ASTRONOMY Ch.1-4 Concept Checks/Quiz Questions
At the beginning of spring, the vernal equinox, what is the right ascension of the Sun?
0
Why is the photosphere considered the Sun's "surface"?
It radiates most of the observable sunlight that produces the bright disk of the Sun.
Compared to Earth's atmosphere, the atmosphere of Mars has surface pressures that are ________.
0.1 times those on Earth; major gases are water vapor and carbon dioxide
A main-sequence star like our sun is expected to be stable for approximately ________.
10 billion years
Earth orbits with the Sun around the galactic center every _________ years
230 million
Mercury reflects ________ percent of the sunlight that hits it into space.
6
How many constellations are currently recognized?
88
What is the modern explanation for "guest stars" suddenly appearing in the night sky?
A guest star or supernova is a normal star that experiences an explosion and suddenly increased in brightness temporarily.
Why did the ancients believe that celestial objects had some influence over their lives?
A majority of their lifestyle was based off of seasonal change. They believed that because the "heavenly objects" could control the seasons, they could also control other aspects of their lives.
Explain the difference between the mean solar day and the sidereal day.
A solar rotation measures Earth 360 degree rotation based on the Sun (from noon to noon). In other words, a solar rotation measures from when the Sun is at the top of the sky (noon) until it reaches that exact same location the next day. This cycle is exactly 24 hours. A sidereal day measures the Earth's 360 degree rotation based on a pin-pointed distant star other than the Sun. Therefore, a star's position is recorded, and whenever that star comes to the exact same spot it was recorded again, that is a sidereal day. This is four minutes shorter than a solar day. This is because the Earth's direction to distant stars only changes minutely, while the Earth's direction to the Sun changes by 1 degree each.
If you determine the number of days in a year with solar time and sidereal time how would they vary?
A year measured in sidereal time would be about one day longer than a year based on solar time.
Name the technique devised by astronomers to greatly eliminate the blurring caused by atmospheric turbulence.
Adaptive optics
List the astronomical contributions of the ancient Greek philosophers Aristotle, Anaxagoras, Aristarchus, Eratosthenes, Hipparchus, and Ptolemy.
Aristotle: established the Earth's shape as spherical Anaxagoras: discovered the cause of ellipses; established that the source of the Mood's light comes from the Sun Aristarchus: proposed the heliocentric theory of a Sun-centered universe; predicted the Earth's distance from the Sun and the Moon; predicted the size of the Sun and Moon based on his formula for calculating distance Eratosthenes: used the comparison of two cities at noon to formulate an equation that would predict the circumference of the Earth Hipparchus: formulated a star catalog which was used to locate stars and divide them into categories based on brightness; proposed a fairly accurate time frame for the length of a year Ptolemy: proposed his own geocentric model of the universe called the Ptolemaic system that attempted to account for retrograde motio
Briefly describe the 11-year sunspot cycle.
At its maximum, the number of sunspots reaches perhaps 100 or more at a given time. Then, over a period of 5 to 7 years, their numbers decline to a minimum, when only a few or even none are visible. Like other solar disturbances, we know that the Sun's magnetic field drives the roughly 11-year sunspot cycle.
The Moon rotates on its axis very slowly (once in 27[1/3] days). How does this affect the lunar surface temperature?
Because it rotates so slowly, the Sun's heat is beaming into one side of the Moon for an extended amount of time, making one side extremely hot and the other extremely cold.
List two advantages of charge-coupled devices (CCDs) over photographic film.
Collect almost all the photons of incoming light that strike the chip > greatly reduces exposure times. Chips can be designed to detect wavelengths of infrared and ultraviolet light > some objects are more visible at these wavelengths than in visible light.
List the contributions to modern astronomy of Nicolaus Copernicus, Tycho Brahe, Johannes Kepler, Galileo Galilei, and Sir Isaac Newton.
Copernicus: Proposed that Earth is a planet just like the five known at the time, and they all orbit around the Sun. Brahe: Introduced the phenomenon known as stellar parallax; rejected Copernicus' theory of a Sun-centered universe Kepler: Supporter of Brahe's work; produced the three laws of planetary motion... The planets orbit the Sun elliptically rather than circularly; a planet's distance from the Sun changes throughout its orbit Planets move faster when closest to the Sun and visa versa "Distant" planet orbit the Sun slower than the regular distanced planets Galilei: Created telescopes, some having a magnification of 30; discovered Jupiter's moons; planets are "Earth-like" rather than "star-like"; Venus has phases similar to the Moon; the Moon is not a perfect sphere; discovered sun-spots Newton: articulated the concept of inertia; produced the law of universal gravitation, stating that every object in the universe is attracted to another body by gravitational force. This force increases with mass and decreases with distance
The first telescopes, and most amateur telescopes, rely on the human eye to observe objects. Modern telescopes record the observations with ________.
