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The longest-lived of these isotopes, and the most relevantly studied, are 90 Sr with a half-life of 28.9 years, 85 Sr with a half-life of 64.853 days, and 89 Sr (89 Sr) with a half-life of 50.57 days. All other strontium isotopes have half-lives shorter than 50 days, most under 100 minutes.
Natural strontium is a mixture of four stable isotopes: 84 Sr, 86 Sr, 87 Sr, and 88 Sr. [11] On these isotopes, 88 Sr is the most abundant, makes up about 82.6% of all natural strontium, though the abundance varies due to the production of radiogenic 87 Sr as the daughter of long-lived beta-decaying 87 Rb. [22]
The age of a sample is determined by analysing several minerals within multiple subsamples from different parts of the original sample. The 87 Sr/ 86 Sr ratio for each subsample is plotted against its 87 Rb/ 86 Sr ratio on a graph called an isochron. If these form a straight line then the subsamples are consistent, and the age probably reliable.
A sidereal day is about 4 minutes less than a solar day of 24 hours (23 hours 56 minutes and 4.09 seconds), or 0.99726968 of a solar day of 24 hours. [7] There are about 366.2422 stellar days in one mean tropical year (one stellar day more than the number of solar days). [8] Besides a stellar day on Earth, other bodies in the Solar System have ...
The day-year principle was partially employed by Jews [7] as seen in Daniel 9:24–27, Ezekiel 4:4-7 [8] and in the early church. [9] It was first used in Christian exposition in 380 AD by Ticonius, who interpreted the three and a half days of Revelation 11:9 as three and a half years, writing 'three days and a half; that is, three years and six months' ('dies tres et dimidium; id est annos ...
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Back then, Babylonians had a massive 12-day religious festival around their New Year called Akitu. Interestingly, New Year did not start in January back then, and instead took place in mid-March ...
The frequency of a particular date being on a particular weekday can easily be derived from the above (for a date from January 1 – February 28, relate it to the doomsday of the previous year). For example, February 28 is one day after doomsday of the previous year, so it is 58 times each on Tuesday, Thursday and Sunday, etc. February 29 is ...