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The first of four total lunar eclipses of 2014–2015 has come and gone, so this is a good time for a post-event discussion. The eclipse occurred on April 15. Unfortunately, it was cloudy over much of the eastern USA that night. Here in northern Kentucky it even snowed a little bit during the eclipse. We had planned to watch the eclipse that night, but we saw nothing of it here at the Creation Museum.
Some people see an apocalyptic sign in these four eclipses...occurring as they do at the time of Passover and Sukkot in 2014 and 2015.Why all the concern over these eclipses? As I’ve previously discussed, some people see an apocalyptic sign in these four eclipses (they call them a tetrad), occurring as they do at the time of Passover and Sukkot in 2014 and 2015. Mark Biltz coined the term “blood moon” to refer to total lunar eclipses. I say that he coined that term because I can’t find any reference to lunar eclipses being called blood moons prior to Biltz’s use just a few years ago.
Previously, blood moon was an alternate name for the hunter’s moon, the full moon after the harvest moon, which in turn is the full moon closest to the autumnal equinox. Biltz has called lunar eclipses “blood moons” as if this had been a common practice for a long time. Unfortunately, with all the media attention to this, this use of the term blood moon may have now slipped into common usage. Biltz started using this term because red is the most common color of a totally eclipsed moon, and blood also is red.
Despite the fact that not all lunar eclipses appear red, Biltz teaches that a lunar eclipse likely was what the prophet Joel had in mind when he spoke of the moon being turned to blood before the great and terrible Day of the Lord (Joel 2:31), and that a lunar eclipse at the time of the Crucifixion was partial fulfillment of this as evidenced by the Apostle Peter’s referencing Joel’s prophecy at Pentecost (Acts 2:20). On a related issue, I’ve recently written critically on the possibility of a lunar eclipse the evening following the Crucifixion being what Peter had in mind.
Not surprisingly, a number of people have taken exception to both of my recent articles on these related subjects. Before discussing some of the objections, it is imperative to discuss some technical aspects of vision, photography, and some physics of the earth’s atmosphere as it interacts with light.
Most people think that photographs faithfully record what the eye sees, but nothing could be further from the truth. There are several differences. First, all manmade light detectors respond linearly. That is, as the amount of light increases, the response increases in direct proportion to the amount of light. On the other hand, the eye responds to light logarithmically. This means that as the amount of light increases, the response that we perceive increases much more slowly. For instance, if two objects differ in brightness by a factor of two, a photograph will record twice the response for the brighter objects than for the fainter object. However, the eye will respond to the brighter object quite a bit less than twice what it records for the fainter object. All sensory perceptions have this behavior.
If you have listened to the playback of a recorder left in a room, you probably have noticed that soft sounds easily heard by the ear often are missed by the recorder. On the other hand, loud sounds don’t record well either, often ending up as muffled noise. Logarithmic response allows for a large dynamic range. Signals that are outside the limits of detectability of a linear detector prevent their faithful recording. Fortunately, our sensory responses don’t respond linearly, so they have a broad range of intensity. Dynamic range refers to the ability to respond to a wide difference in intensity of a signal. Our eyes can respond to an incredible range in light levels. We can see quite well in bright sunlight, but we also can see well in dim light, such as at night. Manmade light detectors that work well in sunlight are blind in dim light. Conversely, detectors designed to work well in dim light can be damaged by exposure to the light of day. Large dynamic range is a wonderful design aspect of vision and other sensory perceptions. However, it sometimes makes for a difficult comparison between what our eyes see and what cameras record.
In addition to the logarithmic response, our eyes can adjust to various light levels by changing the diameter, and hence area, of our pupils. When exposed to bright light, our pupils constrict so that less light enters our eyes. When in dim light, our pupils dilate, allowing far more light to enter. This process takes time. This is why we blink and shut our eyes at first when we are suddenly exposed to bright light, and why we can’t see well when lights rapidly dim, such as when stepping outdoors from a well-lit room at night. With time, our eyes adjust to dim light, though total dark adaption takes hours. Photographers adjust cameras in a similar way by changing the size of a diaphragm behind the lens. This practice is measured by f-number, given by the equation
N = F/D,
where N is the f-number, F is the focal length of the lens, and D is the diameter of the opening of the lens, known as the aperture. The movie industry calls it the “iris” on their cameras, but it refers to the same thing. For instance, a setting of f/1 means that the focal length and lens aperture diameter are the same, while f/2 means that the focal length is twice the lens diameter.
