Disproving Two Flat-Earther Claims about Lunar Eclipses

Flat-earthers believe that the sun, moon, and stars move in circles above the flat plane of the earth. Therefore, in the flat-earth model, it is obvious that the earth can never come between the sun and earth, so the earth’s shadow cannot fall onto the moon. Consequently, flat-earthers must reject the conventional explanation for lunar eclipses. What do flat-earthers think causes lunar eclipses? They don’t know, nor do many flat-earthers spend much time thinking about that question. Instead, flat-earthers spend much more time trying to poke holes in the conventional explanation for lunar eclipses. In their attempts to refute the conventional explanation for lunar eclipses, flat-earthers often make two false claims. One claim is that the shadow on the moon moves the wrong direction, from left to right as opposed to right to left (this orientation is for those in the Northern Hemisphere—directions are reversed for those in the Southern Hemisphere). The other claim is that the shadow moving on the moon changes direction during the eclipse. For instance, here is a flat-earther’s video showing this apparent change in direction. Sure enough, in this video, the shadow seems to move in from the lower left, but the shadow seems to depart to the lower right. Can looks be deceiving? Yes, indeed.

The Evidence to Be Examined

The video that I referenced above appears to be one made during the March 13–14, 2025, total lunar eclipse, visible over much of the Western Hemisphere. That night, I led an eclipse watch party at the Johnson Observatory at the Creation Museum. During the watch party, I photographed the eclipse with cameras attached to two telescopes. For instance, here are some photographs I took with the observatory’s 3.5-inch Questar telescope.

I also took 922 photographs with the observatory’s 127 mm (5-inch) Televue refracting telescope. I removed the lens from my Nikon D5400 camera and, using an adaptor, attached the camera to the telescope, making the telescope lens the camera lens. I programmed the camera to take photographs about every 15 seconds, starting shortly before the partial phase of the eclipse began and ending shortly after the partial phase ended. The field of view of the Televue is about twice that of the Questar, so the moon appears around half as large in the photographs taken with the Televue than with the Questar. After polar aligning the mount of the Televue, I set the drive on the mount to the solar rate so that the telescope would track the earth’s umbra, the shadow of the earth, rather than tracking the moon (I could have used that option). I made this time-lapse video of the 922 photographs.

I should explain a few things about this video. You may wonder about the gaps in the video. Though the sky was clear most of the time, some clouds occasionally passed through. A few thin clouds will dim the images, but opaque clouds will not allow any moonlight through. There was a time prior to totality and again at the start of totality that I stopped taking photographs for a few minutes as I waited for clouds to pass through.

You also may notice that the earth’s umbra on the moon appears to jump ahead a few times before totality and retreat a few times after totality. That is because I changed the ISO settings and exposure times on the camera during the eclipse. That is necessary because the light level of the moon changed tremendously throughout a lunar eclipse, much more than from the impression one gets from watching an eclipse. I began and ended my sequence with exposure times of 1/2000 seconds and an ISO setting of 200. During totality, I often used exposure times of six seconds and an ISO setting of 800. That means that the sensitivity of the camera changed by (800/200) x (6)(2000) = 48,000. If I had kept the same camera settings throughout the eclipse that I began with, then the photographs during totality would have been blank (dark). If I had used the camera settings throughout the eclipse that I used during totality, then the lit part of the moon would have been grossly overexposed in the partial phases. Those not familiar with the details of photography may have difficulty understanding this because our eyes seem to capture the entire eclipse effortlessly. Our eyes respond to light logarithmically, which compresses large differences in brightness. However, cameras respond to light linearly. Consequently, the camera does not record exactly what the eye sees.

The earth’s umbra is surrounded by the earth’s penumbra, or partial shadow. The portion of the moon in the penumbra is still lit by sunlight, but not as much as it would be if no eclipse were occurring. Since our eyes compress light differences, penumbral shading appears very subtle to our eyes, and penumbral shading is apparent just before the partial phase and shortly after the partial phase ends. On the other hand, because cameras respond to light linearly, penumbral shading can show up well in photographs. The edge of the earth’s umbra is a little fuzzy because the earth’s atmosphere refracts light into the umbra. Because cameras respond to light linearly, depending upon the camera settings, the edge of the umbra in photographs may be less distinct than it is to the eye. As I increased the sensitivity of the camera (such as by increasing the exposure time), the edge of the earth’s shadow appeared to jump ahead before totality. The reverse happened after totality as I decreased the sensitivity of the camera. If you carefully watch the flat-earther’s video linked above, you will see the same effects in that video as you see in mine, due to the same causes.

Examining the Evidence

Wrong Direction?

Why do flat-earthers think that the earth’s shadow moves the wrong direction during a lunar eclipse? The eclipse spanned a few hours. Everyone knows that during the day the sun moves east to west across the sky. In north temperate latitudes, we look southward to look at the sun, so the sun moves left to right across the sky (in south temperate latitudes, those directions are reversed). Most of us understand that this east-to-west motion of the sun each day is due to the earth’s rotation. However, flat-earthers reject that explanation and insist that it is the sun that moves east to west across the sky. To avoid endorsing either explanation, let us simply call the observed east-to-west motion of the sun its daily motion. Less known to the public is that all celestial objects, such as the moon and stars, share in this daily motion. Therefore, during March’s lunar eclipse, the moon moved east to west (left to right) across the sky. But if that is the case, wouldn’t one expect that as the moon moved left to right across the sky that the right side of the moon would enter the earth’s shadow first, causing the earth’s shadow to move across the moon from right to left? But the earth’s shadow appeared to move left to right across the moon. To see this, look again at the flat-earther’s video. In this video, you see the shadow move left to right across the moon.

