The Sun rules over our planetary system and is our main source of light and heat. It occupies a prominent place in cultures around the world, has shaped our sense of time, and remains a gateway to better understand the universe. Join the Adler in celebrating the Sun and solar observing throughout the centuries.
Shadows of Time
Sundials of varied designs and forms have been used all over the world to find the time using the Sun. The oldest surviving sundials were made in Egypt around 1,500 BCE. The example shown here was made in Japan in the 19th century, when sundials were still in use but losing ground to newer timekeeping systems based on clocks. The disc on the upper left side of this sundial includes an hour scale and can be adjusted for the desired latitude. The apparent solar time was given by the shadow of a missing pointer that was originally attached to the center of the disc.
Following the Solar Cycles
Tracking the motions of the Sun in the sky was essential for the development of calendars. The twelve constellations of the zodiac, which feature prominently in this 18th-century perpetual calendar, are particularly important, as they mark the apparent path of the Sun in the sky during the course of one year. This knowledge is also central to astrology, which was closely connected with astronomy until the 17th century. People looked into celestial cycles and phenomena seeking to learn more about themselves and their fortunes, and the Sun had a prominent place in that quest.
The Sun and Prayer
The daily apparent motion of the Sun in the sky has a particular importance for Muslims, as it provides a basis to determine the times of the five daily prayers. Astrolabes, which double as observing instruments and analogue computers, were used from the 9th century through the early 20th century to assist with the necessary observations and calculations. This astrolabe was likely made in the 14th or 15th century in the Maghreb, a subregion of Northwest Africa significantly shaped by Arab and Islamic cultures.
Navigating by the Sun
Celestial navigation techniques were developed and used by seafaring peoples around the world. These include the Europeans who, from the 15th century onwards, engaged in oceanic travels that gave rise to the modern seaborn empires. Observations of the Sun played a prominent role in those travels. This illustration from an Italian book on navigation shows how to observe the altitude of the Sun from a ship with an instrument called a backstaff. These observations were performed in order to find the latitude of the ship.
A Spotty Sun
This image shows two Jesuit scholars studying sunspots with a telescope, by projecting the solar image onto a screen. In the early 17th century it was still widely believed that the Sun and the other celestial bodies remained perfect and immutable as they orbited a central and static Earth. The existence of sunspots seemed to contradict this idea and generated passionate debates, which paved the way to the modern view of the Earth orbiting the Sun along with the other planets of the solar system.
Worlds on Fire
This rendition of the Sun follows the ideas of Athanasius Kircher, a 17th-century scholar known for his wide array of intellectual interests. The latter included geology and volcanoes, with Kircher allegedly having descended into the crater of Mount Vesuvius in a study mission. Kircher believed that fires percolate in the interior of the Earth causing phenomena such as volcanic eruptions and earthquakes. In a similar vein, he posited that the Sun is a fiery world and that sunspots result from volcanic eruptions. These ideas did not hold, but they denote an important conceptual shift: the same kind of physical explanations may apply to the Earth and to the celestial bodies, including the Sun.
One Sun Among Many
This 18th-century illustration shows several stars, each harboring its own planetary system. Our very own solar system is portrayed at the center. The curved lines filling in the spaces refer to an obsolete theory to explain planetary motion. The multitude of planetary systems in the image is purely speculative, reflecting past debates about our own place in the Universe and on the possible existence of other inhabited worlds. Now we know that the Sun is one among billions of stars in our galaxy, the Milky Way, and astronomers have detected thousands of planets orbiting other stars. The Sun is precious to us, but not so special after all.
A New Science Emerges
This photograph of the Sun, in which sunspots are visible, was obtained by Lewis Rutherford in New York in 1870, using a specially adapted telescope and camera. In the 19th century astronomers started to employ new techniques such as spectroscopy and photography to better understand the physics and the chemical composition of the Sun. These techniques were eventually applied to the study of other celestial bodies, resulting in a whole new science: astrophysics.
Scientist Spotlight: Dr. Maria Weber
Dr. Maria Weber is an astrophysicist who studies how sunspots are created and why they appear on the solar surface. Sunspots are regions of intense magnetism thousands of times stronger than the Earth’s surface magnetic field. Magnetic ropes are created inside the Sun by the motion of its very hot gas, called plasma. Dr. Weber's computer simulations show that these ropes are lifted by upwellings of the Sun’s plasma. They then rise to the solar surface much like a helium-filled balloon floats upward through the air. The end result is a pair of dark regions on the Sun’s surface – sunspots! The number of sunspots increases and decreases over the course of 11 years. We still don’t know why but part of Dr. Weber's work looks to solve this mystery.
Scientist Spotlight: Dr. Teresa Monsue
Studying the Sun helps us better understand what happens in other stars as well. Dr. Teresa Monsue is a NASA Postdoctoral Fellow at NASA’s Goddard Space Flight Center, specializing in the oscillations, or waves, that happen in the outer layers of stars like our Sun. These oscillations make stars get subtly brighter and dimmer as they pulse through the star - these pulses are too faint to see with our eyes, but special telescopes can catch them in action. Dr. Monsue is studying how flares, energetic explosions in the outer layers of the Sun and other stars, create, disrupt, or amplify these waves.
Looking Up with Adler
Observing the Sun safely requires special and careful steps - but when viewed properly it is something no one will forget, especially if the experience is shared by others! In the early 2000s, the Adler Planetarium began recruiting volunteers as telescope facilitators, bringing safe daytime views of the Sun to guests. Adler volunteers are trained to operate our fleet of small telescopes and the telescope in our Doane Observatory, helping to facilitate thousands of observations each year.
Looking Up with Adler - From Home
In June 2020, the Adler Planetarium debuted a live YouTube program, "Sky Observers Hangout" to engage our audiences remotely, featuring images of the Sun, Moon, and stars, activities that audiences can re-create at home, Q&A opportunities, and more. This program allows guests from anywhere in the world to see real time observations of the Sun - like this one captured in May 2020 from Aurora, Illinois.
Thank you to the staff of the Adler Planetarium for their assistance in creating these images of our collection and this exhibition.
The Adler also thanks Dr. Teresa Monsue, Dr. Maria Weber, and Dr. Taha Yasin Arslan (Istanbul Medeniyet University) for their permission and assistance in creating this exhibition.