Japan earthquake shortened days on Earth | Hacker News Reader

Japan earthquake shortened days on Earth

mb.com.ph

31 points_grrr14 comments

> The Earth's figure axis is not the same as its north-south axis in space, which it spins around once every day at a speed of about 1,000 mph (1,604 kph). The figure axis is the axis around which the Earth's mass is balanced and the north-south axis by about 33 feet (10 meters).

Could someone explain this paragraph? how does one measure a rotation speed in terms of distance over time ? And I just cant figure what the second sentence means at all...

I think they're trying to describe http://en.wikipedia.org/wiki/Precession

I wonder if we will finally get to use negative leap seconds.

I don't think this will directly lead to that happening. Assuming 1.8µs/day, then it will take about 1/(365.25*1.8e-6) ≈ 1500 years for a 1 second difference to accumulate. I believe the effects of terrestrial bodies have a much larger effect.

Oh boy!

That means the monthly pay only is only 11 days- 19.8microseconds away.

And we will all live longer (in terms of days anyway)! Who needs a fountain of youth? Just invent and earthquake ray. :)

This explains why I feel so tired this morning.

This is nothing more than an educated guess. While Gross is theoretically correct, I'm not certain our implements can detect a 5.4 µSec change over 3 days. Not only that, I doubt it matters enough for us to care.

Assume that our sensors are sensitive enough to detect this for a moment. The day-length of the earth changed by:

    0.0000000000208333350570911 %

Who bloody well cares about that? I think scientific navel gazing just got a new mascot.

Woah...

1) our instruments can detect that much time change, no problem. NIST standards measure time of day accurate to the nanosecond, an error of thousands of those is noticeable.

2) Cumulative effects of this add up to close to a millisecond per year. That is certainly noticeable to various applications.

3) Cries of "scientific navel gazing" almost always come from those who feel slighted because they don't get it. This anger of course is misplaced, not getting it is a strict result of not bothering to learn enough -- it has nothing to do with anyone but the accuser.

Point 3 is nothing more than character assassination, and I'm disappointed that you are voted up with that in your comment. I do get it.

Point 2 is moot. Yes, the cumulative effect is felt—but I'm pretty sure we can adjust for that. In fact, I'm certain that the applications which would notice the change are adjusted for accuracy every so often.

Point 1 I concede; I just wasn't certain because I do not know the exact methods by which we measure day length and the level of accuracy they have. I am not blindly assuming that the day is exactly 86400 or 86400.25 solar seconds.

---

I do not consider the OP news-worthy. Aside from the attentions of these incredibly accurate applications, which likely get their data from their own mathematicians or from scientific journals, why should the rest of us care?

Perhaps I was wrong: this is story dredging, not scientific navel gazing. No mainstream journal would care about this, except to raise its search rankings by covering ANYTHING related to the Japan quake.

You have a point about the story dredging in the OP. Here's a more carefully sourced story that has more context:

http://www.nytimes.com/2011/03/14/world/asia/14seismic.html?...

I think the overall displacement (around 13 feet as quoted in the article above) is of interest to both specialists and to the lay public. Just as an indicator of size.

The main thing that's of interest to earthquake people is not so much the peak displacement, as the underlying stress/strain field (i.e., the forces and displacements as a function of space). There will most certainly be a slew of journal publications, as well as press releases, once the displacement data are analyzed.

Here's an example of the latter, for the Landers earthquake, which was a M7.2 in 1992 in the desert east of LA:

http://www.youtube.com/watch?v=giJaGdfavfs&feature=chann...

The closing frames show how the strain probably accumulated in the centuries prior to the earthquake.

It may be helpful to say: what they're driving at with all this hyper-precise GPS and displacement modeling is a forecast capability for earthquakes, same as is done for weather. In both cases you have sparse measurements of fields that are assimilated into a forward model.

With regards to your point 2: how do you propose we adjust for the effects if we can't determine how much to adjust for? It is either scientific navel gazing, or we can adjust for the effect using the results of this to properly adjust.

This is not an educated guess. Filtering of civilian GPS can be used to back these displacements out. See the comments under:

http://news.ycombinator.com/item?id=2315839

The history of science is full of instances of precise measurements uncovering new phenomena by ruling out all known explanations. So it's important to understand these changes in day length (mass distribution, really). These calculations are actually being done on a regular basis, someone just decided to make a press release out of this jump because of the obvious interest.

> I think scientific navel gazing just got a new mascot.

Aside from breakthroughs made during World War II, I think that most of the technology surrounding you can be traced back directly to "navel-gazing".

Reply on news.ycombinator.com