Waltz of the Cosmos: Galileo's Steps of Discovery Quiz

Answer: All objects fall at the same rate

Around 1604, Galileo showed that, when air resistance is neglected, all objects fall at the same rate regardless of their mass. Before this, Aristotle had taught that heavier objects fall faster.

Galileo's experiments in this area are often said to have involved dropping balls from the Leaning Tower of Pisa to show that, in a vacuum and without air resistance, all bodies accelerate equally under gravity. This story came from his student, Vincenzo Viviani, and was written decades later. Most historians now believe it's untrue.

He did, however, investigate falling motion very carefully using balls rolling down inclined planes. This allowed him to study motion in a controlled way and support his principle.

Answer: Telescope

In 1609, Galileo improved the telescope. He worked with skilled lens grinders and spectacle lenses to build instruments that increased in power from about 3x magnification to roughly 20-30x.

With his enhanced telescopes, he observed the Moon, planets, and the Milky Way between 1609 and 1613 and discovered features such as the surface of the Moon, Jupiter's moons, and countless faint stars in the Milky Way.

Answer: Mountains and craters

In 1610, Galileo, using his improved telescope to observe the Moon, discovered that it had mountains and craters. This showed that its surface wasn't a perfect, unblemished sphere.

His sketches showed that the lunar landscape was rugged, with peaks, craters, and valleys, making the moon more like the Earth than previously believed. It contrasted with Aristotle's idea that heavenly bodies were smooth, perfect, and unchanging.

He also estimated the heights of some lunar mountains by measuring the shadows they cast, and published these discoveries in his famous work 'Sidereus Nuncius' ('Starry Messenger') in 1610.

Answer: Jupiter's four moons

Galileo discovered Jupiter's four largest moons (Io, Europa, Ganymede, and Callisto) in 1610. These are now known as the Galilean moons.

This proved that not all celestial bodies orbit Earth and showed that Jupiter had its own system. Before this, the geocentric model held that Earth was the fixed centre of all motion. Galileo's discovery supported the Copernican heliocentric model.

Answer: It was made of countless stars

A discovery by Galileo in 1610 changed humanity's understanding of the cosmos. Using his improved telescope, he found that the Milky Way was made of countless stars packed together.

This overturned older ideas that it was just a cloud or atmospheric phenomenon, as it had previously appeared as a hazy band of light to the naked eye. It also expanded humanity's sense of the universe's scale. Galileo's observations showed how important the telescope was as a scientific tool, by revealing that the universe contained far more stars than was believed.

Answer: The Sun rotates

In 1611, Galileo observed dark spots on the Sun's surface, which showed that it rotates on its axis with a period of about 27 days as seen from Earth. This challenged the old belief that heavenly bodies were flawless and unchanging, as Aristotle had proposed.

By tracking sunspots moving across the solar surface, he showed the Sun was dynamic and spinning. Although others, like Christoph Scheiner, also observed sunspots and there was some priority controversy, Galileo's observations and interpretations were important to understanding their significance.

Answer: Phases of Venus

In 1610, Galileo observed the phases of Venus, providing evidence for the heliocentric model (published in 1613). By showing Venus going through a full set of phases like the Moon - from crescent to gibbous to full and back - he demonstrated it must orbit the Sun, not Earth.

He also noted Venus appeared larger in crescent phase and smaller when nearly full, exactly as expected in a Sun-centred system. This supported Copernicus and was incompatible with the Ptolemaic geocentric model.

Answer: Rings

Between 1610 and 1616, Galileo saw strange shapes around Saturn through his telescope. At first, he thought Saturn might have 'ears' or small bodies attached to it, as his telescope wasn't powerful enough to show them clearly.

Over time, the shapes seemed to disappear and then reappear, which completely puzzled him. The true nature of what he was seeing remained a mystery during his lifetime.

Later, in 1655, using a better telescope, Dutch astronomer Christiaan Huygens realised these shapes were actually rings surrounding Saturn. Galileo's early observations, though unclear, were the first glimpse humanity had of Saturn's ring system.

Answer: Two New Sciences

While under house arrest following his trial by the Inquisition in 1638, Galileo published 'Discourses and Mathematical Demonstrations Relating to Two New Sciences' (often called 'Two New Sciences'). It summarised his lifetime work on motion and the strength of materials. It was published in Leiden, Netherlands, outside the reach of the Catholic Church's censorship.

This book is considered important because it laid the foundations for modern physics by analysing kinematics (motion science) and material resistance. It also introduced uniformly accelerated motion and scaling laws for structures. It influenced Isaac Newton's laws of motion and classical mechanics.

Answer: Inertia

In his later work, Galileo described the principle of inertia, a foundation of modern physics. It states that 'an object remains at rest or continues in uniform straight-line motion unless acted upon by an external force'.

He illustrated this with his famous ship analogy: experiments in a ship's cabin yield the same results whether the ship is at rest or moving smoothly at constant speed.

This challenged Aristotle's view that objects need continuous force to stay in motion and paved the way for Newton's First Law. Galileo's shift from 'why do things move?' to 'why do they stop?' transformed physics and mechanics.