The Milky Way Flashcards
Describe the appearance of the Milky Way by the naked eye.
Faint Fuzzy Band of light Stretching across the sky With some darker patches
What key constellations does the Milky Way pass through?
Auriga
[Asterism the Summer Triangle]
Cassiopeia
What can you see of the Milky Way with binoculars or a telescope?
It is possible to resolve some individual stars.
Where is the Milky Way visible in the Northern hemisphere?
In a line from Cassiopeia to Cygnus.
Galactic centre lies in Sagittarius.
What do we look at when we view the Milky Way?
The plane of our galaxy, where most stars are located.
What does the Milky Way look like when viewed from above?
A disc-shape/Catherine Wheel, rotating around a central bulge.
How big is the disc?
30kpc wide
1-2kpc thick
How many spiral arms are there?
4
Where is the bulge?
It surrounds the nucleus.
Where is the halo?
It lies outside the spiral arms.
Where is the sun / solar system located?
In one of the 4 spiral arms, roughly 10kpc or 2/3 from the nucleus.
How many stars are in the galaxy?
200-400 billion
What are the two companion galaxies of the Milky Way?
Large and Small Magellanic Clouds.
How far away is the Andromeda Galaxy?
The Andromeda galaxy is one of our closest neighbours, at 700kpc away.
What are globular clusters?
A spherical collection of relatively old stars all orbiting a galactic core.
Where is the supermassive black hole?
In the nucleus
Where is gas and dust found?
In the nucleus, but mostly in the spiral arms.
Where are the sites of star formation?
In the spiral arms - NOT in the nucleus!
Where are the globular clusters?
In plane view: close to the bulge.
In cross-sectional view: close to the halo or central bulge.
Why do astronomers use 21cm radio waves instead of visible light to observe the galaxy?
- Visible light cannot penetrate the dust in the spiral arms of the galaxy, or the atmosphere (fully).
- 1420MHz radio waves (or 21cm radio waves) can.
- 1420MHz radio waves are absorbed and emitted by hydrogen in the spiral arms of the galaxy when its electron reverses its spin.
- Radio telescopes tuned to this frequency detect this.
- The wavelength of the radio waves in the lab can be measured and compared with the radio waves emitted from hydrogen.
- This allows their wavelengths to be determined.
- This allows Dopppler shift to be determined.
- This means that by using 21cm radio waves, the galaxy’s speed of rotation can be determined.
