Astronomy 1 Midterm 3 Study (Ch. 15)

Approximately what is the parallax angle of a star that is 20 light-years away?

0.16 arcsecond d(in light-years) = 3.26 × 1 -------- p(in arcseconds) or p(in arcseconds) = 3.26 × 1 -------- d(in light-years) *Using a distance of d = 20 light-years, this formula gives the parallax angle to be p=3.26/20=0.163 arcsecond.

Stars that are cooler than the Sun yet 100 to 1,000 times as luminous as the Sun are classified as ____________.

giants

Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________.

hotter and smaller in radius

Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________.

less luminous, cooler, smaller, and less massive

Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?

3.3 light-years *1 parsec = 3.26 light-years.

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

All five stars appear at the same place along the horizontal axis showing spectral type. Because spectral type is related to surface temperature, all five stars must have the same surface temperature. Now proceed to Part C to determine how these stars vary in luminosity.

Five stars are shown on the following H-R diagrams. Rank the stars based on their luminosity from highest to lowest; notice that these are the same five stars shown in Part D. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

All five stars have the same luminosity because they are all at the same height along the vertical (luminosity) axis. Continue to Parts F and G for more practice in reading surface temperature and luminosity on the HR diagram.

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part F. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

As always, the H-R diagram shows surface temperature along the horizontal axis and luminosity along the vertical axis.

Listed following are several fictitious stars with their luminosities given in terms of the Sun's luminosity (LSun) and their distances from Earth given in light-years (ly). Rank the stars based on how bright each would appear in the sky as seen from Earth, from brightest to dimmest. If two (or more) stars have the same brightness in the sky, show this equality by dragging one star on top of the other(s).

Brightest to dimmest: Nismo: 100LSun, 8 ly Shelby: 100LSun, 10 ly & Ferdinand: 400LSun, 20 ly (overlapped) Enzo: 200LSun, 20 ly Lotus: 400LSun, 40 ly

Listed following is the same set of fictitious stars given in Part A. Rank the stars based on how bright each would appear in the sky as seen from Jupiter, from brightest to dimmest.

Brightest to dimmest: Nismo: 100LSun, 8 ly Shelby: 100LSun, 10 ly & Ferdinand: 400LSun, 20 ly (overlapped) Enzo: 200LSun, 20 ly Lotus: 400LSun, 40 ly

What is the cause of stellar parallax?

Earth's orbit around the Sun.

The following figure shows how four identical stars appear in the night sky seen from Earth. The shading is used to indicate how bright (white) or dim (dark gray) the star would appear in the sky from Earth. Rank the stars based on their distance from Earth, from farthest to closest.

Farthest (darkest) to closest (brightest)

Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.

Highest to lowest: -a blue white dwarf star -Sun -an orange main-sequence star -a red supergiant star

Which of the following is a valid way of demonstrating parallax for yourself?

Hold up your hand in front of your face, and alternately close your left and right eyes.

Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part B. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).

Luminosity is shown along the vertical axis, with stars higher up more luminous than those lower down. Note that each tickmark along the luminosity axis represents a change by a factor of 10 from the prior tickmark, so the range of luminosities is quite large. Continue to Parts D and E to investigate surface temperature and luminosity for a different set of five stars.

Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are correct).

Observe directly:

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram.

Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________.

cooler and larger in radius

Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.

Red giant or supergiant stars: -very cool but very luminous -found in the upper right of the H-R diagram Main-sequence stars: -the majority of stars in our galaxy -the hottest and most luminous stars -the Sun, for example White dwarfs: -very hot but very dim -not much larger in radius than Earth

Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).

Spectral type is related to surface temperature, with stars of spectral type O having the highest surface temperature and stars of spectral type M having the lowest surface temperature. In other words, spectral type increases to the left on the H-R diagram. Now proceed to Part E to determine how these stars compare in luminosity.

Before we can use parallax to measure the distance to a nearby star, we first need to know __________.

The Earth-Sun distance

_________________ are no longer generating energy through nuclear fusion.

White dwarfs

Stars are classified on the basis of their spectral type and _____________.

luminosity class

The _____________________ is greater for low-mass stars than it is for high-mass stars.

main-sequence lifetime

Most of the stars near the Sun are ____________________.

main-sequence stars

Cepheids are examples of ___________________.

pulsating variable stars

The more distant a star, the __________.

smaller its parallax angle

The stars known as _________________ are the very largest and brightest of all the stars.

supergiants