Last Monday, the United States of America was treated to a spectacular transcontinental solar eclipse: the first such eclipse since 1918! We at the Biblical Science Institute traveled to Allensville, Kentucky (which is in the path of totality) to document this wonderful event. We have posted a video of the experience on our YouTube channel. We hope you enjoy it!
Having experienced the event live, I do have to say that no photograph or video footage I have ever seen (including ours) adequately captures the beauty of a total solar eclipse. The human eye is uniquely designed to handle a great range of contrast, allowing us to see something very bright without washing out something else that is much fainter. I noticed this effect most prominently during the “diamond ring” phase of the eclipse. Having seen many pictures of this phase, I thought I knew what to expect. But the brightness of the “diamond” produced a sparkling effect that was surprising to me and utterly breathtaking.
But I’m getting ahead of myself. What is a solar eclipse, and what makes it so spectacular? Is it a sign of the “end times” as some have claimed? When do they occur? What is their purpose? Do eclipses provide evidence of biblical creation? Let’s explore these issues.
An eclipse is when the shadow of one object falls on another. The two kinds of eclipses that people are most familiar with are a solar eclipse – where the moon’s shadow falls upon the earth, and a lunar eclipse, where the earth’s shadow falls upon the moon. But there are other kinds as well. Jupiter’s moons sometimes eclipse each other. For example, the shadow of Ganymede will fall upon Io, causing Io to fade out over the course of 15 minutes or so. These are easily visible in a small telescope. But solar and lunar eclipses are more spectacular because you can enjoy them without a telescope.
Lunar Eclipses
Let’s start by examining a lunar eclipse. The sun is responsible for illuminating all other objects in our solar system. Since all planets, large moons, and large asteroids are spherical, the sun illuminates only half of their surface at any given time. As the moon orbits the earth, we see different fractions of its day and night sides respectively. This is why the moon has phases. When the moon is full, we are seeing the day side entirely. When the moon is new, its night side is facing us and we don’t see anything at all. During first quarter, the right half of the moon is illuminated, and the left side is not; so we are seeing half of the day side, and half of the night side.
Phases of the Moon
It takes about a month for the moon to orbit the earth. From our perspective as observers on earth, we therefore see a changing fraction of the illuminated verses the non-illuminated hemisphere, taking about 29.5 days to complete the cycle. An observer on the moon would see the earth go through phases as well, since his position relative to the earth and sun would change, making a complete cycle in 29.5 days. The phase an observer on the moon sees for the earth is the opposite of the phase an observer on earth sees for the moon (e.g. new moon means full earth). Phases have absolutely nothing to do with earth’s shadow. Rather, they depend solely on the location of the observer relative to the position of the moon and the sun. If an observer could somehow survive on the sun, he or she would see all planets and moons in their full phase all the time.
Lunar Eclipse
A lunar eclipse can only happen during the full moon. In this phase, the earth is in between the moon and the sun, and so we might expect that the earth’s shadow would fall on the moon. But usually, this doesn’t happen. Why? The answer is that the moon’s orbit around the earth is not in exactly the same plane as the earth’s orbit around the sun. The latter is called the ecliptic. The moon’s orbit is tilted about five degrees relative to the ecliptic. And so, normally, when the moon reaches its full phase, it is as much as five degrees above or below the earth’s shadow and no eclipse occurs.
Since the moon’s orbit is centered on earth, it must intersect the ecliptic at two points. These are called nodes. As the earth orbits the sun, eventually the nodes of the moon’s orbit will align with the sun and earth. Since there are two nodes, this happens twice a year. If the moon happens to be in its full phase when the nodes are aligned, a lunar eclipse occurs. Conversely, if the moon is in the new phase when the nodes are aligned, a solar eclipse occurs. This is why we can experience a maximum of only two total lunar eclipses per year. If the full moon happens shortly before or after the alignment of nodes, a partial lunar eclipse occurs. This is when part of the earth’s shadow falls on the moon, but not all.
Two Shadows
If the sun were a bright point source of no size, the earth’s shadow on the moon would be perfectly sharp and distinct. But the sun is a large sphere, much larger than the earth or the moon. When a large, extended light source like the sun illuminates a smaller one, it forms two types of shadows. The outer shadow is called the penumbra. It represents regions for which the sun’s light is partially blocked. A person standing in the penumbra of earth could see part of the sun, but part is blocked by earth. This occurs at every sunrise and sunset; when only part of the sun is above the horizon, you are in earth’s penumbra. The penumbra is always larger than the object casting this shadow, and its size increases with distance.
