Our Galaxy and the Classification of Galaxies
On a dark night the Milky Way arches overhead, our home galaxy among hundreds of billions. Explore its barred-spiral shape, the Local Group it belongs to, how astronomers sort galaxies on the Hubble tuning fork, and the fierce energy of active galaxies.
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Our place in the cosmos 🌌
On a dark night the **Milky Way** arches across the sky, a faint band of countless stars. It is our home **galaxy**, just one of hundreds of billions in the universe. This module explores the shape of the Milky Way, the family of galaxies it belongs to, how astronomers **classify** galaxies, and the fierce energy of **active** galaxies.
The language of galaxies 🔑
Four ideas run through this module:
Inside the Milky Way 🌀
Our galaxy, the **Milky Way**, is a **barred spiral**: winding arms sweep out from a central **bar** of stars. The **Sun** lies about **two thirds** of the way out, in one of the spiral arms. The disc holds **dust**, glowing star-forming nebulae, and ancient **globular clusters** in the surrounding halo. Because dust blocks visible light, astronomers map the galaxy structure and rotation using **21 cm radio waves** from hydrogen gas.
What shape is our galaxy? 🎯
In the Hubble classification, what type of galaxy is the Milky Way?
- A barred spiral galaxy
- An elliptical galaxy
- An irregular galaxy
- A single giant star
Sorting galaxies: the tuning fork ⚖️
Edwin Hubble sorted galaxies by their shape on a tuning fork diagram. The main types are spirals and ellipticals, with irregulars off to one side.
Match each galaxy type 🔗
- Spiral galaxy
- Barred spiral
- Elliptical galaxy
- Irregular galaxy
- Winding arms of stars sweeping from a central bulge
- Arms that begin from a straight central bar of stars
- A smooth ball of mostly old stars, with little gas
- A galaxy with no regular or symmetrical shape
The Local Group ✅
The Milky Way belongs to a small cluster called the Local Group. Select the TWO galaxies that are also members.
- Andromeda, also called M31
- The Magellanic Clouds
- A quasar in the distant universe
- The Sun
Galaxies in words 🧩
Our galaxy, the _____ Way, is a barred spiral. It belongs to a small cluster of galaxies called the _____ Group, whose largest member is _____. Astronomers map the Milky Way using 21 cm _____ waves that pass through the dust. Some galaxies have a bright active centre powered by a super-massive black _____.
Active galaxies 🕳️
Some galaxies pour out enormous energy from a tiny central region called an **Active Galactic Nucleus**, or **AGN**. It is powered by a **super-massive black hole** pulling in the matter around it. Seen from different angles, active galaxies appear as **Seyfert galaxies**, **quasars** or **blazars**. Because an AGN shines across many wavelengths, astronomers study it with **multi-wavelength** observations, from radio waves to X-rays.
What powers an AGN? 💫
What is thought to power the Active Galactic Nucleus of an active galaxy?
- A super-massive black hole pulling in matter
- A single very bright star
- A large nearby planet
- A star like our Sun at the centre
From small to vast 🪜
An interactive activity.
Spot the true statements 🖍️
An interactive activity.
Classify the galaxy 🧭
An interactive activity.
Our place in the Galaxy ✍️
An interactive activity.