- In China, the Milky Way is called “The Silver River.” In ancient Chinese myth, the river was placed in the heavens by the gods trying to separate a weaver who made their clothes and the herdsman who loved her.
- The Romans called our galaxy the Milky Road because it reminded them of milk. The Greeks called it the Milky Circle. In fact, the word “galaxy” is from the Greek word for milk.
- In Sanskrit, the Milky Way is called Akash Ganga, or “Ganges of the heavens.”
- Visible light, the light we can see, is only one form of energy given off by stars and other objects in the Milky Way. Our galaxy also consists of other types of energy, such as infrared light, radio waves, gamma rays, dark matter, and X-rays.
- When a person sees the Milky Way at night, they are seeing only about 0.0000025% of the galaxy’s hundreds of billions of stars.
According to Greek mythology, the Milky Way was formed when Hera was surprised to find another woman's son (Hercules) suckling her breast while she was asleep
- In Greek mythology, the Milky Way was created when Hera spilled her milk while suckling Heracles. It was also described as the road to Mount Olympus, or the path of ruin made by the Helios’ (the sun god’s) chariot.
- The very center of the Milky Way contains a powerful gravitational force that scientists believe is a black hole, which they have named Sagittarius A*. Astronomers believe this black hole weighs as much as 4 million of our suns put together.
- The Milky Way is a galaxy—a huge group of stars, gas, dust, and other matter held together in space by their mutual gravitational pull. The Milky Way is just one of billions of galaxies in the universe.
- The Milky Way is a barred spiral galaxy that has curved arms that spin out from its center. Astronomers discovered it was barred (meaning the center is bar-shaped) rather than an ordinary spiral galaxy (meaning the center is a spherical bulge) in the 1990s. It is 100,000–120,000 light-years in diameter.
- It would take a phenomenal amount of energy for a star or other object to leave the galaxy. Stars must reach speeds 1 million mph faster than the 600,000 mph at which objects already speed around the Milky Way. Astronomers have discovered 18 such giant blue stars being ejected out of our galaxy. Scientists are unsure how the stars are being propelled.
- There aren’t more stars in the arms of the Milky Way’s spiral than elsewhere. The stars in the arms are bigger stars, which die out quicker and burn brighter, which illuminates those around them and make the arms more visible.
Many consider Democritus to be the "father of modern science"
- The ancient Greek philosopher Democritus, who lived from about 460 to 370 B.C., was the first known person to suggest that the Milky Way is made of stars. Galileo Galilei (1564–1642) was the first to identify and resolve the band of light as many individual stars with his telescope in 1610.
- The oldest star in the Milky Way is at least 13.6 billion years old and most likely formed shortly after the Big Bang.
- The space between planets in the solar system is relatively dense because of the particles in the solar wind, though the density is much lower than the air on Earth, at about 10 million atoms per cubic meter on average. The interstellar medium in the Milky Way is thinner than in our solar system, but the galaxy’s gravity keeps most gas and dust nearby, at about 10,000 atoms per cubic meter on average. The matter in the space between galaxies has the lowest density in the universe, at 1 atom per cubic meter on average.
- If our solar system were the size of a U.S. quarter, the sun would be a microscopic piece of dust and the Milky Way would be about the size of the United States.
- The Milky Way rotates at a speed of 168 miles per second. So, the actual place in space where you were an hour ago is now roughly 600,000 miles away.
- The Milky Way has a halo of dark matter that makes up over 90% of its mass. What this means is that all we can see, even with telescopes, is less than 10% of the mass of our galaxy.
- Scientists call the Milky Way and about 40 other galaxies nearby the Local Group. They are held together by mutual gravitational attraction. The Local Group belongs to an even larger group of galaxies called the Local Supercluster. This supercluster is about 100 million light years across.
As, pricked out with less and greater lights, between the poles of the universe, the Milky Way so gleameth white as to set very sages questioning.
- Dante Alighieri
- The center of the Milky Way is full of mostly old stars. Its spiral arms contain more newborn stars.
- The center of the Milky Way has both the greatest concentration of stars and the most massive stars.
- Scientists believe that the Milky Way contains up to 400 billion stars, and at least as many planets. The largest galaxy known, IC 1101, has over 100 trillion stars. Smaller galaxies, like the Large Magellanic Cloud, have about 10 billion stars. The most stars a person can see from any point on Earth are about 2,500.
- The Milky Way galaxy is 100,000 light-years from edge to edge. If a rocket could travel at the speed of light, it would take 100,000 years to cross the galaxy. By comparison, light can go from Earth to the moon in just one second.
Hubble is considered one of the most important astronomers of the 20th century
- Edwin Hubble (1889–1953) is credited with discovering the shape and scope of the Milky Way.
- The Milky Way is 100,000 light-years in diameter, which is small compared to M87, an elliptical galaxy 980,000 light-years in diameter. Bigger still is the galaxy Hercules A, which is 1.5 million light-years across.
- The central bulge of the Milky Way is about 10,000 light-years thick.
- Our solar system orbits the center of the galaxy at the speed of 514,000 miles per hour relative to the Galactic Center. An object this fast could circumnavigate Earth’s equator in 2 minutes and 54 seconds. It takes about 250 million years for the solar system to go just once around the galaxy, or to complete one galactic year.