The inner darker shadow is called the umbra. The umbra represents the region in which the sun’s light is entirely blocked. A person standing in the umbra would not see the sun at all. That is why the umbra is much darker than the penumbra. After the sun has set and no portion of it is visible, you are in the earth’s umbra and will remain in it all night until sunrise. The umbra is always smaller than the object casting the shadow, and its size decreases with distance.
When a lunar eclipse occurs, the moon enters earth’s penumbra first. This is usually barely noticeable until the moon is fairly deep within the penumbra. Eventually, the moon begins to enters the umbra, which is quite dark and very noticeable. The moon orbits the earth from west to east, so the earth’s shadow on the moon seems to sweep from east to west. When the moon is completely inside earth’s umbra, it becomes very dark. This portion of the eclipse is called totality. Depending on the parameters, the total portion of a lunar eclipse can last as long as one hour and forty minutes. The total duration during which any portion of the moon is in the penumbra can be as long as 3 hours, 40 minutes. Partial lunar eclipses are those that never reach totality.
Total lunar eclipses are fairly common and can be seen by everyone on the night side of earth at the time of the eclipse – weather permitting. I have seen many. Sometimes during a total eclipse, the moon will be rather orange during totality. But how can it have any light at all if the earth is blocking sunlight? The answer lies in earth’s atmosphere. The atmosphere bends some sunlight around the earth, allowing it to strike the moon. The higher frequency light from the sun tends to be scattered away – that’s what makes the earth’s sky blue. All that is left is the lower frequencies – the orange and red colors. So, the moon turns orange or reddish for the same reason that sunsets are red. On the other hand, if earth has experienced recent volcanic eruptions, even the red light can be blocked by particulates in the atmosphere, and the moon will appear quite dark.
Yes – the Earth is Round
Lunar eclipses prove that the earth is round. By round, I do not refer to a circular disk, but rather to a sphere (approximately). We know this because the shadow of the earth on the moon is always a circle. If the earth were a flat, circular disk, then its shadow on the moon would only be a perfect circle if the moon were directly overhead. But at lower angles, a circular disk will project an elliptical shadow (try it!) In fact, I have seen a lunar eclipse that took place at sunset/moonrise. If the earth were flat, its shadow would have been a straight line. But it wasn’t. It was a circle. Furthermore, since the sun was setting, it was plain to the eye that the moon was exactly opposite in the sky relative to the sun with the earth in between. So, there can be no doubt it is the earth’s shadow that falls on the moon, and that this shadow is always circular.
Even the ancient Greeks knew this. Aristotle argued that the earth must be spherical because of the shadow that falls on the moon during a lunar eclipse. He offered other proofs as well. But it is impressive that the Greeks already had such knowledge of astronomy; they understood that the earth was between the sun and moon during a total lunar eclipse, and that geometry demanded a spherical earth in order to produce the shadow. The idea that Christopher Columbus was the first to suppose that the earth might be round and that the purpose of his voyage was to prove it, is false. Educated people already knew that the world was round for millennia.
Solar Eclipses
The corona of the sun at totality. The bright star to the upper left is Regulus.
Although solar eclipses are about as frequent as lunar eclipses, far fewer people have seen a total solar eclipse for the following reasons. First is that in order to see a solar eclipse, you must be within the moon’s shadow. Recall that with a lunar eclipse, everyone on the night side of earth can see it (if the skies are clear) – statistically about half the population of earth. But the moon is much smaller than the earth, and consequently its shadow is much smaller. In fact, the moon’s umbra is only about 100 miles wide on average at earth’s surface. To see the totality phase of a solar eclipse, you must be within the moon’s 100-mile wide umbra.
As the moon orbits, its umbra traces a path across the surface of earth called the path of totality. Only observers within the path of totality will see a total solar eclipse – a very small fraction of earth’s surface for any given eclipse. Furthermore, the path sometimes occurs over sparsely populated and inconvenient regions, such as Antarctica or the middle of the Pacific Ocean. Statistically, if you are going to see a solar eclipse, you will likely have to travel. Of course, to see a partial solar eclipse, you only need to be within the moon’s penumbra, which is much larger and can cover an entire continent. Therefore, far more people have experienced a partial solar eclipse than a total solar eclipse. Since solar eclipses are location-based, one observer on earth might see a total solar eclipse while another observer sees a partial eclipse at the same time. (Conversely, during a lunar eclipse all observers see the same thing at the same time.)
