The orbit of the Moon is tilted 5.145° to Earth’s orbit around the Sun. As a result, a lunar eclipse does not occur every month, and a full moon is never 100% illuminated.
Flat-Earthers claim a full moon should not be possible due to the tilt of its orbit, incorrectly assuming a full moon means 100% illumination. In reality, a maximum full moon is at least 99.8% illuminated, and we cannot tell a 98% illuminated moon from a 100% illuminated one. We call it a full moon, even if it is never 100% illuminated.
Continue reading “Illuminated Fraction of a Full Moon”
The “Flat Earth Dome Model” (walter.bislins.ch/FED) is an app created by a fellow flat Earth debunker, Walter Bislin. The app attempts to map observed reality to the flat Earth model. Lines in the app portray how light rays must have traveled if Earth were flat. They demonstrate that light must bend in a physically impossible way if Earth were flat, disproving a flat Earth.
Videos of the app are circulating in flat-Earth communities, and flat-Earthers fail to understand what the app is showing. They incorrectly assume the app “proves” a flat Earth when in reality, it thoroughly disproves the flat Earth model.
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The DSCOVR satellite orbits around the Lagrangian point L1 between the Sun and Earth. We can say the DSCOVR satellite lies between the Sun and Earth, but it is not exactly between them.
Flat-Earthers discovered images taken by the DSCOVR satellite showing the Moon in front of Earth and a solar eclipse shadow on Earth’s surface. Then they concluded it should be impossible if DSCOVR is really between the Sun and Earth. In reality, the DSCOVR satellite is not exactly between the Sun and Earth. It orbits a point between the Sun and Earth.
Continue reading “Orbit of DSCOVR Satellite”
The Allais effect is the alleged anomaly of pendulums or gravimeters, which is purportedly observed during a solar eclipse. The effect has not been able to be consistently measured and was most likely caused by experimental error.
Flat-Earthers use the Allais effect to dismiss the result of Foucault’s pendulum. In reality, the Allais effect is still not conclusive. Even if it is true, it only occurs during an eclipse and does not rule out that the pendulum’s precession is due to Earth’s rotation. Not to mention that there is plenty of other evidence that Earth is in motion.
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The Saros is a period of 18 years, 11 days, and 8 hours between related eclipses. The eclipses with the same Saros cycle are classified into a Saros series which is numbered for identification.
Flat-Earthers claim the usage of the Babylonian term Saros “proves” that eclipses are predicted using ancient Babylonian technology. In reality, the Saros is now used to classify related eclipses. For example, the solar eclipse on August 21, 2017 is the 22nd member out of 77 in the Solar Saros 145.
The term Saros was first used in association with eclipse by Edmond Halley in 1691. The Babylonians never used the term Saros to describe eclipses. And the numbering system of the Saros series was created by G. van den Bergh in 1955.
Continue reading “The Saros Cycle and Saros Series”
Flat-Earthers like to mention an astronomical event or a specific celestial geometry and insist it cannot possibly occur if Earth is a rotating sphere orbiting the sun. They would incorrectly proclaim it as “evidence” of a flat, stationary Earth.
We can ask them the time of the event and the observer’s location, then use Stellarium or a similar app to simulate the event. If it produces the same result as the actual observation, then they have nothing to complain about. And the problem was just caused by their failure to understand and to create the correct model.
Continue reading “Stellarium”
Saros is a period of 6585⅓ days separating the occurrence of two eclipses. One Saros after an eclipse, a similar eclipse will occur. The eclipses that belong to the same cycle are grouped in a Saros Series.
Flat-Earthers claim that we can only predict eclipses using the Saros Cycle. In reality, it is impossible to determine many characteristics of an eclipse from its Saros Cycle alone.
Continue reading “Saros Cycle and Prediction of Eclipses”
The images showing the progress of a lunar eclipse were taken in increasing exposures to compensate for the decrease in brightness. The exposure increase from full moon to totality can reach 12EV or 4000× increase in light-gathering power.
Images showing the progress of a lunar eclipse appear in a constant brightness, and flat-Earthers —presumably never seen it in person— use it to “prove” a lunar eclipse is not caused by Earth’s shadow. In reality, the images were kept in a constant brightness by increasing the exposure of the camera.
Continue reading “Constant Image Brightness in Images of a Total Lunar Eclipse”
The Moon becomes red during a total lunar eclipse because Earth’s atmosphere acts like a lens and refracts sunlight toward the Moon. It also scatters bluish components of sunlight more strongly and lets more reddish components reach the Moon.
The Moon does not become totally dark during a total lunar eclipse, and flat-Earthers use it as “evidence” the Moon is not in Earth’s shadow during a lunar eclipse. In reality, it occurs due to optical phenomena involving Earth’s atmosphere.
Continue reading “Blood Moon: Why The Moon Turns Red During a Total Lunar Eclipse”
Diagrams of the Sun, Earth, and the Moon or any other celestial bodies are rarely made to scale because of their extreme smallness relative to the vast distances between them.
Flat-Earthers assume that the diagrams are not made to scale as a form of deception. In reality, it is just impossible to draw a diagram of celestial bodies with the real scale on physical media and still convey what we want to describe.
