Astronomy (C894)

Correct Answer D. We sometimes see apparent retrograde motion of Mars, and that's because Mars sometimes reverses its orbital direction around the Sun due to its gravitational interactions with Earth.

Explanation

Apparent retrograde motion occurs when Earth, in its orbit, overtakes and passes another planet, such as Mars. This makes it appear as though Mars is moving backward across the sky, but in reality, Mars is not reversing its orbit. This optical illusion occurs due to the relative motion between Earth and Mars, not because of any gravitational interactions that reverse the planet's orbital direction.

Why other options are wrong

A. Tycho's observation of the first supernova is one of the evidences against the old belief that the sky is perfect, permanent, and never changes.

This statement is true. Tycho Brahe's observation of a supernova in 1572 (SN 1572) challenged the Aristotelian view that the heavens were immutable and unchanging, as it demonstrated that new stars could appear in the sky, contradicting the belief in a permanent and perfect celestial realm.

B. Galileo's observation of Jupiter's moons showed that not everything in the sky orbited the Earth.

This statement is true. Galileo's discovery of four moons orbiting Jupiter in 1610 demonstrated that not all celestial bodies orbited the Earth, supporting the heliocentric model of the solar system and challenging the geocentric model.

C. The reason Tycho did not detect stellar parallax is because stars are too far away for the parallax to be seen with naked eye observations.

This statement is true. Tycho Brahe could not detect stellar parallax because stars are so distant that the parallax shift is extremely small and beyond the resolving power of the naked eye. This was one of the key observations that led to later advancements in our understanding of the cosmos.

Correct Answer B. about 4 light-years.

Explanation

The nearest star to the Sun is Proxima Centauri, which is approximately 4.24 light-years away. Light from this star takes about 4.24 years to reach us, making it the closest known star to our solar system. This distance is much smaller compared to distances to stars in other parts of the galaxy, which can be thousands or even millions of light-years away.

Why other options are wrong

A. about 8 light-minutes.

This distance refers to how far light travels in 8 minutes, which is the distance from the Earth to the Sun, not to the nearest star. The distance to the nearest star is vastly greater than this, so this answer is incorrect.

C. about 100,000 light-years.

This is roughly the distance across our entire Milky Way galaxy, not the distance to the nearest star. The distance to the nearest star is much smaller, about 4 light-years.

D. about 14 billion light-years.

This distance refers to the estimated size of the observable Universe, not the distance to the nearest star. The Universe itself is much larger, but the closest star is far closer, around 4 light-years away.

Correct Answer A. astronomy

Explanation

Astronomy is the scientific study of celestial bodies such as stars, planets, comets, and galaxies, as well as the phenomena that originate outside Earth's atmosphere. It involves the observation and understanding of the universe beyond Earth.

Why other options are wrong

B. astrology

This is incorrect because astrology is a belief system that suggests that the positions and movements of celestial bodies influence human events. It is not a scientific discipline like astronomy.

C. earth sciences

This is incorrect because earth sciences involve the study of the Earth itself, including its structure, processes, and history. While astronomy may overlap in some areas (such as studying the Earth from space), earth sciences are distinct from astronomy.

D. physics

This is incorrect because physics is the study of the fundamental principles of matter and energy in the universe. While physics is essential to understanding the mechanics of astronomy, it is a broader field that includes many other areas, not just celestial phenomena.

Correct Answer B. Galaxies are moving apart from each other due to the expansion of the universe.

Explanation

The primary motion of galaxies in the Universe is that they are moving apart due to the expansion of the universe. This phenomenon was first observed by Edwin Hubble, who noted that distant galaxies appear to be moving away from us, with their speed increasing as their distance from us increases. This is consistent with the concept of the expanding universe, where space itself is stretching, causing galaxies to recede from each other over time.

Why other options are wrong

A. Galaxies are stationary and do not move relative to each other.

This is incorrect because galaxies are not stationary. Instead, they are in motion relative to each other, with the overall trend being the expansion of space itself, causing galaxies to move away from each other.

C. Galaxies are all moving towards each other at a constant speed.

This is incorrect because while some galaxies, such as those in the Local Group, are gravitationally bound and may move towards each other (like the Andromeda Galaxy approaching the Milky Way), the overall motion in the universe is that galaxies are moving away from each other due to the expansion of space.

D. Galaxies orbit around a central point in the universe.

This is incorrect because there is no central point in the universe. The universe is expanding uniformly, and galaxies are not orbiting a central point. The motion of galaxies is more accurately described by the expansion of space itself rather than orbital movement around a single center.

Correct Answer A. star

Explanation

A star is a massive ball of gas, primarily hydrogen and helium, that is held together by gravity. At the core of a star, nuclear fusion occurs, where hydrogen atoms fuse to form helium, releasing enormous amounts of energy in the process. This energy is what powers stars and provides their light and heat.

