Robert Coolman

The use of "anno domini" and "before Christ" to mark time began in the early days of Christianity, when clerics needed to know when Easter would fall.

Reference Quantum mechanics, or quantum physics, is the body of scientific laws that describe the wacky behavior of photons, electrons and the other subatomic particles that make up the universe.

Dividing the day into hours, minutes and seconds is a recent practice with thousands of years of science and tradition behind it.

The Gregorian calendar — used by most of the world — was introduced to fix errors in the Julian calendar mostly having to do with leap years.

Euler's Identity is a remarkable equation that comprises the five most important mathematical constants.

Topology is a branch of mathematics that describes mathematical spaces, in particular the properties that stem from a space’s shape.

Pascal's triangle, a simple yet complex mathematical construct, hides some surprising properties related to number theory and probability.

In geometry, an object exhibits symmetry if it looks the same after a transformation, such as reflection or rotation. Symmetry is important in art, math, biology and chemistry.

Trigonometry is a branch of mathematics that studies relationships between the sides and angles of triangles.

A logarithm determines how many times a certain number must be multiplied by itself to reach another number.

Calculus is a branch of mathematics that explores variables and how they change by looking at them in infinitely small pieces.

Quadratic equations are basic to algebra and are the math behind parabolas, projectiles, satellite dishes and the golden ratio.

Algebra is a branch of mathematics dealing with symbols and the rules for manipulating those symbols.

Tessellation is a repeating pattern of the same shapes without any gaps or overlaps. These patterns are found in nature, used by artists and architects and studied for their mathematical properties.

Classical mechanics is the mathematical study of the motion of everyday objects and the forces that affect them.

A proof is a rigorous argument that shows a mathematical claim to be true. Arguments that are proven become theorems, such as the Pythagorean Theorem.

Transistors are tiny switches that can be triggered by electric signals. They are the basic building blocks of microchips.

Our modern Western calendar is almost entirely a Roman invention, but it has changed significantly throughout history.

The Romans named the days of the week after their gods. The Germanic people adapted the Roman system and gave us the English names of the days.

The Egyptians started dividing the day into 24 units, a practice that continues to influence how we tell time.

A convergent series is a mathematical series in which the sequence of partial sums converges to a finite number. A divergent series is just the opposite — the sums do not meet a finite limit.