Continue reading “Scale in a Diagram of the Solar System”
The lunar phase is the shape of the Moon’s directly sunlit portion as viewed from Earth. The lunar phases change continuously, with a cycle over a period of 29½ days.
A lunar eclipse occurs when the Moon moves into Earth’s shadow. It is a rarer event that occurs only during a full moon and when the Sun, Earth, and Moon are very closely aligned.
Flat-Earthers claim it is impossible that the gibbous phase of the Moon is caused by Earth’s shadow, and they use it to discredit science. In reality, nobody claims Earth’s shadow causes it. They confuse the lunar phase with a lunar eclipse.
Continue reading “Lunar Phase and Lunar Eclipse”
The plane of the Moon’s orbit around Earth does not coincide with the plane of Earth’s orbit around the Sun. The two orbital planes form an angle of 5.145°. This is the reason an eclipse does not occur every month.
Flat-Earthers claim an eclipse should occur every month, but it does not, and they use it to discredit the science. In reality, they are unaware of the inclinations of the orbits.
Continue reading “Orbital Inclination: The Reason an Eclipse Does Not Occur Every Month”
Using the current computing power, predicting eclipses is usually done iteratively. We determine the position of the Sun and the Moon at a time and calculate their elongation to determine if an eclipse happens. This same procedure is then repeated many times, each for a different time.
Flat-Earthers insist that nobody can predict eclipses from the position of the Sun and the Moon. They incorrectly believe NASA used the ancient Saros cycle to predict eclipses by calculating the interval between eclipses. A tiny Python script can easily debunk it.
Continue reading “Predicting Eclipses Does Not Require the Saros Cycle or NASA’s Involvement”
The Sun and the Moon appear about the same size in the sky, but they are not perfectly the same size, and their sizes are not constant because their orbits are not perfectly circular.
Flat-Earthers claim it is too much of a coincidence that the Sun is perfectly 400× larger than the Moon and perfectly 400× farther, making them appear perfectly the same size. In reality, the Sun and the Moon are not perfectly the same size in the sky.
Continue reading “Apparent Size of the Sun & the Moon”
The path of a solar eclipse moves eastward because the Moon moves in its orbit faster than the motion of the observer due to Earth’s rotation. The path is influenced more by the Moon’s linear speed, not its angular speed.
The Moon rises from the east and moves westward. Flat-Earthers incorrectly claim if the Moon moves westward, then its shadow should also move westward. In reality, the Moon’s shadow moves across the Earth, not around it. The path is influenced more by the Moon’s linear speed, not angular speed, as in the case of the Moon’s motion across the sky.
Continue reading “Eastward Direction of the Path of a Solar Eclipse”
The distances to the Sun and the Moon are 149,600,000 km and 384,400 km. These figures are average values, and the actual values are around these averages. In a solar eclipse, the actual distances determine whether a total or annular solar eclipse occurs.
Flat-Earthers calculated the geometry of a solar eclipse using these average distances and discovered the umbra does not reach Earth’s surface. They wrongly concluded that an eclipse should not occur. In reality, the numbers are only averages, not the real values. And if the umbra does not reach Earth’s surface, it will still produce an annular solar eclipse.
Continue reading “Solar Eclipse: Length of the Umbra & Earth-Moon Distance”
A selenelion is a rare lunar eclipse where the Sun and the Moon are both visible at the same time. An even rarer form of selenelion occurs if it is a partial lunar eclipse, and the upper part of the Moon is eclipsed. Some call this an “impossible eclipse.”
Flat-Earthers claim that such an eclipse should not be possible to occur because the Earth’s shadow is in the wrong position. In reality, it is possible to happen because the observer is looking slightly downward due to the dip of the horizon and atmospheric refraction.
Continue reading “The Impossible Eclipse”
A selenelion occurs during a lunar eclipse when the sun and moon are observed above the horizon. Atmospheric refraction bends light rays and lifts the image of the sun, and the moon typically up to 0.6°, so both can appear above the horizon.
Flat-Earthers assert that a selenelion should not be possible if Earth is a sphere due to the fact during a lunar eclipse, the sun and moon are 180° apart. In reality, a selenelion is possible because Earth’s atmosphere refracts light.
Continue reading “Selenelion: The Phenomenon Where Both the Sun and Moon Are Visible During a Total Lunar Eclipse”
Light generally travels in a straight line. We can use this property of light to determine the umbra, penumbra, and antumbra part of a shadow by drawing lines from the edges of the light source toward and past that of the occluding object.
Flat-Earthers regard the lines in an eclipse diagram as a violation of the fact that a light source emits light in every direction. In reality, the lines are there only to determine the boundaries of the shadow’s regions in an eclipse diagram.
Continue reading “Umbra, Penumbra, and Antumbra in an Eclipse Diagram”
The sun is a huge light source. It is larger than anything on Earth. As a result, the umbral part of a shadow formed by sunlight will always be smaller than the object casting the shadow.
Flat-Earthers assert that a shadow cannot be smaller than the object casting the shadow. They would use that to “disprove” the scientific explanation about the occurrence of a solar eclipse. In reality, it is not difficult to demonstrate that the umbral part of a shadow can be smaller than the object casting the shadow, especially if the light source is the sun.
Continue reading “Sunlight Creates Umbral Shadow Smaller than the Object Casting the Shadow”