photoperiod that responds to the function of light day hours changes observed in the transition winter-spring at the latitude of the place where the specimens were captured, starting from the photoperiod of the winter solstice (9.8L: 14.2D), and applying daily increases corresponding to the sum of that observed in three successive days in the environment until reach the light-hours
observed at the spring equinox (13.3L: 10.7D) (See Figure 1).
Beyond the small compass of the solar system--8 light-hours
across at the orbit of Neptune--the look-back times swell into years, millennia, and eons.
During its orbit, it comes as close as 17 light-hours
to the black hole, which is about 120 times the distance between the sun and Earth.
It's four light-hours
to the edges of the solar system; to the closest star, four light-years.
In 2018 the S2 star will be at its closest to the black hole, just 17 light-hours
away from it and travelling at almost 30 million kilometres per hour, or 2.5% of the speed of light.
"The ionized gas at the head of the cloud is now stretched over more than 150 light-hours
(about 160 billion kilometers) at the pericenter of the orbit around the black hole, with the closest approach being about 25 light-hours
(or a bit more than 25 billion kilometers)," Stefan Gillessen from MPE, who led the observing team, said.
22, more than four hours of light-hours
have moved over to the dark side.
By mid-2013 the gas cloud is expected to pass in its vicinity at a distance of only 36 light-hours
(equivalent to 40,000,000,000 km), which is extremely close in astronomical terms.
Even way up here in Canada we're only 8 light-minutes from the Sun, whereas Pluto is more than 5 light-hours
Being only 11 light-hours
away after a speedy voyage of 30 years gives one an appreciation for the true extent of a light-year, which in the cosmic scheme is itself quite tiny.
At its closest approach last March, S2 swung within just 17 light-hours
(125 astronomical units) of the black hole, only three times the average distance of Pluto from the Sun.
from the home star (more than 10 light-hours
away) and 44 a.u.