Welcome to the PAC Astronomy Trivia Page!

Each day a new Trivia question, along with it’s answer, is posted to provide unique and interesting astronomical related facts.

We hope these trivia items inspire folks to learn something new and interesting everyday, while expanding their knowledge of the Universe.

If you have a special trivia item you would like posted contact the webmaster at or call (928) 778-6502.

March 27, 2017 (00011)
What did the Earth do in 1910 that caused unnecessary fear for many people around the world?
Passed through Halley’s Comet tail.

March 26, 2017 (00010)
Just after New Moon, we can faintly see the part of the Moon that is still in shadow.
What famous person is the first one known to recognize that this is from “earthshine” (sunlight reflected off the Earth, to the Moon, and back)?

Leonardo da Vinci

March 25, 2017 (00009)
When there are two full moons in the same calendar month the second one is called a “Blue Moon.”
How often does this event happen on average?
2 1/2 to 3 Years

March 24, 2017 (00008)
What is the name of the most prominent crater on the Moon?
Answer: Tycho

March 23, 2017 (00007)
In 1609 Galileo discovered four moons orbiting Jupiter. Three of them are named “Io”, “Ganymede” and “Callisto.”
What did he name the other one?

Answer: Europa

March 22, 2017 (00006)
What color is on the outside of the arc of a rainbow?
Answer: Red

March 21, 2017 (00005)
If the Universe Is Expanding, Why Are the Milky Way and Andromeda Galaxies on a Collision Course?

To get to the answer, we will need to look at which forces operate on small and large astronomical scales (distances). The two fundamental forces at play in this case are gravity and dark energy. Gravity is certainly the more familiar of the two, so let’s start there…


March 20, 2017 (00004)
In 4-5 billion years the Sun is forecast to expand enough to engulf the earth.  How fast is the Sun currently expanding each day?
Right now (and for the past 5 billion years or so, and for the next 4-5 billion years) the sun is pretty much in equilibrium — the tremendous pull of gravity due to its mass is balanced by the outflow of energy from nuclear fusion. It’s size changes a tiny, tiny fraction now and then, but this is an in-and-out type of motion, almost like respiration, as the two forces mentioned above fight to stay in balance.


March 19, 2017 (00003)
What is the Antikythera mechanism?
The Antikythera mechanism is an ancient analogue computer and orrery used to predict astronomical positions and eclipses for calendrical and astrological purposes, as well as the Olympiads, the cycles of the ancient Olympic Games.


March 18, 2017 (00002)
How did the Sun get its name?

The sun has had multiple names over the centuries, including the French word “soleil,” the Latin term “sol” from the ancient Romans and “helios” from the ancient Greeks. However, after Germany coined the term “sonne,” the word translated into English became “sonne” and later just “sun,” according to NASA.

March 17, 2017 (00001)
What is Planck time and how many units are in one second?

The Planck time is the length of time at which no smaller meaningful length can be validly measured due to the indeterminacy expressed in Werner Heisenberg‘s Uncertainty Principle. Theoretically, this is the shortest time measurement that is possible. Planck time is roughly 10−44 seconds. However, to date, the smallest time interval that was measured was 10−21 seconds. One Planck time is the time it would take a photon traveling at the speed of light to cross a distance equal to one Planck length.