May 1, 2026 • 9 mins
OK, this is a trick question -- 'SOS' doesn't stand for anything at all. Learn the history of these three terms, including what astronomy and telegraphy have to do with it, in today's episode of BrainStuff, based on this article: https://people.howstuffworks.com/am-pm.htm; https://people.howstuffworks.com/what-does-sos-mean.htm
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Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren
bolbabam here. Because language is a wide and wondrous thing,
we humans encounter new or new to us words all
the time. Anything from a book you're reading for fun,
to an article about a subject you're only sort of
(00:23):
familiar with, to a fancy restaurant menu might have you
diving for a dictionary, and even dictionaries have to update
all the time to accommodate our linguistic innovations. For example,
just in March of twenty twenty six, the Oxford English
Dictionary added a definition for doom scroll. But on the
flip side, there are some words or abbreviations that we
(00:45):
know the practical meaning of that we might even use
every day without having any idea of what they actually mean. Today,
let's talk about a few of those. AM and PM
and sos. First, up, AM and PM. Okay, many parts
of the world use a twenty four hour clock instead
(01:07):
of one o'clock in the afternoon. Someone in Turkey or
Brazil might tell you it's thirteen hundred hours. But in
places that use the twelve hour clock, like the United States,
we use the concept of AM and PM. One of
the inconvenient things about breaking your twenty four hour day
into two twelve hour chunks numbered one through twelve, which
(01:28):
turnover at midday and midnight, is that it becomes necessary
to tell someone which chunk you're talking about. Are we
meeting at eight in the morning or eight at night?
You can often use context clues, but it is for
this reason that the two periods are called AM, which
is short for the Latin term anti meridium or before midday,
(01:48):
and PM, which is short for post meritium or after
mid day midday or meridium. Here is in the astronomical
sense of when the sun passes the meridian overhead. The
meridian is an imaginary circle that runs around our planet
from any given point of view from wherever you're standing,
(02:09):
the meridian passes through the north and south celestial poles,
you know, the north and south points of the planet's axis,
and it's also perpendicular to the horizon, so it includes
the highest point in the sky above you. The sun
passing through the meridian is essentially high noon. But let's
back up a little. Why are we complicating things with
(02:32):
a twelve hour clock in the first place, When the
twenty four hour clock seems so much more straightforward and convenient.
The answer to this has a lot to do with
early clocks. The concept of AM and PM comes from
the fact that ancient people used the convenient dark light
contrast of each twenty four hour cycle to talk about
what time it was. The sun pulled them what time
(02:55):
it was in the day, and the moon and stars
did the same at night. As early as thirty five
hundred BCE, the ancient Egyptians built shadow casting obelisks that
shaded sections of the ground throughout the day. These sections
weren't as precise as modern hours, but the concept was
the same. By fifteen hundred BCE, they had invented the
(03:16):
more precise sun dial, and with it the hours we
still know and love, ten daytime hours with a sunrise
and sunset hour tacked on to either end. By six
hundred BCE, that invented a timekeeping instrument for the night
time as well. A person could align it with a
pole star to track the passage of other stars through
the meridian to tell time. Later clockmakers used the circular
(03:41):
model of the sun dial to base the layout of
their new technology. Although the first mechanical clocks in Europe
built for medieval clock towers were twenty four hour devices.
By the thirteen hundred CE, mechanical clocks began to be
built with twelve hour faces, perhaps to save space and
eyestrain for people carrying pocket watches. By the mid fifteen hundreds,
(04:04):
English speaking people in the maths and sciences like John Deeve,
who were using twelve hour cycles, had adopted the Latin
phrases anti meritium and post meridium, Latin being the scientific
lingua franca of the time. By the mid sixteen hundreds,
the abbreviations AM and PM were in use by scientists
like Nicholas Culpepper. Both the full terms and the abbreviations
(04:27):
trickled into common usage after that, even though these designations
didn't have much to do with the astronomical bodies anymore. However,
by the late eighteen hundreds, starting with the Canadian Pacific
Railway in eighteen eighty six, more countries and military entities
started telling time based on the twenty four hour clock. Again.
(04:49):
With the exception of countries like the US, Australia, Canada,
and the Philippines or where the twelve hour system is
officially used, most other countries officially use a twenty four
hour clock, but ancient habits die hard. If you ask
someone in Ireland, China, or France the time, they're equally
likely to use AM and PM. But okay, let's switch
(05:12):
over to another common term, SOS. Even children at play
know that when you are in a life threatening emergency,
maybe you need to be rescued from an island filled
with man eating crabs that's also surrounded by lava. The
way you let the world know that you're in trouble
is to shout three simple letters SOS. You can write
(05:34):
them on the beach, send them via Morse code, or
write them on your hand and flash them at pastors by.
