Principle of Mirror
Why is the incident angle and the reflection angle the same? ‘Law of reflection’ has the word ‘law’ attached. ‘Law’ refers to a situation in which a natural phenomenon happens repeatedly and without exceptions. In other … more
Is Sun Rays Parallel?
Parallel sunlight The radiant energy of the sun spreads in every direction. However, since the sun and the earth are far apart, we assume that they are usually almost parallel. Ancient Greece’s Eratosthenes measured Earth’s size … more
Parallax of Eyes
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 … more
Law of Reflection
The law of reflection Consider a light-ray incident on a plane mirror, the angle of reflection is equal to the incidence angle. This is the law of reflection. When looking at the end of the head … more
Maximum Elongation of Inner Planets
Maximum Elongation of Inner Planets From the Earth’s perspective, the inner planets seem to stay near the sun. This is because it orbits the inside of the earth. So We cannot see the inner planets in … more
Fourier Analysis
Fourier series A Fourier series is a way to represent a function as the sum of simple sine waves. A simple trigonometric function consists of a smooth surface. If you continue to add these trigonometric functions, … more
Formation Model of Columnar Joint
Formation of Columnar Joint A columnar joint appears as a polyhedral pillar, such as a tetragonal, pentagonal, or hexagonal shape. Its shape depends on the rate at which the lava solidifies. Columnar joints are often mistakenly … more
Differentiation
Differentiation The differentiation is to find the amount of change at a point on a graph f(x). This is like the process of finding the slope of the tangent line when you can draw a tangent … more
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 … more
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 … 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 … more