Why other options are wrong

B. fart

A fart is a release of gas from the digestive system and has nothing to do with the physical properties or processes of a star. This is not related to nuclear fusion or gravity.

C. element

An element is a basic chemical substance made up of atoms. While stars are made of elements (like hydrogen and helium), the term "element" does not describe a ball of gas undergoing nuclear fusion.

D. electron

An electron is a subatomic particle with a negative charge. It is part of an atom but does not represent a large ball of gas or a nuclear fusion process.

Correct Answer B. a half-circle extending from your horizon due north, through your zenith, to your horizon due south

Explanation

The meridian is an imaginary line that runs from due north to due south, passing directly through your zenith, the point directly overhead. It divides the sky into the eastern and western halves and is an important reference for celestial navigation and determining the position of celestial objects. This line helps in tracking the motion of celestial bodies as they move across the sky.

Why other options are wrong

A. a half-circle extending from your horizon due east, through your zenith, to your horizon due west

This option describes the local horizon, not the meridian. The meridian is oriented along the north-south direction, not east-west.

C. a half-circle extending from your horizon due east, through the north celestial pole, to your horizon due west

This description refers to the celestial equator's projection, not the meridian. The meridian does not involve the celestial pole, but rather the north-south direction through your zenith.

D. the point directly over your head

This is the definition of the zenith, not the meridian. The zenith is the point in the sky directly above you, but the meridian is the imaginary line that passes through the zenith, running north to south.

Correct Answer A. The set of constellations through which the ecliptic passes.

Explanation

The zodiac refers to a band of the sky that extends about 8° on either side of the ecliptic, which is the apparent path of the Sun across the sky. This band contains the constellations that the Sun, Moon, and planets appear to pass through during their motion along the ecliptic. These constellations are traditionally used in astrology and have been recognized since ancient times.

Why other options are wrong

B. The projection of the earth's equator on the celestial sphere.

This refers to the celestial equator, not the zodiac. The celestial equator is the projection of Earth's equator into space, dividing the sky into the northern and southern hemispheres, but it does not describe the path of the Sun or the zodiac.

C. The path of totality on the earth's surface during a solar eclipse.

This is the region on Earth where a solar eclipse is total, not related to the zodiac. The zodiac has no connection to the path of totality of solar eclipses, which occurs based on the relative positions of the Earth, Moon, and Sun.

D. The circle of 56 chalk-filled holes at Stonehenge.

This refers to the ancient monument Stonehenge, which is not related to the zodiac. Stonehenge is believed to have been used for astronomical observations, but it is not itself a definition of the zodiac.

E. The path that the earth's pole makes on the celestial sphere over 26,000 years.

This describes the precession of the Earth's axis, a phenomenon that causes the direction of Earth's axis to shift over time, but it is unrelated to the concept of the zodiac.

Correct Answer B. a star that always remains above your horizon and appears to rotate around the celestial pole

Explanation

A circumpolar star is a star that never sets below the horizon for an observer located at certain latitudes. These stars appear to move in circular paths around the celestial pole and remain visible at all times, rotating around the pole without dipping below the horizon. This behavior is most commonly observed at higher latitudes near the poles.

Why other options are wrong

A. a star that makes a daily circle around the celestial sphere

While this describes the motion of most stars, it does not specifically define a circumpolar star. All stars make a circle around the celestial sphere due to the Earth's rotation, but circumpolar stars are distinguished by always staying above the horizon.

C. a star that is visible from the Arctic or Antarctic circles

This option is misleading. While circumpolar stars are visible from the Arctic or Antarctic regions, the definition does not require the star to be visible only from these areas. Circumpolar stars are defined by their motion relative to the celestial pole, not by their visibility in specific geographical regions.

D. a star that is close to the north celestial pole

While many circumpolar stars are near the north celestial pole (in the Northern Hemisphere), the term "circumpolar" refers to the star's behavior (remaining above the horizon) rather than its proximity to the celestial pole.

E. a star that is close to the south celestial pole

This is incorrect because circumpolar stars can be found around both the north and south celestial poles, depending on the observer's location. The term is not limited to stars near the south celestial pole.

Correct Answer A. An object that revolves around another object in space

Explanation

A satellite is any object that orbits or revolves around a planet, moon, or other celestial body. The most common examples are moons that orbit planets. Satellites can be natural (like moons) or artificial (like communication satellites).

Why other options are wrong

B. Something that cools down the sun

This statement is incorrect because satellites do not have any effect on the Sun's temperature. The Sun's heat is primarily a result of nuclear fusion, not influenced by satellites.

C. A calculator

A calculator is a device for performing mathematical operations and has nothing to do with the definition of a satellite.

D. Another portal to the multiverse

A portal to the multiverse is a concept in science fiction, not related to the scientific definition of a satellite. Satellites are real, physical objects that orbit celestial bodies.