Humans are explorers. Throughout our history, we were driven by the insatiable curiosity for the unknown. The urge to travel beyond the next hill or to find new lands across the sea led to some of the boldest adventures ever. Such as the epic journeys of Polynesian tribes who traveled thousands of miles across the open sea in brittle boats to settle islands scattered across the Pacific. Or the brave Norsemen journeymen, who reached North America centuries before Columbus. And what to say about fearless explorers who traversed across Africa, many of whom died, to discover the source of Nile?
We constantly pushed our limits, always created new challenges, just to be able to go above and beyond until we explored every continent in detail. And each of these explorers had one thing in common – every single one looked to the stars to navigate, among other navigation techniques. And once we traversed the Earth and explored the bottom of the sea, our focus moved towards the heavens. Space indeed is the final frontier and the ultimate cartographic challenge. But mapping the heavens isn’t a modern idea. The first star charts are more than a thousand years old.
The early days and Hubble’s Law
Humans were hypnotized by stars since the dawn of our species. Prehistoric monuments such as Stonehenge had a clear astronomical purpose. Many ancient cultures such as Babylonians, Greeks, Indians, Egyptians, and Chinese, studied astronomy.
The first detailed star chart originated in China. It was drawn in 650 A.D at the site of a town called Dunhuang, which was on the famous Silk Road. It survived through modern days because it was sealed until it was rediscovered in 1907. The atlas consists out of 13 maps. Together, they depict the complete sky visible from the Northern Hemisphere. There are 1339 stars mapped in total. The Dunhuang star chart looks simple by today’s standards since it was based on naked-eye observations but back then, it was a work of art.
Dunhuang star chart Image source: Wikipedia
Jump to 17th century and we finally got more detailed star maps thanks to the invention of first telescopes. This led to the quantum leap in astronomy. The field developed immensely in a short time. We got many famous astronomers such as Johannes Kepler and Galileo Galilei. Their work was important but we are most interested in the first map of the Milky Way. The map, called “On the Construction of the Heavens” was created by William and Caroline Herschel, a brother and sister who manually charted thousands of stars in 1785.
The first map of the Milky Way by William and Caroline Herschel Image Source: Wiki Commons
This map of our galaxy is the first systematic map of the night sky. It showed the Milky Way in all its glory and paved the way for the future. And the future moved at a tremendous pace. 19th and early 20th century brought lots of new technology to the table, all of which improved star-making. The invention of the cosmic distance ladder allowed astronomers to calculate the exact distance of objects for up to 1,000 light-years away. Recently, new techniques allowed us to expand exact measures for up to 10 times.
The arrival of photography allowed anyone to take still images of the world and astronomers embraced the technology. Astrophotography meant no more direct observations. Instead of having to sketch stellar bodies, astronomers could use film to record accurate images of various parts of the night sky. And by using long exposures, they were able to discover dim objects not visible to the naked eye. With the arrival of the 20th century came new techniques that pushed our knowledge even further.
Edwin Hubble confirmed there are galaxies beyond our own in 1925 when he measured the distance of stars in the Andromeda galaxy. And four years later he discovered the cosmological redshift, which revolutionized our view of the universe. Hubble discovered that almost every galaxy moves away from our galaxy, which introduced the idea of the expanding universe. This meant that distant stars always move away from us, another variable to take when trying to chart them.
The Discovery of Dark Energy and Map of the Cosmic Microwave Radiation
During the 20th century, the universe was mapped by astronomers manually. They would use photographic films attached to giant telescopes and take thousands of photos of the night sky. These would later be analyzed and stitched together to create maps of different parts of the sky. It was a long and arduous process, but it gave results. These surveys were used to build a complete map of the northern sky, which was a pretty big deal back then. With the invention of electronic detectors, the scope increased greatly. Instead of manually taking photos of the sky, astronomers could equip telescopes with digital cameras and use computers to analyze photos. The increase in speed was astounding.