There is another reason why total solar eclipses seem less common than total lunar eclipses; it concerns angular size. The moon is approximately 400 times smaller than the sun, but is also 400 times closer to earth. For this reason, the moon has the same angular size as the sun: meaning they appear the same size in the sky. But the moon’s orbit around the earth is elliptical; it is sometimes a bit closer to the earth, and sometimes a bit farther. When the moon is at its closest point to the earth (called perigee), it appears just a bit larger than the sun. During totality, it will completely cover the disk of the sun and a bit more. However, when the moon is near its farthest distance from earth (called apogee), it will appear a bit smaller than the sun. Even if the moon is directly in front of the sun, it will not completely block the disk in this case. A thin ring or annulus of the sun will appear surrounding the moon. This is called an annular eclipse.
Recall that the umbra of an object decreases in size with increasing distance from its source. At the distance of earth, the moon’s umbra can be as large as 170 miles in diameter when the moon is near perigee. But when the moon is near apogee, its umbra does not quite reach the earth; it reduces to zero at some distance away from earth’s surface. And you must be within the moon’s umbra to see the totality phase of a solar eclipse. Therefore, during an annular eclipse, it is not possible to see totality. This further reduces the number of total solar eclipses that a person can see in his or her lifetime.
Generally, the moon is somewhere in between perigee and apogee. Therefore, the size of the moon’s umbra on earth varies from one eclipse to the next, or will not reach earth’s surface at all for an annular eclipse. For this reason, some solar eclipses are better than others. Since the moon’s shadow moves rapidly across the surface of earth, a larger shadow tends to produce a longer eclipse. The location on earth and angle of motion all factor in, but the moment of totality is never longer than 7.5 minutes. However, the duration of the entire eclipse (in which any part of the sun is obscured by the moon) can be up to three hours.
Occasionally, a solar eclipse occurs in which the umbra does not quite reach earth’s surface at one point during the eclipse, but does during another point. (The earth is round, after all.) This is called a hybrid eclipse. Depending on their location, some people will see a hybrid eclipse as annular, while others will experience (brief) totality.
Why So Spectacular?
During totality, the horizon looks like sunset in all directions.
Is it worth traveling to see a solar eclipse? Why would anyone consider traveling a great distance to “not see the sun”? You can stay right where you are and probably see several partial solar eclipses in your lifetime. Is it really so impressive and spectacular to see a total eclipse? Frankly, yes. The moment of totality during a solar eclipse is absolutely stunning and surreal. The sky becomes dark as twilight, and the brighter stars are easily visible. In the middle of the day, wildlife responds by acting as if it is night. Cicadas stop singing, and the crickets begin. The sky appears to be twilight, but slightly brighter around the horizon. It is as if the sun has set in all directions. In place of the sun, a beautiful unearthly halo faintly illuminates the surroundings.
In between the shadows of leaves we see many images of the partially eclipsed sun.
Even the deep partial phases produce strange effects. The sky darkens substantially even before totality, but you are not likely to see any stars or planets other than Venus until totality. The temperature usually drops substantially even before totality by ten degrees or more. Shadows begin to look strange. In fact, the shadows of tree leaves form little crescent images on the ground of the nearly-eclipsed sun. Essentially, the gaps between the leaves act like tiny pinhole cameras.
In the seconds just before totality, the eclipse undergoes the “diamond ring” phase. The mostly-eclipsed sun resembles a diamond ring, a faint halo with a stunningly bright “diamond” representing the last light of the photosphere. During this phase, things happen quite rapidly and you can actually see the moon moving and the remaining light from the photosphere shrink and vanish. The transition to darkness is rapid and breathtaking. At the end of totality, we are treated to another diamond ring, this time in reverse.
Most significantly, a total solar eclipse allows viewers to see with their own eyes the chromosphere and corona of the sun: two layers that are normally hidden by the overwhelming brightness of the solar surface. The sun is an enormous sphere of hydrogen and helium gas, about one hundred earths in diameter. The visible surface of the sun is called the photosphere. The hydrogen gas there has a temperature of about 6000 Kelvins. Surrounding the photosphere is a very thin layer of rarified hydrogen gas called the chromosphere. The chromosphere is around 4000 Kelvins, significantly cooler and much fainter than the photosphere.
