“And God said, “Let there be lights in the vault of the sky to separate the day from the night, and let them serve as signs to mark sacred times, and days and years, 15 and let them be lights in the vault of the sky to give light on the earth.” And it was so. 16 God made two great lights—the greater light to govern the day and the lesser light to govern the night. He also made the stars. 17 God set them in the vault of the sky to give light on the earth, 18 to govern the day and the night, and to separate light from darkness. And God saw that it was good. 19 And there was evening, and there was morning—the fourth day”
- - Genesis, Chapter 14.
In previous blogs in this series, trying to reconcile the creation story of Genesis with the limited speed of light left us scratching our heads. According to Genesis, God created the stars to light up the night on the fourth day of the seven days that He took to create the universe. The purpose of creating the stars, as you just read in Chapter 14, was to provide light during the night. In a single day, though, the light generated by creating even the nearest star, Alpha Centauri, would cover only about 1/1500 of the distance to the Earth, so even Alpha Centauri wouldn’t have appeared in the sky for four years after the fourth day. All the other stars in the sky would have taken longer – some over a thousand years longer – to add their luster. If God’s purpose in creating the stars was to light up the night on the Fourth Day, it is difficult to understand why He placed them much too far away to achieve His goal.
But we also discovered that the stars aren’t the only sources of light in the night sky. Take the fuzzy patch of light in the Southern Hemisphere known as the Small Magellanic Cloud (SMC). At the beginning of the last century, astronomers were able to use Henrietta Leavitt’s discovery of Cepheid Variables in the SMC to determine, for the first time, that the SMC lies at least 30,000 light years away (close to 200,000 light years distant by modern calculations). In a single day, therefore, light from the SMC covers only about one seventy-three millionth of the distance to the Earth. If the SMC was created, along with the rest of the Universe, some 6,000 years ago, there is no way the cloud would have been visible to Ferdinand Magellan and his band of explorers in the early 1500’s; no way it (and its Cepheids) would have showed up on Henrietta Leavitt’s photographic plates in the first decade of the 20th century, and no way it would be visible today. We would be completely ignorant of SMC’s presence until about 194,000 A.D., when its light would finally arrive!
The fact that the SMC (and its neighbor, the Large Magellanic Cloud) has been visible throughout recorded history is proof that the universe is at least 200,000 years old, a far cry from 6,000. But the story of Cepheid Variables, and the headaches they create for Genesis, doesn’t end with the SMC; not by a long shot. Almost 600 years before Ferdinand Magellan set out on his voyage of discovery and saw the Magellanic clouds that would come to bear his name, a Persian astronomer named Abd al-Rahman al-Sufi left a diagram suggesting that he had noticed the existence of another mysterious patch of light, this one in the constellation Andromeda, the maiden. Shown in the left figure below, the diagram includes a maiden, Andromeda, a fish, and a mysterious collection of dots just to the right of the fish’s nose. This is the first record of anybody actually noticing the mysterious smudge of light that is now known as the Andromeda Galaxy. If you have clear skies tonight, and live in an area with minimal light pollution, this smudge will be visible to you, too. As shown in the figure below and to the right, find the Great Square of Pegasus in the northwest about an hour after sundown. Count two stars over and then look up a little to the location indicated by the red arrow. The fuzzy patch you see is the focus of today’s blog.
By the beginning of the 20th century, centuries of observations with previous generations of telescopes had revealed many other wispy patches just like the Andromeda Galaxy. With no way to determine their distances, though, these “nebula” had become the focus of a battle royal in astronomical circles: Were they some sort of mysterious agglomerations of matter inside our own galaxy, solar systems in the making perhaps, or were they other galaxies, far further away than our Milky Way, but otherwise resembling our own? Solving this thorny question would fall to no other than Edwin Hubble, the famous American astronomer that the Hubble Space Telescope is named after (we’ll see presently one of the primary reasons why that naming was so appropriate). In the 1920’s, Hubble was fortunate enough to be one of the first astronomers to utilize a marvelous new telescope on Mount Wilson in Southern California, the first in the world to have a primary mirror more than 100 inches (8 feet!) in diameter. It was Hubble who realized that this telescope would be powerful enough to actually resolve the brightest stars in the Andromeda galaxy. Luckily, Cepheid Variables are supergiant stars that have moved off the “main sequence” – a concept I’ll be glad to clarify in the comment section, if anyone’s interested – and have swollen to a gigantic size as a result. Even the dimmest Cepheids outshine the Sun by a considerable margin, and the very brightest, those with the longest periods, are 100,000 times as bright. Hubble knew that if he could find Cepheids in the Andromeda Nebula, he could measure the distance to it, and put an end to the raging debate once and for all.
The figure below is an example of one of the photographs of the Andromeda “nebula” taken by Hubble with his new gigantic telescope. And lo and behold, as you can see from the label in the center, Hubble was successful in his quest; some of the individual stars in these photos did indeed demonstrate the periodic brightening and dimming cycles that marked them as Cepheids! Carrying out the usual computations based on comparing the brightness of these Cepheids as measured in the photographs against their true intrinsic brightness as determined by their location along the period/luminosity function, Hubble announced his determination to the world: The Andromeda “Nebula” was actually 600,000 light years away! At that enormous distance, it couldn’t be a part of our galaxy, but instead must be a galaxy in it’s own right, a magnificent “island universe” like the Milky Way containing billions and billions of stars.
The mystery of the nebulas was solved, and in one magnificent step, Edwin Hubble was able to provide humanity with a true perspective on the size of the cosmos. The Earth wasn’t the center of the universe; it was located in a spur of a spiral arm of a galaxy named the Milky Way, an insignificant spec of the universe surrounded by untold numbers of other galaxies in every direction, all at unimaginable distances from our own. The modern value for the distance to the Andromeda galaxy is 2.5 million light years.
The fact that you can go out tonight and actually SEE the Andromeda galaxy, when its light takes a full two and a half million years to reach us, starts to reveal just how completely nonsensical the timeline for the creation of the universe in Genesis really is. And the fun doesn’t stop there. Hubble was able to resolve Cepheids in many other galaxies, some as far as 10 million light years distant. As he analyzed the light from the unimaginably distant stars in these galaxies, he noticed another quality of their light that would profoundly change our understanding of the history of the universe and how it all began.
But that’s a topic for another blog!
