Earth's Rotation Day

Most of us probably know that the Earth rotates on a nearly vertical axis every 24 hours, which is one Earth day But this basic knowledge was not always so certain In 1851, French physicist Leon Foucault demonstrated how our planet rotates using his now famous pendulum Today, Foucault pendulums are an integral part of science museums around the world This simple but brilliant invention uses a suspended lead ball to show the Earth's rotation throughout the day The pendulum is surrounded by small pins arranged in a circle, which the pendulum knocks down one by one, eventually making a full revolution Earth Rotation Day commemorates the first public demonstration of the Foucault pendulum and, as far as we know, has historically been observed on the anniversary of this event, January 8th At the same time, it is not known exactly who was the first to celebrate Earth Rotation Day The Earth's rotation and its connection to our daily cycles have fascinated philosophers and scientists for thousands of years As early as 470 BC The ancient Greeks assumed that the Earth itself was moving, and not the rest of the sky rotating around us In the 10th century AD, Muslim astronomers began building the astrolabe (astronomical observatory) and other instruments to measure the Earth's motion relative to the stars The first human images of space date back to 1600 BC A bronze disk found in northern Europe depicts the Sun, a crescent moon and the Pleiades star cluster, and Babylonian written records record the positions of the celestial bodies These records, probably the earliest scientific observations, make astronomy the oldest known science Although people had been observing the stars for thousands of years—some early theories suggested that the Earth was moving—geocentric theory remained dominant in Europe until the work of Nicolaus Copernicus in the 1500s proved that the Earth did indeed revolve around the sun After his work, others tried to prove the rotation of the Earth through various experiments While the theory was accepted by the mid-1800s thanks to observations of astronomical movements, it was Foucault's pendulum that clearly demonstrated the rotation of the Earth Foucault first conducted his pendulum experiment at the Paris Observatory and then at the Pantheon, where it remains an impressive centerpiece today Although they vary in size, pendulums work best with long lines, typically 12 to 30 meters A heavy swinging lead bob is suspended from the end of a fishing line Rocking back and forth, it moves slowly clockwise as the Earth rotates beneath it Today, Foucault pendulums are an integral part of science museums, observatories and universities around the world Foucault's device can now be found in science and astronomy museums around the world Check out your local museums and see if you can find one near you! Did you know that an astronomical day is not exactly 24 hours? Or that the Earth is tilted at an angle of 221 to 245 degrees? Earth Rotation Day is a great opportunity to brush up on astronomy facts Science teachers are some of the people who help us make sense of the world and spark our curiosity about how things work Take time to thank your science teacher for all of his or her work The Earth's molten iron core creates a strong magnetic field that directs the solar wind around the Earth, protecting us from the harmful effects of solar radiation Although our calendar year has 365 days, a full solar year contains an extra quarter day, leading to the tradition of adding "leap" days every 4 years The Earth's rotation speed decreases by about 17 milliseconds every hundred years At this rate, it will take more than 100 million years for our day to lengthen to 25 hours The Earth's surface is 70% covered with water Of this, 97% is salt water and only 3% is fresh! By studying rocks in different parts of the globe, scientists have calculated that our planet is about 45 billion years old!