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Eppur Si Muove: Galileo’s Big Night

Jupiter and its four largest “Galilean” moons photographed on April 16, 2016. © Jason Major

On this night in 1610 the Pisan astronomer Galileo Galilei looked up at a bright Jupiter at opposition through his handmade telescope and noted three little “stars” next to it, piquing his natural scientific curiosity. Further observations over the next few nights showed that the planet wasn’t moving relative to the little “stars” as it would have if they were indeed background stars. In fact the smaller objects (of which he soon saw four) were moving along with Jupiter, each in its own little path. He realized that the little objects weren’t stars at all but rather moons orbiting the giant planet—and, most importantly, not the Earth. This revelation helped change our entire view of the Solar System… and caused no end of trouble for Galileo as the Church didn’t appreciate a restructuring of their conveniently Earth-centered Universe. But it also opened the door for later discoveries of many more moons around other planets.

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Eppur Si Muove: Galileo’s Big Night, 407 Years Ago Today

Jupiter and its four largest "Galilean" moons photographed on April 16, 2016. © Jason Major

Jupiter and its four largest “Galilean” moons photographed on April 16, 2016. © Jason Major

407 years ago tonight, on January 7, 1610, the Pisan astronomer Galileo Galilei looked up at a brilliantly-shining Jupiter through his own handmade telescope and saw three bright little “stars” next to it, stirring his natural scientific curiosity. Further observations over the next several nights showed that the planet wasn’t moving relative to the little “stars” as it should if they were distant background stars, but rather the bright objects (of which he soon saw four) were moving along with Jupiter. Galileo correctly concluded that those little objects weren’t stars at all but rather moons that orbited the distant planet—and, most importantly, not the Earth. This cosmic revelation forced a change of the entire view of our solar system (causing no end of trouble for Galileo as the Church didn’t appreciate a challenge to their Earth-centered Universe) but also opened the door for the discovery of many more moons around other planets.

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Watch a Moonwalker Prove Galileo Right: Dave Scott’s Famous Hammer-Feather Drop

On August 2, 1971, at the end of the last EVA of the Apollo 15 mission, Commander David Scott took a few minutes to conduct a classic science experiment in front of the TV camera that had been set up just outside the LM Falcon at the Hadley Rille landing site. Scott, a former Air Force pilot, recreated a famous demonstration often attributed to Galileo (which may or may not have actually been performed by the astronomer in Pisa in 1586) that shows how objects of different masses react the same way to gravity when dropped – that is, they fall at the same rate.

By performing the “acceleration test” in the vacuum environment of space (but where there is still an observable downward pull of gravity) the Earthly factor of air resistance is negated – especially on such a low-mass and low-density object as a falcon feather – thereby creating a more “pristine” setting for the centuries-old experiment than could ever be achieved here.

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Watch Juno’s Arrival at Majestic Jupiter, Moons and All

We are the stewards of over 400 years of scientific exploration of our Solar System, which it could be said began in earnest when Galileo Galilei first observed the motions of Jupiter’s moons in his homemade telescope in 1610. Over the centuries our knowledge—and our curiosity—about the seemingly endless variety of worlds in the Solar System has grown in leaps and bounds since Galileo’s first peeks at Jupiter, with increasingly more powerful telescopes both on Earth and in space and eventually even machines sent to join the planets in orbit around the Sun.

Last night NASA’s Juno spacecraft became humanity’s most recent emissary to the Solar System’s biggest planet, successfully performing the rocket burns needed to enter orbit around Jupiter—the first spacecraft to do so in 13 years. Amongst much excitement and deserved congratulations of the mission team, the video above was released showing Juno’s view as it approached the enormous planet the week before arrival after five years and 1.7 billion miles of travel. It’s dramatic and impressive and beautiful…just as it should be, considering the scope and achievement of the mission and the information that will soon be returned. Congratulations Juno!

“With Juno, we will investigate the unknowns of Jupiter’s massive radiation belts to delve deep into not only the planet’s interior, but into how Jupiter was born and how our entire solar system evolved.”
— NASA Administrator Charles Bolden

Learn more about the Juno mission here and visit the NASA site here.

(HT to Rachelle Williams @AstroAnarchy for the video tip.)

The Hammer-Feather Drop: Watch Apollo 15 Commander Dave Scott “Do a Science” on the Moon

On August 2, 1971, at the end of the last EVA of the Apollo 15 mission, Commander David Scott took a few minutes to conduct a classical science experiment in front of the TV camera that had been set up just outside the LM Falcon at the Hadley Rille landing site. Scott, a former Air Force pilot, recreated a famous demonstration often attributed to Galileo (which may or may not have actually been performed by the astronomer in Pisa in 1586) that shows how objects of different masses react the same way to gravity when dropped – that is, they fall at the same rate.

By performing the “acceleration test” in the vacuum environment of space (but where there is still an observable downward pull of gravity) the element of air resistance is negated – especially on such a low-mass and low-density object as a falcon feather – thereby creating a more “pristine” setting for the centuries-old experiment than could ever be achieved on Earth.

According to a report on the mission’s science objectives: “During the final minutes of the third extravehicular activity, a short demonstration experiment was conducted. A heavy object (a 1.32-kg aluminum geological hammer) and a light object (a 0.03-kg falcon feather) were released simultaneously from approximately the same height (approximately 1.6 m) and were allowed to fall to the surface. Within the accuracy of the simultaneous release, the objects were observed to undergo the same acceleration and strike the lunar surface simultaneously, which was a result predicted by well-established theory, but a result nonetheless reassuring considering both the number of viewers that witnessed the experiment and the fact that the homeward journey was based critically on the validity of the particular theory being tested. ” (Joe Allen, NASA SP-289, Apollo 15 Preliminary Science Report, Summary of Scientific Results, p. 2-11. Source.)

Launched on July 26, 1971, Apollo 15 was the first of the “J” missions capable of a longer stay time on the moon and greater surface mobility, thanks to the use of the Lunar Roving Vehicle (LRV).Learn more about the Apollo 15 mission here.

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