Questions and Answers
How does the diameter of the disk of the Milky Way Galaxy compare to its thickness?
The diameter is about 100 times as great as the thickness.
What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way Galaxy?
the galaxy's bulge
The Sun's location in the Milky Way Galaxy is _________.
in the galactic disk, roughly halfway between the center and the outer edge of the disk
What do we mean by the interstellar medium?
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What are the Magellanic Clouds?
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How do disk stars orbit the center of the galaxy?
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How do we know the total mass of the Milky Way Galaxy that is contained within the Sun's orbital path?
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Elements heavier than hydrogen and helium constitute about _________ of the mass of the Milky Way's interstellar medium.
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What do we mean by the star-gas-star cycle?
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What are cosmic rays?
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The primary way that we observe the atomic hydrogen that makes up most of the interstellar gas in the Milky Way is with _________.
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Which of the following molecules is the most abundant in molecular clouds?
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Interstellar dust consists mostly of _________.
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Which of the following models best explains why our galaxy has spiral arms?
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What do we mean by a protogalactic cloud?
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Study Notes
Milky Way Galaxy Overview
- The diameter of the Milky Way Galaxy is approximately 100,000 light-years, with a thickness of about 1,000 light-years, making the disk appear thin.
Central Bulge
- The bright, spherical region of stars in the center of the Milky Way is known as the galaxy's bulge, visible to the naked eye, especially in the direction of Sagittarius.
Sun's Location
- The Sun is positioned in the galactic disk, about 27,000 light-years from the center, which is slightly over half the disk's radius of 50,000 light-years.
Interstellar Medium
- The interstellar medium refers to the gas and dust that exists between stars in the Milky Way, filling the spaces in the galaxy.
Magellanic Clouds
- Two small galaxies that orbit the Milky Way are called the Large Magellanic Cloud and the Small Magellanic Cloud.
Star Orbits
- Disk stars in the Milky Way orbit in a common plane and direction, exhibiting a bobbing motion that maintains their positions within the disk.
Mass Calculation
- The total mass of the Milky Way within the Sun's orbital path can be determined using Newton's version of Kepler's third law or the orbital velocity formula.
Chemical Composition of Interstellar Medium
- Elements heavier than hydrogen and helium account for about 2% of the mass of the Milky Way's interstellar medium, with hydrogen making up around 70% and helium about 28%.
Star-Gas-Star Cycle
- This cycle describes the continuous recycling of gas between stars and the interstellar medium, crucial for incorporating elements produced by earlier stars into new star systems.
Cosmic Rays
- Cosmic rays are subatomic particles traveling near the speed of light, likely generated by supernovae, although their exact origin remains unclear.
Observing Atomic Hydrogen
- Atomic hydrogen in the interstellar gas is primarily observed using radio telescopes that detect a wavelength of 21 centimeters.
Molecular Clouds
- The most abundant molecule in molecular clouds is hydrogen (H2), with molecular hydrogen being the primary form of hydrogen in these regions.
Interstellar Dust
- Interstellar dust is mainly composed of microscopic particles of carbon and silicon, making up less than 1% of the interstellar medium, yet significantly impacting galactic processes.
Spiral Arms
- The spiral arms of the Milky Way are formed by a spiral density wave that induces star formation, creating a stationary pattern while stars and gas clouds orbit through them.
Protogalactic Cloud
- A protogalactic cloud is a dense cloud of hydrogen and helium that contracts to form a galaxy, serving as the initial stage in galaxy formation.
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Description
Test your knowledge on the Milky Way Galaxy with these flashcards from Astro 3 Chapter 15. Each card covers key concepts including the structure and dimensions of our galaxy, helping you reinforce your understanding of astrophysics. Perfect for students looking to prepare for exams or enhance their learning.
