Chapter 13
The star Wemadeit shows a stellar parallax angle of 0.3 seconds of arc while the star Waytoofar shows a stellar parallax angle of 0.2 seconds of arc. From this, you can conclude that
Wemadeit is closer to our Sun than Waytoofar.
The main reason that telescope mirrors can be much larger than lenses is that the mirrors
are lighter because they are thinner.
Think of the `front' of a telescope as the end that light enters. A telescope with Cassegrain Focus has the eyepiece
at the back of the telescope.
The problem of stars "twinkling" due to atmospheric turbulence
can be corrected by using a guide star
Ham radio operators sometimes operate receivers for the 2 meter wavelength. The 2 meters refers to the
distance from one maximum of the radio waves to the next.
A converging lens will send the light from a distant star through a point
on the focal plane of the lens
For a visual binary star system, we can determine
the masses of both stars in the system.
Heliocentric Stellar Parallax causes
nearby stars to shift back and forth once a year.
Which of the following magnitudes corresponds to the dimmest star?
+4
A star is seen to move by 2 seconds of arc between February 1, 1999 and August 1, 1999 and then back to its starting point on February 1, 2000. What is the parallax angle for this star?
1 seconds of arc
The velocity of sound waves is roughly the same for all wavelengths. Suppose that a sound wave has a wavelength of one meter and a frequency of 500Hz. The wavelength of a 1000Hz sound wave would then be
1/2 m
A starship observes that a nearby star has apparent magnitude 4.0. The spectrum of the star indicates that it is a type that normally has absolute magnitude 4.0. From these observations, the starship knows that it is
10 parsecs from the star.
The apparent brightness of our Sun is roughly 1000 watts per square meter. Saturn is at roughly 10 astronomical units from our Sun (slightly less actually). Viewed from Saturn, the apparent brightness of our Sun would be
10 watts per square meter.
A star is found to have absolute magnitude 9 and apparent magnitude 24. How far away is it?
10,000 parsecs
Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude 4.8. If the star's apparent magnitude is found to be 14.8, how far away is it?
1000 parsecs
A star at a distance of 1000pc should have an apparent brightness equal to its absolute brightness multiplied by
10⁻⁴
Barnard's Star shows a heliocentric stellar parallax near 1/2 seconds of arc. The distance from our Sun to Barnard's Star is
2 parsecs.
The violet lines in the Hydrogen spectrum are normally seen with wavelengths 410 nm and 434 nm. In the light of a star that is moving away from us, we might expect to see those lines at wavelengths of
415 nm and 439 nm
You hear a 1000Hz tone from a radio that is 20 feet away from you and listen for 5 seconds. How many pressure maxima pass by your ear?
5000
A star whose apparent brightness is 1/100 that of a first magnitude star would have magnitude
6
The star Vega is 25 parsecs from our Sun. The light from Vega has been traveling for about
80 years.
Epsilon Eridani shows a proper motion of 0.97661 arc seconds per year. In 100 years, its position in the sky changes by
97.661 seconds of arc.
Of all the things that might go wrong with distances found by using the method that astronmers refer to as the "distance ladder," which of these is the one that an astronomer would say is most likely?
Distant objects are not behaving the same as nearby objects.
We see what appears to be a single star. However, when the light from the star is put through a spectrometer, we see two distinct spectra, shifting back and forth. The star is actually
a double-line spectroscopic binary system.
A mirror that is supposed to bring light from a star directly overhead to a focus must be shaped like
a shallow bowl with the open part facing up.
To see a large but faint object such as a nebula, you would need a telescope with large
light gathering power
Suppose that a star has a spectrum that includes red, blue, and violet lines spaced in the pattern of the lines from hydrogen but the red line is has a wavelength of 660 nm instead of the usual 656 nm. From this evidence, you can conclude that the star is
moving away from us.
For a spectroscopic binary star system, we can determine
only a minimum mass for each star.
Consider a light source whose absolute magnitude can be deduced from the properties of the light that reaches us from that source. Astronomers often refer to this sort of object as a
standard candle.
A star with an apparent magnitude of 8.4 and an absolute magnitude of -1.0 would appear in our sky as a star
that is visible only with a telescope.
To calculate the velocity of a wave, you need to know
the distance traveled by a wave crest and the time taken.
For an eclipsing spectroscopic binary star system, we can determine
the masses and diameters of both stars in the system.
