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.
Continue reading “Galilean Moons: First Objects Observed to Orbit Another Object”
Earth’s gravity pulls things toward Earth. Satellites can stay up there because they are orbiting. They are moving at the right speed and right direction to counter the pull of gravity.
Flat-Earthers claim that satellites should fall down if gravity pulls toward Earth. In reality, we do not just launch satellites to space. We also give them the correct speed & direction, so they neither fall toward Earth nor keep going farther away.
Continue reading “How Satellites Can Orbit and Stay Up There”
“Down” is the same direction as Earth’s gravitational acceleration, toward Earth’s center. “Up” is the opposite, or away from Earth’s center. This applies to all observers on Earth.
Flat-Earthers like to question & ridicule about what would occur on the people “down” there. They just do not understand that to the people on the other side of Earth, “down” is still toward Earth’s center, like it appears to everyone else.
Continue reading “Directions of Up and Down”
A human eye can only visually perceive the curvature of the Earth if we are at a considerable altitude from the surface, which is still beyond the reach of most humans today. A commercial jet airliner is the highest position realistically attainable by most humans today. We can only perceive very slight curvature at such altitude and, even then, only in an ideal condition.
The basis of flat-Earthers’ belief is that the horizon appears flat. They would say if we cannot see the curvature, then there’s no curvature, and therefore, the Earth is flat. In reality, only a few people can travel high enough to see the curve. The highest we can realistically go is by getting on a commercial jet airliner, which can only go about 11-15 km up, only a fraction of Earth’s radius.
Continue reading “Where’s the Curvature?”
A frame of reference consists of an abstract coordinate system and physical reference points that uniquely fix the coordinate system and standardize measurements. Speed or velocity is relative to a specific frame of reference. It is possible that two speeds/velocities are measured relative to a different frame of reference and thus cannot be directly compared.
Flat-Earthers like to compare two different speed measurements like an airplane moving at 900 km/h (560 mph) and Earth’s surface near the equator at 1674 km/h (1040 mph). They would conclude the airplane should not be able to catch up with Earth’s surface and would not land if the Earth is rotating. In reality, both the speeds are measured relative to a different frame of reference, and therefore, cannot be compared directly.
Continue reading “Frame of Reference”
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”
Newton’s cannonball was a thought experiment Isaac Newton used to explain the principle of orbital motion. It was the first explanation of an orbit and still the easiest to understand.
Newton visualizes a cannon on top of a very tall mountain where the air resistance is no longer a factor. As more charge is used with each cannon shot, the speed of the cannonball will be greater, and the cannonball will hit the ground farther and farther. Finally, at a certain speed, it will not hit the ground at all. It will fall toward the spherical Earth just as fast as the Earth curves away from it. In the absence of drag from the atmosphere, it will continue forever in orbit around the Earth.
Continue reading “Newton’s Cannonball”
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 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”
In orbit, objects are weightless because both the objects and the spacecraft have the same speed and direction, and both are affected by the same gravitational influence. We use the spacecraft as the frame of reference. Because the objects are not in motion relative to the spacecraft, they appear to float.
In Earth orbit, the objects are still affected by Earth’s gravity, but yet they float. Flat-Earthers use it to disprove spaceflight. In reality, the objects float because we are using the spacecraft as the frame of reference, which is also moving by the same amount and is affected by the same gravity as the objects themselves.
Continue reading “Weightlessness, Free Fall, and Microgravity”
Rocket launches have a curved trajectory because their objective is not only to reach space but also to enter Earth orbit. To achieve it, a spacecraft needs to gain a sufficient horizontal speed, parallel to Earth’s surface.
Flat-Earthers claim the curved appearance of a rocket launch trajectory “proves” rockets never reach space. In reality, it is caused by the motion of the rocket parallel to Earth’s surface, perspective effect, and the curvature of the Earth.
Continue reading “Curved Appearance of a Rocket Trajectory”
If a satellite is placed in an orbit 35786 km above the equator, it will be in motion at the same speed as the Earth’s rotation. As a result, the satellite will appear practically motionless from an observer on Earth’s surface. Many communication satellites are in this orbit so that a satellite receiver does not need to track the satellite continuously.
Flat-Earthers often take the fact that satellites are in motion, and most satellite dishes have a fixed direction as ‘proof’ the receivers cannot be pointing to satellites. In reality, it is possible to place a satellite in a geostationary orbit to make it appear in a fixed position in the sky relative to an observer on Earth.
Continue reading “Geostationary Satellites”
The Moon is tidally locked. Half of the Moon is always facing the Earth. However, due to libration, we can take a glimpse of areas of the moon that are not always visible.
Flat-Earthers invented many “scenarios” to “explain” how the so many lunar-related phenomena can happen on the flat Earth model. Some of these “explanations” include “transparent Moon”, “hemisphere-shaped Moon”, “flat circular Moon”, etc. Lunar libration rules out the majority, if not all, of these “explanations.”
Continue reading “Lunar Libration”
A satellite in a high enough orbit can remain operational for a very long time because in space there is practically no air resistance. This is a situation that never occurs in our everyday life. A car requires a constant consumption of fuel to keep running, but a satellite can remain in motion without consuming any fuel because there’s practically no force stopping it.
Flat-Earthers claim that satellites cannot stay up there for such a very long time because ‘we never refuel any satellites.’ They are wrong. In space, there is practically no drag, and satellites only need to consume fuel to adjust their speed periodically.
Continue reading “Orbital Station-Keeping”