Test: Astronomy - 1 - ACT MCQ

The correct answer is (c) Copernicus. Nicolaus Copernicus, a Polish astronomer, proposed the heliocentric model of the solar system in the 16th century. He argued that the Earth and other planets revolve around the Sun, challenging the prevailing geocentric model where Earth was believed to be the center of the universe. Galileo Galilei provided observational evidence supporting Copernicus's heliocentric model through his telescopic observations in the 17th century, but Copernicus was the first to propose the idea.

The natural satellites Phobos and Deimos are both moons of the planet Mars. They were discovered in 1877 by American astronomer Asaph Hall. Phobos is the larger and closer of the two moons to Mars, while Deimos is smaller and orbits further away. These moons are thought to be captured asteroids due to their irregular shapes and low densities compared to the rocky bodies found in the asteroid belt. They are named after the sons of the Greek god Ares, who is equivalent to the Roman god Mars.

The device employed to measure the diameters of stars and our galaxy (Milky Way) is called an interferometer. So, the correct answer is (d) Interferometer. Interferometry is a technique that utilizes the interference of waves to make precise measurements of distances or sizes, particularly in astronomy. By combining the light from different telescopes or using multiple paths of light, interferometers can achieve very high resolution, allowing astronomers to measure the diameters of distant stars and galaxies.

The individual who first speculated that our universe is expanding is Edwin Hubble. So, the correct answer is (b) Edwin Hubble. Edwin Hubble, an American astronomer, made observations in the 1920s that showed galaxies were moving away from each other, implying that the universe is expanding. This discovery fundamentally changed our understanding of the cosmos and led to the development of the Big Bang theory, which proposes that the universe began from an extremely hot and dense state and has been expanding ever since.

The geocentric model of the solar system was proposed by (b) Ptolemy. Ptolemy was an ancient Greek astronomer who lived in the 2nd century AD. He developed a comprehensive cosmological model known as the Ptolemaic system, which placed the Earth at the center of the universe with all celestial bodies, including the Sun, Moon, planets, and stars, orbiting around it. This geocentric model was widely accepted for centuries until it was replaced by the heliocentric model proposed by Copernicus in the 16th century.

Halley's Comet completes one revolution around the Sun in approximately (d) 76 years. This periodic comet is visible from Earth roughly every 75–76 years. It was last seen in 1986 and is predicted to return in 2061. Named after the astronomer Edmond Halley, who calculated its orbit in 1705, Halley's Comet is one of the most well-known and studied comets in history.

The correct answer is (a) Copernicus. Nicolaus Copernicus, a Polish astronomer, proposed the heliocentric model of the solar system in the 16th century. He argued that the Sun, not the Earth, was the center of the solar system, and that the planets, including Earth, revolve around the Sun. This model replaced the geocentric model proposed by Ptolemy and became a foundational concept in modern astronomy.

The halo around the Sun is produced by the refraction of light through ice crystals in the atmosphere. Among the options provided, the correct one is:

(c) Ice crystals in Cirrus clouds

Cirrus clouds are thin, wispy clouds found at high altitudes, typically composed of ice crystals. These ice crystals can refract sunlight and create optical phenomena such as halos around the Sun.

The approximate mean velocity with which the Earth moves around the Sun in its orbit is about:

(b) 30 km/s

This velocity can vary slightly depending on the Earth's position in its elliptical orbit, but on average, it's around 30 kilometers per second.

One Astronomical Unit (AU) is a unit of measurement used in astronomy to represent the average distance between the Earth and the Sun. It's a convenient way to describe distances within our solar system.

So, the correct answer is indeed:

(a) Earth and the Sun

If the stars appear to rise perpendicular to the horizon, the observer is likely located at the North Pole. At this extreme northern latitude, the observer is positioned directly on the axis of Earth's rotation. Consequently, the stars would seem to rise and set nearly vertically as the Earth rotates, creating a unique celestial view. This phenomenon is due to the observer's proximity to the rotational axis, providing a perspective where the stars' motion aligns perpendicularly with the horizon.

Among the options provided, the planet that takes the maximum time for one revolution around the Sun is:

(b) Jupiter.

Jupiter has the longest orbital period of approximately 11.86 Earth years. This means it takes Jupiter about 11.86 Earth years to complete one full orbit around the Sun. This is longer than the orbital periods of Earth, Mars, and Venus. Therefore, Jupiter takes the maximum time for one revolution around the Sun among the listed options.

Assertion (A): To orbit around the Sun, the planet Mars takes lesser time than the time taken by the Earth.
Reason (R): The diameter of the planet Mars is less than that of the Earth.

While the assertion (A) is true, the reason (R) provided is not a correct explanation for why Mars takes less time to orbit the Sun. The orbital period of a planet primarily depends on its distance from the Sun, not its diameter. Therefore, assertion (A) is true, but reason (R) is not.

So, the correct answer is indeed:

(d) A is false but R is true.

To determine which planets lie between Mars and Uranus in order of their distances from the Sun, let's list the planets in their correct order:

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune

From this list, the planets that lie between Mars and Uranus are Jupiter and Saturn. Therefore, the correct answer is option (b) Jupiter and Saturn.

Asteroids are indeed small rocky planetoids, while comets are formed of frozen gases held together by rocky and metallic material.
Comets show a perceptible glowing tail due to the sublimation of volatile materials when they approach the Sun, while asteroids typically do not exhibit such tails.
Statement 2 is incorrect. Asteroids are found mostly between the orbits of Mars and Jupiter in a region called the asteroid belt, while comets are generally found further out in the solar system, though they can appear anywhere in the sky when they enter the inner solar system.

Ganymede, the largest moon in our solar system, orbits Jupiter. It is even larger than the planet Mercury. Ganymede is a fascinating world with its own magnetic field and a diverse surface featuring both heavily cratered regions and smooth plains. It is also thought to have a subsurface ocean beneath its icy crust, making it a target of interest for scientific exploration in the search for potential habitats for extraterrestrial life.

The planet(s) in our solar system with no moons are Mercury and Venus. Mercury, the closest planet to the Sun, lacks any natural satellites orbiting around it. Venus, often referred to as Earth's sister planet due to its similar size and composition, also does not have any moons. While both planets have been extensively studied, their lack of moons sets them apart from other planets in the solar system, contributing to their unique characteristics and features.

Venus, the second planet from the Sun, is often referred to as the "morning star" or "evening star" due to its brightness and visibility in the sky. Depending on its position relative to Earth, Venus can be seen either in the eastern sky before sunrise, where it is called the morning star, or in the western sky after sunset, where it is called the evening star. This dual appearance has fascinated skywatchers throughout history and has earned Venus its celestial nicknames.

Johannes Kepler proposed the Laws of Planetary Motion. In the early 17th century, based on meticulous observations by Tycho Brahe, Kepler formulated three fundamental laws describing the motion of planets around the Sun. Kepler's laws state that planets move in elliptical orbits with the Sun at one focus (First Law), the line joining a planet to the Sun sweeps out equal areas in equal times (Second Law), and the square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit (Third Law).

Proxima Centauri is the nearest star to the Sun. It is part of the Alpha Centauri star system, located about 4.24 light-years away from Earth in the constellation of Centaurus. Proxima Centauri is a red dwarf star, much smaller and cooler than the Sun, making it faint and challenging to observe with the naked eye. Despite its proximity, Proxima Centauri is still quite distant on astronomical scales, but it holds significance for astronomers studying exoplanets and potential habitability in its vicinity.