Science GK becomes easier when a fact is tied to a model. The Sun is a star, planets orbit it, and light takes time to travel. These questions use approximate quantities where the source does, rather than treating a rounded classroom number as an exact constant. Reviewed against NASA resources on 2 October 2026.

Is the Sun a star or a planet?

Answer: the Sun is a star. NASA describes the solar system as our star, the Sun, together with objects that orbit it. Planets do not produce sunlight in the way a star does. This distinction helps with questions about the solar system's structure: the Sun is the central star, and the planets are among the objects bound to it.

How many planets are in the solar system?

Answer: eight recognized planets. From the Sun outward: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Learn the order in groups: the four inner terrestrial planets, then the four outer giants. This classification explains more than a mnemonic alone. NASA's solar-system reference describes the terrestrial group.

Which planets are terrestrial?

Answer: Mercury, Venus, Earth and Mars. “Terrestrial” refers to the rocky inner planets. Jupiter is not in this group merely because it has a solid core hypothesis or moons; the usual classification is about the planet as a whole. When a multiple-choice question mixes planet and moon names, first identify which objects are planets.

How long does sunlight take to reach Earth?

Answer: about 8.3 minutes at the average Earth–Sun distance. NASA gives about 149.6 million kilometers, or one astronomical unit, with a corresponding light-time of 8.3 minutes. The distance varies during Earth's orbit, so “about eight minutes” is a sensible short GK answer. A light-minute is a distance measure, not the duration of a day.

Is a light-year a measure of time?

Answer: no, it is a distance. A light-year is the distance light travels in one year. The word “year” names the travel interval used to define the distance. NASA's light-year explanation gives this distinction and a scale comparison.

How far away is the Moon on average?

Answer: roughly 384,400 kilometers from Earth on average. The distance changes over the Moon's orbit. NASA uses the average in its solar-system reference. If a question asks for an exact instantaneous distance, it needs a date and position; the rounded average is the appropriate general-knowledge answer.

Test understanding, not just recall

Explain why sunlight seen now left the Sun minutes ago, group the eight planets by inner and outer categories, and distinguish light travel time from a light-year distance. Then check one uncertain fact against NASA before sharing it. Visit the GK questions hub for the other subjects.

Primary sources: NASA solar-system basics; NASA planet reference; NASA light-year explanation.