Beyond the chromosphere is a very large region called the corona. Unlike all the other layers of the sun, the corona is not spherical, but forms wispy leaf-like structures that are constantly changing from day to day. These coronal projections extend great distances into space – several solar diameters. The density of hydrogen atoms in the corona is extremely low, more so than the best vacuum we can produce on earth. But the temperature of the corona can exceed one million Kelvins. The chromosphere and corona are quite faint and are therefore overwhelmed by the brightness of the photosphere. This renders them completely invisible to the eye at all times – except during a total solar eclipse.
At totality, the corona of the sun suddenly becomes visible: a beautiful light blue gossamer curtain surrounding a glowing halo. No special equipment is needed. During totality – and ONLY during totality – it is safe to look at the eclipse directly with no eye protection. Pictures really don’t compare to the real thing; photographs either overexpose the inner regions of the corona or underexpose the outer regions. But the human eye can see it all. Binoculars will enhance the experience.
Unlike the corona, the chromosphere is a very thin layer, only slightly beyond the visible photosphere. So, the moon will tend to obscure it as well during the middle of totality. But during the first seconds of totality, the chromosphere may be seen just off the eastern limb of the moon, or during the last few seconds it may be seen off the western limb. The chromosphere is a vibrant scarlet red, and brighter than the corona. This color is responsible for the name; “chromo” means “color.” Binoculars or a telescope are the best way to see the chromosphere. Additionally, prominences – loops of solar plasma extending up through the corona – may be seen at any time during totality. During this past Monday’s eclipse, I was treated to a spectacular binocular view of the chromosphere on the western limb during the last seconds of totality.
Safely Viewing an Eclipse
During totality, it is safe to view the eclipse directly with no filters. However, it is NOT safe to view a partial eclipse without eye protection. The photosphere of the sun is very bright and emits dangerous levels of ultraviolet radiation (UV), even when only part of the photosphere is showing. Many sunglasses block the UV, but they still do not block enough of the visible light to be safe. The cornea and lens of the eye focus light onto the retina, just as a magnifying glass can focus sunlight onto paper, and even burn the paper in some cases. But the retina has no pain receptors. You can burn the cells of the retina without realizing it. So it is crucial to take steps to reduce sunlight to a safe level.
One way to do this is with eclipse glasses. These are inexpensive, usually cardboard style glasses which cover each eye with black or silver filters. They block 99.999% of the light coming through them, which means when you put them on you cannot see anything at all except the sun. Welder’s glass works too, but only if it is shade 12 or higher. Lower shades do not block sufficient light to be safe. You can also purchase solar filters for binoculars or a telescope. These work extremely well, but can be more expensive than eclipse glasses.
The projection method using binoculars.
Projection is also a safe method to view the sun. This method projects an image of the sun onto white paper. The simplest projection method is to use a “pinhole camera.” Take any type of thick paper or cardboard, and poke a pin-sized hole in it. Then hold it over a different sheet of white paper. As sunlight streams through the pinhole, it will form a tiny image of the sun on the white paper. It works well enough. But a much better method is to use projection with binoculars or a small telescope as follows.
Cut two holes in a piece of cardboard so that the binocular eyepieces will fit snugly into them. (The cardboard isn’t strictly necessary, but it dramatically increases the contrast.) Put the binoculars on a tripod, aimed at the sun (but do NOT look through them). Leave the lens cap on either the right or left sun-facing lens; we only need one of the two sides to produce a single image of the sun. Then put a sheet of white, non-glossy paper several feet away from the binoculars, and perpendicular to them. A blurry image of the sun will form on the paper. Then just focus the binoculars until the image becomes sharp. It is perfectly safe to look at this image. Note that moving the paper farther from the binoculars will make the image larger, but fainter. Decide for yourself what tradeoff you prefer between brightness and size. This is a great way to view the sun at any time; you don’t have to wait for an eclipse! A similar setup can be used for a small telescope. But it is not advised for telescopes with apertures larger than six inches, because the build-up of internal heat can crack the eyepiece in some cases.
A Sign of the Times?
Sometimes people will ask if solar or lunar eclipses are a fulfillment of biblical prophecy. After all, many passages describe the “day of the Lord” as a day in which the sun will be darkened, and the moon either darkened or red as blood (Isaiah 13:10, Ezekiel 32:7-8, Joel 2:10,31, 3:15, Amos 8:9, Matthew 24:29, Mark 13:24, Revelation 6:12-13, 8:12). We would do well to remember that, unlike Genesis, biblical prophecy is not written primarily in literal historical narrative. Prophecy is usually written in a poetic style, with figures of speech and symbolic imagery. Indeed, the very first time that the sun moon and stars are used in prophecy, they are used symbolically, not literally (Genesis 37:9). Joseph dreamed that the sun, moon, and eleven stars were bowing down to him. These celestial lights were not literal, but symbolized his father, mother, and eleven brothers, as Jacob correctly interpreted (Genesis 37:10).
