June quiz is open

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OzEclipse Online Australia
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Re: June quiz is open


Post by OzEclipse »

AntennaGuy wrote: Mon Jul 08, 2024 10:32 pm Thanks for the explanations. Very educational. One question. In regard to number 9 above, you noted that "Leap seconds have been periodically added to universal time to account for the Earth's rotational period slowing down." OK, but then you also noted that "The shift of mass from the polar ice sheets to water increasing the equatorial bulge is slowing the Earth and for the first time a leap second needs to be subtracted." But... that would seem inconsistent? I mean, if both cases correspond to the Earth's rotation slowing down, shouldn't both cases correspond to the same direction of the necessary time correction? Or am I missing an important/subtle detail?
Thanks for asking this. In attempting to be brief, I did not explain it correctly. With the redistribution of polar ice to equatorial water, although the water causes an equatorial bulge, the absence of polar ice mass has resulted in the mantle also redistributed mass causing a speed up. See here for a detailed description.
https://apnews.com/article/leap-second- ... 04897032a4

The article doesn't explain the mechanism clearly but the way I think of it is to imagine the Earth as a balloon. The Earth's crust is thin compared to the mantle so it is somewhat elastic. Push on the top and bottom (polar caps) and the centre bulges. Release the pressure and the centre contracts. That mass redistribution associated with the contraction will cause a speed up of the rotation due to conservation of angular momentum. That's the best I can do. If there are any members who work in geophysics/geodynamics please chime in here and rescue me before I drown. :lol: :lol: :lol:

Joe Cali

34 South - The Hilltops Observatory
Hilltops region, Young, New South Wales, Australia. [148E, 34S]

Amateur astronomer since 1978.........Web site : http://joe-cali.com/.........Total & Annular Eclipses Observed : 18
Scopes: ATM 18" Dob, Vixen VC200L, Hand Made 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ mounts. Losmandy, Vixen and Skywatcher compact trackers.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5.
Cameras : ZWO ASI2600MC, Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships The Sky Searchers (moderator); Astronomical Association of Queensland; RASNZ Occultations Section.
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