Stars as Friends

Stars as Friends

After Eratosthenes’ discovery, many great voyages were attempted by brave and venturesome sailors. Their ships were tiny, they had only rudimentary navigational instruments, they used dead reckoning and followed coastlines as far as they could. In an unknown ocean they could determine their latitude, but not their longitude, by observing, night after night, the position of the constellations with respect to the horizon. The familiar constellations must have been reassuring in the midst of an unexplored ocean.

The Mediterranean world at that time was famous for seafaring. Alexandria, in Egypt, was the greatest seaport on the planet. Once you knew the Earth to be a sphere of modest diameter, would you not be tempted to make voyages of exploration, to seek out undiscovered lands, perhaps even to attempt to sail around the planet? Four hundred years before Eratosthenes, Africa had been circumnavigated by a Phoenician fleet in the employ of the Egyptian Pharaoh Necho. The set sail, probably in frail open boats, from the Read Sea, turned down the east coast of Africa up into the Atlantic, returning through the Mediterranean. This epic journey took three years, about as long as a modern Voyager spacecraft takes to fly from Earth to Saturn.

The stars are the friends of explorers, then with seagoing ships on Earth and now with spacefaring ships in the sky. Image : Elena

Stars High in the Sky

Some stars, the supernovae are as bright as an entire galaxy that contains them; others, the black holes, are invisible from a few kilometers away.

Some stars shine with a constant brightness; other flicker uncertainly or blink with an unfaltering rhythm.

Some rotate in stately elegance; others spin so feverishly that they distort themselves to oblateness.

Most shine mainly in visible or infrared light and others are also brilliant sources of X-rays and radio-waves.

Blue stars are hot and young; yellow stars, conventional and middle-aged; red stars, often elderly and dying; and small white or black stars are in the final throes of death.

Let’s remind you that the Milky Way, one of the billions of galaxies, contains some 400 billions of stars of all sorts moving with orderly and serene grace.