Astronomy news for the two weeks starting Friday, July 3,
2015.
The next skylights will appear July 17, 2015. Happy Independence
Day. And Bastille Day too.
We begin as usual with the Moon, which starts our fortnight in its
waning gibbous phase as it heads toward
third quarter on Wednesday, July 8. It
then takes a week to go through waning
crescent, which ends at new Moon on Wednesday the 15th. The
morning of Saturday the 11th finds the Moon to the right of the Pleiades of Taurus. By the following morning,
the crescent will lie at the western edge of the Hyades cluster with Aldebaran down and to the left,
the Pleiades now on top. Your last look at the thin rising
crescent will be morning of Tuesday the 14th. With a good horizon
you then might spot the waxing
crescent in the west the twilit evening of Friday the 17th, Jupiter and
Venus shining up and to the left. (Reserve the evening of
Saturday the 18th for a spectacular gathering of the crescent
Moon, Venus, Jupiter, and the star Regulus.) The Moon goes through perigee, where
it is closest to the Earth, on Sunday the 5th.
A day after lunar perigee, at 2;41 PM CDT on Monday, July 6, the
Earth goes through aphelion, where it is farthest from the Sun, a distance
of 94.507 million miles (152.093 million kilometers), 1.7 percent
farther than average. That aphelion occurs during the high heat
of northern summer tells that distance from the Sun has little to
do with the seasons, which
are caused by the 23.4 degree tilt of the Earth's rotation axis
against its orbital axis. All things equal, the eccentricity of
the Earth's orbit should produce wider seasonal swings in the
southern hemisphere than in the northern, but the effect is
largely absorbed by the oceans, which dominate the southern
hemisphere.
Venus and Jupiter remain close together in western evening
twilight, Jupiter the fainter, the two making a memorable pairing.
Venus reaches maximum brilliance the night of
Thursday the 9th, magnitude -4.7. A telescope shows it to
be a crescent with only a sliver of daylight showing.
If you know where to
look, it's visible in the daylight sky.
With Mars
and Mercury pretty much out of sight, all
that's left is Saturn,
which by the time the sky darkens is already past the meridian low to the south to the
northwest of Antares in Scorpius.