During exposure, the focal length of the lens remains unchanged, so the factor that is altered is the lens aperture diameter, which is accomplished by the changing the diaphragm size. In photography the f-number often is called an f-stop, which is adjusted by a dial on the camera body where the desired f-stop is selected; however the aperture remains wide open for maximum light while looking through the viewfinder. When the shutter button is pressed the camera instantly sets the aperture opening of the lens to the selected f-stop. Note that on older cameras the aperture is set by a dial on the side of the lens. Although present-day cameras can set the aperture or f-stop of the lens to 1/2 or even 1/3 increments between full stops, the standard full-stop aperture settings of all lenses differ by approximately the square root of two.
Because the amount of light admitted increases in direct proportion to the area of the diaphragm, and the area of the diaphragm increases with the square of the diameter, then each adjacent f-stop corresponds to a change by a factor of two in brightness. In this way a photographer can adjust the f-stop of his lens to mimic what the eye does automatically with changing light levels. A camera lens that has eight f-stops can alter the amount of light entering the camera by a factor of 28 = 256. The eye easily can exceed this. Note that the camera’s light sensitivity, known as ISO setting (similar to film speed) can be adjusted to provide the same doubling or halving of light, but this does not increase the dynamic range of the camera. It merely shifts the f-stop range of the lens to different parts of the overall luminance range.
However, a photographer can do something with his camera that the eye cannot do—he may change the exposure time or the aforementioned ISO setting. Adjacent shutter speeds usually differ by a factor of two in full-stop increments such as 1/125, 1/250, or 1/500, so the same difference in the amount of light that enters the camera can be achieved by altering shutter speeds as by altering f-stops. For instance, suppose that a photographer decreases or closes the aperture by one full f-stop. That allows half the light per unit time into the camera than before. However, if the photographer decreases or slows the shutter speed by one full f-stop, the total amount of light remains unchanged. Generally, the sensor (light-sensitive surface in a camera) responds the same way to the total amount of light, whether that light is acquired through a longer exposure with a higher f-stop or with a shorter exposure and lower f-stop. The same principal applies for the ISO setting that dictates how sensitive to light the sensor is. ISO 100 is native to most sensors and directly relates to ISO 100 film speed, also known as ASA 100 prior to 1987.
Unlike film days where you couldn’t easily alter film speed without changing rolls of film or using different ISO emulsions, changing ISO on the fly in a digital camera to double or halve light is quite common if not running the camera in Program mode. Increasing ISO to 200 effectively doubles the sensor sensitivity one f-stop and therefore provides the same doubling of light as opening the aperture one stop or reducing shutter speed by half. We call this property of altering shutter speed, aperture, and ISO to maintain proper exposure reciprocity. In film days there was a phenomena called “reciprocity failure” where film would lose its light-gathering capability during long exposure. This failure does not exist with the digital sensor, making it much more useful for astrophotography.
One of the issues that does arise from using digital sensors is noise in the image for long exposures, which was exceptionally bad in early days of digital capture when sensors were mostly CCD format. This type of sensor runs quite hot during long exposures and therefore creates noise or “grain” in the image. Also, processors in cameras were limited in power so it wasn’t feasible to run noise filter software in-camera at the time of exposure. This would cause extended save times when writing the data to the memory card and drastically affect battery life. Today’s digital DSLRs, especially those with full-frame sensors where the sensor is the size of a 35mm slide and therefore contain larger cells on the sensor, are mostly CMOS based, which run much cooler and provide cleaner imagery for very long exposure times. Full frame sensors are exceptional at gather low-light imagery and therefore are the best choice for astrophotography. The faster processors in today’s cameras can also easily apply the built-in long-exposure and high-ISO filters that get applied prior to writing the 14-bit RAW image file to the memory card.
Another way that the eye and the camera differ is in color sensitivity. The normal human retina has both rods (black and white sensitive cells) and cones (color sensitive cells). Rods are far more sensitive to light than cones are. This is why animals with eyes designed for superior night vision lack cones, the trade-off being the sacrifice of color vision. In dim light, our eyes fail to record significant color, so we see in black and white. This is why most views of faint astronomical bodies through a telescope lack color. With increasing light levels, our perception gradually shifts from black and white to color, but we are so accustomed to the transition that we hardly notice the difference. Normal human vision relies upon three different types of cone cells with different, but overlapping, color responses. The blend of the sensation from those three sets of cells produces all the color that we see. In a similar manner, most color reproduction relies upon the use of three primary colors, though the primary colors of light and pigment differ.
