Use the Starry Night Enthusiast™ program to measure the
dimensions of the Milky Way Galaxy. Select Favorites
Stars Sun in Milky Way to move to a position 0.15 Mly
above the galactic plane, directly above the position of the
Sun. (If the Milky Way does not appear immediately, click
once on the Zoom button.) Remove the image of the astronaut’s feet by clicking on View Feet. You can rotate the
Milky Way Galaxy by putting the mouse cursor over the image, holding down the Shift key and the mouse button, and
moving the mouse. (a) Rotate the Galaxy so that you are seeing it face-on. Use the Hand Tool to measure the distance on
the screen from the position of the Sun to the center of the
Galaxy, noting this value in both linear distance in light-years
and in the subtended angle when viewed from the observer’s
position. This measurement will calibrate angular measurements in terms of linear distance when seen from this viewpoint. (b) Use the Hand Tool to measure several distances
from galactic center to the fringes of the galaxy. (Note: These
distances will often be displayed in both angular and linear
dimensions.) Estimate the diameter of the galaxy in lightyears. (c) Rotate the Galaxy so that you are seeing it edgeon. Use the Hand Tool to mea sure the angle subtended from
the center of the galaxy to the upper edge of the central bulge
of the Galaxy. Use the above measurements of the Sun-Galactic Center in both angle and linear dimension and simple proportions to calculate the half-width of the galactic bulge and
multiply this number in light years by 2 to determine the
bulge diameter. You can use the relationship between parsecs
and light-years (1 pc 3.26 light-years) to calculate this diameter in parsecs. (d) Calculate the thickness-to-diameter ratio of the Milky Way Galaxy.