10 Astonishing Things You Should Know About the Milky Way

Anne Dirkse, Flickr // CC BY-SA 2.0
Anne Dirkse, Flickr // CC BY-SA 2.0

Our little star and the tiny planets that circle it are part of a galaxy called the Milky Way. Its name comes from the Greek galaxias kyklos ("milky circle") and Latin via lactea ("milky road"). Find a remote area in a national park, miles from the nearest street light, and you'll see exactly why the name makes sense and what all the fuss is about. Above is not a sky of black, but a luminous sea of whites, blues, greens, and tans. Here are a few things you might not know about our spiraling home in the universe.


The Milky Way galaxy is about 1,000,000,000,000,000,000 kilometers (about 621,371,000,000,000,000 miles) across. Even traveling at the speed of light, it would still take you well over 100,000 years to go from one end of the galaxy to the other. So it's big. Not quite as big as space itself, which is "vastly, hugely, mind-bogglingly big," as Douglas Adams wrote, but respectably large. And that's just one galaxy. Consider how many galaxies there are in the universe: One recent estimate says 2 trillion.


artist's illustration of the milky way galaxy and its center
An artist's concept of the Milky Way and the supermassive black hole Sagittarius A* at its core.
ESA–C. Carreau

The Milky Way is a barred spiral galaxy composed of an estimated 300 billion stars, along with dust, gas, and celestial phenomena such as nebulae, all of which orbits around a hub of sorts called the Galactic Center, with a supermassive black hole called Sagittarius A* (pronounced "A-star") at its core. The bar refers to the characteristic arrangement of stars at the interior of the galaxy, with interstellar gas essentially being channeled inward to feed an interstellar nursery. There are four spiral arms of the galaxy, with the Sun residing on the inner part of a minor arm called Orion. We're located in the boondocks of the Milky Way, but that is OK. There is definitely life here, but everywhere else is a question mark. For all we know, this might be the galactic Paris.


If you looked at all the spiral galaxies in the local volume of the universe, the Milky Way wouldn't stand out as being much different than any other. "As galaxies go, the Milky Way is pretty ordinary for its type," Steve Majewski, a professor of astronomy at the University of Virginia and the principal investigator on the Apache Point Observatory Galactic Evolution Experiment (APOGEE), tells Mental Floss. "It's got a pretty regular form. It's got its usual complement of star clusters around it. It's got a supermassive black hole in the center, which most galaxies seem to indicate they have. From that point of view, the Milky Way is a pretty run-of-the-mill spiral galaxy."


On the other hand, he tells Mental Floss, spiral galaxies in general tend to be larger than most other types of galaxies. "If you did a census of all the galaxies in the universe, the Milky Way would seem rather unusual because it is very big, our type being one of the biggest kinds of galaxies that there are in the universe." From a human perspective, the most important thing about the Milky Way is that it definitely managed to produce life. If they exist, the creatures in Andromeda, the galaxy next door (see #9), probably feel the same way about their own.


John McSporran, Flickr // CC BY 2.0

We have a very close-up view of the phenomena and forces at work in the Milky Way because we live inside of it, but that internal perspective places astronomers at a disadvantage when it comes to determining a galactic pattern. "We have a nice view of the Andromeda galaxy because we can see the whole thing laid out in front of us," Majewski says. "We don't have that opportunity in the Milky Way."

To figure out its structure, astronomers have to think like band members during a football halftime show. Though spectators in the stands can easily see the letters and shapes being made on the field by the marchers, the band can't see the shapes they are making. Rather, they can only work together in some coordinated way, moving to make these patterns and motions on the field. So it is with telescopes and stars.


Interstellar dust further stymies astronomers. "That dust blocks our light, our view of the more distant parts of the Milky Way," Majewski says. "There are areas of the galaxy that are relatively obscured from view because they are behind huge columns of dust that we can't see through in the optical wavelengths that our eyes work in." To ameliorate this problem, astronomers sometimes work in longer wavelengths such as radio or infrared, which lessen the effects of the dust.


Astronomers can make pretty reasonable estimates of the mass of the galaxy by the amount of light they can see. They can count the galaxy's stars and calculate how much those stars should weigh. They can account for all the dust in the galaxy and all of the gas. And when they tally the mass of everything they can see, they find that it is far short of what is needed to account for the gravity that causes the Milky Way to spin.

In short, our Sun is about two-thirds of the way from the center of the galaxy, and astronomers know that it goes around the galaxy at about 144 miles per second. "If you calculate it based on the amount of matter interior to the orbit of the Sun, how fast we should be going around, the number you should get is around 150 or 160 kilometers [93–99 miles] per second," Majewski says. "Further out, the stars are rotating even faster than they should if you just account for what we call luminous matter. Clearly there is some other substance in the Milky Way exerting a gravitational effect. We call it dark matter."


