Projection Alarm Clocks

15 Comments

1. Bob Monk
   Posted February 15, 2010 at 11:39 pm | Permalink

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2. morningfoxnorth
   Posted August 14, 2010 at 8:48 pm | Permalink

   There are a lot of answers here — some good, some not.

   One of the fundamental problems of timekeeping is that the earth's rotation is not uniform. In the long run, the earth gradually slows down; but there are larger short-term irregularities. For a long time, the second was defined as a certain fraction of the length of the year 1900 (based on the equinoxes). In 1967, scientists came up with a physical definition of the second (based on a certain transition of the element cesium) that matched, as well as possible, the definition based on 1900; and we have been using that definition ever since.

   Nominally, a day contains 86400 seconds (=24*60*60). The earth is now rotating a bit more slowly than it was in 1900. Even if the rotation remained fixed from now to the rest of eternity, the average number of seconds in the mean solar day would not be 86400, but about 86400.0004 (the current length of the mean solar day, in terms of the atomic definition of the second). Thus, we would have to add a leap second roughly every 2500 days (6.8 years) to keep Universal Time (which uses atomic seconds) in sync with the rotation of the earth. Adding this leap second periodically does not mean per se that the earth is slowing down; it simply means that the atomically-defined second is not exactly 1/86400 of a mean solar day.

   But the earth's rotation speed continues to change. In the long run it slows down, but this does not happen at a steady pace. The irregularity of this process means that leap seconds are not added at a regular interval, but rather whenever it is found observationally that the two systems of timekeeping (UT vs. the earth's rotation) have drifted apart by about a second.

   As the earth continues to slow down in the long term, we will have to add leap seconds more and more often, and that will make time calculations more difficult in the future. For this reason, some scientists have suggested that we replace the leap-second system with something else. (This is an ongoing debate at the present time.)

   Note that leap seconds have absolutely nothing to do with a leap year. Leap seconds come about because the atomic second doesn't currently match 1/86400 of the mean solar day, and because the earth's rotation continues to change irregularly (with a long-term slowing trend). Leap years come about because the number of days in a year is not an exactly integral number of days. Even if the earth's rotation were perfectly uniform, we would have the problem of leap years. The earth's changing rotation speed will, however, eventually lengthen the number of days in the year enough that we will have to modify the calendar system (but that won't happen for a long time).

   Now I'll discuss the common misconception people have. As I said, a leap second occurs for a combination of the following two reasons:
   1) The atomic second and the astronomically defined second do not match.
   2) The earth's rotation speed continues to change.

   Even if only #1 was true, we would have leap seconds. (And if #2 alone were true at first, then #1 would also soon be true.)

   Some people, however, incorrectly interpret a leap second to mean that the earth's daily rotation has changed by a full second. (In reality, the one-second discrepancy has accumulated over a few years.) Starting from this false premise, they jump to the conclusion that after we've added tens of thousands of leap seconds, it will mean that the earth's rotation will have stopped. This is a completely erroneous interpretation.

   In the long run, the length of the day is increasing very slowly — about 0.00025 seconds per century. You might think that this will bring the rotation almost to a stop eventually, but the rate will diminish over time. Eventually (after billions of years!), the earth and moon will become tidally locked. At that point, the sidereal rotation period of the earth will be fixed at about 47 current days (and this will also be the sidereal period of the moon's orbit). When that happens, not only will the same side of the moon always face the earth, but the same side of the earth will always face the moon.

   Hope that helps. Add some more notes in your question or email me if there's any confusion.

   – edit — comment on your note
   You're right that even if each leap second meant that the earth's rotation has slowed down by a second (and it doesn't mean that), it would take an infinitely long time for the rotation to stop. So whoever reaches that conclusion would be piling one misconception on top of another. I've never actually heard this combination of misconceptions, so I don't think I can explain the reasoning behind it.