Digital cameras
What term is used to collectively describe gamma rays, x-rays, ultraviolet light, visible light, infrared radiation, and radio waves?
Electromagnetic radiation
Why is the Sun significant to the study of astronomy?
Everything from the food we eat to the fossil fuels we burn is ultimately derived from solar energy. Also, it is the only star we can study close up.
This scientist wrote a book entitled Dialogue of the Great World Systems that compared the Earth-centered system with the Sun-centered system.
Galileo
Explain how Galileo's discovery of the phases of Venus supported the Copernican view of a Sun-centered universe.
Galileo discovered that the phases of Venus indicate its position to the Earth depending on its visibility. This discovery supports that there is a source of light that is orbited by both planets simultaneously.
Which one of the following is not found on Mars: polar ice caps H2O-rich atmosphere sand dunes extinct volcanoes
H2O-rich atmosphere
What data did Tycho Brahe collect that was useful to Johannes Kepler in his quest to describe planetary motion?
He discovered the phenomenon of stellar parallax. This states that overtime (6 months) the position of a star should shift with respect to distant stars.
Tycho Brahe set out to disprove Copernicus, so why is he famous for developing modern astronomical theory?
He made very precise measurements that were key data used by Kepler.
Describe the relationship between the temperature of a radiating body and the wavelengths of light it emits.
Hotter objects radiate more total energy per unit than colder objects; they also radiate a larger proportion of their energy at shorter wavelengths (higher energy). Thus, hotter objects emit more light per unit area and emit more of their light as shorter wavelengths (higher energy).
What "fuel" does the Sun consume?
Hydrogen fuel
Explain the geocentric view of the universe.
Introduced by Ptolemy in 141 CE. The view that planets move about of epicycles while simultaneously orbiting the Earth in deferents.
Who discovered that planetary orbits are ellipses rather than circles?
Johannes Kepler
Which color of the visible spectrum has the longest wavelength? Shortest?
Longest, red; shortest, violet
Describe what produces the retrograde motion of Mars. What geometric arrangements did Ptolemy use to explain this motion?
Mars takes twice as long to orbit the Sun than Earth. Because of this, Earth eventually passes and overtakes Mars. This combined with the background of distant stars causes it to appear as though Mars is moving backwards. Planets making epicycles while orbiting the Sun.
How long can a total eclipse of the Moon last? How about a total eclipse of the Sun?
Moon: ~ 4 hours Sun: Max is 7 minutes
The problems encountered with lenses caused this scientist to build reflecting telescopes of his own design.
Newton
Axial precession is sometimes called the precession of equinoxes because it results in a gradual shift, relative to the celestial background, of the position where the Sun crosses the celestial equator at the equinox. Astrology is a mythology based on things like your "sign" which refers to the position of the Sun in the celestial zodiac (the 12 constellations along the ecliptic) on your birthday. This system was established almost two thousand years ago. If this mythology were true (and you believe your horoscope) can you use the dates for your "sign" based on this 2000 year old system?
No, because 2000 years is almost 1/12, or one full sign shift, in the zodiac, so the 2000 year old signs are off by almost one full sign.
What phenomenon results from the fact that the Moon rotates once on its axis for every orbit that it makes around Earth?
Phases of the Moon.
The first telescopes, and most amateur telescopes, rely on the human eye to observe objects. The first improvement on this observation method used ________.
Photographic film
Why are radio telescopes much larger than optical telescopes?
Radio dishes must be large because radio signals from celestial sources tend to be very weak.
List and describe the primary motions of Earth.
Rotation: daily spin; determines day and night Orbit: yearly elliptical journey around the Sun The Earth following the Sun's journey through Space
How does the amount of energy contained in a photon relate to its wavelength?
Shorter wavelengths correspond to more energetic photons, and longer wavelengths correspond to less energetic photons.
In your own words, describe the law of universal gravitation. Who discovered this important concept?
Sir Isaac Newton. Every body in the universe is attracted to another body by gravitational force. This force increases with mass and decreases with distance.
Briefly describe the Doppler effect and explain how astronomers determine whether a star is moving towards or away from Earth.
