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Leap Second Day

posted Saturday, 30 June 2012

Today is longer than yesterday and tomorrow by one second.

The hyperfine transition is the basis of International Atomic Time (TAI). By definition, the outermost electron in an ordinary cesium 133 atom cycles through this transition 9,192,631,770 times in one second.

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International Atomic Time (abbreviated TAI after the French Temps Atomique International) began at midnight GMT on the first day of 1958 and has continued advancing forward at the rate of one second every 9,192,631,770 periods of the hyperfine transition in 133Cs. TAI is maintained by the Bureau International des Poids et Mesures (BIPM) in Paris, which periodically averages the time kept by various atomic clocks around the world. The BIPM then disseminates correction factors needed to synchronize these clocks with the master clock in the Observatoire de Paris.

Coordinated Universal Time (abbreviated UTC) is the basis of legal time throughout the world. All local civil times differ from UTC by either a whole number of hours or an odd number of half hours, but never by any other amount. One second of Coordinated Universal Time is the same as one second of International Atomic Time, but UTC and TAI are slightly out of step. TAI marches forward uniformly, while UTC is adjusted from time to time to keep it synchronized with the earth’s rotation.

The earth is not an effective timekeeper. For most of the last two hundred years the mean solar day has been slightly longer than the 86,400 s currently defined by the International System. Universal Time UT, or more specifically UT1, is in effect the mean solar time. It is continuous (i.e. there are no leap seconds) but has a variable rate because of the Earth’s non-uniform rotation period. It is needed for computing the sidereal time, an essential part of pointing a telescope at a celestial source.

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When UT1 lags too far behind UTC, a leap second is inserted at the end of the day before January 1 or July 1 as appropriate. When this happens, 23:59:59 is followed by the unusual time of 23:59:60 before turning over to 00:00:00 and starting the next day. In the unlikely event that UT1 were to lead UTC (that is, if the earth’s rate of rotation were to increase) the provision exists for the insertion of a negative leap second. Were this to ever occur, 23:59:58 of one day would be followed by 00:00:00 of the next, skipping 23:59:59 altogether. In any case the absolute difference between UTC and UT1 must never exceed 0.9 s.

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Leap Seconds and Cumulative Adjustments to UTC
year month offset   year month offset   year month offset
1971   n/a*   1986   23   2001   32
1972 July 11   1987   23   2002   32
1973 January 12   1988 January 24   2003   32
1974 January 13   1989   24   2004   32
1975 January 14   1990 January 25   2005   32
1976 January 15   1991 January 26   2006 January 33
1977 January 16   1992 July 27   2007   33
1978 January 17   1993 July 28   2008   33
1979 January 18   1994 July 29   2009 January 34
1980 January 19   1995   29   2010   34
1981 July 20   1996 January 30   2011   34
1982 July 21   1997 July 31   2012 July 35
1983 July 22   1998   31   2013   ?
1984   22   1999 January 32   2014   ?
1985 July 23   2000   32   2015   ?
Adjustments from 1961 to 1971 follow a different, more complicated protocol and were omitted

Are leap seconds even necessary?

  • In seven or eight centuries the difference between TAI and UT1 will be about an hour.
  • By the year 5000, day and night will have reversed; that is, 12 noon will occur in the middle of the night and 12 midnight will synch up with the midday sun.

What would be so wrong with that? Does it really matter what number we assign to a position of the sun in the sky?

In 1582 Pope Gregory XIII managed to extract ten days from the calendar. On 4 October 1582 the Catholic world went to sleep. When they woke up it was 15 October 1582. By 1752 the protestant nation of England and her American colonies also accepted the change. (They needed to add 11 days to catch up.) In 1873 Japan made the switch. (They needed 12 days.) Then Russia in 1917 and China in 1949. (13 days.) The Greek Orthodox Church is possibly the only European agency that has not accepted this change (although the nation of Greece made the switch in 1923).

I think the big thing is that everyone agrees what time (or day) it is. Not that the time is any particular number. Time is a social construct, remember.

physics.info/news/?p=3661

Wordbook

posted Thursday, 23 September 2010

Wordbook says …

Hi, Glenn!

Wordbook appears to be configured and working just fine.

I Disagree. Wordbook does not appear to be posting anything to Facebook anymore … or is something else going on?

physics.info/news/?p=2603

Science caught in the Web 2010-02-13

posted Saturday, 13 February 2010

physics.info/news/?p=1073

Science caught in the Web 2010-02-06

posted Saturday, 6 February 2010

physics.info/news/?p=973

Science is the most interesting thing in the world

posted Saturday, 14 November 2009

I have paperwork to do today getting ready for the Intel Science Talent Search (STS). Of course this means I am busy surfing the net for interesting rubbish to soothe my brain in lieu of doing actual work. (And now I am writing about not doing any work. What an awesome role model I am.) I came across this gem of a quote today from Alun Anderson, a former editor at New Scientist magazine.

…science is the most interesting thing in the world, and if you don’t agree with me just fuck off….

Sometimes people pull quotes out of context. Here’s the context so you can see it’s not a mistake. Mr. Anderson really meant to say this. Anyone who who doesn’t have an interest in science is a "fucking idiot".