- The sun and our solar system have orbited the galaxy fewer than 20 times since our solar system was born about 4.6 billion years ago. It has made 1/1250 of a revolution since the origin of humans.
- The orbital speed of the solar system around the center of the Milky Way galaxy is about 220 km/s, or 0.073% of the speed light. It takes about 1,400 years for the solar system to travel 1 light-year.
- If the Milky Way had the same diameter as a Frisbee, the thickness of the disk would be about that of a sheet of paper.
- All galaxies are not alike, but most fit into one of three main groups: 1) spiral galaxies (such as the Milky Way), 2) elliptical galaxies, and 3) and irregular galaxies.
- The Milky Way has at least three giant streams of stars that wrap around it. The streams, which are from 13,000 to 130,000 light-years from Earth, are likely the remains of ancient star clusters that the Milky Way ripped apart with its gravitational force.
These streams high over the Milky Way are between 13,000 and 130,000 light years from Earth and contain millions of stars
- Scientists believe that the Milky Way is consuming a small galaxy called the Sagittarius Dwarf Galaxy.
- Besides the Andromeda galaxy, two other galaxies are close to the Milky Way: the Large Magellanic Cloud, which is about 170,000 light-years away from the Milky Way, and the Small Magellanic Cloud, which is about 200,000 light-years away. They are named after Ferdinand Magellan, the first sailor to travel all the way around the globe.
- The sun, Earth, and the rest of the solar system are located about 27,000 light-years away from the Milky Way’s Galactic Center, on the inner edge of a minor arm of the galaxy, named the Orion Arm.
- Astronomers must study the Milky Way with telescopes that detect radio waves, infrared light, and X-rays. Optical telescopes, which detect only visible light, cannot pass through the thick clouds of gas and dust.
- It would take a spaceship thousands of years traveling at the speed of light to get far enough to capture a picture of the entire galaxy. Every picture of the Milky Way that we have is either a picture of another galaxy or an artist’s interpretation.
- The Milky Way has only two major arms rather than four. The major arms, the Scutum-Centaurus Arm and the Perseus Arm, extend from the ends of the galaxy’s central bar of stars. The solar system lies on the Orion Spur, a branch of the Sagittarius Arm.
- Astronomers estimate that seven new stars form in the Milky Way each year. They form inside huge clouds of dust and gas.
- The Milky Way and another spiral galaxy, Andromeda, will collide in about 2 billion years, and the collision may last about 5.5 billion years. However, the sun and Earth may not be greatly affected because the distance between stars in the galaxies is so large. When the collision is over, the Milky Way and Andromeda will no longer be two spiral galaxies, but one elliptical galaxy.
Astronomers predict that the Andromeda Galaxy will collide with the Milky way in 4 billion years
- Astronomers believe that the universe began in an explosion called the Big Bang. The Milky Way formed soon after the Big Bang from a cloud of gas and dark matter that pulled in surrounding material through gravity.
- Astronomers discovered that the Milky Way has already consumed several smaller galaxies. Even now, the Milky Way is consuming two nearby dwarf galaxies and pulling matter away from the Large and Small Magellanic clouds, two small galaxies.
- Earth’s closest star in the Milky Way, Proxima Centauri, is more than four light-years away (a light-year is about 5.9 trillion miles, about 10 trillion kilometers). Proxima is Latin for “close.”
- In the 1920s, astronomer Edwin Hubble created a new way to measure the distance between other galaxies based on how bright a star is. He was able to prove that there were other galaxies outside the Milky Way and that the universe is millions of times bigger than our galaxy.
- If Earth orbited the sun at the same speed that stars orbit the center of the Milky Way, our planet would travel around the sun in only 3 days instead of 365.
- In addition to the rotation around the center of the Milky Way, stars (such as our sun) oscillate, or move up and down, through the plane of the galaxy.
Until fairly recently, astronomers believed the Milky Way was the universe
- Up to about 100 years ago, astronomers believed the Milky Way was the entire universe.
- Right now, the Milky Way and another spiral galaxy called Andromeda are moving toward each other. They are approaching each other at about 75 miles (120 kilometers) per second.
- Scientists believe that the Milky Way is one of the older galaxies in the universe. It was formed about 13.6 billion years ago and is almost as old as the universe itself, which formed about 13.7 billion years ago.
- Since the dinosaurs died out about 65 million years go, the sun is estimated to have travelled about 1/3 the way around the Milky Way’s center.
- According to Cherokee legend, the Milky Way was formed when a dog stole some cornmeal and was chased way. He ran to the north, spilling cornmeal as he ran. The Milky Way is thus called “The Way the Dog Ran Away.”
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2“How Far Is It across the Milky Way?” Harvard. Accessed: July 29, 2014.
3Kortenkamp, Steve. The Milky Way (First Facts). Mankato, MN: Capstone Press, 2008.
4Redd, Nola Taylor. “Strange, Hypervelocity Stars Get Ejected from Milky Way.” Space. January 27, 2014. Accessed: July 29, 2014.
5The Milky Way (volume in Explore the Universe encyclopedic set). 2010. Chicago, IL: World Book.
6Trammel, Howard K. Galaxies (A True Book). New York, NY: Scholastic Inc, 2010.