Happy Galileo Day!

Star Walk
4 min readFeb 15, 2021


On February 15, astronomy lovers celebrate Galileo Day. In today’s article, we’ll talk about who Galileo was and give tips on how you can join the celebration.

Especially for Galileo Day, we’ve prepared a fun and educational quiz about great astronomers of the past — you should definitely check it out and test your knowledge about astronomy!

Who was Galileo Galilei?

Galileo Galilei (February 15, 1564 — January 8, 1642) was an outstanding Italian scientist who made significant contributions to astronomy, physics, engineering, and mathematics.

Due to his studies and discoveries, he’s considered one of the key figures in the history of modern science and the initiator of the Scientific Revolution.

What did Galileo do for astronomy?

Galileo’s astronomical achievements include the telescopic confirmation of the phases of Venus, the observation of the four largest moons of Jupiter, the observation of Saturn’s rings, and the analysis of sunspots. He’s often called the “father of observational astronomy”, because he was the first person to use a telescope to observe celestial bodies.

What is Galileo’s telescope?

All his famous observations Galileo made with the help of a telescope he created himself. As a prototype, he used spyglasses invented in 1608 — low-powered telescopes capable of magnifying objects three times. In 1609, after figuring out how spyglasses worked, the scientist built his own improved version that could magnify a normal vision 8 times. As Galileo kept working on his invention, he made a telescope capable of 20x magnification a few years later. Nowadays, amateur astronomers use telescopes with 20x or 30x magnification for planet viewing.

Galileo’s telescopes were not flawless, as they had a very narrow field of view, making finding objects more difficult. Nevertheless, it didn’t stop Galileo from observing. With the help of his optics, the scientist proved that the Moon isn’t a smooth sphere but has a unique landscape, revealed Venusian phases similar to the Moon, and confirmed that Venus orbits the Sun, not the Earth (as people commonly believed back then).

Galileo and the Copernican theory

Galileo also supported Copernican heliocentrism, which was considered a heretical teaching by the Catholic Church. Because of his scientific views about the model of the Universe, he was condemned by the Inquisition and sentenced to imprisonment and then house arrest for the rest of his life. He was also forced to publicly recant the Copernican theory. There’s a legend that after recanting, Galileo said the phrase “And yet it moves!” meaning: “despite my recantation, the Earth does move around the Sun and not vice versa!”.

5 facts about Galileo

Galileo didn’t invent the telescope

Despite popular misconception, all credits for the invention go to a Dutch eyeglass maker Hans Lippershey. However, Galileo became the first person to use a telescope to study the sky systematically.

Four years before death, Galileo became blind

But not because of the multiple Sun observations — most likely, the cause was a cataract or glaucoma.

Galileo’s middle finger is on display in a museum

Around a century after the scientist’s burials, the middle finger of his right hand was removed from his corpse and has been housed at various museums in Italy since then.

The Vatican didn’t admit Galileo was right until 1992

Only 30 years ago Pope John Paul II officially declared that Galileo Galilei was right in his support of heliocentrism, and the Inquisition made a mistake by imprisoning him.

Galileo dropped out of university

Initially, his father sent him to the University of Pisa to study medicine, but Galileo became interested in mathematics and left the university without a degree.

Galileo quotes

  • “In the sciences, the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man.”
  • “Curiosity is the key to problem solving.”
  • “All truths are easy to understand once they are discovered; the point is to discover them.”
  • “He who does not know the truth is only a fool. But he who knows it and calls it a lie is a criminal.”
  • “Wine is sunlight, held together by water.”
  • “Mathematics is the language in which God has written the universe.”

Find more of Galileo Galilei’s quotes at Goodreads.com.

How to celebrate Galileo Day?

On February 15, on Galileo’s birthday, people around the world celebrate an unofficial holiday in honor of this great scientist. The best way to celebrate Galileo Day is to gather your friends for a dinner party and then take part in some activity connected with astronomy — like going stargazing together or taking a quiz about famous astronomers of the past.

If it’s too cold outdoors, you can watch the night sky from home with the Star Walk 2 app! No matter if you’re inside or outside, this app will help you see and identify the stars and constellations above your location — just launch the app and point your device at the sky.

Another app that will allow you to dive into the world of astronomy without leaving home is Solar Walk 2. It’s a beautiful 3D planetarium with realistic models of celestial objects and lots of scientific facts about them.

We wish you a happy Galileo day and successful observations!



Star Walk

Point your device at the sky and see what stars, constellations, and satellites you are looking at 🌌✨ https://starwalk.space