Furthermore, solar eclipses do not correctly match the poetic imagery associated with the day of the Lord. The moon may appear somewhat orange during a lunar eclipse – but it is never red as blood (Revelation 6:12). The sun does appear darkened during a solar eclipse, but the stars of heaven actually appear brighter (by contrast), not fainter (Isaiah 13:10, Revelation 8:12). Nor do the stars of heaven fall to earth during a solar or lunar eclipse (Revelation 6:12-13). Moreover, the prophetic imagery in Ezekiel 32:7 gives the mechanism for the darkening of the sun, moon, and stars as a cloud – not as the shadow of the earth or moon. The prophetic imagery is clearly not describing an eclipse.
Solar and lunar eclipses have been happening since creation. They are not new phenomenon. We also note that solar and lunar eclipse are predictable down to the second. We can even predict them thousands of years in advance. But the coming of the Lord will be unpredictable (Matthew 24:36). Clearly, solar and lunar eclipses are not signs of the end times.
The Significance of Eclipses
If not a sign of the times, what is the purpose of eclipses? First, they confirm Genesis 1:14-19. God created the celestial lights on the fourth day of the creation week. But He made two great lights – lights that are somehow superior to the others from earth’s perspective. Of all the lights in the heavens, only the sun and moon have noticeable size. And their angular size is the same: both cover about one half of a degree in the sky. They are both “great” in this sense. And yet, the Bible teaches that of these great lights, one is greater and the other lesser. This seems to reference their brightness; the sun shines much brighter than the moon. Additionally, the sun’s light is self-generated, but the moon shines by reflected light. So, indeed we have two great lights, equal in size, but one is much greater in brightness.
Interestingly, the earth is the only planet in the solar system whose moon has the same angular size as the sun, making it possible to see the chromosphere during a total solar eclipse. Other moons appear from their planet either much larger than the sun or substantially smaller. The matching angular size of the sun and moon as seen from earth allowed human beings to discover the chromosphere far earlier than we would have otherwise. This unique aspect of earth may not be required for life, but it certainly suggests that our planet is quite special.
The orbit of our moon is unique. All other large moons except Triton orbit around their planet’s equator. Our moon, however, orbits close to the ecliptic – the path of earth’s orbit around the sun. This makes eclipses far more common than they would be otherwise. On the other hand, the orbit of the moon is not exactly in the ecliptic, but is tilted just five degrees from it. If the moon orbited exactly in the ecliptic, then one solar eclipse and one lunar eclipse would happen every month, and they wouldn’t seem so special. God gave the moon a unique orbit perhaps so that eclipses would happen but not be taken for granted.
As mentioned above, lunar eclipses allowed us to discover that the earth is round, in confirmation of passages such as Job 26:10 and Isaiah 40:22, and that earth is suspended on nothing, in confirmation of Job 26:7. Aristarchus used the earth’s shadow on the moon to compute the distance to the moon for the first time. Apparently, God has not only created the solar system to function, but also to allow us to discover our place within it.
The predictability of eclipses is powerful evidence of biblical creation. In Genesis 8:22, God promised that the basic cycles of nature will be in the future as they have been in the past. God is the only person in a position to know such a thing on His own authority. He is beyond time and knows all future events (Isaiah 46:9-10). Furthermore, God is the person actually responsible for ensuring that the universe behaves in a consistent fashion, since He is the one who constantly upholds it (Hebrew 1:3).
God thinks in a mathematically perfect way, and upholds the universe by the expression of His mind. Hence, the universe obeys mathematical laws. And God has created human beings in His own image (Genesis 1:26-27) with the capacity for rational thought. For these reasons, we are able to rely upon the consistent and predictable way that God upholds His universe to make computations about future states in many situations. We are able to predict eclipses down to the second only because God makes the universe to operate in a perfect and clockwork fashion. Eclipses therefore remind us of the faithfulness and sovereignty of God.
The United States will experience an annular eclipse on October 14, 2023. The next total solar eclipse in the United States will occur on April 8, 2024. The path of totality will range up from Texas through Maine. I assure you that it is well worth the trip.