July 1, 1770: Lexell’s Comet misses Earth. The comet was discovered by French astronomer Charles Messier in June 1770. It was named for Anders Johan Lexell, a Swedish-born Russian who computed the course of the heavenly body. It is noted for being the comet to pass closest to Earth in all of recorded history. The comet passed by at a distance of 0.0146 astronomical units (au) or 1,360,000 miles. The moon is 238,857 miles from our planet. Because distances are so great in space, the au was developed and is defined at the mean distance between the Earth and Sun or 92,960,000 miles.
Scientists of the time recorded sightings and listed the comet as having a nucleus as large as Jupiter and “surrounded with a coma of silver light, the brightest part of which was as large as the moon’s orb.” Messier not only was the first to find the comet in the constellation Sagittarius, but also the last to see the space traveler as it passed from view on October 3. The comet has not been seen since and is considered to be a lost comet. It may have been so affected by the gravitational forces of Jupiter as to have its course completely altered.
Comets are small solar system bodies bigger than meteoroids. As they near the sun, they exhibit a visible coma and sometimes a tail. Both become visible due to solar radiation affecting the comet’s nucleus. Most are made of ice, dust, and small rocky particles and can be a few hundred yards to miles across. Comets have a variety of orbital periods, some arriving every few years and some with orbits so erratic they only come near after thousands of years. Comets are different from asteroids because comets have a coma and tail. When they lose their volatile substances, they are more like asteroids and become known as extinct comets.
Comets can be ejected from the solar system usually by interacting with the gas giant planets with high gravity wells. They may become extinct after repeatedly approaching the sun and having their volatiles burned away. They may break apart or disintegrate if hit by enough conflicting gravitational forces. They may also collide with other objects, some fall into the Sun and some strike planets or moons. Four billion years ago, when the Earth was young, it is thought many comets collided with the planet and may have been responsible for bringing along water and the precursors of life, if not life itself to Spaceship Earth.
The cosmos is all that is or ever was or ever will be. Our feeblest contemplations of the Cosmos stir us—there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, or falling from a height. We know we are approaching the greatest of mysteries. – Carl Sagan
I have loved the stars too fondly to be fearful of the night. – Sarah Williams
The moon and the stars no longer come to the farm. The farmer has exchanged his birthright in them for the wattage of his all-night sun. His children will never know the blessed dark of night. – Leslie Peltier
Those who study the stars have God for a teacher. – Tycho Brahe
Also on this day:
Four Score and Seven Years Ago – In 1861, the Battle of Gettysburg begins.
Can I Get a Witness? – In 1879, The Watchtower was first published.
Russians Reading – In 1862, the Russian State Library is founded.