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Comment Re:Fluctuations? (Score 3, Informative) 255

There is a drift, and there are fluctuations.

Regarding the drift: The day length is getting gradually longer by about 1.7 milliseconds every century (+2.3ms due to tidal braking, -0.6ms due to glacial rebound). In about 1820 the day was 86400 seconds; now it is longer than that. In a thousand years, the day will be about 86400.017 seconds, and we will need a leap second every couple of months.

[Note: I am simplifying a little here for the sake of clarity by ignoring the difference between a solar day and the stellar and sidereal days, which are about 4 minutes shorter].

Regarding the fluctuations: There are fluctuations of the earth's angular velocity on many timescales. It fluctuates with weather, with the seasons, and with major events on the surface (e.g. a dam creating a new reservoir) and in the earth's crust (e.g. an earthquake or major volcanic eruption) and deeper interior (e.g. we don't really know). All these events are minor rearrangements of the mass of the earth, which change its moment of inertia. Conservation of angular momentum dictates that the angular velocity must change, and it does. Of course the earth isn't a rigid body and that complicates all this. Learn about Geodesy if you want to know more.

In the 1990s the day length was approximately 86400.003 seconds, so we needed a leap second every year. For poorly-understood reasons (possibly some sort of deep mantle activity), the earth's rotation speeded up around the year 2000, and for a while the day length was about 86400.0004 seconds. Now it is slower again, about 86400.001 seconds. These changes all come under the "fluctuations" heading.

There is an organisation called the IERS - International Earth Rotation and reference Systems Service - which collects measurements of all this stuff to very high accuracy and produces all sorts of reports, bulletins, data sets, etc etc.

Comment Re:Fluctuations? (Score 5, Informative) 255

I'm sorry? Fluctuations in the rotation of the earth? You mean the earth is accelerating and breaking?

Yes, that's exactly what we mean (well, "braking" rather than "breaking"). The earth does not have a constant angular velocity. To conserve angular momentum, as the mass distribution of the earth changes (e.g. due to glacial rebound), the spinning of the earth speeds up and slows down. It also slows down a little due to tidal braking. So a "day", as measured by the rotation of the earth relative to the fixed stars, is not exactly 86400 seconds. It's generally a little more, around 86400.001 seconds at present, and it varies from day to day and from year to year. Now that civil time (UTC) is kept with atomic clocks, this is a genuine problem. Leap seconds are introduced to keep UTC close to UT1 (astronomical time).

It has nothing to do with the fact that a rotation around the sun is not exactly 365.25 rotations around our own axis? hmm...

That's right. Leap seconds have nothing whatsoever to do with that. They don't affect the calendar. That's what leap days are for. Leap days keep the calendar in sync with the seasons (by setting the average calendar year length to 365.2425 days, very close to the vernal equinox year which is currently 365.242374 days).


Number of ET Civilizations In Our Galaxy Is 37,964 544

KentuckyFC writes "The famous Drake equation calculates the number of advanced civilizations in our galaxy right now. But the result is hugely sensitive to the assumptions you make about factors such as the number of habitable planets that orbit a host star, how many of these actually develop life and what fraction of these go on to become intelligent etc. Disagreements about these figures leads to estimates for the number of advanced civilizations ranging from 10^-5 to 10^6. Now an astronomer in Scotland has worked out how to make the calculations more precise so that different theories about the origin of planets, life and civilizations can be compared. His calculations say that the rare-life hypothesis predicts only 361 advanced civilizations in the Milky Way now. However, the so-called tortoise and hare hypothesis predicts 31,573 and the theory of panspermia says that there ought to be 37,964 extraterrestrial civilizations more advanced than our own in the Milky Way."

Comment Re:And? (Score 4, Insightful) 397

Nintendo is brilliant for turning their backs on the gamers that supported them for decades and designing games for grandma

I'm one of the gamers that supported Nintendo for decades. Guess what? I don't have time to play hardcore games. I don't have an XBox or a 360, don't have a PS3 or a PS2. But I love an hour or two of Mario Kart or Wii Play or Boom Blox with my kids.

And in fact, the game that's had most play in my house this weekend has been Goldeneye, on our N64.

So have Nintendo turned their backs on me? Um, no. They've worked out a way to create and sell new games to me. Have they stolen back from a losing position in the last console generation, to eat Sony's and Microsoft's lunches, by redefining console gaming and finding a new and much larger group of gamers? Yes, in fact. Are you a sad loser who can't deal with the fact that Nintendo have revolutionized gaming by opening it up to this new group, people who would never have bought a console before the Wii? Well, it kind of looks that way.


Spammers Hijacking IP Space 233

Ron Guilmette writes "As reported in the Washington Post's Security Fix blog, a substantial hunk of IP address space has apparently been taken over by notorious mass e-mailing company Media Breakaway, LLC, formerly known as OptInRealBig, via means that are at best questionable. The block in question is, which I documented in depth in an independent investigation. (Apparently, the President of Media Breakaway has now admitted to the Washington Post that his company has been occupying and using the block and that front company JKS Media, which provides routing to the block, is actually owned by Media Breakaway.) Remarkably, the president of Media Breakaway, who happens to be an attorney, is trying to defend his company's apparent snatching of this block based upon his own rather novel legal theory that ARIN doesn't have jurisdiction over any IP address space that was handed out before ARIN was formed, in 1997."

Submission + - Arctic sea ice at record low

Nick Barnes writes: "Arctic sea ice has reached a record low. Every year sea ice melts through the summer and reaches a low in mid-September. These end-summer lows have been getting lower as the climate warms. The previous record was September 2005, and September 2006 had similar numbers, about 20% below the 1979-2000 average. This year there is less ice than ever before, and the September 2005 record has been broken in early August, with a month or more of melting still to go."

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