Sirius Transit Data

According to Dr. Myles Standish of JPL, Karl-Heinz Homann's measurements of Sirius are sufficiently accurate.

If Earth's inertial spin period is supposed to be 86164.09966 seconds (i.e. whether or not the Earth wobbles) and the measurements are taken from a precessing Earth, and furthermore assuming the unit 'second' is a physical measure of time that is NOT corrected for lunisolar precession, then:

2197 transit periods of the star Sirius are equivalent to a time interval of 189,302,527 seconds, and 2197 transits of the mean equinox (mean sidereal day of 86164.09054 s - a primary astrodynamic constant and the absolute criterion for time; see also http://ssd.jpl.nasa.gov/astro_constants.html ) are equivalent to a time interval of 189,302,506.9 seconds.

Obviously, a time difference of about 20 seconds.

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Below are the actual transit data from a 6-year continual observation period of Sirius. These transits were measured using the unit 'second' provided by the atomic clock time signal from Fort Collins, Colorado. The periods of a solar, sidereal and tropical day are therefore not important for the process of the actual measurement.

1st transit at 21h11'50" on April 6, 1994

2197th transit at 21h13'41" on April 5, 2000

It took 189,302,511 atomic seconds for exactly 2197 absolute transits of the star Sirius, and NOT 189,302,527 seconds.

The mean transit period of Sirius is calculated by taking the physical time interval of 189,302,511 s and dividing it by the total number of transits. The mean time interval of Earth's inertial spin period, as measured with respect to Sirius, is therefore:

189,302,511 s* ÷ 2197 = 86164.0924 seconds

*(2191 solar days × 86400 s + 111 s)

In other words, whether or not the Earth wobbles (according to the current understanding of precession) the result is 86164.0924 seconds and not 86164.09966 seconds.

If one were to apply precession, 0.00912 seconds must be removed from 86164.0924 seconds. The result would be a mean sidereal day of 86164.08328 seconds.

It appears that Sirius does not abide by the rules of the current precession model - unless of course, astronomers want to suggest that the mean transit time of other stars is also not 86164.09966 seconds.