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 of water.)
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 9:49 am.
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 during daylight.
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 Cancer.
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
You will find extensive descriptions of what's worth looking for,
and you can download and print a single copy for your personal use.