Milky Way Galaxy: All You Need To Know

~6 min
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 is our place in the galaxy, and when is the best time to view the Milky Way.

Contents

What is the Milky Way?

The Milky Way galaxy is a huge collection of dust, gas, and stars, including our Sun. The Earth is located inside this galaxy, so it is often called “our home galaxy” or simply “our galaxy.”

It might be hard to believe, but that starry band across the night sky that we can see from the Earth is actually a huge galaxy that extends billions of kilometers around our planet. How big is it? Let’s find out.

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.

Why is it called the Milky Way?

The name of our home galaxy, like the names of many other astronomy 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 Romans 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, and 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.

In total, the Milky Way has four known arms — two major connected with the bar (Scutum-Centaurus and Perseus) and two minor (Norma and Sagittarius) located between them. Previously scientists thought that all of these arms were major, but with the help of infrared images from NASA's Spitzer Space Telescope, they found otherwise.

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 neighbor 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.

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.

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:

  1. 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.

  2. 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.

  3. 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 the 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.

Here are things you need to know to get the best of the Milky Way and the Galactic Center:

  • The Galactic Center is located in the constellation Sagittarius and like the constellation, it can be visible only from latitudes between +55º and -90º. If you live above +55º latitude, you won't see the Galactic Center! You’ll catch only part of the core, and the best time is before and after summer.
  • 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 located too close to the Sun.
  • From the southern latitudes, the observation conditions are better as the peak of visibility there happens in winter when the nights are longer and darker.
  • At the beginning of its visibility season, the Galactic Center can be seen shortly before sunrise. Over time, it becomes visible for a longer period each night and reaches its peak in June-July. During these months, the core is visible all night long.
  • 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.
  • 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 is vital. A new Moon is ideal, as it doesn’t interfere with observations.
  • 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 advice 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.

Hopefully, in this article, we answered all the major questions about the Milky Way. Don’t hesitate to ask us any questions on social media and share your Milky Way observation experience.

We wish you clear skies and happy observations!

Image Credit:Kota Hamori
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