### Galilean Moons: First Objects Observed to Orbit Another Object

Jupiter has four moons (Io, Europa, Ganymede, & Callisto) that we can easily observe using a binocular or telescope. They are the first objects found to orbit another, proving it is possible for a satellite to orbit planets other than Earth.

Flat-Earthers like to demand evidence of an object orbiting another. All they have to do is use a telescope to observe Jupiter. Its moons have short orbital periods (1.8 to 16.7 days), & thus, it is not hard to observe the orbiting motion.

### Archimedes’ Principle and Gravity

Archimedes’ principle states that any object, totally or partially immersed in a fluid, is buoyed up by force equal to the weight of the fluid displaced by the object. Meanwhile, Newton’s law of universal gravitation states that every particle attracts each other with force directly proportional to their masses & inversely proportional to the square of their distances.

Flat-Earthers like to characterize gravity as if it was “invented” to “replace” Archimedes’ principle & that the two are competing theories. In reality, these are two different theories that explain different phenomena. Gravity does not explain anything that Archimedes’ principle explains and vice versa. Gravity does not replace Archimedes’ principle; both are valid and in use today.

### Countering Gravity

Gravity is not the only force. Other forms of force exist. Multiple forces can affect an object at the same time. Forces can counteract gravity, making an object move against the direction of gravity. These cases do not disprove gravity.

Objects can move against the direction of gravity, and flat-Earthers use it as “evidence” that gravity does not exist. In reality, there is at least a force other than gravity affecting the object, in the opposite direction from gravity, with a larger magnitude. Continue reading “Countering Gravity”

### Analemma

An analemma is an image or diagram showing the change in the position of the Sun in the sky, seen from a fixed location on Earth, at the same time every day, over the course of a year.

The north-south component of an analemma results from the change in the Sun’s declination due to the tilt of Earth’s axis of rotation. The east-west component results from the non-uniform rate of change of the Sun’s right ascension, governed by the combined effects of Earth’s axial tilt and orbital eccentricity.

### Overlay in Geographic Information System (GIS)

In geographic information system (GIS), overlay is an operation that superimposes layers of geographical data —like maps, satellite photos, roads, borders, etc— on top of each other.

Some satellite photos of Earth at night show country borders and shorelines. Flat-Earthers use the fact to dismiss the images as fake. They claim there are no lights illuminating the border on the ground, therefore the borders should not be visible. In reality, the borders are just an overlay added on the top of the original image. They are not part of the original satellite image.

### Albert Michelson in “Michelson and the Speed of Light”

In 1881, Albert A. Michelson experimented to prove the existence of aether. Aether was a hypothesized material that fills the region of the universe. Scientists knew light is a form of a wave, and because all other waves require a medium to propagate, they formulated the aether hypothesis, in which light can propagate. However, Michelson’s attempt produced a null result. Michelson concluded that the hypothesis of a stationary aether is erroneous.

In 1960, Bernard Jaffe wrote Michelson’s biography in the book “Michelson & the Speed of Light.” Unscrupulous flat-Earthers quoted a lone paragraph from the book out of the intended context and presented it as if Michelson proved the Earth is stationary.

### Antipodal Flight Route: Jakarta–Bogota

Jakarta & Bogota are a near antipodal pair: the opposite points on Earth’s surface. We can fly from Jakarta in any direction and arrive at Bogota after traveling a similar distance, irrespective of the direction we leave Jakarta.

Any flight between an antipodal pair has a similar duration even though the different flights have different directions. This fact is only consistent with spherical Earth and cannot possibly be explained if Earth is flat.

For example, on a flat Earth, the flight route of Jakarta–Hong Kong–New York–Bogota is almost a straight route between the two locations. Meanwhile, the Jakarta–Sydney–Auckland–Santiago–Bogota route involves a massive detour, and it should take much longer than the aforementioned straight route. However, contrary to what is expected in the flat Earth model, both routes have a similar flight duration.

## Flight Durations

• Jakarta–Istanbul–Bogota: 12h 0m + 13h 45m = 25.75 hours
• Jakarta–Hong Kong–New York–Bogota: 5h 5m + 16h 0m + 5h 42m = 26.783 hours
• Jakarta–Tokyo–Houston–Bogota: 7h 35m + 12h 5m + 4h 55m = 24.583 hours
• Jakarta–Sydney–Auckland–Santiago–Bogota: 6h 55m + 3h 5m + 11h 0m + 6h 14m = 27.23 hours

### Mark Twain’s Fake Quote

The following quote is often attributed to Mark Twain. But there is no evidence Mark Twain ever wrote this phrase, despite the fact his writings were very well-documented.

“It’s easier to fool people than to convince them that they have been fooled”

Flat-Earthers like to use the quote to ridicule & describe those who understand Earth is a sphere. In an ironic twist, by attributing the quote to Mark Twain, these flat-Earthers demonstrate that they are being easily fooled themselves.

### The Polar Azimuthal Equidistant Map is NOT the Flat Earth Map

The azimuthal equidistant map is a projection of spherical Earth on a two-dimensional medium. The map has distortions, like every other type of map.

