he Milky Way is our home galaxy which consists of countless other stars and planets. All the stars and planets, including Earth, are bound together by gravitational forces which is what creates the swirling spiral we see in pictures.
Our solar system, of which our Sun is at the heart, is situated within the Milky Way.
From what we have discovered so far about the seemingly endless number of entities in space, including our solar system and the Milky Way galaxy, is that everything is constantly travelling at enormous speeds through space.
You may already be aware that our Sun is moving but, on an even bigger scale, the Milky Way is also in motion, along with literally everything else that makes up the Universe, including gas clouds, black holes, stars, planets and dark matter.
It is thought that the Milky Way galaxy is moving through space as fast as 2.2 million kilometers per hour! Speed in space is measured using Cosmic Microwave Background (CMB). This is the remaining radiation from the Big Bang.
The Milky Way moves as part of the ‘Local Group’. This is a large group made up of over 50 other galaxies of which the Milky Way is one of the biggest.
As it moves, it travels in the direction of the Virgo and Leo constellations, also where the Great Attractor is situated.
Not only is the Sun moving around the Milky Way, the Milky Way is moving around the Local Group. The Local Group is part of an even larger group called the Virgo Supercluster in which the Local Group is also in motion.
Does the Milky Way rotate?
We know the Milky Way is moving through space at incredible speeds but, is it also rotating?
Before we understand how the Milky Way might rotate, first we must understand the difference between rotate and revolve (or orbit). What the average person understands is that things in space typically orbit other things.
For example, we know the Earth orbits the Sun in the same way the Sun orbits the center of the Milky Way galaxy.
Rotate, in this context, means to spin on an axis. It is common knowledge that the Earth rotates on its axis every 24 hours. Beyond this, though, it gets a little more complicated.
To understand how the Milky Way might rotate, we need to understand how the Sun rotates. The Sun rotates differently to Earth. While it does rotate, it does so not just in a single rate across its surface.
So, whereas the entire Earth rotates on its axis once every 24 hours, the Sun rotates once every 31 days at its poles and once every 27 days at its equator, thereby rotating at two separate rates.
The Milky Way galaxy also rotates. But, similarly to the Sun, the Milky Way galaxy is rotating at different rates from the center outwards.
For example, at its center, the galaxy rotates around every 225-250 million years. This is the time taken for the Sun to orbit the center of the Milky Way.
Many people question whether the Milky Way galaxy is rotating in a clockwise or anti-clockwise direction. This actually depends on the angle from which you are looking at it.
This is because there is no up or down in space. So, the Milky Way rotates in the direction in which its four spiral arms trail the rotation movement.
The names of the four spiral arms are Norma and Cygnus, Scutum-Centaurus, Sagittarius and Perseus. The arms are split into major and minor categories.
The major arms are Scutum-Centaurus and Perseus, and the minor arms are the Norma and Cygnus, and Sagittarius - these are situated between the major arms.
The Sun is situated in a minor arm, within a spur called the Orion Spur. The Orion Spur is a major Milky Way structure and crosses the Perseus arm.
The rotation of these spiral arms is what gives the Milky Way its spiral look in pictures. The spiral is created by the rotation of matter around the center of the galactic disk.
The spiral arms are also known as density waves or standing waves. The stars within them revolve faster in the center than those further out which means the stars do not remain within the spiral arms and rotate around the galaxy’s center.
Does the Milky Way orbit anything?
From what we know about how objects orbit in space, everything in the universe is orbiting both itself and something else.
Our Moon orbits the Earth as well as itself, the Earth orbits itself and our Sun, and the Sun revolves around itself and the supermassive black hole located in the center of the Milky Way galaxy.
The Milky Way galaxy orbits in the same way. It revolves around both itself and another object. What the Milky Way orbits is called the Andromeda galaxy, which is our neighboring galaxy. The Andromeda galaxy is also orbiting itself.
Moreover, the Milky Way is just one galaxy of a collection of over 50 galaxies also known as the ‘Local Group’. Within this group, the Milky Way is one of the biggest galaxies, considered to consist of around a trillion solar masses.
The other biggest galaxy is the Andromeda galaxy. Andromeda has between 700 billion and a trillion solar masses. The rest of the Local Group is made up of small galaxies such as ‘Magellanic Clouds’.
These will also be orbiting the Local Group and bow to the gravitational force of the Milky Way or the Andromeda galaxy.
The Local group relents to the gravitational pull of the ‘Virgo Supercluster’. So, the Milky Way, as part of the Local Group is moving within the Virgo Supercluster.
On an even greater scale, the Virgo Supercluster moves within a larger group made up of 100,000 galaxies. This is called the ‘Laniakea Supercluster’.
The other large galaxy involved is Andromeda, our closest galactic neighbor; our galaxy and Andromeda are slowly orbiting each other.