Topic Three: Stars Flashcards
How many stars can you see with the naked eye?
2,000 if:
-moonless night, no light pollution
What is a constellation?
An area in the night sky containing a particular pattern of stars
88 total
What are asterisms?
Groups of stars that form familiar shapes
Give an example of an asterism:
The plough
Describe the constellation Orion:
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
Describe the Winter Triangle:
Sirius, Procyon, Betelgeuse
Describe the Bayer Designation Naming Scheme:
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.
Use the BDNS to name the 2nd brightest star in constellation Centaurus:
β cent
How would you find Andromeda in the night sky?
From the top left corner of the square of Pegasus, jump two stars left and two up
What is Fomalhaut?
The star of which the first exoplanet was discovered
What is Declination?
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
What is right ascension?
The angle between the star and the celestial prime meridian.
Measured in hours and minutes
What is the Celestial Prime Meridian?
The point on the celestial equator on which the sun moves from the southern to northern equator
What is the zodiacal band?
The part of the sky that contains the constellations of the Zodiac
Why do stars appear to rotate about Polaris?
Anticlockwise
How can we determine if a star will be circumpolar using the observer’s latitude and the stars declination?
Declination > 90 - latitude
What is a circumpolar star?
A star that is always above the observer’s horizon
Explain how a star will be circumpolar from a given latitude so long as the declination is > 90 - latitude:
For example:
My latitude is 52 degrees
- 90-52 = 38 degrees
- Therefore any state with a declination>38 degrees will be circumpolar
Name 4 considerations when planning an observation:
Phase of the moon
Equipment
What else is ideal for observing stars?
Dark adapted vision
Relaxed eye
Averted vision
Explain the difference between Optical Double stars and True Binary stars:
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
Give an example of a Binary star:
Castor in Gemini
How many times brighter is a star with a magnitude of 5 compared with a star with a magnitude of 1?
100 times
Give 4 factors that affect the apparent magnitude of a star:
Energy radiated by star: - Size - Temperature Interstellar gas and dust Amount of light absorbed by Earth's atmosphere Distance from Earth
What is the magnitude of the brightest star in the sky?
1.5 Sirius
What is the Absolute Magnitude?
A measure of Apparent magnitude if observed from a distance of 10pc
Name two types of variable star:
Cepheid Variables
True Binaries
What is a Cepheid Variable?
A giant yellow star that regularly expands and contracts in size
What is an eclipsing Binary?
If two binary stars orbit each other in a plane along our line of sight, two stars will eclipse each other
What is the Primary Star in a Binary Star?
The brighter star
What is a Parallax?
The apparent motion of near and more distant objects in respect to each other, caused by the motion of the observer
What is the definition of a parsec?
The distance at which a star would have a parallax angle of one arc-second
How are Cepheid Variables used to determine stellar distances?
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
What are stars formed from?
From huge clouds of gas and dust called nebulae
Where are nebulae usually found in a Galaxy?
In the spiral arms
How are stars formed?
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
Describe a star’s death (up to red giant):
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
Describe a main sequence star’s death (from red giant):
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
Describe a larger star’s death (from red giant):
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
What is a supernova?
A massive explosion at the end of a supergiant star’s life
Outer layer blown away at speeds of 5000km/s
What is a neutron star?
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
How can we deduce the chemical composition of a star?
Each element has its own unique set of spectral line wavelengths
Analysis of starlight can tell us what the star is made of
How can we deduce the temperature of a star?
The temperature of a star determines its colour, so spectral analysis can determine its temperature
How can we determine the radial velocity of a star?
Analysis of the Doppler shift of spectral lines
What is a HR diagram?
This is a plot of luminosity against spectral type
Which stars will run out of fuel sooner?
Massive stars
Give evidence for the existence of Neutron stars:
Regular pulsating radio signals from Pulsars
Give 3 pieces of evidence for the existence of black holes:
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
