Q 01/05

Which planet is the hottest in the Solar System, even though another planet sits closer to the Sun?

A) Venus

B) Mars

C) Jupiter

D) Saturn

Answer · why

A) Venus

Venus. Its thick atmosphere traps the Sun's heat like a blanket in a runaway greenhouse effect, so the surface is hot enough to melt lead.

Q 02/05

Which is the smallest planet in the Solar System?

A) Mars

B) Mercury

C) Neptune

D) Uranus

Answer · why

B) Mercury

Mercury. It is so small that two moons, Jupiter's Ganymede and Saturn's Titan, are actually bigger than it is.

Q 03/05

In 2006, Pluto was officially reclassified as what kind of object?

A) A giant comet

B) A moon of Neptune

C) A dwarf planet

D) A rogue asteroid

Answer · why

C) A dwarf planet

A dwarf planet. Astronomers ruled in 2006 that a full planet must clear other objects from its orbit, and Pluto shares its path with many icy bodies i...

Q 04/05

A light-year is a unit used to measure what?

A) Time

B) Brightness

C) Speed

D) Distance

Answer · why

D) Distance

Distance. A light-year is how far light travels in one year, about six trillion miles, so the light you see from a star 100 light-years away set off a...

Q 05/05

Which scientist used his own telescope to spot the four largest moons of Jupiter?

A) Isaac Newton

B) Albert Einstein

C) Galileo Galilei

D) Nicolaus Copernicus

Answer · why

C) Galileo Galilei

Galileo Galilei. Seeing moons circle Jupiter in 1610 was strong evidence that not everything revolves around Earth, a serious blow to the old Earth-ce...