We all know that sending out an SOS signal is
a request for rescue. So what does SOS mean? Is
it an abbreviation? What did the letters stand for? This
was new to me today. The letters SOS stand for nothing,
(05:56):
not save our ship, not save our souls. It wasn't
even originally designed to stand for letters of the English alphabet.
SOS came to us as a replacement for visual distress
signals during the early days of long distance electromagnetic communication.
Samuel Morse developed what would become Morse code, alongside his
contributions to a telegraph machine that could send messages using
(06:19):
electrical signals over a wire in the eighteen forties. In
Morse code, dots and dashes are assembled in different configurations
to represent the different letters of the alphabet. In this way,
messages could be sent across countries via wired telegraph networks, and,
starting in the early nineteen hundreds, wirelessly across oceans and
(06:40):
then around the world using radio equipment. SOS came in
during the transition between the two. In nineteen oh five,
the German government, but which had leaned into telegraph systems early,
published their regulations for the control of Spark Telegraphy. It
mandated that German wireless operator use dot dot dot dash
(07:02):
dash dash dot dot dot to signal an emergency. This
didn't really have anything to do with letters of the alphabet,
but it was quick and easy to type and difficult
to mistake for anything else. It also happened to spell
SOS in Morse code. Everyone agreed it was way better
(07:22):
than SSSDDD, which is what the Italians were pushing for.
At the International Radio Telegraph Convention in nineteen oh six,
the term SOS was voted in as the official international
distress signal and went into effect July first of nineteen
oh eight. It didn't catch on everywhere immediately. For instance,
(07:42):
the British Marconi International Marine Communication Company, which outfitted ships
with radio equipment, preferred the distress code CQD in Morse code,
and continued using it after the SOS call was established
as the international standard. In fact, CQD was the first
distress code sent by the radio operators on the Titanic
in nineteen twelve when the ship hit Iceberg, although they
(08:05):
did send the SOS signal as well. Early radios, like
the Titanics couldn't transmit sounds, only electrical signals. Once inventors
figured out how to encode speech, the verbal signal may
day was picked up at the International Radio Telegraphic Convention
in nineteen twenty seven. As we've talked about on the
show before, may day is derived from the French madeir,
(08:28):
which means help me, but SOS cannot be ousted. Although
mayday is used in voice communication, SOS is still used
as shorthand or anywhere that non verbal communication must be used.
Today's episode is based on the articles what do am
(08:49):
and PM stand for and what does SOS Mean? On
HowStuffWorks dot Com, both written by Jesslynshields. Brain Stuff is
production of by Heart Radio in partnership with houstuffworks dot
Com and is produced by Tyler Playing Before. More podcasts
from my heart Radio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren
bolbabam here. Because language is a wide and wondrous thing,
we humans encounter new or new to us words all
the time. Anything from a book you're reading for fun,
to an article about a subject you're only sort of
(00:23):
familiar with, to a fancy restaurant menu might have you
diving for a dictionary, and even dictionaries have to update
all the time to accommodate our linguistic innovations. For example,
just in March of twenty twenty six, the Oxford English
Dictionary added a definition for doom scroll. But on the
flip side, there are some words or abbreviations that we
(00:45):
know the practical meaning of that we might even use
every day without having any idea of what they actually mean. Today,
let's talk about a few of those. AM and PM
and sos. First, up, AM and PM. Okay, many parts
of the world use a twenty four hour clock instead
(01:07):
of one o'clock in the afternoon. Someone in Turkey or
Brazil might tell you it's thirteen hundred hours. But in
places that use the twelve hour clock, like the United States,
we use the concept of AM and PM. One of
the inconvenient things about breaking your twenty four hour day
into two twelve hour chunks numbered one through twelve, which
(01:28):
turnover at midday and midnight, is that it becomes necessary
to tell someone which chunk you're talking about. Are we
meeting at eight in the morning or eight at night?
You can often use context clues, but it is for
this reason that the two periods are called AM, which
is short for the Latin term anti meridium or before midday,
(01:48):
and PM, which is short for post meritium or after
mid day midday or meridium. Here is in the astronomical
sense of when the sun passes the meridian overhead. The
meridian is an imaginary circle that runs around our planet
from any given point of view from wherever you're standing,
(02:09):
the meridian passes through the north and south celestial poles,
you know, the north and south points of the planet's axis,
and it's also perpendicular to the horizon, so it includes
the highest point in the sky above you. The sun
passing through the meridian is essentially high noon. But let's
back up a little. Why are we complicating things with
(02:32):
a twelve hour clock in the first place, When the
twenty four hour clock seems so much more straightforward and convenient.
