4.1: Our Galaxy-The Milky Way

Question 1

What are galaxies

Answer 1

Stars grouped in huge gravitationally-bound collections

Question 2

Why is our galaxy called the Milky Way

Answer 2

It appears as a faint band of light with some darker patches stretching across the sky, passing through constellations such as; Cassiopeia, Auriga and those whose brightest stars create the asterism the Summer Triangle

Question 3

What are milky ways two satellite galaxies

Answer 3

The small and large Magellanic Clouds- SMC AND LMC

Question 4

How far away is andromeda

Answer 4

It one of our closest galactic neighbours at just 700 kpc away

Question 5

Why are the three main components of the structure of the Milky Way

Answer 5

• the disc
• the bulge
• a halo

Question 6

Tell me about the Milky ways disc

Answer 6

• Has a diameter of roughly 30 kpc and a thickness of 1-2 kpc
• contains young stars,gas,dust and sites of star formation in the 4 major spiral arms
• solar system is in one arm about 10 kpc from nucleus

Question 7

Tell me about the Milky ways bulge

Answer 7

• surrounds nucleus

- astronomers believe there’s a massive black hole at centre

Question 8

Tell me about the Milky ways halo

Answer 8

-mainly contains globular clusters

Question 9

What are globular clusters

Answer 9

Dense groups of relatively old stars,in a spherical distribution about the galactic centre

Question 10

How can we see our galaxies spiral arms if clouds of gas and dust block astronomers from viewing it

Answer 10

• spiral arms contain hydrogen atoms
• model of hydrogen is a single electron in motion around nucleus
• we picture the electron as spinning in one of two ways.when electron reverses its spin it emits EM radiation of frequency 1420Hz;corresponding to a wavelength of 21cm which is in the microwave/radio region of spectrum
• EM radiation at this wavelength can penetrate dust, so neutral hydrogen that pervades the spiral arms of our galaxy can be detected by radio telescopes ‘tuned’ to this frequency
• as galaxy rotates wavelengths become slightly Doppler-shifted to shorter and longer wavelengths because of relative motion of hydrogen with respect to us
• radio astronomers use these changes to determine the relative velocities of spiral arms.this then allows them to determine how various parts of galaxy rotate