | He replaced circular planetary orbits with ellipses and showed that planets change speed along their orbits. |
| What are Kepler's three laws of planetary motion? | First planets orbit in ellipses. Second equal areas are swept in equal times. Third period squared is proportional to semimajor axis cubed. |
| How did Galileo contribute to astronomy? | He used telescopic observations and experiments to provide strong evidence against the traditional geocentric model. |
| What were Galileo's key astronomical discoveries? | He observed Jupiter's moons Venus's phases sunspots and mountains and craters on the Moon. |
| How did Galileo's discoveries change astronomy? | They showed that not everything orbits Earth and that heavenly bodies are not perfect and unchanging. |
| What were Isaac Newton's major discoveries relevant to astronomy? | Newton developed the three laws of motion and the law of universal gravitation. |
| What is the difference between speed velocity and acceleration? | Speed is how fast something moves. Velocity is speed with direction. Acceleration is the rate at which velocity changes. |
| What are the components of angular momentum? | Angular momentum depends on mass velocity and distance from the rotation axis. For circular motion L equals mvr. |
| What are Newton's three basic laws of motion? | First inertia. Second force equals mass times acceleration. Third every action has an equal and opposite reaction. |
| What is the law of mutual gravitational attraction and how are mass and distance related? | Gravity increases with the product of the masses and decreases with the square of the distance. F equals G times m1 times m2 divided by r squared. |
Created by:
Sasha Petruccelli
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