Even though humans have studied the heavens for thousands of years, we still know very little about the universe. As we continue to explore, we learn more about the stars, planets, and galaxies. Some of the things we find out are amazing, and others are confusing. Here is a collection of amazing, interesting, and strange astronomy facts, based on our current knowledge of the cosmos.
- We can only detect about 5% of the matter in the universe. The rest is made up of invisible matter (called dark matter) and a mysterious form of energy known as dark energy.
- Neutron stars are the leftovers of the deaths of massive stars in supernova explosions. These stars are so dense a soup can full of neutron star material would have more mass than the Moon. They are among the fast-spinning objects astronomers have studied, with spin rates up to 500 times per second!
- The Sun’s core releases the the equivalent of 100 billion nuclear bombs every second. All that energy works its way out through the various layers of the Sun, taking thousands of years to make the trip. The Sun’s energy is emitted as heat and light.
- Galileo Galilei is often incorrectly credited with the invention of the telescope. Historians now think the Dutch eyeglass maker Johannes Lippershey was its creator. Galileo was probably the first to use the device to study the heavens.
- Black holes are so dense, and produce such intense gravity, that nothing — not even light —can escape their gravitational clutches. However, there are some unusual situations where a form of radation — called Hawking radiation — can slip away.
- When supermassive black holes collide, gravitational waves are released. These waves were known to exist, and were finally detected in 2015.
- If you somehow got too close to a black hole and were sucked in by its gravitational pull, it would pull harder on your feet than on your head. You would get stretched out — or spaghettified — by the intense pull.
- Light from distant stars and galaxies takes so long to reach us that we are actually seeing these objects as they appeared in the past. As we look up at the sky, we are really looking back in time. For example, the Sun’s light takes almost 8.5 minutes to travel to Earth, so we see the Sun as it looked 8.5 minutes ago. The nearest star to us, Proxima Centauri, is 4.2 light-years away, so it appears as it was 4.2 years ago. The nearest galaxy is 2.5 million light-years away, and it looks as it did when our australopithecus hominid ancestors walked the planet.The farther away something is, the further back in time it appears.
- The Crab Nebula was produced by a supernova explosion that appeared in our skies in the year 1054 A.D. The Chinese and Arab astronomers at the time noted that the explosion was so bright that it was visible during the day, and it lit up the night sky for months. It was likely also observed by the Anasazi people of the U.S. southwest.
- Shooting stars really aren’t stars. They are usually just tiny dust particles falling through our atmosphere and they vaporize due to the heat of friction with the atmospheric gases. Earth sometimes passes through cometary orbits. As comets travel around the Sun, they leave behind dust trails. When Earth encounters that dust, we see an increase in meteors.
- Even though Mercury is the closest planet to the Sun, temperatures there can reach -280 degrees F on its surface. How can this happen? Since Mercury has almost no atmosphere, there is nothing to trap heat near the surface. So, the dark side of Mercury (the side facing away from the Sun) gets very cold.
- Venus is considerably hotter than Mercury, even though it is farther away from the Sun. The thickness of Venus’s atmosphere traps heat near the surface of the planet. Venus also spins very slowly on its axis.
- A day on Venus is 243 Earth-days long, while Venus’s year is only 224.7 days. Even weirder, Venus spins backwards on its axis compared to the other planets in the solar system.
- Space isn’t completely empty. We often hear about the vacuum of space, but it turns out that there are a few atoms of matter in each cubic meter of space. The space between galaxies, which was also once thought to be quite empty can often be filled with molecules of gas and dust.
- The universe is filled with galaxies and the most distant ones are moving away from us at more than 90 percent of the speed of light.
Edited and updated by Carolyn Collins Petersen.