Comets and Suicidal Sperm

Photo credit: Ana Trisini/Russ Hauser
Harvard School of Public Health
USA
www.hsph.harvard.edu

A trail of tiny pieces of DNA flow from a dying human sperm cell nucleus. Damaged cells are placed in gel on a microscope slide and stimulated by an electric current. The gel acts like a molecular sieve separating the bits of DNA relative to their size. Fragments are stained with a fluorescent label and can be viewed under the microscope in a darkened room. Long tails are an indicator of severe damage.

Photo credit: Astronomy and Astrophysics
University of Glasgow
Scotland
www.astro.gla.ac.uk

Comets have rocky, dusty, icy hearts. These floating lumps travel around the Sun. Sometimes you can see their tail. As they get closer to the Sun they begin to melt. With time their path may be influenced by other planets. In this way, they can be thrown out of the Solar System or get so close to the Sun that they burn up. The Hale-Bopp comet (pictured) was probably the most famous of the twentieth century being visible to the naked eye for a record eighteen months.