Space Quiz — 50 Questions That Will Not Go Out of Date

Which planet is the hottest at the surface?

Answer Venus, because its atmosphere traps the heat

Mercury is closer to the Sun, but it has almost no atmosphere, so its heat escapes at night. Venus is wrapped in thick carbon dioxide that holds the heat in, and its surface stays hot enough to melt lead — day and night, everywhere on the planet.

Where is the asteroid belt?

Answer Between Mars and Jupiter

The belt sounds crowded, but it is mostly empty. Spacecraft have flown through it without any special aiming, because the average gap between objects is measured in hundreds of thousands of kilometers.

What makes Mars look red?

Answer Iron-bearing dust that has rusted

The dust contains iron that has oxidized — the same chemistry as rust on a gate. Under that reddish layer the rock is closer to gray, which is why rover wheel tracks look darker than the ground around them.

Which of these is not a gas giant?

Answer Mercury

Mercury is a small ball of rock and metal with barely any atmosphere. The gas giants are Jupiter and Saturn; Uranus and Neptune are often separated out as ice giants because so much of their bulk is water, ammonia and methane.

Why was Pluto reclassified as a dwarf planet?

Answer It has not cleared other objects out of its orbital path

The 2006 definition asks three things of a planet: it orbits the Sun, it is round under its own gravity, and it has cleared its neighborhood. Pluto passes the first two and fails the third — it shares its zone with many other icy bodies.

A year on a planet is defined by what?

Answer How long it takes to orbit the Sun once

A year is one lap around the Sun, so it differs for every planet: Mercury takes about 88 Earth days, Neptune about 165 Earth years. A day, by contrast, is one spin on the axis, and the two have nothing to do with each other.

Which planet has the most extreme axial tilt, rolling on its side as it orbits?

Answer Uranus

Uranus is tipped about 98 degrees, so it effectively rolls along its orbit. That gives each pole roughly 42 years of continuous sunlight followed by 42 years of darkness.

What is the Sun made mostly of?

Answer Hydrogen and helium

By mass the Sun is roughly three quarters hydrogen and most of the rest helium, with everything else adding up to a small remainder. That mix is close to what the universe as a whole is made of.

Which way does a comet's tail point?

Answer Away from the Sun, whichever way the comet is traveling

The tail is blown outward by sunlight and the solar wind, so it always points away from the Sun. On the way back out, the comet is traveling tail-first.

What powers the Sun?

Answer Nuclear fusion of hydrogen into helium

Fusion in the core turns hydrogen into helium, and the tiny mass difference becomes energy. Light from that core takes a very long time to work its way to the surface, even though it crosses the distance to Earth in about eight minutes.

What is the Sun?

Answer An ordinary star, seen close up

Nothing about the Sun is unusual except its distance. It is a middling star in size and temperature, and if you moved it to a typical stellar distance it would look like any other point of light.

Which galaxy do we live in?

Answer The Milky Way

The pale band across a dark sky is our own galaxy seen edge-on from the inside — we are looking along the disk we sit in, which is why it appears as a band rather than a spiral.

What is a light-year a measure of?

Answer Distance

A light-year is how far light travels in a year, so it measures distance, not time. It is a useful unit precisely because it also tells you how old the view is.

A star's color tells you mainly about what?

Answer Its surface temperature

Color tracks surface temperature: blue and white stars are hotter, orange and red ones cooler. It says little about size, and a red star can be either a tiny dwarf or an enormous giant.

Which is hotter at the surface, a blue star or a red one?

Answer The blue one

This one runs against everyday intuition, because we associate red with hot taps and blue with cold ones. In physics it is the other way around — hotter surfaces peak at shorter, bluer wavelengths.

What is a black hole's event horizon?

Answer The boundary from inside which nothing can escape

The event horizon is not a surface you could touch; it is the distance at which escape would require exceeding the speed of light. From outside, nothing that crosses it can send anything back.

