Stellar Parallax
Parallax When an object is close to me, you can use a ruler to measure the distance. But, it isn’t easy to measure when the object is away from me. In this case, how can you measure the distance? Humans … more
Astronomy Simulation
Horizontal Coordinate System
Celestial coordinate system A celestial sphere is an abstract sphere centered on an observer. All objects in the sky can be conceived as projected upon the celestial sphere’s inner surface. Horizontal Coordinate System The horizontal Coordinate System is a celestial … more
Equatorial Coordinate System
Celestial coordinate system A celestial sphere is an abstract sphere centered on an observer. All objects in the sky can be conceived as projected upon the celestial sphere’s inner surface. Equatorial system The equatorial coordinate system is the most basic … more
Constellations
Constellations If you look at the sky where there is no light on a clear night, there are so many stars that can not count. Thousands of years ago, the ancients linked stars to create constellations named after animals, objects, … more
Celestial Equator and the Ecliptic
The tilt relationship of the celestial sphere and ecliptic The celestial equator is the enlargement of the earth’s equator to the celestial sphere. Therefore, the celestial equator can be represented by a line fixed on the celestial sphere. The ecliptic … more
Apparent Motion of Mars
Apparent Motion of Mars If you observe the motion of Mars, you can see that you go forward and go backward. This procession of Mars has been regarded as mysterious since ancient times. In the past, the human did not … more
Eratosthenes’ Calculation of Earth’s Circumference
Eratosthenes’ Calculation of Earth’s Circumference The first person to measure the earth’s size was Eratosthenes, an ancient Greek scientist about 2,000 years ago. Eratosthenes lived in Alexandria, near the Nile River’s mouth by the Mediterranean coast, in northern Egypt. He … more
Tidal Force
Tidal force Earth is not an object like a point (· ), but a rigid body (●) with a certain volume, so the gravity applied to each part is slightly different. This difference in gravity applies to all celestial bodies … more
Galilean Moons
* This simulation refered the link below for Jupiter’s satellite data. https://en.wikipedia.org/wiki/Galilean_satellite Galilean satellite Jupiter, the largest planet in the solar system, has many moons. Jupiter’s representative moons include Io, Europa, Ganymede, and Calisto. These four satellites are called Galileo … more
Path of Satellite
From the perspective of an observer on Earth, the orbits of satellites with an orbiting period of less than 24 hours appear to move westward little by little with each turn. This phenomenon occurs because of the Earth’s rotation.