A Timely Study

I am writing this sentence at 11:40 AM PDT. That means that it’s 20 minutes until noon? That’s true — to a certain degree. And, it means that in 20 minutes the sun will be directly overhead? Uh, no. But, it does mean, doesn’t it, that I wrote that sentence exactly 11 hours and 40 minutes after the sun crossed over the prime meridian? Again, no. Okay, I’m just confused… Well, let’s take a shot at trying to understand this whole time thing — in one measly column. (Normally, this would require a several-hundred page book.)

I’ll begin by defining some terms that get used a lot, when we’re dealing with time:

AM: this stands for “ante meridiem,” translating as “before midday.” This is the time between midnight and noon.

PM: this stands for “post meridiem,” translating as “after midday.” This is the time between noon and midnight.

Noon: also known as “midday.” This is 12 o’clock in the daytime. Solar noon is the instant when the Sun reaches its apparent highest point in the sky, i.e., is directly overhead.

Midnight: the opposite of noon, differing from it by 12 hours, i.e., 12 o’clock in the nighttime. Solar midnight is the instant when the Sun is directly opposite from where one is on the Earth. It is when the night is equidistant from sunset to sunrise. It marks the beginning and ending of each day, in civil time. As such, midnight defies easy classification as either part of the preceding day or of the following day, and is associated with the hour 00:00.

Prime Meridian: a line of longitude (running north/south) at which longitude is defined to be 0°. On a spheroid (such as Earth), a prime meridian and it’s anti-meridian (the 180th meridian in a 360-degree system) form a great ellipse which divides the body into two hemispheres: eastern and western. Longitudes for Earth’s longitudes are measured from 0° at the Prime Meridian to 180°, east and west. Between 1884 and 1984, the meridian of Greenwich, England, was the world standard for Earth’s Prime Meridian. Since 1984, new techniques have resulted in the International Earth Rotation and Reference System Service (IERS) Reference Meridian, which is located about 5.3” east of the Greenwich prime meridian.

Universal Time: simply put, this is the time at the IERS Reference Meridian. It is the same everywhere on Earth.

Coordinated Universal Time (UTC): the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, and facilitates international communication, navigation, scientific research, and commerce. It divides time into days, hours, minutes, and seconds — defining the length of each.

Time Zones: an area of the Earth’s surface which observes a uniform standard time for legal, commercial, and social purposes. Time zones tend to follow the boundaries between countries and their subdivision, instead of strictly following longitudinal lines. The Earth’s surface is divided into 24 time zones, each defined by a standard offset from Coordinated Universal Time, increasing generally by one hour, moving westward around the Earth’s surface from the IERS Reference Meridian.

Standard Time: the synchronization of clocks within a time zone to a single standard time. This is normally the offset from the IERS Reference Meridian. For us, this is known as Pacific Standard Time (PST).

Daylight Savings Time: the practice of advancing clocks ahead of standard time by one hour in spring or late winter. In theory, this is to make better use of the longer daylight available in the summer by having darkness fall at a later clock time. For us, this is known as Pacific Daylight Time (PDT).

And, so, we are ready to take another look at my original questions. Is 11:40 AM PDT 20 minutes prior to noon? Yes, if noon is considered to be 12:00. No, if noon is considered to be when the sun is directly overhead — which, under Daylight Savings Time, would fall at 1:00 PM. Did I write that opening sentence 11 hours and 40 minutes after the sun crossed the prime meridian? No — or was it that amount of time after the sun crossed the IERS Reference Meridian. Because of daylight savings time, I wrote it only 10 hours and 40 minutes after that event.

One other thing about time: if we take the time to look around us, we’ll notice that, despite humans ongoing attempts to redefine nature for our own profit and pleasure, the rest of creation seems fine with the eternal laws of nature.