2. As discussed in section 27.3 of Carroll & Ostlie, the Virgo Cluster of galaxi
ID: 1770852 • Letter: 2
Question
2. As discussed in section 27.3 of Carroll & Ostlie, the Virgo Cluster of galaxies contains 250 large galaxies (as larger or many times larger than the Milky Way) and thousands of smaller galaxies. In contrast, the Local Group (in which our Milky Way Galaxy is a member) contains only 3 large galaxies and dozens of smaller ones. The Virgo cluster is 16 Mpc distant from the Milky Way Galaxy. Suppose you are an astronomer orbiting a star in the Virgo Cluster, and you are observing the Milky Way and the Local Group of galaxies.
(a.) What would be the angular size of the Local Group ?
(b.) What would be the angular size of the Milky Way ?
(c.) What would be the apparent B magnitude of the Milky Way ? Be sure to justify values you choose (that is, if you use a physical size of the Local Group, Milky Way, etc, be sure to explain where you obtain that number).
Explanation / Answer
(a) the angulr size of the group depnds upon the angular diameter and the plane paerpendicular to the diameter of the group.
So, the local group's diameter will be thrice the diameter of a galaxy
= 3*1.8*10^5 LY
= 5.4*10^5 LY
(b) The angular size of the milky way depends upon the its angular diamter. so, the angilar diameter of the milky way is given as
= 1.8*10^5 LY
(c) The apparent B magnitude describes the brightness of a particular star. There are many stars having B value in negative which are quite bright and visible but then there are some stars whose B value is greater than 6.5 and they are invisible.
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