If we plot the apparent brightnesses of stars in a globular cluster versus their surface temperatures in a similar way as in the HR diagram , there will be a horizontal branch . Which of the following statements about these horizontal branch stars is wrong ? (A)They have the same absolute magnitude . (B)They have different sizes . (C)Their sole source of energy is hydrogen shell burning . (D)They can help us estimate the distance of the globular cluster from us .

If we plot the apparent brightnesses of stars in a globular cluster versus their surface temperatures in a similar way as in the HR diagram , there will be a horizontal branch . Which of the following statements about these horizontal branch stars is wrong ? (A)They have the same absolute magnitude . (B)They have different sizes . (C)Their sole source of energy is hydrogen shell burning . (D)They can help us estimate the distance of the globular cluster from us .

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If an open cluster contains 650 stars and is 27 pc in diameter, what is the average distance between the stars? (Hint: On average, what share of the volume of the cluster surrounds each star?)
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Can you please help with Part 2 of 2? Thank you.
If interstellar dust makes an RR Lyrae variable star look 7 magnitudes fainter than the star should, by how much will you over- or underestimate its distance? (Hint: Use the magnitude-distance formula d = 10 mv - Mv + 5)/5.) destimate dactual = Is your calculated value an over- or underestimate? O overestimate O underestimate
Identify the location in the H-R diagram of the phases of stellar evolution. (For each statement select the proper symbol in the picture.) 1) red giant, helium flash2) white dwarf3) red giant with helium burning shell4) hydrogen fusion in shell around core5) helium fusion in core6) envelope ejected, planetary nebula7) main-sequence star8) helium used up, core collapses9) hydrogen used up, core collapses
The figure above shows a track on the H-R diagram corresponding to the evolution of a star like the one you’ve just considered. Six stages are numbered. Six stages of stellar evolution are listed below – for each stage, write the number corresponding to its position on the diagram (four of these stages are the same stages you considered in the first part of this tutorial). Horizontal branch: Asymptotic giant branch: White dwarf: Main sequence: Planetary nebula: Red giant branch: What is the approximate mass of this star, in solar masses? Explain how you can tell.
A galaxy's rotation curve is a measure of the orbital speed of stars as a function of distance from the galaxy's centre. The fact that rotation curves are primarily flat at large galactocen- tric distances (vrot(r) ~ constant) is the most common example of why astronomer's believe dark matter exists. Let's work out why! Assuming that each star in a given galaxy has a circular orbit, we know that the accelera- tion due to gravity felt by each star is due to the mass enclosed within its orbital radius r and equal to v?/r. Here, ve is the circular orbit velocity of the star. (a) Show that the expected relationship between ve and r due to the stellar halo (p(r) xr-3.5) does not produce a flat rotation curve. (b) Show that a p(r) ∞ r¯² density profile successfully produces a flat ro- tation curve and must therefore be the general profile that dark matter follows in our galaxy.
Figure 2 shows the "rotation curve" of NGC 2742. It plots the “radial velocity (V)" (how fast material is moving either toward or away from us) that is measured for objects at different distances (R = radius") from the center of the galaxy. The center of the galaxy is at 0 kpc (kiloparsecs) with a speed of 9 km/sec away from us. (These velocities have been corrected for the observed tilt of the galaxy and represent true orbital velocities of the stars and gas.) 200 100 U4779 -100 As you can see, one side of the galaxy is moving with a negative velocity (spinning toward us), while the other side has a positive velocity (spinning away from us). Using Newton's gravity equation, we will be able to determine the gravitational mass of the entire galaxy and how the mass varies versus distance from the galaxy's center. -200 -8 8 -4 Radius (kpc) Read the following text carefully and follow the instructions: Select five radii spaced evenly from 0-10 kpc across the galaxy. Your selections should…
The answer is not 0.04. I need help!
Why is it that stars of greater mass (and thus possess more fuel for nuclear fusion) spend less time on the main sequence of the H-R diagram than their lower mass counterparts?