Milky Way


For thousands of years, people of all different cultures around the world have gazed up at the skies and watched the beauty of our Milky Way galaxy. Our solar system, including our sun and all of the planets and objects within it, is just a small part of the Milky Way galaxy. All of the stars that we see in the night sky are part of our galaxy, and when you think of the number of them, it’s almost overwhelming.

Milky Way

A galaxy is a huge group of gas, stars, dust, and rocks that are held together through gravity. Galaxies come in a lot of shapes and sizes, and our Milky Way is called a large barred spiral galaxy. If you look up at night, you can see the milky band of light that crosses the sky.

While ancient astronomers could only make educated guesses about our galaxy, the astronomer of today use high technology telescopes combined with the information gathered from the interstellar spacecraft and probes. In the past, astronomers thought that the Milky Way had four major “arms” that stretched out around the galaxy, however, we now know that there are only two major arms that are at the ends of the stars in the central bar area, and two minor arms. They have given names to these two major arms of: Scutum-Centaurus and Perseus. The two minor arms are called Norma and Sagittarius.

Milky Way Galaxy Statistics:

  • Galaxy Type: Barred Spiral
  • Age: 13.6 billion years
  • Diameter: 100,000-180,000 light-years
  • Mass: 800-1,500 M☉
  • Constellation: Sagittarius
  • Group: Local Group
  • Number of Stars: 100-400 billion
  • Distance to Galactic Center: 27,000 light-years

Scientists have had a major challenge in attempting to count the stars in the Milky Way galaxy. The problem is that Earth and our solar system is located on one of the outer “arms” and we can’t get a really good view. We are 25,000 light-years from the galaxy center and the best estimate that they can come up with is around 100 billion stars. The stars are part of a large disk that has a diameter of 100,000 light-years.

The Milky Way arching at a high inclination across the night sky.


The first astronomer to recognize that the band of light that was viewed in the celestial sky was actually stars was in Galileo Galilei in 1610. The telescope that he used then was very simple. From that time until the early 1920s, a majority of astronomers assumed that the Milky Way made up all of the stars in the universe.


Astronomers have used telescopes as well as mathematic calculations to analyze the Milky Way galaxy. One of the clues about the shape of the galaxy happens when astronomers map the bright young stars along with the ionized hydrogen that’s in the disk of the Milky Way. They call these clouds the “HII regions” and they are caused by the ionization of the hot, new stars that have little or no protons and electrons.

Astronomers noted that this situation occurs in the arms of other spiral galaxies and helped to confirm the shape of our own Milky Way. Astronomers also measure the dominant colors and the quantity of dust in our galaxy to match them with other galaxies.

They have noted that the major arms of our galaxy seem to contain the most old and young stars and the minor arms seemed to be filled with the kind of gas and dust that is needed to make new stars. Our sun exists in a smaller, partial arm that is called the “Orion Arm or Orion Spur.” It, along with our solar system is positioned between the Perseus and Sagittarius arms.

The Milky Way

The study of our Milky Way galaxy has allowed scientists to understand that the universe contains billions of other galaxies. However, other than our own Milky Way, there are only three other galaxies that we can see as fuzzy images without a telescope. When in Earth’s southern hemisphere, astronomers can see the Small and Large Magellanic Clouds which are considered to be satellite galaxies of the Milky Way.

Both of these are around 160,000 light-years away. The Andromeda galaxy is a bigger galaxy that can be viewed from the northern hemisphere of Earth, and it’s around 2.5 million light-years away. Andromeda is moving closer to our Milky Way galaxy and it’s thought that it will collide with us in around 4 billion years. To give you an idea of distance, it takes the light from our neighbor galaxies around 2.5 million years to get to Earth.

Interesting Information:

  • Astronomers have to use calculations to configure the number of stars in the Milky Way galaxy. This is a very sophisticated process because they have to calculate the galaxy mass and then the part of that mass that consists of the stars. The next step is to decide on an average star’s mass to figure out the total number of stars. It isn’t easy because we know that stars, including our sun, come in a variety of sizes. Scientists have used a number of different models to estimate the number of stars in our galaxy, including computer models. Although they are unsure of the exact number they believe that on the high end estimate there is 400 billion stars and 100 billion stars on a low end estimate.
  • Scientists have to configure the speed of galaxies based on respect to the Cosmic Wave Background Radiation. Our Milky Way galaxy is speeding through space at around 343 mi/552 km per second.
  • We have a supermassive black hole at the central core of the Milky Way galaxy that is named Sagittarius A*. They believe the central core area has around 4.3 million suns.
  • Not that long after the Big Bang, the Milky Way galaxy started to form from a series of dense regions. It’s believed that globular clusters that exist today was the area where the first stars began. These are considered to be some of the oldest stars within the Milky Way.
  • The Milky Way of the past isn’t the one that we have today. Over time, it has collided and merged with other galaxies.
  • The Milky Way galaxy’s gas, stars, and dust orbit around the center of the galaxy at around 220 km per second.
  • The Milky Way is currently growing by getting stars from a little galaxy that’s really close to us called the Sagittarius Dwarf Spheroidal and some of the Magellanic Clouds’ material.

