Photo of the Week. Jupiter, as seen through 26-inch
refractor of the US Naval Observatory at 10:48 PM EDT on April 5,
2016, is covered with turbulent ammonia and hydrocarbon clouds.
The southern hemisphere's obvious Great Red Spot, an anticyclone
twice the size of Earth, has been diminishing over the past
century or so. Image by Geoff Chester, with thanks.
Astronomy news for the two weeks starting Friday, May 6, 2016.
The next skylights will appear May 20.
Again the fortnight tracks the lunar phases. We start at new Moon
on Friday, May 6, the thin crescent
first becoming visible in western twilight the evening of
Saturday, May 7. The evening of Sunday the 8th finds the waxing
crescent to the right of Betelgeuse in Orion. The phase is terminated at
first quarter on Friday the 13th (good
luck to all) with the Moon beneath Regulus in Leo. The waxing gibbous Moon
then finds itself southwest of Jupiter the night of
Saturday the 14th, while the following evening it moves off to the
east of the planet heading toward full
phase on Saturday the 21st, when it will be to the left of Mars and above Saturn
. Our period ends the previous night with the Moon to the
northwest of the red planet. During the fortnight the Moon also
moves slightly away from the Earth on its elliptical path,
crossing apogee
(farthest from Earth, 5.5 percent more distant than average) three
days before full, which will weaken the high tides at the coasts.
Jupiter, high in the sky to the western side of the celestial meridian by the end of evening
twilight, ceases
retrograde (westward motion against the background stars) on
Monday the 9th. The giant planet sets shortly before dawn. On the other side
of the sky Mars rises in the southeast as twilight fades, followed
half an hour later by Saturn, the two making a nice show with Antares in Scorpius.
The big event belongs to Mercury
, which not only goes through inferior conjunction with the
Sun on Monday the 9th, but also transits across the Sun.
The transit begins at 6:12 AM CDT, when Mercury hits the
eastern solar limb. Mid-transit just south of the solar disk is
passed at 9:58 AM CDT and the event is over at 1:42 PM CDT when the Moon
leaves the western solar limb. (Add an hour for EDT, subtract an
hour for MDT, two hours for PDT). A properly-filtered telescope is
needed to see little Mercury, which will appear as a small but
very black dot just 10 seconds of arc across. Do NOT attempt
viewing without a proper, commercially-made, solar filter. Home-
made ones have been known to burst into flame. Projection is safest.
Transits of Mercury
are centered around November 9 and May 7 separated by intervals of
7 and 14 years, the November events twice as common. The next one
will be November 11, 2019. Transits of
Venus are much rarer. The last one took place in 2012 and we
won't see another until 2117. The transits of Mercury have a long
history in the establishment of longitude, as they make a natural
clock with which to tell Greenwich time (which compared to local
time yields east-west global position).
Though the whole constellation is
not visible from mid-northern latitudes, the northern portion of
Centaurus, the Centaur, crosses
the meridian to the south in late evening. It's followed by the
stars of Lupus, the Wolf, then by
Scorpius, the Scorpion and by Sagittarius, the Archer, which is yet another Centaur,
the mythological figure apparently quite popular among the
ancients.