   Let me just add one more thing to contrast leap seconds with leap years. The purpose of leap seconds is to make sure that the sun reaches its highest point at noon (on the average, after allowing for time zones, day-to-day variations related to the earth's elliptical orbit, etc.); in other words, it prevents the time of the sun's highest point from drifting in time from year to year. The purpose of leap years is to make sure that the vernal equinox always occurs on about the same day each year; that is, it prevents the vernal equinox (or any other equinox or solstice) from drifting through the calendar year. Leap seconds keep the time of day in sync with the sun, and leap years keep the calendar in sync with the seasons. (Nature didn't make it easy! It's our job to come up with a scheme to adapt to whatever nature has given us.)

   By the way, you can see that timekeeping is a messy subject, and there's quite a bit more to it than has been discussed here. Fortunately, most people in their everyday lives are not concerned with time to the nearest second, and most people don't adjust their watches when there's a leap second. (But today's "atomic" clocks and wristwatches do that automatically.)

3. Ron
   Posted September 5, 2010 at 12:46 am | Permalink

   Atomic Alarm Clock has an “alarm’ feature that at the specified time will: Shut down the computer; Restart the computer; go to Standby; Hibernate; Logon as different user; Turn off monitor; and can Close all programs immediately as well as Wake PC Up from Standby or Hibernate modes.

4. Justin
   Posted September 5, 2010 at 8:35 am | Permalink

   Hello, I am not sure if this “Fix” has been posted here yet. I could not find it. I too have had problems with the White Screen poping up secinds after load. Here is the fix: Your iPod/phone system clock need to correct. go to find out the atomic time, and reset your iPod’s clock to the official time. Go into the netflix settings and just for good measure switch the reset switch. back out, and launch the app. it should work. This seems to be a copyright/time thingy. Let me know if it works for you!

5. KWL
   Posted September 7, 2010 at 1:51 am | Permalink

   i’ve had pretty good luck over the last year negev, syncing with atomic time

6. mrdevineskater
   Posted September 7, 2010 at 10:44 pm | Permalink

   GO SCATMAN

7. oiramletoh
   Posted September 9, 2010 at 3:15 pm | Permalink

   YOU KILLED PICCARD NOOOOOOOOOOOOOOOO

8. Mercury 2010
   Posted September 26, 2010 at 10:28 pm | Permalink

   It's because there are two different definitions of "second", both derived from Earth's rotation, but at different times. The atomic clock second is from the rate of Earth's rotation a century ago, which was slightly different from the rate of Earth's rotation today.

9. Trublood
   Posted October 17, 2010 at 6:57 am | Permalink

   Doomsday clock is just cr*p, the idea is to reflect the stability in the nuclear world, right now they are scared about the Iranian nuclear and where it might go, and China. It really has no practical application, and is one of the weapons of mass distraction used in the western world.

10. SonicRap
    Posted November 22, 2010 at 7:43 am | Permalink

    Sync up, time's come for Zion I's Atomic Clock

11. Universal coordinated time « Lalit Patil’s blog
    Posted January 23, 2011 at 6:22 am | Permalink

    [...] Responding to Navneet’s question, “what time zone is wordpress on?” Well, looks like WordPress is on something called UTC – Coordinated Universal Time! Wikipedia says: Coordinated Universal Time (UTC) is a high-precision atomic time standard. UTC has uniform seconds defined by International Atomic Time (TAI), with leap seconds announced at irregular intervals to compensate for the earth’s slowing rotation, and other discrepancies. The leap seconds allow UTC to closely track Universal Time (UT), which is a time standard based on the earth’s angular rotation, rather than a uniform passage of seconds. [...]

12. Pastysrv
    Posted September 26, 2011 at 1:58 am | Permalink

    #free #KateGosselin #SarahPolley #JessicaSimpson #Zirconia #Pendant #Heart #K #Slide #Charm #Finally #Amano #Atomic #Ti

13. CosmicalRupture
    Posted October 26, 2011 at 3:14 pm | Permalink

    Did you ever have a project in chemistry on an atomic timeline or something?

14. TeamSMQ
    Posted January 14, 2012 at 12:39 am | Permalink

    I Would Rob You For Dat Watch Lol!!!hahahah (DeadSurious) How Much Did You Pay For Dat

15. Karen_writes
    Posted January 22, 2012 at 12:19 am | Permalink

    Atomic time or Gmt?