Is it difficult to map the Milky Way?
By: Christian H. Oslapas
Tags: Milky Way Galaxy, NASA, Astronomy, Space, Hubble Space Telescope

Is it difficult to map the Milky Way?

Written by Christian H. Oslapas on 18 July 2020

The Andromeda Spiral Galaxy (The Galaxy Next Door. Photograph taken by NASA’s Galaxy Evolution Explorer (GALEX). 1

If you live on Earth, then you reside in the Milky Way Galaxy. Since the Milky Way Galaxy is the closest galaxy to Earth, then shouldn’t it be the easiest Galaxy to map, study and photograph? The answer is a resounding, “no”. When we view other galaxies we can examine an entire side of the galaxy. With the Milky Way Galaxy, we have to map it from the inside out.

No top-view photographs of Milky Way

Many people believe that they have seen top-view photographs of the iconic spiral shape in the Milky Way Galaxy. They may even find a picture like the two posted here and explain how they have observed that the galaxy has a spiral shape. The truth is that no one on Earth has seen a top-view picture of the Milky Way Galaxy. This is because that picture doesn’t exist. The farthest that a spacecraft has gone away from Earth is just barely out of our Solar System. That is a distance of just under 14 billion miles away from Earth. This distance may sound impressive but it is a very small span compared to the size of the vast expanse of the Milky Way. To be able to take a top-view picture of the Milky Way Galaxy, a spacecraft would have to leave the galaxy. The Milky Way is about 1,000 light years thick and 200,000 light years in diameter. For reference, one light year is almost 6 trillion miles. The pictures above and below are actually of the Andromeda Galaxy. This galaxy is similar in size to the Milky Way and also has a spiral shape. Although this is not truly the Milky Way Galaxy, the picture below accurately represents how our Solar System is about halfway between the center and the perimeter of the galaxy. 2

A picture commonly used to show where we are located within the Milky Way Galaxy (1997 Jerry Lodriguss). 3

Galactic Address

If you wanted to be specific about where you live, you could include your home address. To be extremely specific you could even include latitude and longitude coordinates. If you asked somebody where they live I doubt they would give you their galactic address. The galactic address for inhabitants on Earth would be: Earth, our Solar System, Orion Arm, the Milky Way Galaxy, Local Group, Virgo Cluster, Virgo Supercluster, and the observable universe.

The Milky Way has four main spiral arms and our Solar System is located in a minor arm named the Orion Arm. The Local Group comprises the Milky Way Galaxy, the Andromeda Galaxy and over 30 other galaxies. The Virgo Supercluster includes the Virgo Cluster that we are in and over 100 other galaxy groups. It is estimated that there are over 10 million superclusters in the observable universe. It is called the observable universe because we have not been able to observe anything outside of it. Some physicists hypothesize that the observable universe is just one of many universes in what is theorized as the multiverse. Just about all the stars that we see with the naked eye from Earth are located within the Milky Way Galaxy. This shows just how vast the observable universe is! 4

Why is it difficult to map the Milky Way?

Astronomers have reported observing through telescopes the spiral shapes of galaxies in the universe since the 1800’s. At that point in time however, these celestial bodies were known as nebulae and it was not realized that the spiral nebulae were actually galaxies with each having over 100 billion stars. The Milky Way Galaxy is relatively flat in shape. Since we are located within the disk, it can be difficult to see past or around other objects within the disc. Imagine that the Earth is a small grain of rice on a large plate of food covered with vegetables, meats and potatoes. From our position on the plate it is difficult to see the other side of the plate because the other food items block our view. When looking at the night sky in a busy city, the unaided human eye is unable to detect the majority of the stars in the Milky Way Galaxy. One of the reasons is because of light pollution. The city lights on Earth overshadow the dim light produced by distant stars. This same light pollution occurs when we try to get a better view of the Milky Way Galaxy. Looking at the night sky you may have seen the familiar band of the Milky Way Galaxy. Although we can see many stars from our position on Earth, light pollution from stars in the Milky Way Galaxy make it very difficult to observe stars on the other side of the Milky Way. There are some techniques that are being used to observe parts of the ‘far side’ of the Milky Way Galaxy. Instead of using telescopes that detect visible light, an array of large radio telescopes are being used to detect wavelengths in the radio spectrum. This technique has successfully observed stars within the Milky Way Galaxy that are about 66,000 light years away. This is a great accomplishment because remember, we are like a small grain of rice on a plate full of light blocking food. 5

If someone in the near future shows you a top-view picture of the Milky Way Galaxy, you can be sure to prove them wrong. There are great photographs of some of the 100 billion galaxies in the universe but there is no picture of the entire Milky Way Galaxy. It is quite difficult to observe the Milky Way Galaxy on Earth because we are within the mostly flat disk of the Milky Way. To best photograph the Milky Way we need to leave the galaxy and no spacecraft has yet left the expanse of the great Milky Way Galaxy. 6

References

1 NASA. (n.d.). NASA Andromeda Galaxy Hi Gloss Poster Fine Art Print. Retrieved July 18, 2020, from https://nhauniverse.com/products/nasa-andromeda-galaxy-space-hi-gloss-poster

2 Young, M. (2020, April 20). Mapping the Milky Way. Retrieved July 18, 2020, from https://skyandtelescope.org/astronomy-news/mapping-the-milky-way/

3 Lodriguss, J. (1997). Andromeda Galaxy. Retrieved July 18, 2020, from https://i.pinimg.com/originals/17/01/4c/17014ca23a7d75f22d4ac9ec00208cd1.jpg

4 Misra, R. (2015, December 16). This Is Why It’s So Hard To Get An Accurate Map Of The Milky Way. Retrieved July 18, 2020, from https://io9.gizmodo.com/this-is-why-its-so-hard-to-get-an-accurate-map-of-the-m-1709283653

5 Billings, L. (2017, October 13). Astronomers Are Finally Mapping the “Dark Side” of the Milky Way. Retrieved July 18, 2020, from https://www.scientificamerican.com/article/astronomers-are-finally-mapping-the-ldquo-dark-side-rdquo-of-the-milky-way/

6 BARTUSIAK, M. (2018). Ch. 11 Our Spiraling Home. In DISPATCHES FROM PLANET 3: Thirty-two (brief) tales on the solar system, the milky way, and beyond. YALE UNIV Press.