What is a constellation?

Answer A pattern we see from Earth, whose stars may be far apart

The stars in a constellation usually have nothing to do with each other. They can lie at wildly different distances and only look grouped because we see them from one particular spot.

Which star is closest to the Sun?

Answer Proxima Centauri

Proxima Centauri is a faint red dwarf, too dim to see without a telescope despite being the nearest star. It is part of the Alpha Centauri system, a little over four light-years away.

Why do stars twinkle while planets mostly do not?

Answer Stars are points of light and our atmosphere bends them about

Twinkling happens in our atmosphere, not in the star. A star is effectively a single point, so a pocket of moving air shifts all of its light at once; a planet is a small disk, and the wobbles average out.

The universe is usually given an age of roughly how long?

Answer Fourteen billion years

The figure comes from several independent lines of evidence that agree — the expansion rate, the ages of the oldest stars, and the faint microwave glow left over from the early universe.

Who was the first human in space?

Answer Yuri Gagarin

Gagarin orbited the Earth once in 1961 aboard Vostok 1, in a flight lasting under two hours. He did not land inside the capsule but ejected and came down by parachute.

In which year did people first walk on the Moon?

Answer 1969

Apollo 11 landed in July 1969, and five more crewed landings followed through 1972. Twelve people have walked on the surface, all within that three-year window.

Why do astronauts float inside a space station?

Answer They are falling around the Earth together with the station

There is plenty of gravity up there — roughly 90 percent of what you feel on the ground. Astronauts float because the station and everything in it are falling around the Earth at the same rate.

Roughly how long does the International Space Station take to circle the Earth once?

Answer About 90 minutes

About an hour and a half, which means the crew sees roughly sixteen sunrises and sunsets in each twenty-four hours. Their working day is set by clocks, not by the light outside.

What was Sputnik?

Answer The first artificial satellite to orbit the Earth

Sputnik 1 was launched in 1957 and did little more than transmit a beep, but that beep could be picked up by amateur radios worldwide, which is much of why it landed so hard.

Why is a rocket built in stages that fall away?

Answer To stop carrying empty tanks that are only dead weight

Every kilogram you carry has to be accelerated by everything that follows. Dropping an empty tank is the cheapest possible saving, and it is why almost every launch vehicle sheds pieces on the way up.

What does a space telescope gain by being above the atmosphere?

Answer A view undistorted by air, including light the atmosphere blocks

Air blurs images and absorbs whole bands of light outright — most ultraviolet, much of the infrared, and all X-rays. A telescope above it sees sharper, and sees colors that never reach the ground at all.

What are the Voyager probes doing now?

Answer Traveling outward beyond the planets

Both probes launched in 1977, passed the outer planets, and are still traveling outward while sending back faint data. They are the most distant human-made objects.

Why is re-entry so hot for a returning spacecraft?

Answer The air ahead of it is violently compressed

Friction is the smaller part of it. The spacecraft is moving so fast that the air in front cannot get out of the way and is compressed violently, and compressed gas gets hot.

What is a geostationary orbit useful for?

Answer Staying above the same point on Earth, which suits communications

At about 36,000 kilometers up, an orbit takes exactly one day, so the satellite hangs over the same spot. That is why a satellite dish can be bolted down and never moved again.

Roughly how long does sunlight take to reach the Earth?

Answer About eight minutes

About eight minutes and twenty seconds. If the Sun went out, we would carry on seeing it for that long — and nothing else about the moment would tip us off.

When you look at a distant star, you are seeing what?

Answer The star as it was when the light left it

You are always looking into the past. For nearby stars that is a few years; for distant galaxies it can be billions, which is what lets telescopes act as time machines.

What happens to the speed of light in a vacuum for different observers?

Answer It is the same for all of them

It is the same for everyone, no matter how fast they are moving or in which direction. That refusal to add up in the ordinary way is the starting point of special relativity.

Why is the night sky dark, when there are so many stars?

