Planetary confusion: why astronomers keep changing what it means to be a planet

Christopher Palma, Pennsylvania State University As an astronomer, the question I hear the most is why isn’t Pluto a planet anymore? More than 10 years ago, astronomers famously voted to change Pluto’s classification. But the question still comes up.

What if Ganymede was the Earth’s second moon?

Jupiter’s moon Ganymede is the largest and most massive of the Solar System’s moons. It has a mean radius of 2634.1±0.3 km (about 1636 miles, 0.413 Earths). For comparison, our Moon’s radius is 1,737.1 km (1079 mi). What if Ganymede was the Earth’s second moon? How would it look in the sky, if it was […]

Top 10 Largest Non-Planets In Our Solar System

There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Two of the largest moons are bigger than the smallest planet, Mercury. Here are the top 10 largest non-planets in our solar system (eight of them are moons and two of them are dwarf planets).

The Size Of Earth Compared to Other Planets and Stars (and the Universe)

When it comes to big numbers, very big numbers, the human brain is weak. In fact, our brains cannot deal with really large numbers. That’s why when the subject is Earth, planets, Solar System, galaxies, and in general, the Universe, we cannot truly conceptualize the things. A lot of people think we’re “conquering” space (we […]