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.

1. THE MILKY WAY IS GIGANTIC.

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.

2. IT'S JAM-PACKED WITH CELESTIAL STUFF.

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.

3. FOR A SPIRAL GALAXY, IT'S PRETTY TYPICAL …

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."

4. …AND YET IT STANDS OUT AMONG ALL GALAXIES.

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.

5. FIGURING OUT ITS STRUCTURE FROM THE INSIDE IS A CHALLENGE.


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.

6. INTERSTELLAR DUST BLOCKS OUR VIEW OF SOME PARTS OF THE GALAXY.

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.

7. THE MILKY WAY SPINS, BUT ITS SPEED DOESN'T ADD UP …

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."

8. … AND WE BLAME DARK MATTER FOR THAT.

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."

9. THE MILKY WAY IS ON A COLLISION COURSE WITH ANDROMEDA. BUT DON'T PANIC.

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.

10. WE'RE THROWING EVERYTHING WE HAVE AT STUDYING IT.

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. 

How to See the Full Sturgeon Moon on Thursday

Brook Mitchell, Stringer/Getty Images
Brook Mitchell, Stringer/Getty Images

The full moon of every month has a special nickname. Some—like September's harvest moon, December's cold moon, and May's flower moon—have obvious connections to their seasons, while other names are harder to decode. August's sturgeon moon is an example of the latter. It may not be the prettiest lunar title in The Old Farmer's Almanac, but that doesn't mean the event itself on August 15, 2019 won't be a spectacular sight to behold.

What is a Full Sturgeon Moon?

The first (and normally the only) full moon that occurs in August is called a sturgeon moon. The name may have originated with Native American tribes living around the Great Lakes in the Midwest and Lake Champlain in New England. These bodies of water contain lake sturgeon, a species of freshwater fish that grows up to 6.5 feet in length and can live 55 years or longer. August's full moon was dubbed the sturgeon moon to reflect its harvesting season. This full moon is sometimes called the green corn moon, the grain moon, and the blackberry moon for similar reasons.

When to See the Full Sturgeon Moon

On Thursday, August 15, the full sturgeon moon will be highly visible around sunrise and sunset. The satellite will be 99.9 percent illuminated by the sun when it sets Thursday morning at 5:57 a.m EDT—just nine minutes before dawn. On the West Coast, the setting moon will coincide perfectly with the rising sun at 6:15 a.m. PDT.

If you aren't interested in getting out of bed early to catch the sturgeon moon, wait until Thursday evening to look to the horizon. Twenty-seven minutes after sunset, the full moon will rise on the East Coast at 8:21 p.m. EDT. On the West Coast it rises at 8:10 p.m. PDT, 30 minutes after the sun sets.

The moon generally looks bigger and brighter when it's near the horizon, so twilight and dawn are ideal times to catch the spectacle. But it's worth taking another peek at the sky closer to midnight Thursday night; the Perseid meteor shower is currently active, and though the light of the moon may wash them out, you're most likely to spot a shooting star in the late night and early morning hours.

A Full Harvest Moon Is Coming in September

suerob/iStock via Getty Images
suerob/iStock via Getty Images

The Old Farmer's Almanac lists a special name for every month's full moon, from January's wolf moon to December's cold moon. Even if you're just a casual astronomy fan, you've likely heard the name of September's full moon. The harvest moon is the full moon that falls closest to the fall equinox, and it's associated with festivals celebrating the arrival of autumn. Here's what you need to know before catching the event this year.

What is a harvest moon?

You may have heard that the harvest moon is special because it appears larger and darker in the night sky. This may be true depending on what time of night you look at it, but these features are not unique to the harvest moon.

Throughout the year, the moon rises on average 50 minutes later each night than it did the night before. This window shrinks in the days surrounding the fall equinox. In mid-latitudes, the moon will rise over the horizon only 25 minutes to 30 minutes later night after night. This means the moonrise will occur around sunset several evenings in a row.

So what does this mean for the harvest moon? If you're already watching the sunset and you catch the moonrise at the same time, it will appear bigger than usual thanks to something called the moon illusion. It may also take on an orange-y hue because you're gazing at it through the thick filter of the Earth's atmosphere, which absorbs blue light and projects red light. So if you've only seen the full harvest moon around sunset, you may think it always looks especially big and orange, while in reality, any full moon will look that way when it's just above the horizon.

When to See the Harvest Moon

This year, the harvest moon will be visible the night of Saturday, September 14—about a week before the fall equinox on September 23. The moon will reach its fullest state at 12:33 a.m. ET—but if you're still convinced it's not a true harvest moon without that pumpkin-orange color, you can look for it at moonrise at 7:33 p.m. on September 13.

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