The answer to this has a lot to do with
early clocks. The concept of AM and PM comes from
the fact that ancient people used the convenient dark light
contrast of each twenty four hour cycle to talk about
what time it was. The sun pulled them what time
(02:55):
it was in the day, and the moon and stars
did the same at night. As early as thirty five
hundred BCE, the ancient Egyptians built shadow casting obelisks that
shaded sections of the ground throughout the day. These sections
weren't as precise as modern hours, but the concept was
the same. By fifteen hundred BCE, they had invented the
(03:16):
more precise sun dial, and with it the hours we
still know and love, ten daytime hours with a sunrise
and sunset hour tacked on to either end. By six
hundred BCE, that invented a timekeeping instrument for the night
time as well. A person could align it with a
pole star to track the passage of other stars through
the meridian to tell time. Later clockmakers used the circular
(03:41):
model of the sun dial to base the layout of
their new technology. Although the first mechanical clocks in Europe
built for medieval clock towers were twenty four hour devices.
By the thirteen hundred CE, mechanical clocks began to be
built with twelve hour faces, perhaps to save space and
eyestrain for people carrying pocket watches. By the mid fifteen hundreds,
(04:04):
English speaking people in the maths and sciences like John Deeve,
who were using twelve hour cycles, had adopted the Latin
phrases anti meritium and post meridium, Latin being the scientific
lingua franca of the time. By the mid sixteen hundreds,
the abbreviations AM and PM were in use by scientists
like Nicholas Culpepper. Both the full terms and the abbreviations
(04:27):
trickled into common usage after that, even though these designations
didn't have much to do with the astronomical bodies anymore. However,
by the late eighteen hundreds, starting with the Canadian Pacific
Railway in eighteen eighty six, more countries and military entities
started telling time based on the twenty four hour clock. Again.
(04:49):
With the exception of countries like the US, Australia, Canada,
and the Philippines or where the twelve hour system is
officially used, most other countries officially use a twenty four
hour clock, but ancient habits die hard. If you ask
someone in Ireland, China, or France the time, they're equally
likely to use AM and PM. But okay, let's switch
(05:12):
over to another common term, SOS. Even children at play
know that when you are in a life threatening emergency,
maybe you need to be rescued from an island filled
with man eating crabs that's also surrounded by lava. The
way you let the world know that you're in trouble
is to shout three simple letters SOS. You can write
(05:34):
them on the beach, send them via Morse code, or
write them on your hand and flash them at pastors by.
We all know that sending out an SOS signal is
a request for rescue. So what does SOS mean? Is
it an abbreviation? What did the letters stand for? This
was new to me today. The letters SOS stand for nothing,
(05:56):
not save our ship, not save our souls. It wasn't
even originally designed to stand for letters of the English alphabet.
SOS came to us as a replacement for visual distress
signals during the early days of long distance electromagnetic communication.
Samuel Morse developed what would become Morse code, alongside his
contributions to a telegraph machine that could send messages using
(06:19):
electrical signals over a wire in the eighteen forties. In
Morse code, dots and dashes are assembled in different configurations
to represent the different letters of the alphabet. In this way,
messages could be sent across countries via wired telegraph networks, and,
starting in the early nineteen hundreds, wirelessly across oceans and
(06:40):
then around the world using radio equipment. SOS came in
during the transition between the two. In nineteen oh five,
the German government, but which had leaned into telegraph systems early,
published their regulations for the control of Spark Telegraphy. It
mandated that German wireless operator use dot dot dot dash
(07:02):
dash dash dot dot dot to signal an emergency. This
didn't really have anything to do with letters of the alphabet,
but it was quick and easy to type and difficult
to mistake for anything else. It also happened to spell
SOS in Morse code. Everyone agreed it was way better
(07:22):
than SSSDDD, which is what the Italians were pushing for.
At the International Radio Telegraph Convention in nineteen oh six,
the term SOS was voted in as the official international
distress signal and went into effect July first of nineteen
oh eight. It didn't catch on everywhere immediately. For instance,
(07:42):
the British Marconi International Marine Communication Company, which outfitted ships
with radio equipment, preferred the distress code CQD in Morse code,
and continued using it after the SOS call was established
as the international standard. In fact, CQD was the first
distress code sent by the radio operators on the Titanic
in nineteen twelve when the ship hit Iceberg, although they
(08:05):
did send the SOS signal as well. Early radios, like
the Titanics couldn't transmit sounds, only electrical signals. Once inventors
figured out how to encode speech, the verbal signal may
day was picked up at the International Radio Telegraphic Convention
in nineteen twenty seven. As we've talked about on the
show before, may day is derived from the French madeir,
(08:28):
which means help me, but SOS cannot be ousted. Although
mayday is used in voice communication, SOS is still used
as shorthand or anywhere that non verbal communication must be used.
Today's episode is based on the articles what do am
(08:49):
and PM stand for and what does SOS Mean? On
HowStuffWorks dot Com, both written by Jesslynshields. Brain Stuff is
production of by Heart Radio in partnership with houstuffworks dot
Com and is produced by Tyler Playing Before. More podcasts
from my heart Radio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
BrainStuff News
Host
Lauren Vogelbaum
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