final exam Flashcards
A star is 230 light-years away. The light we see tonight from that star left it
Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.
The point in the sky directly above your head at any given time is called the
zenith
The path that the Sun appears to make in the sky over the course of a year is called the celestial equator
FALSE
The great astronomer of ancient times who summarized and improved a system of circles upon circles to explain the complicated motions of the planets (and published the system in a book now called The Almagest) was
Ptolemy
The scientist who first devised experimental tests to demonstrate the validity of the heliocentric model of the solar system was
Galileo
The celestial sphere turns around once each day because
Our position on a rotating Earth causes the stars, planets, and Sun to appear to revolve around us.
Which ancient Greek thinker suggested (long before Copernicus) that the Earth is moving around the Sun?
Aristarchus i
In this diagram of the celestial sphere, there are five lines that point to different parts of the picture. Use the drag-and-drop environment to label the indicated parts of the figure.
The location of the figure defines which direction the zenith is located: always directly overhead of the observer. This point travels with the observer, in a sense, and the horizon with it since the horizon is 90° from the zenith in all directions.
The North Celestial Pole, on the other hand, is fixed against the background stars based on the direction our planet’s rotational axis points, so its position in one’s local sky may vary as a result of one’s location on the Earth’s surface, and the Celestial Equator with it since the Celestial Equator is 90° from the North Celestial Pole in all directions.
At the Earth’s equator, you would see the celestial poles on your horizon.
true
How did Eratosthenes measure the size of the Earth?
The memory aid “altitude = latitude” applies to the north celestial pole’s altitude as seen from a particular latitude on Earth, but the idea translates to observing the Sun as well. Although the Sun’s altitude from a particular latitude depends on the time of year, the difference between the observed altitude of the Sun from two latitudes at local solar noon, tells you the difference in latitude between those two locations.
Eratosthenes took advantage of this idea by comparing the altitude of the Sun h1
at noon as seen from his town (measured by observing the shadow cast by a pillar or post in the ground) with the altitude of the Sun h2
at noon as seen from a different town to the south. He recognized that the difference between the two observed altitudes compared to the full 360 degrees in a circle is equal to the distance between the two towns d
compared to the full circumference of the Earth C
:
h1−h2/360∘=dC
From this expression he was able to calculate the circumference of the Earth in the same physical units as the distance between the two towns.
In an ellipse, the ratio of the distance between the foci and the length of the major axis is called
eccentricity
remember newtons laws
ok
Consider an ellipse with a major axis of l = 6 cm and an eccentricity of e = 0.71.
Part (a) What is the length of the semimajor axis a
, in cm?
The semimajor axis a
of an ellipse is half the major axis; the eccentricity plays no role in this calculation.
a=l/2 =6 cm / 2
a=3.000 cm
Kepler’s third law relates a planet’s orbital period to the semi-major axis of the orbit.
TRUE
The diagram below shows the seasons that our planet Earth undergoes for the Northern Hemisphere. The position of the Earth is labeled for one of the key seasonal dates, the Autumnal (Fall) Equinox. Label the other three positions correctly. Note the blue arrow on the circle of the Earth’s orbit, which shows which way the Earth moves.
just google it
Which of the following statements about electromagnetic radiation is FALSE?
Not only are photons (the particles of light) massless, but they are also electrically neutral.
Which, from among the following options, has the longest wavelength?
The lowest-energy forms of light have the longest wavelengths. These forms of light include infrared waves, microwaves, and (at the absolute longest) radio waves.
A star has a surface temperature of 8800 K. At what wavelength (in nanometers) will it give off maximum light?
This form is useful when we are given a temperature in kelvins (K) or a wavelength in nanometers (nm). Since this is the case, we can solve for the temperature with a little algebra and plugging in the given value of the temperature:
λmax=2.9×10^6 nm⋅K/T
= 2.9×10^6 nm⋅K/ 8800 K
T=329.5 nm
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Understanding Blackbody Radiation: It turns out that stars behave like an idealized object that scientists call a blackbody. Thus, understanding blackbodies and how they give off energy helps us to understand how stars shine. For a blackbody, the higher its temperature, the smaller the wavelength at which it gives off the peak amount of radiation. This is described by wien’s law. Thus, really hot stars will shine most intensely with ultraviolet radiation. Also, the higher a star’s temperature, the greater the flux of radiation coming from it. This last statement is called stefan-Boltzman law.
For all electromagnetic waves, the frequency multiplied by the wavelength will be the same constant number.
True
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When someone who has never thought much about astronomy looks up at the sky, it’s easy to believe that everything turns around the Earth and that we are in the middle of things; such a view is called the geocentric model. Astronomers call the point in the sky above our heads our Zenith, and where the dome of the sky meets the Earth our Horizon. In the 20th century, astronomers divided the sky into 88 boxes, and each box is now called a Constellation. The belt of the sky through which the Sun, Moon, and planets are seen to move in the course of the day and the course of a year is called the Zodiac.
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If you were standing at Earth’s north pole, and you looked up to the zenith (the point directly above your head), you would be looking at the point where the North Celestial pole is located. At the Earth’s North Pole, the celestial equator would be at your Horizon . If, on the other hand, you were at the Earth’s equator, you would see one point of the celestial equator pass through your Zenith If you are looking at the sky from the continental United States, the north celestial pole would have an angular height (an altitude) equal to your Latitude. Right now, the star located very close to our north celestial pole is Polaris.
A light-year is
Equal to approximately 9.5 trillion km, or 5.9 trillion miles, the distance that light travels in one Earth year is a commonly-used unit of length or distance in astronomy.
A star is 230 light-years away. The light we see tonight from that star left it
Because light travels a distance of one light-year in one year of time, it will travel a distance of 230 light-years in 230 years of time. This means that if we are receiving the light tonight, it has been traveling for 230 years from the source in order to reach us.