Stellar and galactic crowding: The comparison of objects' sizes to the distance between them gives a sense of their relative density, i.e., how "crowded" they are. A typical human is about 1 meter across the shoulders
Compare the relative density of people in the case where they are standing on average 1 meter apart compared to a situation where they are on average 10 meters apart (hint: describe the separation in units of person-size). Now, compare the "crowding" of stars to that of galaxies. A typical star has a diameter of about 1 million km, while the average space between stars is about 5 light-years. A typical spiral galaxy in a cluster (such as the Milky Way) is 100,000 light-years across, and has another spiral galaxy within about 10 million light years.
Students should reference the ratio of distance to size (or vice versa), to show that compared to their size, stars are much, much further apart than galaxies.
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If you measure a parallax of 0.006 arc seconds from an observatory on the ground, your uncertainty will be about _____
A) 10 percent B) 75 percent C) 30 percent D) 57 percent
) Based on observations, which of the following statements about stars in the Milky Way is generally true?
A) the older the star, the lower its abundance of heavy elements B) the older the star, the bluer its color C) the older the star, the faster its orbital speed D) the younger the star, the higher its mass E) the less massive the star, the older it is
The efficiency of classroom-demonstration lasers is typically
A) about one percent. B) about ten percent. C) about twenty percent. D) more than twenty percent.
The average distance of the electron from the proton in the hydrogen atom is 0.51 × 10^-10 m. What is the electric field from the proton's charge at the location of the electron? (ke = 8.99 × 10^9 N×m2/C2, e = 1.6 × 10^-19 C)
a. 8.8 × 10^-8 N/C c. 3.2 × 10^2 N/C b. 1.0 × 10^6 N/C d. 5.5 × 10^11 N/C