December Exam Flashcards
Why does the Sun’s size remain stable?
Because it is in gravitational equilibrium
How did the Sun become hot enough for fusion?
As the sun was forming, it grew hotter as it shrank in size
How luminous are stars?
The brightness of a star depends on the light it emits into space and its distance from Earth
How hot are stars?
Surface temperature of the hottest stars exceed 40,000 K and the coolest are less than 3,000 K
What are the spectral types from hottest to coolest?
OBAFGKM
How massive are stars?
0.08 times the mass of the Sun to 100 times the mass of the Sun
How do we classify stars?
According to spectral type and luminosity class
Why is a star’s mass its most important property?
A star’s mass at birth determines virtually everything that happens to it.
What is a Hertzsprung-Russell diagram?
An H-R diagram plots stars according to their surface temperatures and luminosities
What does an H-R diagram depict?
Temperature Color Spectral Type Luminosity Radius Mass
At the centre of the sun, fusion converts hydrogen into…?
Helium
Energy
Neutrinos
The phase of matter in the Sun is…?
Plasma
Core temperature of the Sun?
10 million K
How does the sun generate energy?
Nuclear fusion
If you put two protons near each other, what will the electromagnetic force make them do?
Repel one another
How do we know what goes on under the Sun’s surface?
Astronomers create models
The sun’s observed composition and mass
Computers predict internal conditions
We observe vibrations of the Sun’s surface
The light radiated from the Sun’s surface reaches Earth in 8 minutes, but that energy of that light was released by fusion in the solar core about…?
A million years ago
What is an UNTRUE fact about the sunspot cycle?
The rate of nuclear fusion in the Sun peaks about every 11 years
What is an UNTRUE fact about neutrinos?
The mass of a neutrino is 30% of the mass of an electron
Based on its surface temperature of 5,800 K, what colour are most of the photons that leave the Sun’s surface?
Green
What are the major layers of the Sun, from inside out?
Core Radiation zone Convection zone Photosphere Chromosphere Corona
What do we mean by “surface” of the Sun?
We consider the photosphere the surface because light can pass through it, but cannot escape from deeper inside the Sun.
What is the Sun made of?
98% hydrogen and helium
Why does fusion occur in the Sun’s core?
The core temperature and pressure are so high that colliding nuclear can come close enough to overcome electromagnetic repulsion and bind them.
How do we know what is happening in the Sun?
We construct theoretical models of the solar interior and check models against observations of the Sun
What’s surprising about the temperature of the chromosphere and the corona?
Temperature decreases from the core to the photosphere, but then rises back up in the chromosphere and corona.
What effect does solar activity have on Earth and its inhabitants?
Particles ejected from the Sun by solar activity can affect communications, electric power delivery, and the electronic circuits in space vehicles.
Describe the sunspot cycle.
The magnetic field flip-flops every 11 years for a 22 year magnetic cycle. Sunspots first appear at mid-latitudes at solar minimum, then become more common near the Sun’s equator.
How can we learn about the lives of stars?
By taking observations of many stars, we can study stars in many phases of life.
What two basic physical properties do astronomers use to classify stars?
Luminosity
Surface temperature
What is luminosity and how do we determine it?
Luminosity - the total power (energy per unit time) that a star radiates into space.
Can be calculated from a star’s apparent brightness and distance using the luminosity-distance formula.
How do we measure the distance to nearby stars?
By parallax, the shift in the apparent position of a stat with respect to more distant stars as the Earth moves around the Sun
How are stars classified into spectral types?
According to their spectra, different spectral types correspond to different temperatures.
Does a star’s spectral type depend on its composition?
No.
What are two main elements in all stars?
Hydrogen and helium
High-mass stars have/are:
High luminosity
Short-lived
Large radius
Blue
Low-mass stars have/are:
Low luminosity
Long-lived
Small radius
Red
What two forces are balanced in the gravitational equilibrium?
Outward pressure and gravity
What do we mean when we say the Sun is in gravitational equilibrium?
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity
What is the Sun made of?
70% hydrogen
28% helium
2% other elements
Which layer of the sun do we normally see?
Photosphere
What are the appropriate units for the Sun’s luminosity?
Watts
If the sun’s core suddenly became hotter, what would happen?
Higher temperatures would cause the rate of nuclear fusion to rise which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal
What observations characterize solar maximum?
We see sunspots
What is the average temperature of the Sun’s surface?
6,000 K
The spectral sequence sorts stars according to…?
Surface temperature
On a H-R diagram, where would we find stars that are cool and dim?
Lower right
A star’s luminosity is…?
The total energy a star radiates each second
If the distance between us and a star is doubled, the luminosity will…?
Stay the same. But the apparent brightness is decreased by a factor of four.
On a H-R diagram, where would you find white dwarfs?
Lower left
On a H-R diagram, where would you find stars with the largest radii?
Upper right
What is NOT a form of electromagnetic radiation?
Sound
The distance between successive wave crests defines the ______ of a wave.
Wavelength
The frequency at which a star’s intensity is greatest depends on its…?
Temperature
Rigel is a bright, bluish star.
Betelgeuse is a bright, reddish star.
Rigel is ______ than Betelgeuse
Hotter
If a light source is approaching you, you will observe…
Its spectral lines are shorter in wavelength
The wavelengths of emission lines produced by an element…
Are identical to its absorption lines
Analyzing a star’s spectral lines can’t tell us about
It’s side-to-side motion
What types of electro-magnetic radiation from space reach Earth?
Visible light and radio waves
Which of the following has a different nature than the others? Proton, electron, photon, neutron, atomic nucleus
Photon
The visible light we see from the sun comes from what part?
Photosphere
The sun is a stable star because…?
Gravity balances forces from pressure
The proton-photon cycle involves what kind of fusion process?
Hydrogen into helium
If a neutrino can escape from the solar core within minutes, then how long does it take a photon to escape?
About a million years
The number of sunspots and solar activity in general peaks…
Every 11 years
Stellar parallax is used to measure…
Distances of stars
What process creates energy in the Sun?
Fusion of hydrogen into helium in the Sun’s core
A star’s proper motion is its:
Annual apparent motion across the sky
Which quantities do you need in order to calculate a star’s luminosity?
Apparent brightness
Distance to the star
What are the two most important intrinsic properties for classifying stars?
Luminosity and surface temperature
Wien’s law tells is that the hotter an object, the ______ the peak wavelength of it’s emitted light.
Shorter
We estimate the surface temperature of the star by using…?
Colour
Pattern of absorption lines
Wien’s law
Differences in brightness as measured through Red and Blue filters
Which spectral classification type corresponds to the star like the Sun?
G
The key difference between the spectra of B stars and G stars is…?
B stars show strong Hydrogen lines. G stars weaker Hydrogen lines.
Astronomers can estimate the size of a star using…?
Temperature
Apparent brightness
Direct observation of diameter
Eclipsing binary stars are very useful for determining the…?
Masses of stars
What is the single most important characteristic in determining the course of a star’s evolution?
Mass
