Milky Way Galaxy: All You Need To Know
In this article, we gathered answers to the most popular questions about the Milky Way. Keep reading, and you’ll learn what it is, where we are located in the Milky Way, and when the best time to view the galaxy is. The free Sky Tonight app will help you navigate through the Milky Way.
Contents
- What is the Milky Way?
- Quick facts
- The size of the Milky Way
- Why is it called the Milky Way?
- What type of galaxy is the Milky Way?
- Where is the Earth in the Milky Way?
- What is at the center of the Milky Way?
- How do we know what the Milky way looks like?
- How to see the Milky Way?
- Bottom line: Milky Way galaxy
What is the Milky Way?
The Milky Way is a large spiral-shaped system of roughly 400 billion stars, including our Sun, bound together by gravity. The space between stars is mostly filled with dust and gas, and in the very heart of this system lies a supermassive black hole. This system is called a “galaxy”.
Quick facts
- Age: 13.6 billion years
- Type: Barred spiral galaxy
- Size: 105,700 light-years across
- Mass: 1.5 trillion solar masses
- Number of stars: 100 to 400 billion
The size of the Milky Way
The Milky Way is the second-largest galaxy in the Local Group of galaxies; the first place goes to Andromeda. The Milky Way is 105,700 light-years wide while the Andromeda Galaxy is 220,000 light-years in width. By the way, the Local Group — a group of multiple galaxies including the Milky Way — extends for roughly 10 million light-years around us in space.
Just like Earth is orbiting the Sun, our Solar System orbits the center of the Milky Way. This galaxy is so enormously large that our Solar System takes about 250 million years to complete a single revolution! In astronomy, it’s called a galactic year.
Since its formation, the Sun has completed only 20 orbits. One galactic year ago, dinosaurs on Earth were just emerging, and mammals were yet to evolve.
Why is it called the Milky Way?
The name of our home galaxy, like the names of many other astronomical objects, came from the ancient Greek and Roman cultures. Both the Greeks and Romans saw the starry band as the river of milk. The Greeks believed that it was milk from the goddess Hera who spilled it across the sky, and the Roman myth said that the Milky Way was milk from their goddess Ops.
Other cultures had their own myths and beliefs regarding the starry band of light in the night sky. People in eastern Asia called it the Silvery River of Heaven; the Finns and Estonians believed it was the Pathway of the Birds; in Southern Africa, it’s called the Backbone of Night.
What type of galaxy is the Milky Way?
There are four main types of galaxies:
- spiral
- elliptical
- peculiar
- irregular.
The spiral-shaped Milky Way belongs to the first type; if you could see it from the top (or the bottom), it would look like a spinning pinwheel.
To be more specific, the Milky Way is a barred spiral galaxy, which means it has a central bar-shaped straight structure composed of stars. This bar contains the galaxy’s nucleus in the center and has two spiral arms attached to its ends. If the Milky Way was a normal spiral galaxy, its arms would lead right to its center (or nucleus) like in the Andromeda Galaxy.
Where is the Earth in the Milky Way?
Speaking about our location inside the Milky Way, we’re far away from its center, which is good news (unless you’ve always wanted to be a neighbor to a huge black hole). Our Sun is located nearly 27,000 light-years from the Milky Way’s nucleus, or about halfway between its center and the edge.
Our Solar System is placed between two main arms — Scutum-Centaurus and Perseus, within the small partial arm named the Orion Arm or Orion Spur. This arm is about 3,500 light-years wide and more than 20,000 light-years long. It got its name after the constellation Orion. Our location inside it is the reason why we see so many bright objects within the constellation Orion — we’re simply looking at our local spiral arm.
Want to know where we are in the observable Universe? Check out this infographic — and discover our cosmic address while you're at it!
What is at the center of the Milky Way?
The center region of the Milky Way is called the Galactic Center, and it contains a supermassive black hole of about 4 million solar masses called Sagittarius A*. To see the black hole, you’ll need a special radio telescope.
However, you can find its location in the sky using the Sky Tonight app. Just type “Milky Way Center” in the search bar and tap the target icon next to the result to see where it is.
A casual observer can view the Galactic Center, which is very bright despite its enormous distance from the Earth (27,000 light-years). However, its brightness is easy to explain — there are around 10 million stars within one parsec of the Galactic Center.
How do we know what the Milky way looks like?
From our position inside the Milky Way, it’s quite hard to figure out its shape. We don’t have pictures of our galaxy from the side as we can’t actually leave it for now. However, we have several clues that helped to figure out what it looks like:
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Astronomers observe the other galaxies and compare them with the behavior of the one we live in. For example, when they measured the velocities of stars and gas in the Milky Way, they saw that an overall rotational motion differs from random motions. This is a characteristic of a spiral galaxy.
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As the Milky Way appears to us as the long stripe across the sky, it means its shape is more likely a disk we see edge-on. We also can find the bulge at the center, and from observing the other galaxies, we know that the spiral ones are disks with central bulges.
