Date: January 10, 2012
Title: Do We Need Leap Seconds? Timekeeping and Astronomy
Podcasters: Rob Sparks & Rob Seaman
Organization: National Optical Astronomy Observatory
Links: www.noao.edu
www.darksky.org
www.globeatnight.org
www.facebook.com/GLOBEatNight
twitter.com/GLOBEatNight
Visiblesuns.blogspot.com/
eol.jsc.nasa.gov/earthobservatory/CITIES_AT_NIGHT_THE_VIEW_FROM_SPACE.HTM
Description: With half of the world’s population now living in cities, many urban dwellers have never experienced the wonderment of pristinely dark skies and maybe never will. This loss, caused by light pollution, is a concern on many fronts: safety, energy conservation, cost, health and effects on wildlife, as well as our ability to view the stars. Even though light pollution is a serious and growing global concern, it is one of the easiest environmental problems people can address on local levels. To provide opportunities for public involvement in dark skies preservation and energy conservation, we invite the public to participate in the GLOBE at Night campaign (www.globeatnight.org).
Bio: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (www.galileoscope.org), providing design, dissemination and professional development. He also pens a great blog at halfastro.wordpress.com.
Since joining the IRAF group at the National Optical Astronomy Observatory in 1988, Rob Seaman has tackled projects in CCD camera control, image processing and archiving, imaging and table compression, metadata standards, and complex observing modes including heliocentric time series cadencing. He was Y2K remediation lead for the Image Reduction and Analysis Facility and chaired the IVOA celestial transient event working group (http://voevent.org). His current position is senior software systems engineer in the NOAO System Science Center. More information about the proposal to decouple civil timekeeping from Earth rotation is available from http://futureofutc.org/.
Sponsor: This episode of the 365 Days of Astronomy podcast is sponsored by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit www.noao.edu for more information.
Transcript:
Sparks: Hi, this is Rob Sparks from the National Optical Astronomy Observatory and I would like to welcome you to this episode of the 365 Days of Astronomy podcast. I am here today with, well, another Rob, Rob Seamen of the National Optical Astronomy Observatory. Good morning, Rob.
Seamen: Good morning and Happy New Year.
Sparks: Thank you, same to you. We are going to be talking about timekeeping today, but first could you tell me a little bit about yourself and what you do here at NOAO.
Seamen: So I am a software systems engineer and my community, my part of the astronomical community, builds the infrastructure that other scientists use to accomplish these fascinating projects.
Sparks: Okay, well, we are here to talk about timekeeping today and I know that is something you are very interested in from seeing you posts. So there was actually a conference held recently on Decoupling Civil Timekeeping from Earth’s Rotation which was co-sponsored by NOAO. So first could you tell us how time is currently kept and why we need leap seconds.
Seamen: Okay, so we all have clocks. We have clocks on our wrists, we have clocks on our computers, we have clocks on our phones and for all of history the biggest and most important clock was the rotating Earth. The nature of this particular conference was that the suggestion has come along to decouple all of our clocks from the rotating Earth. This is something that has never happened in history and is going to have some fascinating technological implications.
Sparks: So why do we need leap seconds?
Seamen: So the technical clocks, the clock that your computer is using right now as we speak here, as my voice is digitally encoded I see a timer ticking away accurate to the millisecond. That timer is ultimately connected to a system of atomic clocks spread all over the world. Dozens and dozens of atomic clocks in Paris and DC and other locations. The clocks keep very regular time like a metronome. The Earth, however, has a terribly quirky personality which changes by the daily change of the weather or the seasonal change of the climate or the long term as Earth’s spin slows down by transferring to the Moon, to the lunar orbit. To keep the two clocks, that is the Earth clock and the atomic clock synchronized every now and then you have to adjust one to keep them synched and you can’t adjust the Earth so you have to adjust the atomic clock.
Sparks: Yeah, it’s hard to adjust the Earth, isn’t it?
Seamen: It is somewhat difficult.
Sparks: So the proposal is to decouple civil timekeeping from Earth’s rotation. What exactly does that mean?
Seamen: So every year or two a leap second Is added to the atomic time signals to bring the atomic clocks back in time with the rotating Earth, the time of day as provided by Mother Earth. If you decouple it, those leap seconds continue to accumulate by we ignore them. Just like Einstein says that space and time have connections, and one thing that means is that the Prime Meridian, in a simple minded interpretation, would start to move several hundred years per year out into the English channel. It also means that our clocks diverge from time of day which for astronomers would be a really big deal because one second of time is 15 seconds of arc on the sky which is a very large distance as far as our instruments are concerned. So after a few years our telescopes would not be pointed in the right direction.
Sparks: We are doing arc second resolution in our imaging and even greater with interferometry.
Seamen: If you want to continue doing that we are going to have to change a lot of software and a lot of systems that the telescopes use.
Sparks: Obviously there would be a lot of changes if leap seconds were eliminated. What are the advantages and disadvantages of eliminating leap seconds?
Seamen: Well, you will have to talk to someone else to get the advantages because I think it is a silly idea. It is a silly idea, however, that is likely to come to pass. In less than three weeks there will be a vote at the, let me say this quick, the Radio Assembly of the International Telecommunications Union, you can say that three times fast, in Geneva, Switzerland and that vote is very likely to decide to cease these leap second adjustments, and thus the Coordinated Universal Time, which is the astronomical time that all of our clocks have been based on, will magically turn into atomic time and the deed will be done.
Sparks: And as time goes on, Universal time will slowly drift away from Earth time.
Seamen: Yes, and it drifts approximately a second every year or two. Over the centuries, in about five centuries, it will accumulate to about half an hour which for some purposes is negligible and for many purposes is not negligible at all and major changes will have to occur to astronomical software, to aerospace software and systems and perhaps to things no one has investigated yet.
Sparks: So how would this effect NOAO and astronomers if leap seconds are eliminated?
Seamen: The most basic similarity is to the Mellenium bug which most people think was a big nothing. There was a big fuss made about it and then Hoover Dam did not collapse.
Sparks: That’s Y2K for our younger listeners and the problem was there were only two digits allowed for years in dates, right?
Seamen: Exactly and it’s somewhat similar now in that the field in the software variable that’s allowed to, that contains the difference between atomic time and Earth time is limited to nine tenths of a second. In a few years it will be much larger than one second and none of the software has been checked to be sure that this is okay. Now Y2K was not a big nothing, The reason we did not have a lot of disasters is that lots of programmers fixed a lot of the bugs before Y2K and this is sort of the reverse in that lots of programmers will have to fix the problems after they start occurring which seems like very poor planning.
Sparks: That’s always difficult. Maybe we should close out by talking about an experiment you did at the conference using Android phones and iPhones to look at the difference between GPS time and Universal time. That’s kind of interesting.
Seamen: So I don’t know the precise details of this but time signals for atomic time and Earth time come in different flavors. It turns out the iPhones listen to one type of time signal and the Android Phones listen to a different type of time signal and they can give you different results. If you and a friend have one of each and you hold them up next to each other you can find, depending on how the software settings are specified that they give distinctly different times.
Sparks: And the difference is what, ten to fifteen seconds?
Seamen: About that, and that also may grow in the future to arbitrary size.
Sparks: Okay, there is an experiment you can do with your friends at home. Anyway, thank you for joining me today, Rob.
Seamen: I was pleased to be here and thank you for airing this issue.
Sparks: So we’ll keep track of what happens on that vote later this week and maybe we will have to do a follow up later this year.
Seamen: Sounds great.
Sparks: Thanks for joining me, this is Rob Sparks for the 365 Days of Astronomy podcast.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.