Topic Three: Stars

Question 1

How many stars can you see with the naked eye?

Answer 1

2,000 if:

-moonless night, no light pollution

Question 2

What is a constellation?

Answer 2

An area in the night sky containing a particular pattern of stars

88 total

Question 3

What are asterisms?

Answer 3

Groups of stars that form familiar shapes

Question 4

Give an example of an asterism:

Answer 4

The plough

Question 5

Describe the constellation Orion:

Answer 5

Asterism of Orion’s belt
-Pointer stars to Aldevaran (up and to the right)
-and Sirius (down and to the left)
Contains the Orion Nebula

Question 6

Describe the Winter Triangle:

Answer 6

Sirius, Procyon, Betelgeuse

Question 7

Describe the Bayer Designation Naming Scheme:

Answer 7

Brightest star in constellation is Alpha
Then Beta, Gamma, Delta, Epsilon… as stars get dimmer
1st 3 letters of the constellation of which the star is found.

Question 8

Use the BDNS to name the 2nd brightest star in constellation Centaurus:

Answer 8

β cent

Question 9

How would you find Andromeda in the night sky?

Answer 9

From the top left corner of the square of Pegasus, jump two stars left and two up

Question 10

What is Fomalhaut?

Answer 10

The star of which the first exoplanet was discovered

Question 11

What is Declination?

Answer 11

If we imagine Earth at the centre of a giant celestial square, declination is almost identical to Latitude

It is the angle of a point above the celestial equator

Question 12

What is right ascension?

Answer 12

The angle between the star and the celestial prime meridian.

Measured in hours and minutes

Question 13

What is the Celestial Prime Meridian?

Answer 13

The point on the celestial equator on which the sun moves from the southern to northern equator

Question 14

What is the zodiacal band?

Answer 14

The part of the sky that contains the constellations of the Zodiac

Question 15

Why do stars appear to rotate about Polaris?

Answer 15

Anticlockwise

Question 16

How can we determine if a star will be circumpolar using the observer’s latitude and the stars declination?

Answer 16

Declination > 90 - latitude

Question 17

What is a circumpolar star?

Answer 17

A star that is always above the observer’s horizon

Question 18

Explain how a star will be circumpolar from a given latitude so long as the declination is > 90 - latitude:

Answer 18

For example:

My latitude is 52 degrees

• 90-52 = 38 degrees
• Therefore any state with a declination>38 degrees will be circumpolar

Question 19

Name 4 considerations when planning an observation:

Answer 19

Phase of the moon

Equipment

Question 20

What else is ideal for observing stars?

Answer 20

Dark adapted vision
Relaxed eye
Averted vision

Question 21

Explain the difference between Optical Double stars and True Binary stars:

Answer 21

True Binary stars are linked together Gravitationally and orbit a common centre of mass

Optical Double stars merely appear nearby but may be light years apart

Question 22

Give an example of a Binary star:

Answer 22

Castor in Gemini

Question 23

How many times brighter is a star with a magnitude of 5 compared with a star with a magnitude of 1?

Answer 23

100 times

Question 24

Give 4 factors that affect the apparent magnitude of a star:

Answer 24

Energy radiated by star:
- Size 
- Temperature 
Interstellar gas and dust 
Amount of light absorbed by Earth's atmosphere 
Distance from Earth

Question 25

What is the magnitude of the brightest star in the sky?

Answer 25

1.5 Sirius

Question 26

What is the Absolute Magnitude?

Answer 26

A measure of Apparent magnitude if observed from a distance of 10pc

Question 27

Name two types of variable star:

Answer 27

Cepheid Variables | True Binaries

Question 28

What is a Cepheid Variable?

Answer 28

A giant yellow star that regularly expands and contracts in size

Question 29

What is an eclipsing Binary?

Answer 29

If two binary stars orbit each other in a plane along our line of sight, two stars will eclipse each other

Question 30

What is the Primary Star in a Binary Star?

Answer 30

The brighter star

Question 31

What is a Parallax?

Answer 31

The apparent motion of near and more distant objects in respect to each other, caused by the motion of the observer

Question 32

What is the definition of a parsec?

Answer 32

The distance at which a star would have a parallax angle of one arc-second

Question 33

How are Cepheid Variables used to determine stellar distances?

Answer 33

Using the period - luminosity law we can work out the absolute magnitude of the star Use the distance modulus formula to calculate distance m - M = -5 + 5logd

Question 34

What are stars formed from?

Answer 34

From huge clouds of gas and dust called nebulae

Question 35

Where are nebulae usually found in a Galaxy?

Answer 35

In the spiral arms

Question 36

How are stars formed?

Answer 36

Nebulae begin to collapse and break up into protostars. There is a rise in temperature and pressure as GPE and KE. When the temperature reaches 15 million K in the core, fusion starts

Question 37

Describe a star's death (up to red giant):

Answer 37

Star runs out of hydrogen No radiation countering gravitational collapse Star collapses Temperature rises further Fusion restarts in a shell surrounding the core, meaning the outer layers of the star expand and cool to form a red giant

Question 38

Describe a main sequence star's death (from red giant):

Answer 38

Helium nuclei fuse to form Carbon When helium is depleted, the red giant loses its outer layers in an expanding shell of gas forming a planetary nebula Core collapses to form White dwarf, cools eventually to brown and then black

Question 39

Describe a larger star's death (from red giant):

Answer 39

Super red giants can form iron through fusion, this makes a Supernova. The star will then become a neutron star, of a Black Hole if it's big enough

Question 40

What is a supernova?

Answer 40

A massive explosion at the end of a supergiant star's life | Outer layer blown away at speeds of 5000km/s

Question 41

What is a neutron star?

Answer 41

A remnant of a supernova Mass of sun collapsed into a sphere of 20 km diameter Intense gravitational fields cause them to spin Emit radio waves from their polar regions

Question 42

How can we deduce the chemical composition of a star?

Answer 42

Each element has its own unique set of spectral line wavelengths Analysis of starlight can tell us what the star is made of

Question 43

How can we deduce the temperature of a star?

Answer 43

The temperature of a star determines its colour, so spectral analysis can determine its temperature

Question 44

How can we determine the radial velocity of a star?

Answer 44

Analysis of the Doppler shift of spectral lines

Question 45

What is a HR diagram?

Answer 45

This is a plot of luminosity against spectral type

Question 46

Which stars will run out of fuel sooner?

Answer 46

Massive stars

Question 47

Give evidence for the existence of Neutron stars:

Answer 47

Regular pulsating radio signals from Pulsars

Question 48

Give 3 pieces of evidence for the existence of black holes:

Answer 48

Light bent by black hole's gravity Speed of rotation of our galaxy and its size hints that the mass at its centre is great enough to be a black hole Charged particles spinning around a Black hole produce x rays which we can detect