Flat-Earthers stole the shape of the azimuthal equidistant map and call it the “flat-Earth map.” While the two are identical in shape, they have different characteristics. The map that they call the “flat Earth map” is claimed to be a scaled-down representation of the supposed flat earth. They claim it to be distortion-free.

Some institutions use the azimuthal equidistant map & flat-Earthers incorrectly claim it as an “endorsement” of flat Earth. These maps are azimuthal equidistant maps and not related to flat Earth.

### Reproduction of the Cavendish Experiment

The Cavendish experiment was the first experiment to measure gravity between masses in the laboratory. The experiment has been repeated numerous times over two centuries with consistent results. Many other types of experiments also confirmed it.

Flat-Earthers incorrectly claim the Cavendish experiment has never been reproduced. They focus solely on the original experiment to discredit it. In reality, there are far too many repeats of the experiment. To discredit the experiment, they have to address all and each of the repeats of the experiment.

### Point Source

A point source is a source or reflection of light with a smaller angular size than the angular resolution of the observer. It is visible as a bright dot if bright enough against a dark background but not resolvable, or no detail is discernible.

Flat-Earthers claim the ISS should not be visible like a distant plane is not visible. In reality, aircraft lights can be seen from 60 km in a dark sky but are not resolvable. We can see them because they are point sources on a dark background.

### Why Lakes or Other Bodies of Water Are Not Tidal

All the seas and oceans around the world are connected. Water can freely flow between them. That’s the reason tide can occur on them.

On the other hand, lakes are isolated from one to another. Water cannot freely flow between them. That is the reason tide in meaningful amount cannot occur on lakes or any other bodies of water.

### Attraction Between Masses

If gravity is the attraction between masses, then why two hanging masses do not appear attracted to each other? Because there is a really huge mass (the Earth) below both masses, attracting both masses with a much significantly larger force compared to that between each other.

The Schiehallion experiment used a massive mountain as one of the masses. And they were able to measure the effect, called the vertical deflection.

The Cavendish experiment controls the vertical attraction from Earth out of the equation. Therefore, we can observe and measure the weak and slow horizontal attraction between the masses, without interference from Earth.

### Polaris Distance and How It Does Not Appear to Move

In a very casual observation, Polaris appears stationary in the sky because it is very far & we do not live nearly long enough.

Flat-Earthers use that Polaris always appears in the exact location as “evidence” of a stationary Earth. In reality, it does not appear in motion the same way mountains do not appear to move if we move less than an inch.

### Buzz Aldrin’s Interview with Conan O’Brien

In a talk show, Conan O’Brien (the host) incorrectly said that he watched Buzz Aldrin (the guest) landed on the Moon. Buzz corrected him that what Conan saw was just an animation.

Flat-Earthers wrongly use Buzz’s statement as “evidence” that the landing was fake. In reality, Buzz informed Conan that news broadcasts of the landing used animations to give audiences a visual representation of the landing. They did not go to the moon in advance to set up cameras to report the landing.

## References

### Dark Part of the Moon & Its Visibility During the Day

Black is a color that results from the absence of light. A dark or black object emits practically no light. It does not emit “black light.”

Flat-Earthers claim the dark part of the moon should appear black during the day. In reality, they fail to understand that black is caused by the lack of light, not by the emission of “black light.”

### Lunar Surface: As Dark As Worn Asphalt

The lunar surface is as dark as worn asphalt. It appears bright at night because everything else is darker. And in photos, its brightness is only a matter of the camera’s exposure settings.

In photos taken on the Moon, its surface looks dark unlike the Moon at night & flat-Earthers dismiss them as fake. In reality, it is just a matter of camera exposure. We can easily turn worn asphalt to look bright in photos by changing the exposure the same way the lunar surface can look bright or dark in photos.

### NCSE’s Satirical Article “Gravity: It’s Only a Theory”

The NCSE is an organization to educate the public & the press about evolution & climate change. They wrote a satirical article, “Gravity: It’s Only a Theory,” to demonstrate what might happen if a science denialist refuses the existence of gravity using the same “logic” that they use to reject the existence of evolution.

NCSE does not deny gravity & it is mentioned at the beginning of the article that it is a satire. Flat-Earthers failed to notice that, and it became a hoax that they use to support their false belief. The author probably did not expect there are far more extreme denialists that can go as far as to reject gravity & even beyond.

### Density and Balance Experiment

Objects fall down because of gravity. Flat-Earthers deny gravity & wrongly claim they fall down because of density. We can disprove flat-Earthers’ claim by setting up two different weights of the same material (thus, the same density) against each other using a balance. We can see the objects’ densities are not why they fall down.

### Images in Newspaper Coverages of the Apollo 11 Moon Landing

Apollo 11 landed on the Moon on July 20th, 1969 & returned to Earth on July 24th. Newspapers reported the landing on tomorrow’s edition, July 21st, 1969, with photos.

Flat-Earthers use the fact that the newspapers already had photos as “evidence” of deception. They claim the images should only be available after July 24th. The explanation is simple. The journalists took the pictures off the live television broadcast of the landing.

In today’s situation, it is analogous to taking a screen capture off a YouTube video, a simple task that even flat-Earthers themselves can accomplish.