2. Galaxies
2. Galaxies
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Explain the unique characteristics of the milky way galaxy and locate the position of solar system in our galaxy
Explain the unique characteristics of the milky way galaxy and locate the position of solar system in our galaxy
Space is a system of moving and interacting objects. Scientists explore these systems and their parts to understand their composition and functioning.
For example, our solar system comprises the Sun, Earth, and other planets. This solar system is just one element of the Milky Way galaxy. The Milky Way galaxy, in turn, is merely one of countless galaxies within the immense universe. The universe encompasses everything in space, including various types of matter and energy1.
Fig. 2.1 Our Place in the Universe
Watch this video to see the universe size comparison:2
Vid. 2.1 Universe Comparison
Galaxies are cosmic communities that are part of the universe. They are made up of stars, planets, and enormous clouds of gas and dust. All held together by a cosmic glue called gravity1.
Some galaxies are gigantic, with trillions of stars and stretching over a million light-years from one end to the other. Others are more like small towns in the universe, with only a few thousand stars and spanning just a few hundred light-years. A light-year is about 6 trillion miles (9 trillion km).
Galaxies come in different shapes; some look like swirling spirals, some are round and smooth like ellipses, and there are also galaxies with random, irregular shapes2. Let's take a look at a few3:
The Milky Way, where our solar system is, is a type of galaxy called a spiral galaxy. Spiral galaxies are shaped like giant spinning pinwheels.
They have a flattened, bulging central disk of stars and spiral arms.
Elliptical galaxies can be shaped like perfect circles or stretched out like ovals. Elliptical galaxies are actually the most common type of galaxy in the universe. However spiral galaxies are more commonly seen due to their brightness and star formation.
Irregular galaxies have unusual shapes, such as rings, toothpicks, or small clusters of stars.
Fig. 2.5 A collection of Galaxies as seen through Hubble
The Milky Way is an enormous, swirling collection of stars, dust, and gas—like a giant pinwheel spinning in space! That’s why it’s called a spiral galaxy.
Our Sun lives on one of its long, curving arms, about 25,000 light-years from the centrre. The Sun is located in a smaller branch of the Milky Way Galaxy called the Orion Spur. This spur lies between two of the galaxy’s bigger arms—one is the Sagittarius Arm, and the other is the Perseus Arm.6
Fig. 2.6 Our location in the Milky Way Galaxy
Fig. 2.7 Our Milky Way
If we could look at our galaxy from the side, it would appear like a giant, flat disk with a bulge in the middle. This flattened shape is due to the galaxy constantly spinning. Luckily, gravity holds everything—stars, planets, and gas—together, so they don’t go flying off into space!
Fig. 2.8 Milky way from the side
It is called the Milky Way because it appears to Earth-based observers as a faint, milky strip of light arcing across the entire sky.4
On a clear, moonless night, far from the glow of city lights, the Milky Way can look like a celestial cloud stretched across the universe. If you were to aim even a modest telescope anywhere along its expanse, you'd be treated to a magnificent view. What might seem like a cloudy haze to the naked eye transforms into an abundance of stars. Unfortunately, their great distances and the fact that they are packed closely together prevent us from distinguishing them individually with just our eyes5.
Fig. 2.10 Our Milky Way as seen from Earth
The Milky Way is surrounded by more than 50 other galaxies.
Glossary
cosmic: the part of space that lies outside Earth and its atmosphere
ellipses: the geometrical figure that planets and other heavenly bodies create as they revolve around our sun
light-year: the distance that light travels in one year; it’s really, really far!
celestial: something related to the sky or space
Summary
Galaxies are massive systems of stars, planets, gas, and dust, held together by gravity.
They come in various sizes and shapes:
Spiral (e.g., Milky Way)
Elliptical
Irregular
The Milky Way is a spiral galaxy where our solar system is located.
Our Sun lies in the Orion Spur, between the Sagittarius and Perseus arms.
The Milky Way appears as a milky band across the night sky due to the dense collection of stars.
It is so vast that even at the speed of light, reaching the center would take 25,000 years.
The galaxy’s shape—a flat disk with a central bulge—is caused by its continuous spinning.
The name "Milky Way" and its cultural interpretations reflect how people worldwide have observed and imagined our galaxy.
References
Extensions
Read this to find answers to some interesting space questions: link
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