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The gas fraction, color, and dust content of our Milky Way are like in the other spiral galaxies.
How to see the Milky Way?
The good news is the Milky Way is visible all year round, no matter where you are on Earth.
However, as our planet rotates, the galaxy also moves across the sky, and so does its core — the Galactic Center, the brightest and most spectacular part.
And sometimes, the core disappears from our view.
Where is the Galactic Center visible?
The Galactic Center is located in the constellation Sagittarius, and like the constellation, it can be visible only from latitudes between 55ºN and 90ºS. If you live above 55ºN latitude, you won't see the entire Galactic Center. You’ll catch only part of the core, and the best time is before and after summer.
When is the Galactic Center visible?
From the Northern Hemisphere, the Galactic Center is visible from March to October. From the Southern Hemisphere, the core is visible from February to October.
The Milky Way’s core isn’t visible for the rest of the months around the world because, during this time, it’s above the horizon only during daylight hours.
At the beginning of its visibility season, the Galactic Center can be seen shortly before sunrise. Over time, it becomes visible for longer periods each night, and in June-July the core is visible all night long from both hemispheres. By the end of the visibility season in October the Galactic Center is visible in the evening. It rises earlier each night, until it disappears in the sunlight.
Interesting fact: From the southern latitudes, the viewing conditions of the Milky Way are better. There, the Milky Way all night long in winter months when the nights are longer and darker.
What do I need to see the Galactic Center?
You need a truly dark place free of light pollution. These tools will help you to find such a place: NASA's Blue Marble, International Dark Sky locations, Dark Site Finder. Or find the closest observatory — they’re always located in dark sites.
Want to check how light-polluted the sky in your city is? Go to our infographic and discover how light pollution affects what you see!
Also, the skies should be cloudless and clear. You can use an astronomy app with a stargazing forecast that indicates observational conditions. For example, Sky Tonight — it’s free and works without an internet connection.
The Moon phase matters! A New Moon is ideal because the moonlight won’t interfere with your observations. To check the Moon phase for any date, use the Sky Tonight app or visit the Moon Calendar on our website.
If you plan to photograph the Milky Way and its core, use tools to visualize the galaxy’s position in the sky over time. Our recommendation is the Ephemeris app, which predicts Milky Way visibility, its core’s exact position, and more. Ephemeris also helps to quickly find and check the detailed information about the Sun, the Moon, and the Milky Way for any date, time, and place.
F.A.Q.
How many stars are in the Milky Way?
It’s difficult to give an exact number, but there are at least 100 billion stars in the Milky Way. Scientists’ current estimate is between 100 to 400 billion stars.
How many planets are in the Milky Way?
Scientists consider that there are at least 100 billion planets in the Milky Way, and more than 10 billion of them are terrestrial.
How many Solar Systems are in the Milky Way?
Well, there is only one Solar System in our galaxy, as only ours is officially called so. But astronomers have found more than 3,200 other stars with planets orbiting them in the Milky Way.
How many constellations are in the Milky Way?
As seen from the Earth, the Milky Way occupies the sky area that includes 30 constellations. The brightest part of our galaxy, the Galactic Center, lies in the constellation Sagittarius.
Is the Milky Way unique?
The Milky Way is just one of billions of galaxies in the Universe — a fact first proven by Edwin Hubble in the 20th century. But while it shares a general shape and structure with many spiral galaxies, recent studies suggest its chemical composition is quite rare. This means the Milky Way may have followed a different evolutionary path compared to similar galaxies.
And of course, for us, the Milky Way is truly one of a kind — it’s our home in the vast space.
Is the Milky Way different in the Southern Hemisphere?
Yes, your view of the Milky Way changes depending on your location. The core of the Milky Way aligns roughly with the constellation Sagittarius, which is located at a declination of about 30°S. This means that for people living around 30° south latitude, the Milky Way’s core appears almost directly overhead — offering a spectacular view filled with bright stars and constellations rich in stunning deep-sky objects.
When is the Milky Way season?
While the Milky Way itself is visible throughout the year, its Galactic Center — the brightest and most spectacular part — is not. The term Milky Way season refers to the time of year when this central region becomes visible in the night sky, offering the most breathtaking views of our galaxy.
In the Northern Hemisphere, the Milky Way season is from March to October. In the Southern Hemisphere, it lasts from February to October. The Galactic Center is visible all night long in June and July from both hemispheres.
Bottom line: Milky Way galaxy
The Milky Way is a massive barred spiral galaxy containing up to 400 billion stars and spanning about 105,700 light-years across. Our Solar System resides inside this galaxy, about 27,000 light-years from its center, safely distant from the supermassive black hole Sagittarius A* at the galaxy’s core. Although the Milky Way is visible year-round, its spectacular core is visible between March and October — to see it, you’ll need dark locations with minimal light pollution. To easily explore and locate the objects of the Milky Way in the night sky, use the free Sky Tonight app.
We wish you clear skies and happy observations!
