AST Test 2
Two rocket ships are each traveling at 90% of the speed of light toward one another. One turns on a beam which is seen by scientists aboard the second spaceship. What speed do the scientists measure for the light?
1.0 c exactly
Helium fusion requires what temperature?
100 million K.
Which main sequence star has the highest core temperature when fusion begins? Hint: recall what drives the core to higher temperatures? Why is a bowling ball cool, and a star hot?
30 solar mass star.
Which of the following is NOT a terminal stage of stellar evolution?
A protostar.
Which of the following is NOT a consequence of an intense coronal mass ejection event aimed at Earth?
A significant disruption of Titan's orbit.
The Sun will become a supernova.
False
A plot of temperature vs. luminosity for stars is known as the ________, and is used to determine when stars are evolved and no longer on the main-sequence.
HR diagram
Where is the chromosphere on the Sun?
It is the layer above the visible photosphere.
From the center outward, the order of the layers or parts of the Sun is:
None of the answers shown are correct.
Of the following locations where do clocks run slowest?
On the surface of a 2 solar mass neutron star.
How do stars in a cluster change with time?
The highest-mass stars evolve most quickly.
What condition is necessary to view eclipses of binary star systems?
The line of sight from Earth to the star system must be in or close to the orbital plane of the stars (i.e., edge-on).
Why are X-rays and gamma-rays dangerous?
They are high energy photons.
What happened to the temperatures in Europe between 1645 and 1715, when virtually no sunspots were seen (now known as the Maunder minimum)?
They were lower than average.
Some neutron stars have rotation periods in milliseconds (by contrast Earth exhibits a rotation period of 24 hours).
True
Somewhat paradoxically, massive stars live relatively short lives compared to low-mass stars. The reason is because massive stars exert a significantly higher pressure on the core, which drives the temperature up and results in part in more nuclear reactions. Despite having more fuel to consume, the reaction rate is so high that massive stars typically last for a few millions years, whereas lower mass stars like the Sun can last 10 billion years (thankfully). It is one of the reasons we likely reside around the Sun, and not a more massive star, namely because the parent star would have gone supernova in a few million years, and life would not have had the time to evolve.
True
Amazingly, near the end of evolution for a single massive star it can become a _____________ .
Type II supernova
The temperature inside a typical molecular cloud, where star formation may take place, is ...
about 10 K.
A stellar-mass black hole is believed to form ...
at the end of the evolution of a very massive star.
An object moving toward you is said to be ________ (hint: the wavelengths are being compressed).
blueshifted
The process by which a spinning object collapses and spins faster is called ________.
conservation of angular momentum
Granulation on the Sun is evidence of ...
convection in the photosphere.
The chemical makeup of a star's surface is obtained by ...
examining the star's spectrum (i.e., sending its light through a prism and examining the dark gaps which are absorption lines).
Remarkably, Galileo discovered that the Sun itself rotates by tracking its sunspots, but in a differential manner. The rotation of the Sun is ...
fastest at the equator, and slowest near the poles.
The wavelength of light near a black hole stretched to longer wavelengths, and the phenomenon is caused by the black hole's ________.
gravity
The Sun appears stable (i.e., not contracting) because ______ and ______ are in balance. The effect is likewise known as hydrostatic equilibrium.
gravity, gas pressure
Toward the left of the HR diagram the stars become ...
hotter and bluer.
The Sun does not expand or contract because it is in a state of ...
hydrostatic equilibrium. That is to say the inward force of gravity is balance by the outward pressure from nuclear fusion.
A key reason astronomers build larger telescopes is to ...
improve the resolution.
The total amount of energy that a star emits is called its ________. Note that the implied units are in Watts, just like a light bulb. So the total energy of a light bulb and a star are placed on the same basis. For reference, the Sun's total energy is an amazing 1026 Watts.
luminosity
Newtonian telescopes use a primary ________ to collect light.
mirror
The basics of _________ fusion in the Sun are detailed in the following important summary (i.e., understand this material). Normally, protons repel each other because their charges are similar, and by analogy consider trying bring together the N of a magnet with the N of another magnet. To overcome that electromagnetic repulsion one needs to smash the protons at a very high speed, and then nuclear fusion can occur. That high speed is not achieved in daily life, thankfully, but in the cores of stars where the temperature is high. Temperature is a proxy for the speed of particles, and as an example consider if it is cold in the room the particles are moving slowly. The temperature is high in the cores of stars because there is the sizable mass of all the overlaying layers exerting a pressure on the core, and causing the temperature to rise, and hence the speed of the protons. By analogy, consider when diving from the t
nuclear
An element is determined by the number of ...
protons
A difference in magnitude of 5 is equal to a ...
ratio of 100 in brightness
The ability of a telescope to see detail is called ________, and is improved with larger apertures and minimal interference from the atmosphere.
resolution
Which of the following is NOT an electromagnetic wave?
sound
In E=mc2 , the constant 'c' stands for ________.
speed of light
The twinkling of the stars is caused by ________.
starlight interacting with Earth's atmosphere
The magnification achievable by a telescope is equal to ...
the focal length of the telescope divided by the focal length of the eyepiece.
The Sun's key source of energy is ...
the fusion of hydrogen into helium.
