Your Birth Star

Name any event in history and you will find a star out there whose light gives you a glimpse of something happening during the year of that event. Provided you are not a very young child, somewhere up in the night sky you can find your personal birth star. Its light is a thermonuclear glow that heralds the year of your birth. Indeed, you can find quite a few such stars (about 40 if you are 40; about 70 if you are 50; about 175 if you are 80 years old). When you look at one of your birth year ...

 Relative Sizes of Structures in the Brain

Linear measure- ments and dimensions generally are given in microns or micrometers (µm) (1 µm equals one- millionth of a meter) or nanometers (nm) (1 nm or millimicron equals one-billionth of a meter). About 240,000 µm equal one inch. As a reference, the following are the dimen- sions of some non-neural structures: human ovum, 100 µm; cross-section of a skeletal muscle fiber, 10-100 µm; erythrocytes, 8–10 µm; bacteria, 0.1–8 µm; and viruses, 0.15–0.5 µm. Cell bodies of neurons...