We live in an amazing place called the Milky Way galaxy. It’s like a busy neighborhood in space, filled with stars, clouds of gas and dust called nebulae, groups of stars known as clusters, and sometimes even exploding stars called supernovae.
In the early 1900s, astronomers were trying to figure out what the universe was like. They saw faint, fuzzy objects in the sky called “nebulae.” These nebulae came in different shapes—some were round, others were stretched out, and some had spiral arms. Scientists wondered what these nebulae were, how they formed, and whether they were close or far away.
In 1920, a big debate happened about the universe. Harlow Shapley thought the Milky Way was the entire universe, while Heber Curtis believed that the spiral nebulae were separate “island universes.” Both had good points, but neither had solid proof. Shapley misunderstood how a spiral nebula rotated, and Curtis didn’t realize how far away galaxies really were.
A few years later, Edwin Hubble and Milton Humason made a huge discovery. They used the biggest telescope of their time to look at the Andromeda galaxy (M31). They found special stars called Cepheid variables, which helped them measure the distance to Andromeda—about 900,000 light-years away. This showed that Andromeda was a separate galaxy, changing how we see the universe.
Over the last 100 years, we’ve learned that galaxies are huge groups of stars, gas, and dust. They can be tens of thousands to hundreds of thousands of light-years wide. Galaxies come in four main types:
Spiral galaxies, like our Milky Way, have flat, spinning disks of stars, gas, and dust, with a central bulge of older stars. They often have spiral arms that can look different depending on how we see them.
Elliptical galaxies can be almost round or stretched out. They don’t have the structure of spiral galaxies and mostly contain older stars, with little gas and dust. Scientists think they might form when galaxies crash into each other.
Peculiar galaxies have strange shapes, often because they’ve collided with other galaxies. These crashes can create odd structures, like ring galaxies, where a smaller galaxy’s gravity affects a bigger one.
Irregular galaxies have chaotic shapes and don’t have a clear structure. They might be the result of collisions or just too small to form a recognizable shape. Many galaxies, including the Milky Way, have smaller companion galaxies, like the Large and Small Magellanic Clouds.
Galactic collisions are dramatic events that can change galaxies over millions of years. Even though galaxies move fast, the stars inside them are so far apart that they rarely crash into each other. However, gas clouds do collide, leading to new stars being born. Bigger galaxies can also swallow smaller ones, a process called galactic cannibalism. Our Milky Way is currently absorbing several smaller galaxies.
The universe is much bigger than we once thought. Every discovery in astronomy reminds us of our small place in the cosmos. As we keep exploring and learning about the universe, we see its vastness and complexity. Today, we know that the Milky Way is just one of many galaxies, each with billions of stars and different structures. Studying galaxies not only helps us understand the universe better but also makes us appreciate the incredible nature of our cosmic home.
Use craft materials to create a model of one of the four types of galaxies: spiral, elliptical, peculiar, or irregular. Think about the characteristics of each type and try to represent them in your model. Present your galaxy to the class and explain its features.
Reenact the Great Debate of 1920. Split into two groups, with one side representing Harlow Shapley and the other Heber Curtis. Research their arguments and present your case to the class. Discuss how Edwin Hubble’s discoveries later resolved the debate.
Learn how astronomers use Cepheid variable stars to measure distances in space. Use a simple formula to calculate the distance to a hypothetical galaxy based on the period of a Cepheid variable. Discuss how this method helped Edwin Hubble in his discoveries.
Use a computer simulation or an interactive online tool to explore what happens during a galactic collision. Observe how galaxies interact and change over time. Write a short report on your observations and what you learned about galactic cannibalism.
Examine images of different galaxies and classify them into one of the four main types: spiral, elliptical, peculiar, or irregular. Share your classifications with the class and discuss any challenges you faced in identifying the galaxy types.
Galaxy – A massive system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. – The Milky Way is the galaxy that contains our solar system.
Stars – Luminous celestial bodies made of plasma, held together by gravity, and generating light and heat through nuclear fusion. – The Sun is the closest star to Earth and is essential for life on our planet.
Nebulae – Clouds of gas and dust in space, often serving as the birthplace of stars. – The Orion Nebula is a well-known region where new stars are forming.
Universe – The totality of all space, time, matter, and energy that exists. – Scientists use telescopes to explore the vast universe and learn more about its origins.
Spiral – A type of galaxy characterized by a flat, rotating disk with a central bulge and spiral arms. – The Andromeda Galaxy is a spiral galaxy that is on a collision course with the Milky Way.
Elliptical – A type of galaxy with an ellipsoidal shape and a smooth, nearly featureless brightness profile. – Elliptical galaxies are often composed of older, red stars and have little gas or dust.
Peculiar – Referring to galaxies that do not fit into the regular categories of spiral or elliptical, often due to unusual features or interactions. – Peculiar galaxies may have distorted shapes due to gravitational interactions with other galaxies.
Irregular – Galaxies that lack a distinct shape or structure, often chaotic in appearance. – The Large Magellanic Cloud is an example of an irregular galaxy visible from the Southern Hemisphere.
Collisions – Events where two or more galaxies come into contact and interact gravitationally, often leading to mergers or new star formation. – Galaxy collisions can trigger bursts of star formation as gas clouds are compressed.
Astronomy – The scientific study of celestial objects, space, and the universe as a whole. – Astronomy helps us understand the origins and evolution of stars, planets, and galaxies.
