Tunguska event / First leap second added to UTC - June 30

On this day in 1908, an explosion occurred near the Podkamennaya Tunguska River in Russia that was likely caused by a meteorite or comet bursting. / At 11:59 p.m. and 60 seconds, a leap second was added to Coordinated Universal Time to synchronize clocks with Earth’s decelerating rotation. 

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Episode Transcript

Speaker 1 (00:00):
Hey, y'all. Eaves here were doubling up today with two
events in history on with the show. Hi, I'm Eves
and Welcome to This Day in History Class, a show
that uncovers a little bit more about history every day.

(00:22):
The day was June night, around seven fourteen in the morning,
in the atmosphere above Siberia's Potka Manya Tunguska River, and
explosion occurred. The ground shook, millions of trees were flattened,
reindeer were killed, windows shattered. Villagers in the area said

(00:45):
they saw smoke and flashes of light. There are no
pictures of the explosion, which came to be known as
the Tunguska event, but scientists have theorized about what caused
the blast. The Tunguska region is a remote area of
the Russian Tiger, so there were no official reports of
people dying from the explosion, though one hunter reportedly died

(01:08):
after he was flung against a tree. The explosion happened
at an altitude of about three to six miles or
five to ten kilometers. It's estimated to have exploded with
hundreds of times the force of the atomic bombs dropped
on Hiroshima and Nagasaki, though some estimates are way higher
and some are lower. Such estimates are hard to get

(01:31):
right since there was no actual impact crater. The blast
killed hundreds of reindeer, knocked down about eighty million trees
over about eight hundred square miles, and affected towns more
than thirty five miles from the event site. It was
visible from hundreds of miles away, and places in Siberia
and Europe had bright nighttime skies for a while after

(01:53):
the explosion. Meteorological stations in Europe even recorded seismic and
atmospheric way, but authorities did not immediately go to the
site of the event to figure out what happened. The
newspapers reported a potential impact or explosion. Tunguska was not
easily accessible and the political climate of Russia was unstable.

(02:16):
Russian mineralogist Leonid Kulik interviewed local eyewitnesses in nineteen one.
People who witnessed the event said they saw a fireball
that caused the ground to tremble, hot winds to blow
people over, and loud noises that sound like guns firing.
It wasn't until nineteen when a team led by Leonid

(02:38):
Kulik traveled to the site to investigate. They found a
large area of flattened trees, with some bear charred trees
still standing at the epicenter of the explosion. They did
not find a large crater or remnants of a meteor,
but they suggested that a meteor had exploded in the
atmosphere anyway. They explained the lack of a crater by

(03:00):
saying that the ground was too soft and swampy to
preserve an impact crater, and that any debris was buried.
In nineteen thirty four, Soviet scientists proposed that the extraterrestrial
body that blew up in the atmosphere was instead a comment.
Since comments are made up of ice rather than rock,
it would have vaporized when it hit the Earth. Later,

(03:22):
more theories cropped up. An engineer and writer said it
could have been the result of an extraterrestrial nuclear explosion.
In nineteen seventy three, physicists suggested that a black hole
had collided with Earth. Others suggested nearby Lake checa formed
after the impact, though this idea was mostly rejected and

(03:44):
yes some have proposed that aliens caused the explosion when
a spaceship exploded in the air, while heading to lake
by call for its fresh water. But in a team
of Ukrainian, German, and American scientists analyzed rocks collected from
this ight earlier and found that they were of meteoric origin,

(04:04):
but that still was not a definitive answer to the
mystery because meteor showers are not uncommon. Though debate over
the cause of the explosion continues, the consensus is that
a meteor or comment collided with substances and Earth's atmosphere
and exploded. It's thought that the cosmic body was broken
into smaller pieces as it approached the Earth's surface, and

(04:28):
any remnants that entered Earth's atmosphere may have been turned
into dust. The explosion is considered the largest impact of
it to happen over land in the recorded history of Earth,
even though there was no actual impact. I'm each Jeffcode
and hopefully you know a little more about history today
than you did yesterday. You can learn more about history

(04:50):
by following us on Twitter, Facebook, and Instagram at T
D I h C podcast. If you have a yet,
listen to a new show that I host called it
in a popular You can get it anywhere you get
this day in history class. Thank you again for listening,
and we will see you tomorrow. Hey, y'all, it's Eves.