Milky Way Panorama by Knut Lundmark Image Source: Lund Observatory
In the early 1990s, we mapped the oldest light in the universe. The cosmic microwave background radiation was a remnant of the earliest moments of our universe. By mapping it during the COBE mission NASA confirmed the Big Bang Theory. The mission also gave us knowledge about the shape of the universe, its size, and the existence of dark energy. The existence of dark energy was officially confirmed in 1998 when supernova researchers discovered that the universe is expanding at an ever-faster rate. This had profound consequences on the whole astronomical community. Distance measures had to take into account the expansion rate and with the discovery of the force driving the expansion, scientists could calculate the rate with greater accuracy.
Planck Map of the Cosmic Microwave Background
And then, in 2009, Europe Space Agency launched the Planck satellite, which refined our understanding of the cosmic microwave background and, in relation to it, the universe. First of all, the Planck satellite mapped the CMB in unmatched precision. The pictures of the early universe taken by the Planck satellite provide the best info about the early stages of our cosmos. The precision along with multiple frequency bands of the images taken gave scientists important information regarding the shape of the universe, distribution of matter in the early universe, as well as the ratio of normal matter, dark matter, and dark energy.
GAIA mission and Sloan Digital Sky Survey
European Space Agency is responsible for another important mission that provided the most precise 3D map of our galaxy. The GAIA satellite launched in 2013, and scanned the night sky for years. The scan data was used to create a marvelous map of the Milky Way galaxy, which includes the position and brightness of more than one billion stars. Further, GAIA also mapped distances and motions of more than 2 million stars. The map is tremendously detailed, giving us the best look at our galaxy ever. This not only provides a cool map of the Milky Way but also gives scientists a sleuth of resources they can use to study the structure and history of our galaxy, to calculate the size and mass of the Milky Way, to better understand how our universe expands.
GAIA Map of the Milky Way Galaxy Image Source: ESA
But mapping the universe doesn’t only include large, single missions. For instance, the Sloan Digital Sky Survey is a project lasting for over 20 years, based in New Mexico with collaborators from all over the world. The survey itself is taking place at Apache Point Observatory in New Mexico. To date, the project provided an incredibly precise map of about one-third of the sky. The survey helped astronomers to map the universe with multiple techniques. Such as creating maps of large-scale structures of the Universe based on the position of quasars. Or using data to come up with new ways to accelerate the mapping of our sky by weighing supermassive black holes. The Sloan Digital Survey is still underway, with the date of the final data release scheduled for July 2021.
DESI project – Creating a 3-D Map of the whole Universe
A new sky surveying project called Dark Energy Spectroscopic Instrument(DESI) is the biggest survey of the universe to date. DESI is the successor of the Dark Energy Survey project (DES), which mapped about a quarter of the visible sky in the Southern hemisphere. Its goal is to provide an incredibly detailed, 3D map of the universe that goes back by 11 billion light-years. The map should encompass 35 million galaxies and quasars, all of them being mapped in 3D, unlike ever we’ve seen before. This accounts for about half of the observable universe. The project is located at the Mayall 4-Meter Telescope at Kitt Peak National Observatory in Tucson, Arizona. DESI won’t only provide the most comprehensive map of the universe; it will also provide data needed to better understand why the universe is expanding as it does. Why the expansion rate is so fast and why the universe keeps expanding.
Proxima Centauri Image Source: Hubble Space Telescope
The map created by DESI should be precise enough to see the expansion history. That includes changes in the expansion rate, which are contributed to the dark energy. By taking images in multiple spectrums, from ultraviolet to infrared, DESI will allow astronomers to observe the expansion of the universe backward trough time in glorious detail. In other words, DESI should shed light on the behavior of dark energy through time. This should answer lots of questions regarding dark energy but it’ll also raise lots of questions, which is why science is so exciting in the first place.
Laniakea Supercluster, with the red dot marking Milky Way Image Source: Nature Magazine
We, as a species, advanced tremendously in less than a century. From not knowing where we are in our galaxy and not being aware of the existence of other galaxies to having super detailed 3D maps of our galaxy and preparing to map half of the observable universe in great detail. The surveys and universe mapping projects won’t only give us better and better charts of our universe, they’ll also give us new knowledge about some of the most important problems in modern astronomy. Such as what early universe looked like, how it expanded, and what exactly is dark energy. The ultimate goal? Creating a 3D map of the entire observable universe, spanning from nearby stars to the furthest quasars.