We often take it for granted that faithful color reproduction is simple, but it isn’t.
We often take it for granted that faithful color reproduction is simple, but it isn’t. Color photography relies upon a three color system, but the three colors do not exactly match the three-color system of the eye. The photographic color system is designed to closely match what the eye sees at a bright and comfortable light level. At extreme light levels there are departures from this match, so photographers must take great care to ensure proper color balance. It is very easy to alter the white balance settings on a digital camera so that a photograph accentuates certain colors. Given this, some photography amounts to art rather than an exact reproduction of what someone present at the time of the photograph was taken might have experienced. Because the light levels during a total lunar eclipse can change by a factor of thousands, this is particularly true of photographs of lunar eclipses. Hence, it is difficult to produce a photograph of a total lunar eclipse that actually matches what most people saw. Another factor is that the human brain processes the images delivered by the eyes to adjust color to a norm. Consider the appearance of objects in a room illuminated by incandescent lights. A color photograph taken without a flash appears redder than what the eye perceives. This is particularly true of photographs made with emulsions rather than electronic cameras. The reason for this is that incandescent light is much redder than sunlight or fluorescent lighting. Thus, the color balance of what the eye sees during a total eclipse and the color balance of a photograph of the same eclipse can be very different.
There are at least two interactions of light with the earth’s atmosphere that are relevant to the appearance of a lunar eclipse, refraction, and scattering. When light enters the earth’s atmosphere from space, the speed of light changes. As the speed of light changes, light generally bends or refracts. Refraction causes the light to bend downward, toward the earth’s surface. The atmosphere refracts light most at the ring around the earth where the sun is either rising or setting. This is why the sky does not get dark instantly after sunset, for light is refracted into the night side of the earth. The amount of refraction depends upon the wavelength of light, with shorter wavelength light being bent more. Shorter wavelength light is toward the blue end of the spectrum, so blue light is refracted more than longer wavelength, bluer light. This is why sunsets and sunrises appear so red—most of the blue light is refracted out of our view before it reaches us. Bluer light being refracted more than redder light contributes to the sky appearing blue.
Another wave effect, diffraction, causes scattering of light. As light encounters air molecules, the light diffracts, or bends around, the molecules. Scattering does just that—it scatters incoming light in different directions. As with refraction, shorter wavelength, bluer light is scattered more than longer wavelength, redder light. Scattering plays a larger role than refraction in making the sky appear blue, but refraction probably dominates at sunset and sunrise to make the sky appear red. For objects appearing low in the sky, scattering plays the dominant role in an effect that astronomers call atmospheric extinction. Extinction causes objects low in the sky to appear fainter and redder than they normally do. As we shall see, this is an important factor in interpreting some lunar eclipse photos.
We divide the earth’s shadow into two parts, the umbra and the penumbra. The umbra receives no direct light from the sun. If the earth had no atmosphere, its umbra would be completely dark, but the earth’s atmosphere refracts and scatters light into the umbra, so the umbra is not completely dark. Rather, the dimly lit umbra typically has a strong component of red light, though other colors are possible. Since the umbra’s color varies from eclipse to eclipse, the color of the earth’s umbra must depend upon atmospheric conditions around the ring on the earth where the sun is rising and setting. The earth’s penumbra is partially shaded from the sun’s light, reducing the amount of light shining on the lunar surface that happens to be in the penumbra. However, there still is a tremendous amount of light in the earth’s penumbra.
The umbra and penumbra have cone shapes. As the lunar surface enters those cones during an eclipse, the intersection of the lunar surface and the cones closely approximates circles. The circle of the umbra is smaller than the penumbra’s circle. The two circles are concentric, so the penumbra is a larger circle surrounding the umbra. When the moon is entirely immersed in the earth’s umbra, we have a total lunar eclipse. The recent lunar eclipse and the next three lunar eclipses are total. If only a portion of the moon enters the earth’s umbra, we experience a partial lunar eclipse. Sometimes the moon misses the earth’s umbra entirely, but it passes through at least a portion of the earth’s penumbra. This is a penumbral lunar eclipse. Both a partial and total lunar eclipse are preceded and followed by penumbral phases. A total lunar eclipse is preceded and followed by partial phases.