(05:21):
Welcome to This Day in History Class, a podcast for
people who can never know enough about history. And it's
a super special episode today because it's the last new
episode that I'll be hosting. We will still continue to
run episodes from the vault, and you'll still hear my
voice for this reason. You'll also hear Tracy V. Wilson's voice,
who previously hosted the show, that said, it's been a

(05:43):
joy being immersed in so much history and getting to
share it with you, and I hope you've enjoyed it
as much as I did, and I hope that you'll
all continue to return to the show to learn about
anything you may have missed, or to give your favorite
episodes a second Listen now on with the show. The

(06:06):
day was June nineteen seventy two at eleven fifty nine
PM and sixty seconds. A leap second was added to
Coordinated Universal Time to synchronize clocks with earth decelerating rotation.
The second has been defined many different ways over the years.
At one point, it was defined as one eight six thousand,
four hundred of the mean solar day, but a more

(06:28):
precise measurement was needed because the length of a day
varies depending on many factors like seasonal and daily weather variations,
as well as oceanic and atmospheric tides. By nineteen sixty seven,
the second was defined as and I quote the duration
of nine billion, one ninety two million, six hundred and
thirty one thousand, seven hundred and seventy periods of their radiation,

(06:52):
corresponding to the transition between the two hyperfine levels of
the ground state of the ses M one thirty three atom.
This was the measurement that the International System of Units
or s I used. Since then, the wording of the
official definition has been updated slightly. Atomic clocks keep time

(07:12):
with extreme precision. On atomic clocks, a day is exactly
eighty six thousand, four hundred s I seconds. International atomic
time is a time scale that is computed by taking
the weighted average of more than four hundred atomic clocks
around the world. It's not connected to any astronomical observations.

(07:33):
Universal time, on the other hand, is a time standard
that is based on Earth's rotation and astronomical observations. Coordinated
universal time or UTC, is under the umbrella of universal time,
which also includes UT zero, U T one, U T
one R, and U T two. Unlike other versions of

(07:54):
universal time, UTC is determined by International Atomic Time. Though
the practice of UTC was already being coordinated internationally, the
International Astronomical Union didn't adopt the name coordinated Universal Time
until nineteen sixty seven. Coordinated Universal time is the primary
standard by which the world regulates time, but Earth's rotation,

(08:17):
as measured by UT one, is gradually slowing, so that
the length of a rotational day is about two milliseconds
longer than the eighty six thousand, four hundred seconds it
was two centuries ago. That means that there's a discrepancy
between UTC and UT one. Scientists determined that UTC would
have to be adjusted to account for the difference between

(08:40):
the definition of the second and Earth's rotation. This keeps
UTC in line with the apparent position of the Sun
and stars. In other words, a second would need to
be added to or removed from clocks to realign them
with Earth's rotation. Occasionally, scientists specified that UTC should not
deviate more than nine of a second from UT one,

(09:02):
So on June thirtieth, nineteen seventy two, the first leap
second was added to UTC. The International Earth Rotation and
Reference System Service decides when to add a leap second.
One is typically added either on June or December thirty one.
From nineteen seventy two to nineteen ninety nine, leap seconds

(09:22):
were added at a rate of about one per year.
After that, they've been added less frequently. There have been
twenty seven leap seconds since nineteen seventy two. The most
recent leap second was added on December thirty one. Many
people have called for the elimination of leap seconds and
the replacement of UTC with a new system. Leap seconds

(09:43):
have caused problems for some computer systems since they're not
that predictable and can't be anticipated far in advance, and
they'll need to be added more frequently as Earth's rotation
continues to slow down. Some people who support abolishing leap
seconds argue that it doesn't matter whether our perception of
time changes along with the rotation of Earth, since that

(10:05):
would happen over a long time anyway. I'm Eves Jeff Coo,
and hopefully you know a little more about history today
than you did yesterday, and if you have any commerce
oar suggestions, you can send them to us at this
day and I heart media dot com. You can also
hit us up on social media where at t D
I h C podcast. Also a shout out to the

(10:27):
extraordinary producers of this show, Alexis and Chandler, who y'all
never get to hear but are a huge part of
why you love the show and are still listening to it.
Thanks to Kenni for listening to the show and we'll
see you tomorrow. For more podcasts from I Heart Radio,

(10:53):
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