The International Day of Planetariums 2021 Is Coming!

Star Walk
4 min readMar 13, 2021


( In the photo: Planetarium at the Royal Observatory, Greenwich, London )

Every year, on the second Sunday in March, the world celebrates the International Day of Planetariums. In today’s article, we’ll tell you why planetariums are so important and how you can join the celebration.

A brief history of the event

The International Day of Planetariums (formerly known as the International Day of Planetaria) is a holiday that is held annually on the second Sunday in March. It celebrates the importance of planetariums as an educational tool that allows us to appreciate the grandeur and beauty of the Universe. The event’s main goals are to inform the public about the significant role that planetariums play in culture, science, and education, and make people understand that astronomy is an enjoyable and enthralling activity. Another important goal of the International Day of Planetariums is encouraging international collaborations between planetariums of different countries.

The Italian Association of Planetaria was the first to organize the Day of Planetariums in 1991 in Italy. The International Planetarium Society (IPS) supported this initiative, and in 1995, the Day of Planetariums was held worldwide for the first time. Originally, the holiday was celebrated on the Sunday before the vernal equinox; however, later, the date was set as the second Sunday in March so that planetariums can more easily schedule the event in advance. Also, planetariums that are not open on Sundays hold the event on Saturday day. In 2021, the International Day of Planetariums is celebrated on March 13 or 14.

What is a planetarium?

A planetarium is a theater built for presenting educational and entertaining shows about the night sky in particular and astronomy in general. As a rule, in planetariums, scenes of sky objects are projected onto a large dome-shaped screen. These shows are usually accompanied by lectures or music.

The term “planetarium” can also be used to describe other devices that illustrate the Solar System or the Universe, such as an orrery or computer simulation. Let’s turn to history to learn more about the predecessors of modern planetariums and their evolution from primitive devices to the wonders of science and technology.

A history of planetarium

The history of planetariums goes back into antiquity. The earliest known depiction of the sky was found in the tomb of Senenmut, an ancient Egyptian architect. Archimedes, a Greek polymath, was the first to create a primitive planetarium device: around 250 BCE, he made a cast-metal globe demonstrating the planets’ motions. Around 150 CE, the mathematician and astronomer Ptolemy recorded his designs for a Celestial Globe. Although this globe has never been found, notes on its construction survived up to today.

In the Middle ages, astronomical clocks displaying the positions of the Sun, Moon, zodiacal constellations, and major planets were used in some cathedrals. In 1584, the Danish astronomer Tycho Brahe constructed the Celestial Globe. This model of a celestial sphere had a diameter of 1,5 meters and showed stars visible with the unaided eye. Several decades later, in 1654, the Globe of Gottorf was constructed in Germany. Inside of this Globe, measuring about four meters in diameter, was a circular bench for several persons. The star map with astrological and mythological symbols was depicted on the inside surface of the Globe of Gottorf.

One of the predecessors of modern planetariums is the orrery, a mechanical model of the Solar System used to recreate the motions of the planets and their natural satellites around the Sun. The first orrery was made in 1704 by clockmakers George Graham and Thomas Tompion; the instrument was named after Charles Boyle, 4th Earl of Orrery, an English nobleman and patron of the sciences. Eise Eisinga’s planetarium, the oldest working planetarium (which, in fact, is an orrery), was built between 1774 and 1781 in the Netherlands.

Another way to show the planetary motions didn’t come up until the 1920s when the first projection planetarium was invented by Carl Zeiss Сompany. In 1919, Walther Bauersfeld, chief design engineer of the Carl Zeiss Company, conceived the idea of projection of the sky objects in a dark room. It took Bauersfeld and a large staff of scientists and engineers several years of calculations and research to implement the idea. As a result, the first modern projection planetarium was constructed and made it possible to demonstrate the wide variety of celestial bodies of our beautiful Universe.

In the 1980s, the first digital projectors displaying computer graphics emerged and opened up modern astrophysics to the public. Today, thanks to computer graphics and the data on the Universe obtained not only through telescopes but also from space probes, we can lift off the Earth and travel across space, visiting other planets and distant stars. Moreover, there are plenty of portable planetariums widely used in schools, universities, and exhibitions and planetarium apps that help astronomy lovers explore the Universe at any time and any place.

How to celebrate the International Day of Planetariums?

Usually, planetariums throughout the world host various educational events, for instance, lectures and exhibitions, on the occasion of the International Day of Planetariums. To attract as many visitors as possible, they offer free or discounted entry. Some planetariums prepare a whole week of events that starts or ends on the International Day of Planetariums.

In our opinion, the best way to participate in this great event and get involved in the wonderful world of astronomy is to visit the planetarium in your city or town, or enjoy the space from the comfort of your home with the stargazing guide Star Walk 2! On March 13 and 14, we offer discounts up to 70% on the Star Walk 2 app (note that there’s no difference between Star Walk 2 and Star Walk 2 Free in terms of content, but the paid version has no ads). Enjoy stars, planets, constellations, satellites, and other space objects in the sky above you with your virtual planetarium!

Happy stargazing!



Star Walk

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