Dark matter is a big problem in galactic studies. "In the Milky Way, we study it by looking at the orbits of stars and star clusters and satellite galaxies, and then trying to figure out how much mass do we need interior to the orbit of that thing to get it moving at the speed that we can measure," Majewski says. "And so by doing this kind of analysis for objects at different radii across the galaxy, we actually have a fairly good idea of the distribution of the dark matter in the Milky Way—and yet we still have no idea what the dark matter is."


andromeda galaxy
The Andromeda galaxy
ESA/Hubble & NASA

Sometime in the next 4 or 5 billion years, the Milky Way and Andromeda galaxies will smash into each other. The two galaxies are about the same size and have about the same number of stars, but there is no cause for alarm. "Even though there are 300 billion stars in our galaxy and a comparable number, or maybe more, in Andromeda, when they collide together, not a single star is expected to hit another star. The space between stars is that vast," Majewski says.


There are countless spacecraft and telescopes studying the Milky Way. Most famous is the Hubble Space Telescope, while other space telescopes such as Chandra, Spitzer, and Kepler are also returning data to help astronomers unlock the mysteries of our swirling patch of stars. The next landmark telescope in development is NASA's James Webb Space Telescope. It should finally launch in 2019. Meanwhile, such ambitious projects as APOGEE are working out the structure and evolution of our spiral home by doing "galactic archaeology." APOGEE is a survey of the Milky Way using spectroscopy, measuring the chemical compositions of hundreds of thousands of stars across the galaxy in great detail. The properties of stars around us are fossil evidence of their formation, which, when combined with their ages, helps astronomers understand the timeline and evolution of the galaxy we call home. 

A Rare Unicorn Meteor Outburst Could Be Visible for Less Than an Hour on Thursday

joegolby/iStock via Getty Images
joegolby/iStock via Getty Images

Your chances of seeing a unicorn this week are slim, but if you look up on Thursday night, you may see something that's almost as extraordinary. As Sky & Telescope reports, the upcoming Alpha Monocerotid meteor shower could produce a meteor outburst, which means there could be multiple shooting stars per second streaming from the unicorn constellation.

What is a unicorn meteor shower?

There's nothing particularly magical about the Alpha Monocerotids. They appear to originate near the star Procyon, which is next to the constellation Monoceros, the Greek name for unicorn.

The shower is known for occasionally packing a dense flurry of activity into a brief viewing window. The meteors appear between November 15 through the 25th of each year, and peak around the 22nd. Several times a century, the shower treats sky gazers to an "outburst" of shooting stars that lasts less than an hour.

Such an outburst is predicted for 2019. According to astronomers Peter Jenniskens and Esko Lyytinen, the Earth is on track to pass through a thick portion of the tail of the unknown comet that provides debris for the shower. The conditions are almost the same as they were in 1995, when the Alpha Monocerotids lit up the sky at a rate of 400 meteors per hour, which is approaching meteor storm levels. For that reason, the scientists are expecting shooting stars to appear in the same numbers this time around.

How to see the meteor outburst

Timing is crucial if you want to catch the Alpha Monocerotids, even more than with regular meteor showers. The outburst is expected to start at 11:15 p.m. EST and last just 15 to 40 minutes. Luckily, the sun will be fully set by then and the crescent moon won't rise until after 2 a.m, creating optimal viewing conditions for the eastern half of the country. The shooting stars are fast—traveling at 40 miles per second—and they come at random. Don't be surprised to wait a minute between meteors during some parts of the outburst and less than a second at others.

[h/t Sky & Telescope]

The Leonid Meteor Shower Peaks This Weekend—Here's the Best Way to Watch It

mdesigner125/iStock via Getty Images
mdesigner125/iStock via Getty Images

We're nearing the end of 2019, but there are still a few astronomical events to catch before the year is s out. This Sunday—November 17—the Leonid meteor shower is expected to peak. Here's everything you need to know before viewing the spectacle.

What is the Leonid meteor shower?

Like all meteor showers, the Leonids are caused by meteoroids from outer space burning up on their descent toward Earth. These particular shooting stars come from the rocky tail of Comet 55P/Tempel-Tuttle. Each November, debris from the comet pummels the Earth's atmosphere, causing meteors to light up the sky at rates that can exceed 1000 per hour.

The Leonids won't reach that frequency this year. According to EarthSky, the meteors would peak at a rate of around 10 to 15 per hour in a dark, moonless sky. But because the moon will be bright this weekend, sky-gazers will likely see less of them, with only the brightest shooting stars shining through.

How to See the Leonids

For your best chance of spotting the Leonids, look up the night of Sunday, November 17 and early in the morning of Monday, November 18. The shower reaches its peak after midnight. The moon will be in its waning gibbous phase at that time, so even with clear skies, viewing conditions won't be ideal. But there are ways to increase your chances of seeing as many meteors as possible. Try finding a large object to stand under—such as a tree or building—that will block your view of the moon. If you don't see anything right away, be patient: The more time you give your eyes to adjust to the darkness, the more likely you are to spot a shooting star.