Are the flat-earthers on to something here? No. Flat-earthers are unaware of another motion that is going on during a lunar eclipse. Each month, the moon moves around the sky. I would attribute that motion to the moon’s orbit around the earth. But flat-earthers don’t think the moon orbits the earth (nothing can orbit the earth in their view). Again, to avoid endorsing one of these positions, then let’s simply call this motion the moon’s monthly motion. Every 24 hours, the sun’s daily motion takes the sun through 360 degrees, so the sun’s daily motion is at the rate of 15 degrees per hour. Meanwhile, the moon’s monthly motion takes 29.5 days with respect to the sun. Note that the moon’s monthly motion is opposite the daily motion, west to east (right to left in north temperate latitudes). Since the moon’s monthly motion takes 29.5 days with respect to the sun, then each day the moon moves an average of 360/29.5 = 12.2 degrees. Dividing by 24 hours, the moon’s monthly motion is at the rate of 0.51 degrees per hour. That is, as the sun moves eastward 15 degrees per hour at the daily rate, the moon shares in the daily rate, but the moon also moves 0.51 degrees westward at the same time. Consequently, the moon’s daily rate is slowed to about 14.49 degrees westward, a little slower than the sun’s daily motion. If you have watched a solar eclipse, you have seen the moon move 0.51 degrees per hour west to east (right to left) across the sun.

Since the earth’s shadow is opposite the sun, then the earth’s shadow (umbra) must move with the daily rate of 15 degrees per hour as the sun does. Though we don’t normally see the earth’s umbra at night, it moves at the daily rate. Therefore, both the moon and the earth’s umbra move east to west (left to right) at the rate of 15 degrees per hour. However, the moon is simultaneously moving the opposite direction (right to left) at its monthly rate of 0.51 degrees per hour, so the moon’s net motion again is 14.49 degrees per hour. Therefore, during a lunar eclipse, the moon moves into the umbra from the right side of the umbra, causing the earth’s umbra to appear to move in on the left side of the moon. When looking at videos of a lunar eclipse with moon’s position fixed (as with the flat-earther’s video linked above), the earth’s umbra appears to move left to right onto the moon. However, when the earth’s umbra remains in a fixed position, as in my video, we see that it is the moon that is moving into the earth’s umbra, not the other way around. Hence, the observed left to right apparent motion is what is expected in the conventional explanation for lunar eclipses , and flat-earthers are wrong when they claim the earth’s shadow moves in the wrong direction during a lunar eclipse.

Hence, the observed left to right apparent motion is what is expected in the conventional explanation for lunar eclipses.

Changing Direction?

What about the second flat-earther claim that the earth’s shadow changes direction during a lunar eclipse? Looking at time-lapse videos of lunar eclipses with the moon’s position fixed (as in the flat-earthers’ video), one certainly gets the impression that the earth’s umbra changed directions. However, if one looks at a time-lapse video of a lunar eclipse with the earth’s umbra remaining stationary, as in my video, one does not get the impression of a changed direction. Remember that it is the moon that is moving to cause a lunar eclipse, not the earth’s umbra that is moving. In my video, the moon’s motion remained in the same direction throughout the eclipse. The fact that the earth’s round umbra is nearly 2 ½ times larger than the moon and that the moon usually does not pass centrally through the earth’s umbra helps give the impression that the motion changes direction. Only during a relatively rare central eclipse does one not get the impression of a changing direction of motion.

This figure shows the circumstances of the March 13–14, 2025, total lunar eclipse. The red circle represents the earth’s umbra, and the gray circle represents the earth’s penumbra. The seven moon images show the motion of the moon through the earth’s shadows, moving from west to east (right to left). The first moon image shows where the moon was at the beginning of the penumbral phase. The second moon image shows the moon’s position at the beginning of the partial phase. The third moon image shows the location of the moon at the beginning of the total phase. The fourth moon image shows the moon’s location at the middle of the eclipse. The remaining three moon images show the moon’s position at the end of the total phase, the end of the partial phase, and the end of the penumbral phase. Notice where the partial phase ended and began on the moon. With the orientation of the moon in this figure, the partial phase began around the 7:30 position on the moon, while the partial phase ended around the 3:00 position on the moon. These two points are not diametrically opposite, which gives the impression of a changing direction in a moon-centered view of the eclipse.

On July 5–6, 1982, I watched a nearly central lunar eclipse. This figure shows the circumstances of that eclipse. Notice that the partial phase began and ended on the moon at nearly diametrically opposite sides of the moon. Even with a moon-fixed view of this eclipse, one would not get the impression of the motion if the umbra’s changing direction.

Conclusion

The photographs that I made of the recent total lunar eclipse disprove two claims that flat-earthers often make about eclipses, that the shadow on the moon moves the wrong way and that the shadow shifted direction during the eclipse. The illusion behind these two claims stem from not realizing that it is the moon moving into the earth’s umbra and by looking at time-lapse videos that tracked the moon as it moved. Once one realizes that the moon is moving to cause lunar eclipses and one records a time-lapse video while tracking the earth’s umbra does one free oneself of the false impressions behind these two false claims.

By the way, I recently blogged about this eclipse a few days before it happened. I noted that this eclipse was three saros cycles after I saw a similar eclipse 54 years ago. It was nice to complete this cycle on this eclipse. It was also nice that the temperature the night of this eclipse was 50 degrees warmer than it was that chilly night in February 1971.