June 2007 Sky from the Keeble Observatory
Ask an astronomer “what’s new?” and you may get a flippant response that there’s
nothing new in the universe. Or, you may be lucky to catch her when she’s just learned
something new, and that newly seen phenomenon will be the subject of a mini presentation
of research results.
Here’s a sample of what we know now that we didn’t know a month ago.
Conventional wisdom (never a good source of astronomy knowledge!) has generally
told us that the planet Mercury had a solid iron core, since it’s so small that
it should have radiated any excess heat into space long ago. The latest radar analysis
of the way the planet wobbles as it revolves around the Sun now suggests that this
small planet has a core which is at least partly liquid. This is actually good news
– it’s easier to explain why Mercury has a weak magnetic field if the core is molten.
The Mars Rover Spirit has a stuck wheel, so the other five wheels just drag the
other one as the rover moves from place to place. On May 6th, this wheel was dragged
through some soil which turned out to be very light in color, compared with the
surrounding dull red more typical of the Martian surface. Upon analysis, this patch
of bright soil is about 90% silica, which planetary scientists take as strong evidence
for water. (On Earth, such a concentration of silica could happen only in the presence
A recently observed supernova in a galaxy some 240 million light years away seems
to be of a type never previously seen. A Type 1 supernova is thought to be the catastrophic
destruction of a white dwarf star, which can typically shine brighter than an entire
galaxy for several months. A Type 2 supernova is the explosion of a massive star
which has run out of nuclear fuel; they are about 100 times fainter than Type 1,
but their brightness decays over a longer time. This particular supernova was originally
thought to be Type 1 because of its brightness, but it’s decaying more like a Type
2. Further, its actually peak brightness is greater than a Type 1. We may be seeing
a “new” phenomenon. Theorists several decades ago proposed a mechanism by which
a super-massive star might explode before exhausting its fuel … this may be our
first observation of that type.
Lunar phases for June: Last Quarter on the 8th, at 7:43 am; New Moon on the 14th,
at 11:13 pm; and First Quarter on the 22nd, at 9:15 am; Full Moon on the 30th, at
We’ve just given the quarter phases of the Moon – let’s follow it around the sky
for the month. Note that it rises a bit over an hour later each day, taking about
28 days to circle the “celestial sphere.” Though Genesis tells us that the Moon
is a “lesser light” to rule the night, for about half the month it’s above the horizon
We begin the month with the Moon in Scorpio, rising just under 90 minutes after
sunset. That bright “star” above the Moon is Jupiter. Over the next few days the
Moon drifts to the east into Aquarius, where we will find it on the 8th at last
quarter. In the predawn on the 10th you can see the Moon near Mars, in Pisces. You’ll
lose sight of Mars, but the Moon should remain visible into the day.
By the New Moon on the 14th, the Moon shares Taurus with the Sun, and will now set
after the Sun to the west. It’s near Mercury, in Gemini, on the 15th. The next evening
you’ll see it pass Castor and Pollux. On the 18th it will pass directly in front
of Venus, but that occultation will occur while both are below our horizon in central
Virginia. You will be able to see the Moon pass Saturn on the 18th, in Cancer. There’s
another occultation on the 19th, also below our horizon. This time the Moon will
pass in front of Regulus in the constellation Leo.
The Moon will be near Spica, in Virgo, on the 24th, then moving into Scorpio near
Antares on the 27th. It will appear nearer to Jupiter now than it did at the start
of the month. For the Full Moon on the 30th, you will be looking into the constellation
Other noteworthy sights for June: Mercury is at its greatest elongation east of
the Sun on the 2nd, so that marks your best chance to see it emerge from evening
twilight. Venus, nearly twice the angular distance from the Sun will reach its greatest
eastern elongation on the 8th. It’s easily the brightest “star” in the evening sky,
so there should be no trouble picking it out. The ongoing celestial ballet will
bring Venus and Saturn close by month’s end, with a conjunction of the two on the
30th, separated by less than a degree.
For your own monthly star chart, you can direct your web browser to
http://www.skymaps.com. You will find extensive descriptions of what's worth
looking for, and you can download and print a single copy for your personal use.