The amount of light reaching the lunar surface is diminished during a penumbral eclipse or during the penumbral phases of a total or partial lunar eclipse. However, the amount of reduced light is not great. Generally, one cannot notice penumbral shading until the moon is deep into the penumbra, on the verge of entering the umbra. Penumbral shading is visible on a photograph, but even then it is subtle. Recall that the eye compresses differences in brightness, making it difficult to detect penumbral shading visually. The light passing into the penumbra from the edge of the earth is slightly reddened, but the much brighter light that is unblocked by the earth is many orders of magnitude brighter, so the light and color of the moon in the penumbra is dominated by the uneclipsed light. Thus, the portion of the moon in the penumbra is not significantly dim or red.
We are now prepared to discuss photographs of the recent total lunar eclipse on April 15. The first photograph is a montage of several photographs made at different times during the eclipse. On the left is an image of the moon early in the partial phase, with the next image being the moon more deeply in the partial phase. Notice that in either image, the umbra appears dark. This is because the exposure time is very short, too short to register any significant light in the umbra. If the exposure time were long enough to record the color of the portion of the moon in the umbra, the uneclipsed portion of the moon would be so overexposed that it probably would have bled over on top of the umbra. The middle images are of the totally eclipsed moon. Those exposures are very long, which allows detection of the faint light in the umbra. If these images had the same exposure time as the first two, nothing would be visible. The final images are of the end of the eclipse as it passed through the partial phases, where once again the exposure times were increased. This series underscores the wonderful design of the human eye—one automatically can see both the partial phases and the total phase. No camera can do that.
Consider this photograph of the penumbral portion of April’s lunar eclipse. You will notice that it does not appear red. This is because this photo was taken when the moon was very high in the sky, and hence it does not suffer from atmospheric extinction. Also notice that the left side of the moon in this image is only slightly fainter than the rest of the moon. This is the earth’s penumbra barely showing up in this photo. However, as I previously discussed, photography responds linearly. The eye would compress this slight difference, meaning that penumbral shading would be even less noticeable to the eye. Hence there was nothing remarkable about the appearance of the moon during the penumbral phase, nor will any penumbral eclipse normally appear unusual.
The third photograph is a comparison of two images of the partial phase made at about the same time, but with very different camera settings. Notice that the short exposure on the left captured the lit portion of the moon well, and the umbra looks very dark. The long exposure on the right grossly overexposed the lit portion of the moon, but the color of the umbra is visible. The image on the left more closely matches what the human eye saw during the eclipse. This illustrates that while it is possible to document the color of the umbra during partial lunar eclipse phases photographically, it is not possible to see the color of the umbra with the eye alone until the moon is almost totally eclipsed. This is why the eclipsed moon on the night of the Crucifixion (supposing an April 3, AD 33, Crucifixion date) would not have appeared red due to the eclipse alone.
One interesting site agrees in discounting Mark Biltz’s claims (and repeated by John Hagee in a well-selling book) about the 2014–2015 tetrad of total lunar eclipses ushering in the return of the Lord.1 However, this site also criticizes Answers in Genesis for several things, and it takes me to task for failing to see the fulfilled prophecy in the lunar eclipse that supposedly happened the night of the Crucifixion. This site objects to my statements that partial lunar eclipses and the penumbral portion of an eclipsed moon cannot appear red. They went on to offer examples of photographs of the partially eclipsed moon and of a penumbral eclipse that appear red.
Three of the photographs of partial lunar eclipses this site used are reproduced here. Notice in each photograph that the umbral portion of the moon appears dark, but that the uneclipsed portion of the moon appears red. This uneclipsed portion is in the earth’s penumbra, so the authors of this website concluded that the uneclipsed portion of the moon in the earth’s penumbra appears red. However, notice how close to the horizon the moon appears in each photograph. The moon is 1/2 degree in diameter, so we can estimate the moon’s altitude to be no more than about 2 degrees. When the moon is that low, atmospheric extinction almost always makes the moon appear red. That is, the moon would have appeared this red even if it were not in eclipse. This website also displayed a composite of multiple photos of a penumbral eclipse as the moon rose over Lisbon, Portugal, along with an image of the same penumbral eclipse as the moon rose over England. The moon in those images appear red, but because of atmospheric extinction rather than the penumbral eclipse.
