Homework 1: Distance to the Galactic Center

Due: By 5 pm, Tuesday, January 23, 2007. Turn in hard-copy; do not submit the assignment electronically.

The Milky Way is an Sb spiral galaxy. The above image shows a nice panoramic view of our Galaxy (an image made from the position of the Sun in the disk). In this exercise we deduce the location of the Sun from the center of the galaxy. To do so, we use globular clusters (ancient star clusters that populate the halo of the Milky Way galaxy--globular clusters are NOT confined to the disk of the Milky Way. The globular clusters are roughly spherically distributed about the center of the Milky Way. The galactic coordinates and distance projected onto the line of sight to the galactic center of several globular clusters are given below.

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                           NGC         l      b      X(kpc)

1. Plot the positions of the globular clusters on the graph below. Set (l,b) = (0^o,0^o) at the center of the disk. The north galactic pole has latitude b=90^o. The south galactic pole has b=-90^o. The longitude increases from l=180^o to 360^o (=0^o) at the center to 180^o at the right edge of the plot.

2. The projected distances can be used to estimate how far the Sun is from the center of the Milky Way galaxy. How can the projected distances be used to find the distance to the galactic center? Estimate the distance to the galactic center using the projected distances.