Stars &EA 1

Question 1

What is astronomy?

Answer 1

Astronomy is the study of stars, galaxies, planets, gas clouds, black holes, pulsars and the universe.

Question 2

Describe a star and a normal person stood on earth.

Answer 2

A star is a point of light in the night sky. They may appear to have different brightness and colours.

Question 3

How can stars be grouped?

Answer 3

Stars can be grouped as constellations, that are chance projections e.g. Orion, Taurus, Ursa Major and Cassopeia.

Question 4

Are constellations constant?

Answer 4

No. Constellations change over the year and over the night due to the rotation of the earth round the sun and the rotation of the earth. They also look very different in 3D space to what we see from earth.

Question 5

What does astronomy not include?

Answer 5

The study of the earth and things on earth,

Question 6

What subject knowledge do you need to study astronomy?

Answer 6

Maths, physics, chemistry and maybe even biology.

Question 7

What is one of the main problems for measuring distances?

Answer 7

It must be independent of the brightness.

Question 8

What is the distance ladder?

Answer 8

A series of methods, that build upon each other to measure the distances in the universe.

Question 9

Briefly describe triangulation and draw a diagram showing the earth (x2), the sun,the parallax angle, the distance and the side.

Answer 9

This is based on geometry and measures the baseline and angles to get the distance.
(See notes for diagram)

Question 10

What equations and assumptions are used to find the distance?

Answer 10

tanP = S/D is the standard equation but because P is so small we use the small angle formula that assumes tanP ~ P therefore D=S/P. S = 1 as the radius of the earths orbit can be referred to as 1 AU (astronomical unit), leaving D= 1/P.
P- parallax angle
S - side or radius of orbit
D - distance from the sun to the star.

Question 11

What is the radius of the earth’s orbit in metres?

Answer 11

1.5x10^11 m

Question 12

What unit is p the parallax angle measured in?

Answer 12

P is measured in arcsecs where 1 arcsec = 1/3600th of a degree and is written as 1’’.

Question 13

What unit is the distance measured in?

Answer 13

Parsecs which refers to the distance of an object that has a parallax angle of 1 arcsec.
Basically measure the parallax angle in arcsecs and get the distance in parsecs; no conversion required.

Question 14

What is 1 parsec in metres?

Answer 14

3.1x10^15m
s = 1.5x10^11m
p = 0.0000048 radians
d= s/p
d=1.5x10^11m/0.0000048 radians
=3.1x10^15m

Question 15

Where is the closest star and what distance is it from the sun?

Answer 15

Centauri System

1. 3parsecs
2. 75 arcsecs

Question 16

Is the parallax method accurate?

Answer 16

It’s good for the cosmic neighbourhood e.g. from earth it can measure 0.05’’ and from satellites it has measured 1 billion stars at 0.0001’’ but this is only 1% of the star in the Galaxy. So other methods are needed for longer distances but these methods are still based on parallax.

Question 17

What is a standard candle? Give an example.

Answer 17

An astronomical object with a known luminosity, e.g. Cepheids.

Question 18

How can standard candles be used to measure distance?

Answer 18

Use the luminosity and the measured flux to derive the distance from the inverse law.

Question 19

What are the 2 required properties of a standard candle?

Answer 19

• Does not vary with distance

- Is related to its real brightness

Question 20

How is apparent brightness and distance of standard candles related?

Answer 20

The apparent brightness of a standard candle is a measure of its distance.

Question 21

Describe Cepheids and how to determine their luminosity.

Answer 21

Cepheids are super giant stars with bright variables. They show pulses of brightness and the pulsation period and true brightness are related.
If you measure the period, you can measure the luminosity.