The people responsible for this website haven’t spent much time watching lunar eclipses or even watching the uneclipsed moon, or else they would not have made such claims. Indeed, as an astronomer who has watched many lunar eclipses and often watched the uneclipsed moon as it has risen and set, I can say that these photographs offer no evidence that a partially or penumbrally eclipsed moon appear red. Rather, what these photographs demonstrate is the effect of atmospheric extinction, something that happens nearly every night that the moon is visible.
If the moon were visible as it rose over Jerusalem on the evening of April 3, AD 33, it likely would have appeared red, even if it were not partially eclipsed. Again, the reason would have been atmospheric extinction rather than the eclipse. Only during the deepest portion of a deep partial eclipse is the color of the earth’s umbra noticeable. And the moon wasn’t that deeply eclipsed that night over Jerusalem. The reason that umbra’s colors are not visible during a partial lunar eclipse is due to the blinding brightness of the uneclipsed portion. The uneclipsed portion of the moon is thousands of time brighter than the eclipsed portion. In moving from the partial to the total phase of a lunar eclipse, a photographer must greatly increase exposure time and/or decrease the f-stop in order to capture any significant light from the umbra during totality. Without sufficient light, there is no image, let alone any color. The eye does a similar thing in dilating the pupils as the lunar eclipse progresses to totality. If even a small portion of the uneclipsed moon is visible, the pupil is so constricted that the cones fail to register any light. Only when nearly the entire moon is in the umbra does the color of the umbra begin to appear. Again, anyone who has watched lunar eclipses knows this.
Those people promoting the blood moon thesis frequently quote from Joel 2:28–32 and Acts 2:17–21. The latter passage has Peter pointing out the fulfillment of Joel when he quotes things like the outpouring of the Holy Spirit and being saved by calling on the name of the Lord at Pentecost. Since Peter here quoted directly from Joel 2, the two passages read almost exactly the same. However, there are other biblical passages that mention the moon being turned to blood or otherwise changes to the heavenly bodies like the sun being darkened that should not be overlooked. There are many other passages that directly relate with the greater image here (e.g., sun. moon. or even the stars of heaven being darkened or otherwise affected). Such passages include Isaiah 13:10, Mark 13:24, Revelation 8:12, Luke 21:25, Revelation 12:1, Joel 2:10 and 3:15, Genesis 37:9–10, Ezekiel 32:2–11, and so on. These all need consultation to have a proper interpretation (Scripture interprets Scripture).
For example, Revelation 6:12–17 doesn’t appear to be a quotation of Joel 2, but there is overlap in the message, such as the sun being darkened and the moon being turned to blood. Furthermore, both Joel 2:28–32 and Revelation 6:12–17 speak of perplexing and troubling signs on the earth and in the heavens, so both passages could be referring to the same things. If so, then why don’t those who believe that the current series of total lunar eclipses are ushering in the Lord’s return mention these verses from Revelation (or elsewhere)? Probably they believe that the Lord’s return will precede the events of Revelation 6 by some considerable time. Hence, in their estimation, the events of Revelation 6:12–17 refer to some events other than those of Joel 2:28–32. However, the similarity of the description of these passages suggests that they be tied to the same events.
Despite criticism that were received, I stand behind my earlier statements regarding the possibility that the moon appeared as blood the night of the Crucifixion due to a lunar eclipse or that the series of four lunar eclipses that is underway in some way fulfills biblical prophecy. When photographs supposedly showing my position to be wrong are properly understood, many of the claims are baseless. Total lunar eclipses frequently, but not always, appear red, so there is nothing unusual about any particular total lunar eclipse appearing red. Neither a partial lunar eclipse nor a penumbral eclipse, in and of themselves, appears red. When either of those eclipses appears red, it is because one is viewing them when low in the sky. But this effect occurs almost any time that the moon appears low in the sky, something that happens nearly every night. These hardly qualify as great signs appropriate for biblical prophecy. I expect that when signs of the end occur, they will be astonishing and defy natural explanation. Lunar eclipses, while beautiful and interesting, hardly qualify.
I wish to thank Mr. Paul DeCesare for taking the eclipse photos and for his kind help in the technical aspects of photography.