Science writing used to be slightly apologetic: [puts on whiny voice] "this is all going to be terribly difficult, but I’ll try and make it easy for you". Like they’ve sugar coated something you don’t really want to take. Our goal was to really change that – change the people and the ideas – to be self-confident. Science often suffers from this sort of cringe factor – "I’m a boring scientist, you probably don’t want to talk to me". My policy was if you’re talking to someone else the approach is: "what’s happening in science is the most interesting thing in the world, and if you don’t agree with me just fuck off, because I’m not interested in talking to you". You had to have that kind of attitude. That tended to be the kind of attitude of people in the arts: [in snooty voice – think Brian Sewell] "Of course I am doing something interesting", so I took the same attitude. If you’re not interested, I don’t want to explain to you – you’re just a fucking idiot, so get out of my way! And it worked, because if you write like, "I’m really interested in this, it’s not only interesting its really important. If you can’t see this, you’re probably a moron!" It works. It has to be true to a degree. Otherwise it’s just piped bullshit, or triumphalism or something. The thing is, it is really interesting and important. People from the sciences do often have massive inferiority complexes.

The full text of the interview with Alun Anderson can be found here.

Folks outside the UK don’t often have experience with New Scientist. It’s a popular science magazine, but it isn’t aimed at science illiterates. It’s sort of like Scientific American for the English (Scientific Britannica?). New Scientist is released weekly, while Scientific American is released monthly. The US and the UK each have an ultimate science journal. In the US it’s Science published by the American Association for the Advancement of Science. In the UK it’s Nature published by the Nature Publishing Group. These periodicals feature a mix of highly technical articles for specialists and more approachable summaries for anyone with an interest in science.

All of these journals employ layperson’s summaries. When a common scientific word comes along, they usually don’t explain it since they assume you’re educated enough to know it. When a more fancy word comes along, they may give you a quick reminder of what it means just to be polite. (An educated person will probably have heard it, but she may not have thought much about what it means.) When a highly technical word comes around, something is wrong with the space-time continuum. Specialized words should not appear outside of articles written for specialists.

Which brings me back to the STS. Page 5 of the 9 page application asks for a 100 word max. "Layperson’s Summary".

Summarize your project in layperson’s terms. Your explanation should provide easily understandable background, procedures, conclusions and relevance. The summary will aid readers, including administrators, journalists and the public.

A student last year called this the "abstract for dummies". Note quite. Dummies don’t need any kind of summary. They won’t understand anything you’d say to them anyway. What she should have said was, a layperson’s summary is like an "abstract for the ignorant". I know that ignorant has a negative connotation, but it shouldn’t. Let me quote the cowboy humorist Will Rogers.

You know everybody is ignorant, only on different subjects.

A physicist will know a lot of physics, but he may not know a lot of biology and vice versa. Write the layperson’s summary of your biology research in such a way that even a physicist could understand it. Ignorance is a part of life. No one can know everything about everything.

Ignorance is also a part of science. If everything was known, there’d be no reason to do science. I refer back to Will Rogers who sounds like he’s talking directly to a scientist about to publish a paper.

An ignorant person is one who doesn’t know what you have just found out.

Once you’ve discovered something new, it’s your duty to tell everyone about it and reduce the quantity of ignorance in the cosmos. If you don’t, you haven’t completed the scientific process and the cosmos will seek revenge. (The quantity of ignorance is also known as dumbth, buy the way.) Writing about your research in incomprehensible technobabble does not get you off the hook. Thus the need for a layperson’s summary.

A layperson’s summary should be well written. Anyone from any walk of life who is of reasonable intelligence or better should understand it. (That’s 50% of the earth, by the way. Just thought I’d remind you.) I wouldn’t take this quite as far as the physicist Leo Szilard did. When asked by a biologist how he should explain his work to a non specialist, Szilard said…

Assume infinite intelligence and zero prior knowledge.

I like quotes. You can quote me on that.

physics.info/news/?p=3817

The first month at physics.info

posted Sunday, 13 September 2009

Today marks the first month of The Physics Hypertextbook at its new location. Well, not really the first month. I obtained this domain on 10 September 2008, but hadn’t made any pages public before 13 August 2009. That was the day I told Google this place existed. On 1 September 2009 I let the rest of the world access this site. I consider the time before this momentous moment the "gestation period" of The [New] Physics Hypertextbook and 1 September 2009 is effectively its birthday.

The release of physics.info into the wilds of the World Wide Web has been a quiet event, but not unexpectedly so. Who even knew this domain existed besides me and a few other fanatic fans of physics? Who would even think to look at a long dead domain name like this one? Does anyone remember what was here in the summer of 2002 when this domain opened? In 2003? In 2004? In two thousand et cetera?

In the last month traffic has increased phenomenally from zero to some nonzero number that will remain confidential forever. The nice thing is that number is still small enough that I can identify individuals accessing this site. The following is a list of the hometowns of the intrepid Internauts who found physics.info while it was still an infant website.

  • New York, Port Washington, Rochester, and Corona, New York
  • Atlanta, Alpharetta, and Roswell, Georgia
  • Los Angeles, California
  • Portland, Oregon
  • Minneapolis, Minnesota
  • Bellevue, Washington
  • Cambridge, Massachusetts
  • Holyoke, Colorado
  • Upper Darby, Pennsylvania
  • London and Godalming, UK
  • Shiraz, Iran
  • Malang, Indonesia
  • Singapore
  • La Candelaria, Mexico
  • Jaipur, India
  • Auckland, New Zeeland
  • Zurich, Switzerland
  • Caracas, Venezuela
  • Givatayim, Israel
  • Milan, Italy

The New York users are obviously me testing the system and my students reading their first homework assignment. The London users are probably also mostly me. I was in London at the end of August for the hell of it. While there I thought I’d test the website out. I can’t really say I learned much since the hotel WiFi was spotty and unreliable in my room. (It worked great in the bathroom, but who wants to spend any more time than is necessary in that space?) Who are the rest of the users? Do you recognize yourself in this list?

physics.info/news/?p=3814