D Astrophysics

Question 1

What are the similarities and differences between a planet and a comet?

Answer 1

both orbit the sun
comet orbits are more elliptical
comets have tail

Question 2

What is the difference between a asteroid and a meteor?

Answer 2

An asteroid is a small rocky object that orbits the Sun.

A meteor is what happens when a small asteroid or comet burns up upon entering Earth’s atmosphere.

Question 3

What is the process that makes stars (including the sun) shine?

Answer 3

nuclear fusion

Question 4

What is binary star?

Answer 4

2 stars that orbit around their common centre of mass

Question 5

Name 3 ways to detect binary stars

Answer 5

• visual binaries (seen through a telescope)
• spectroscopic binaries (red/blue shift)
• eclipsing binaries (change in brightness)

Question 6

What is galaxy and galaxy cluster?

Answer 6

Galaxy is a giant assembly of stars, gas, and dust held together by the gravitational forces they have on each other.
A galaxy cluster is two or more galaxies that are close enough to affect each other through gravitation.

Question 7

What is meant by eclipsing binaries and how can you tell that they are binaries?

Answer 7

They pass in front of each other as they orbit → change in brightness

Question 8

How are spectroscopic binaries detected?

Answer 8

The stars move towards and away from earth as they orbit→ blue and redshift in their spectra

Question 9

What is the difference between a constellation and a cluster?

Answer 9

a constellation appears as a pattern of stars as viewed from earth but may NOT actually be close together; a cluster is a group of stars physically close together and bound by gravity

Question 10

What are the main differences between open and globular clusters?

Answer 10

Globular clusters contain more stars, is more tightly bound, and older than an open cluster.

Globular clusters are spherical while open clusters are irregular.

Question 11

What two forces keep stars in equilibrium during their lifetime?

Answer 11

Gravity pulls in and radiation pressure pushes outwards.

Question 12

Define 1AU, 1 light year, and 1 parsec. Then place
them in order from smallest to largest.

Answer 12

• 1 AU = distance from earth to sun
• 1 ly = distance that light travels in one year.
• 1 parsec = distance that gives a parallax angle of 1 arcsec (1/3600˚)

AU < ly < parsec

Question 13

Describe the process of stellar parallax.

Answer 13

1. Measure the angular position of the star; in 2 positions 6 months apart; relative to the background stars
2. Parallax angle is half the angle of separation
3. The distance to the star is calculated by d = 1/p

Question 14

Give the equation for stellar parallax and explain the condition for this method to be used.

Answer 14

d=1/p
This method can only be used for relatively close stars because the parallex angle becomes too small to be measured accurately for distant stars

Question 15

Define luminosity and apparent brightness for a star.

Answer 15

L: total power emitted by a star
b: the amount of light that strikes 1 m² on Earth

Question 16

What 3 factors will affect the brightness of a star?

Answer 16

b = L/4πd²
Its temperature, size and distance from the observer can affect its brightness

Question 17

What causes the seasons on Earth?

Answer 17

the tilt of the Earth’s rotational axis away or toward the sun as it orbits around the sun

Question 18

What is an asteroid and where are they found in the Solar system?

Answer 18

A relatively small, inactive, rocky body orbiting the Sun. Between Jupiter and Mars.

Question 19

What shape are the orbits of the planets?

Answer 19

elliptical

Question 20

Why do stars appear to move at night?

Answer 20

Earth spinning on its axis

Question 21

Explain why the night sky looks different at different times of the year.

Answer 21

Earth orbits around Sun, different constellations are visible at different positions in the orbit

Question 22

What would happen to the** absolute luminosity** and apparent brightness of the sun if it moves twice as far away from Earth as it is at present?

Answer 22

L stays the same;
b decreased to 1/4

Question 23

define parsec

Answer 23

d = 1/p
the distance at which one astronomical unit subtends an angle of one arcsecond

Question 24

state the stefan-boltzman relationship

Answer 24

L =σAT^4
no e becuase emissivity of a star (black body) is 1

Question 25

Explain how the chemical compositionof a star may be determined from its spectrum

Answer 25

1. stars emit white light
2. electrons on the outer cool gas layers of the star absorb photons of specific wavelength and transition up energy levels
3. electrons re-emit photons in all directions and transition down energy levels, forming the black absorption lines.
4. We can use the absorption spectra to determine the cool gas surrounding of the stars.

Question 26

With reference to the HR diagram, explain how we know the white dwarfs are small and the red giants are big

Answer 26

white dwarf: as T is high and L is low, SA must be small

red giants: as T is low, SA must be big to achieve high L