Photo of the Week.The Esquel (Argentina)
pallasite is a stony iron meteorite with large mineral
crystals. It probably came from the mantle-core boundary of a
smashed up asteroid. A piece of the Sikhote-Alin iron is at
the far right. (From the Goose Kaler memorial meteorite
collection at Staerkel Planetarium).
Astronomy news for the week starting Friday, April 11,
2014.
A busy week lies ahead (or lay behind, depending on when you
read this). The Moon starts off in the waxing gibbousphase as it grows to full the night of Monday, April 14
(really the morning of Tuesday the 15th), when it will undergo
a fine total
eclipse that's visible throughout almost all of North
America plus western South America (but not in Europe). It
then rather anticlimactically spends the remainder of the week
in the waning gibbous phase, which
is terminated at third quarter next
week, on Monday the 21st. The evening of Sunday the 13th
finds the Moon to the west of
Mars. By the following night, it will have flipped to the
other side. The morning of the eclipse the darkened Moon will
be in a lovely setting just to the northeast of Spica, with Mars to the west.
The morning of Wednesday the 16th, the waning Moon goes just
south of Saturn.
The heart of the eclipse begins at
12:58 AM CDT the morning of Tuesday, April 15, when the full
umbral shadow of the Earth takes its first bite out of the
leading (eastern) edge of the lunar disk. The partial phase
ends when the Moon enters totality at
2:07 AM, which maximizes at 2:46 AM with the northern edge of
the Moon just missing the central core of the shadow. The Moon
starts to leave full shadow, when it gets the first glimpse of
sunlight, at 3:25 AM, and then completely leaves the full
shadow behind at 4:33 AM, not long before moonset. Add an
hour for Eastern Daylight Time, subtract one for MDT, two for
PDT, three for Alaska, and five for Hawaii. Even in totality,
though quite dark and red, the Moon is visible as a result of
sunlight scattered and refracted by the Earth's atmosphere
into the umbral shadow. The degree of darkness depends on the
state of the Earth's atmospheric blanket, particularly on
recent volcanic action that makes it more opaque. Since the
Moon passes just south of the central shadow, the northern
limb of the Moon will be the darkest at mid-eclipse. The
penumbral stages, where the Moon is in just partial earth
shadow, are not much worth bothering with, though the effect
can be seen as a slight dimming just before and after the main
eclipse.
In addition to the eclipse, we get to admire a fine array of
planets. First up is Jupiter,
which has already entered the high western sky by the time the
sky is dark, and is with us until 2 AM. By midnight, reddish
Mars, making a fine color contrast with Spica to the
southeast, has also crossed the southern divide. Just past
opposition to theSun, the
planet's motion is obvious over only a few nights. It makes
its closest approach to the Earth (0.62 Astronomical Units, 93
kilometers, 58 million miles) for this orbital round on Monday
the 14th. Next is Saturn, which rises just past the end of
evening twilight and crosses to the south around 3 AM.
Finally, just before dawn,
Venus rises in the east and takes over the sky, not fading
away in the until bright morning twilight.
If that is not enough, Venus passes less than a degree north
of
Neptune on Saturday the 12th, Vesta
(the brightest asteroid) and Ceres (at 470 km, 290 miles,
the largest) both go through opposition to the Sun
(respectively on Sunday the 13th and Tuesday the 15th), and Pluto begins retrograde motion on Monday the 14th.
From Mars and Spica, look toward the north to the brightest
star in the northern hemisphere, Arcturus, the Bear Driver,
who follows Ursa Major around
the northern pole. As Ursa Major's Big Dipper passes nearly overhead, the Little
Dipper of Ursa Minor rises up
to meet it.
