Summary: Henry A. Rowland Department of Physics and Astronomy
The Johns Hopkins University, Baltimore, MD 21218
email@example.com 410-516-7350 http://henry.pha.jhu.edu/rch.html
2011 March 22
City, State, USA
I am in receipt of your interesting letter of last week, in which you requested
information for your project on Dark Matter. I am happy to help!
I enclose a copy of one of the most important astronomical images ever
assembled, which shows the presence of your Dark Matter (the two blue
patches), and which also verifies its genuine existence.
The photograph is a composite from several different sources.
Let me identify the various components, in the following list:
The two blue patches are gravitational lens images of some of your Dark
Matter. Dark Matter makes up about 20% of all the stuff in the Universe.
The two red patches (one of which is bullet shaped) are ordinary matter
(same as you and I are made of) in the form of very hot gas--a few million
degrees. Ordinary matter makes up about 5% of all the stuff in the Universe.