Exploration and Study:

The amount of time that it takes for a spacecraft to leave our solar system and enter the outer areas is far too long. There have been only five robotic spacecraft that have speed fast enough to travel into interstellar space and so far, only NASA’s Voyager 1 has actually gone across that boundary in 2012. Voyager 2 will be transitioning next. NASA’s New Horizons spacecraft did a flyby of Pluto in 2015 and is exploring beyond Neptune to the Kuiper Belt where it will eventually exit the solar system. NASA’s Pioneer 10 and 11 spacecraft are both inactive but will also leave the solar system.

To get answers to our questions at a faster rate we need to use technology. The James Webb Space Telescope has given scientists the ability to collect information on a number of star types that existed far back in the early galaxy development. Observations using spectroscopy has allowed astronomers to research hundreds of thousands of galaxies and get answers to their formation and watch how they changed.

Facts about Milky Way Galaxy for Kids:

  • Our Milky Way is warped! Scientists have been studying the central bulge of our galaxy and has noted that the warped shape may be due to two of our galactic neighbors. The Small and Large Magellanic clouds are two dwarf galaxies that are part of our Local Group. They believe that they are orbiting around the Milky Way in a kind of tug-of-war game that is pulling our galaxy’s dark matter. This constant pulling changes the frequency of the hydrogen gas in our galaxy.
  • The Milky Way has a halo! Astronomers think that there is a mysterious halo around our galaxy that is due to dark matter. Around 90% of the mass of the Milky Way is dark matter that we can’t see. All of the matter that we can see is called “luminous matter” and that makes up 10% of the mass of the galaxy. The halo isn’t visible but scientists have demonstrated that it exists when they create simulations without the mass that is invisible combined with the speed of the stars in the galaxy’s center disk orbit.
  • The Milky Way is average in size. Galaxies range in size with the number of stars. The smaller dwarf galaxies have around 10 billion stars and the larger galaxies can have as many as a trillion stars. It’s estimated that the Milky Way has between 100-400 billion stars. The number is constantly changing as we gain new stars and then lose others through supernovae.
  • The most stars that you can see from anywhere in the world in the night sky is around 2,500.
  • New stars a being produced in the Milky Way galaxy at a rate of around 7 per year.
  • Our galaxy is filled with so much dust and gas that it makes up around 10-15% of the visible or luminous mass. Astronomers us infrared telescopes to detect the dust and gas.
  • Galaxies change their size and volume by colliding with other galaxies as well as consuming the smaller ones. The Milky Way has altered its size by doing the same thing and is currently adding new stars from the close by Canis Major Dwarf galaxy.
  • Earth is located inside the galactic disk which is around 26,000 light-years from the galactic center. We can’t take a picture of the Milky from above due to where we live. This means that all of the pictures that you have seen of the full Milky Way are really just guesses done by really good artists.
  • The Milky Way is almost as old as the universe! Astronomers place the age of the universe at around 13.7 billion years and the Milky Way at 13.6 billion years. This means that the Milky Way came about fairly close to right after the Big Bang. The oldest stars that we have are in globular clusters, but some areas of the Milky Way, such as the disk and bulge didn’t form until nearing 10-12 billion years ago.
  • Our Milky Way is part of a bigger group that includes 50 other galaxies in the Local Group. This may sound like a lot but as we expand out we find that the Local Group is part of an every bigger group known as the Virgo Supercluster. The superclusters are galaxy groups on a huge scale that have diameters that are thousands of light-years. There are lots of open spaces in between the superclusters. There are around 100 galaxy groups in the Virgo Supercluster and are located in a 110 million light-year diameter.
  • A study in 2014 indicated that the Virgo Supercluster is just one lobe of an even bigger supercluster centered on the Great Attractor called Laniakea.
  • Everything in the universe is moving, including the Milky Way galaxy! It’s almost mind boggling to think about the idea that our Earth is rotating around the sun, the sun is moving in the Milky Way galaxy, the Milky Way is part of the Local Group that is moving relative to the CMB (Cosmic Microwave Background) which is leftover radiation from the Big Band. Our Local Group is moving at around at 600 km/s or 2.2 million km/h. These are speeds that human beings can’t even imagine, especially because we don’t feel like we are moving as we just stand on the Earth.