Sound: As a siren approaches, its motion causes its sound waves to bunch together, resulting in a shorter wavelength and a higher pitch. When the siren goes further away, it motion causes sound waves to spread out, therefore emitting a lower tone. Light: When a source is moving away, the light appears redder than it actually is because its wavelengths are lengthened. Approaching objects have their light waves shifted towards blue because the wavelength is getting shorter. Distant stars: Established by comparing the absorption (dark) lines in the spectrum of a star with spectra produced in the laboratory. When the spectral lines are shifted toward the long end of the electromagnetic spectrum, called a redshift, the star is moving away from the observer. By contrast, when the spectral lines are moving toward the short end of the spectrum, it will produce a blue/violet color which means the star is approaching Earth.
Describe the equatorial system for locating stars.
The Earth is divided by the equator and latitude and longitude. When this division is applied to the celestial sphere, astronomers are able to determine the hours of right ascension that gives them an idea as to where certain stars are located.
What major change from the Ptolemaic system did Copernicus propose? Why was this change a philosophical departure?
The Ptolemaic system suggested that the five known planets orbited around the Earth. Copernicus proposed that the Earth was a planet just like the others and that they all orbited the Sun. At the time, people wanted to believe that Earth was superior to the other planets and was literally the center of the universe. Copernicus' suggestion that the Earth was equal did not set well with modern science at the time.
What did Galileo learn about the Sun from his observations of sunspots?
The Sun rotates on its axis about once a month.
What can be learned about a star (or other radiating objects) from its absorption line spectrum?
The composition of distant objects in the universe.
Earth hits its perihelion position in January. Solar radiation is proportional to the distance squared between the Sun and the earth, so why isn't it hot in "winter" at perihelion?
The ellipticity of the orbit is small, so the affect is small; seasons are caused by tilt of Earth's orbit.
Why are sunspots cooler than the surrounding photosphere?
The magnetic field disrupts the convective flow below the sunspot, which normally carries hot gases to the Sun's surface.
What is spectroscopy?
The study of the properties of light and the way light interacts with matter. Initiated by Newton.
Compare the synodic month with the sidereal month.
The synodic month describes the Moon's cycle through its phases in relation to the Earth. When measuring the cycle in relation to the Sun, it takes a slightly shorter time to get from phase to phase (27.5 days as opposed to 29 days in relation to the Earth).
Why do the planets "drift" east relative to the stars and then move west for periods of time?
They are moving in the same rotation sense as the earth around the Sun, but as the earth moves faster (or slower, depending on the planet) the motion appears to be backwards.
How are constellations used in modern astronomy?
They are used to divide the sky into regions and therefore identify which area of the sky they are observing.
What two properties make telescopes with large mirrors more useful than those with small mirrors?
They collect far more photons of light and can therefore detect fainter objects. The larger the primary lens or mirror of a telescope, the greater its potential resolution.With greater resolution, they can produce sharper images.
Describe the Ptolemaic model of the universe.
This came from Claudius Ptolemy's attempt to explain retrograde motion. It describes planets as moving about in epicycles, or small circles, while simultaneously orbiting the Earth in deferents, or large circles.
In a radio telescope, the electromagnetic energy is gathered by ________.
a parabolic metallic mirror, commonly wire mesh
A very slow motion of Earth's axis that requires 26,000 years to complete is called ________.
axial precession
The layer of the solar atmosphere directly above the photosphere is referred to as the ________.
chromosphere
Planets appear to move ________ each night, but occasionally they appear to stop and reverse direction
eastward
The spectra of most stars are dark-line spectra because ________.
elements in the Sun's outer atmosphere absorb in these dark-line bands, blocking the radiation in those bands
Moon orbits Earth in an __________ orbit
elliptical
Fluorescence is a characteristic of ________.
emission nebulae
The red color of emission nebulae comes from the ________.
energy emission of hydrogen
The temperature of a red giant increases rapidly because ________.
gravitational energy is converted to heat
A blue star is ________ our Sun.
hotter and larger than
Interstellar matter is composed primarily of ________.
hydrogen
Several of the moons of Saturn, Uranus and Neptune display evidence of volcanic activity. What is the most common type of volcano on these moons?
ice volcanos
Regolith is not a true soil because it ________.
lacks organic material
The source of the Sun's energy is ________.
nuclear fusion
Low mass stars generally end up as ________ dwarfs.
red
As the temperature of a radiating surface is increased ________.
the total amount of energy emitted increases a larger portion of the energy is radiated at shorter wavelengths
Why did Hubble think the Cepheid variables he saw in "Fuzzy Patches" were outside the Milky Way?
they were dim
