1905 A.D. Albert Einstein published his special theory of relativity, giving time a whole new dimension.

1906 A.D. The first self-contained battery-driven clock was developed.

1916 A.D. Germany was the first country to adopt a system of Daylight Saving Time. Belgium, Denmark, France, Italy, Luxembourg, Netherlands, Norway, Portugal, Sweden, Turkey and Tasmania immediately followed suit. Britain jumped on board three weeks later. It was not formally adopted in the U.S. until 1918.

Timely expressions

Time is measured in many ways, both scientific and non-scientific. Here are some of the daily expressions we use to discuss time:

Twilight: The first soft glow of evening, when the sun has dipped below the horizon, but is still at an angle that allows for some light. Areas with mountains tend to have a longer period of twilight, and the sun goes down behind them.

Daybreak: The first appearance of the sun.

Dawn: A gradual increase of sunlight.

Noon: The point of time when the sun is highest in the sky, and when morning becomes afternoon.

Dusk: The gradual decrease of sunlight.

Sunset: The last glow of sun as it sinks below the horizon, perhaps turning clouds pink or gold.

Evening: Can mean a lot of things, but is often associated with the period between sunset and bedtime.

Night: The period of darkness, lasting from sunset to dawn.

The time it takes

The actual time it takes the earth to complete one rotation around the sun: 365 days, 5 hours, 48 minutes, 46 seconds.

The time the year has slowed since 1 A.D. : 10 seconds

Average decrease in the year due to a gradual slowing of the earth's rotation: 1/2 second per century.

Thinking about time

• Don't keep saying, "I don't know where the time goes." It goes the same place it's always gone and no one has ever known where that is. — Andy Rooney

• Time heals what reason cannot. — Seneca

• Our costliest expenditure is time. — Theophrastus