Free Astronomy and Space MCQs with Answers

91. A light year is a unit of ?

• A. Time
• B. Energy
• C. distance
• D. Mass

Explanation: A light-year measures distance, specifically the distance light travels in one year, about 9.46 trillion kilometres. Despite containing the word year, it is not a unit of time.

92. What is the main composition of the sun?

• A. Oxygen and Ammonia
• B. Hydrogen and Helium
• C. Hydrogen and Oxygen
• D. Methane and Hydrogen

Explanation: The Sun is composed mainly of hydrogen, which provides most of its mass, and helium, produced and already present through stellar processes. Oxygen, ammonia and methane are only trace or minor constituents.

93. Which of the followings planet can float on water?

• A. Saturn
• B. Mars
• C. Venus
• D. None

Explanation: Saturn has an average density lower than that of water, about 0.69 g/cm³, so it would float in a sufficiently large water body. The other listed planets are denser than water.

94. What is the distance of the star Proxima Centauri from the planet Earth ________?

• A. 4.2 light years
• B. 3.2 light years
• C. 2.4 light years
• D. 1.5 light years

Explanation: Proxima Centauri is the nearest known star to the Sun after the Sun itself, at about 4.24 light-years from Earth. Therefore, 4.2 light-years is the appropriate rounded value.

95. Which is the Coldest Planet ?

• A. Earth
• B. Venus
• C. Mercury
• D. Uranus

Explanation: Uranus has the lowest recorded atmospheric temperature among the planets, reaching about −224°C. Although Neptune is farther from the Sun, Uranus has colder measured upper-atmosphere temperatures.

96. The distance between Earth and Sun is greatest during ____________?

• A. Apehelion
• B. Astronomical
• C. Lopsided
• D. Astronomi

Explanation: Aphelion is the point in Earth’s elliptical orbit at which Earth is farthest from the Sun, occurring in early July. Perihelion is the opposite point, when Earth is nearest the Sun.

97. Nearest star to the sun is: ___________?

• A. Proxima Centauri
• B. Alpha Scorpius
• C. Beta Orionis
• D. Vegetal

Explanation: Proxima Centauri is the nearest known star to the Sun, at about 4.24 light-years away. Alpha Scorpii and Beta Orionis are much more distant stars.

98. A solar eclipse occurs when _________?

• A. Venus between Earth and sun
• B. Moon is between Earth and sun
• C. Sun is between Earth and moon
• D. Moon is between Earth and Neptune

Explanation: A solar eclipse occurs when the Moon passes between the Sun and Earth and casts its shadow on Earth. The alignment must occur near a new moon.

99. _______ is the average distance between the Earth and the sun ?

• A. Moon unit
• B. Light unit
• C. Astronomical unit
• D. Solar unit

Explanation: An astronomical unit, or AU, is the mean Earth-Sun distance, approximately 149.6 million kilometres. The other units listed are not standard astronomical distance units.

100. The correct age of solar system is approximately __________?

• A. 4.3 Billion years
• B. 4.4 Billion years
• C. 4.5 Billion years
• D. None of these

Explanation: The solar system formed about 4.6 billion years ago, commonly rounded to approximately 4.5 billion years in general science questions. Thus 4.5 billion years is the closest listed choice.