Answer The universe has a finite age, so light from the most distant places has not arrived

The question is old enough to have a name — Olbers' paradox. The answer is that the universe has a finite age, so light from the most distant regions simply has not had time to get here.

What does redshift tell astronomers about a distant galaxy?

Answer That it is moving away from us

Light from a receding source is stretched toward the red end. Measuring that stretch gives the speed, and for distant galaxies the speed grows with distance, which is how we know the universe is expanding.

Sound does not travel through space because of what?

Answer There is almost nothing there to carry the vibration

Sound needs a medium to push against. Space is not a perfect vacuum, but it is empty enough that there is nothing to carry a pressure wave from one place to another.

What is an astronomical unit?

Answer The average distance from the Earth to the Sun

One astronomical unit is roughly 150 million kilometers. It is a convenient ruler inside the solar system, the way light-years are convenient outside it.

Why does the sky look blue from the ground?

Answer Air scatters short wavelengths more than long ones

Air scatters short wavelengths much more strongly than long ones, so blue light bounces around the sky and reaches you from every direction. At sunset the light travels through more air, the blue is scattered away, and what is left is red.

What is a nebula?

Answer A cloud of gas and dust in space

Nebulae are where stars are born and also what some leave behind when they die. Many are invisible to the eye and only show their colors in long exposures.

Why do telescopes on the ground prefer high, dry mountaintops?

Answer There is less air and less water vapor to look through

Height puts you above much of the atmosphere, and dryness matters because water vapor absorbs infrared light. Steady air matters as much as clear air, which is why some sites beat others of the same height.

What causes the phases of the Moon?

Answer How much of its lit half we can see from where we are

The Moon is always half lit; what changes is how much of that lit half faces us. The Earth's shadow has nothing to do with it — that only appears during a lunar eclipse.

Why do we always see the same side of the Moon?

Answer It turns once for each orbit it makes

The Moon spins once for every orbit, a state called tidal locking, so the same face stays turned toward us. It is not that the Moon does not rotate; it rotates in step.

What causes the tides?

Answer Mainly the Moon's gravity pulling on the oceans

The Moon pulls hardest on the near side and least on the far side, and that difference stretches the oceans into two bulges. The Sun contributes too, and when the two line up the tides run larger.

What is happening during a solar eclipse?

Answer The Moon passes between the Sun and the Earth

A solar eclipse needs the Moon between us and the Sun; a lunar eclipse has the Earth between the Sun and the Moon. Eclipses are not monthly because the Moon's orbit is tilted a few degrees.

What causes the seasons?

Answer The tilt of the Earth's axis

The Earth's axis is tilted about 23.5 degrees, so each hemisphere leans toward the Sun for part of the year. Distance is not the cause — the Earth is actually closest to the Sun in January.

What are meteors, the streaks people call shooting stars?

Answer Small pieces of rock and dust heating the air as they enter it

Most are no bigger than a grain of sand. They glow because they compress the air in front of them at enormous speed, and almost all of them burn up long before reaching the ground.

What protects the surface of the Earth from most solar radiation?

Answer The magnetic field and the atmosphere together

The magnetic field deflects charged particles and the atmosphere absorbs most of the harmful light. The aurora is what you see when some of those particles are funneled down near the poles.

Why does the Moon have so many visible craters when the Earth does not?

Answer The Earth erases them through weather and moving crust

The Earth takes just as many hits, but rain, wind and moving crust erase the scars. The Moon has neither weather nor plate tectonics, so its record goes back billions of years.

Which of these can be seen with the naked eye from a dark site?

Answer The Andromeda galaxy

Andromeda is about two and a half million light-years away and still visible as a faint smudge from a dark site. It is the most distant thing most people will ever see unaided.

Why does the sky appear to turn through the night?

Answer The Earth is rotating

The sky is not moving; we are. The Earth turns once a day, and the stars appear to wheel around the pole in the opposite direction.