Download june 2011 - Holt Planetarium

FRIENDS OF THE PLANETARIUM NEWSLETTER – JUNE 2011
The winter solstice has passed so we can look forward to an increase in daylight hours, even if the
temperatures are a bit on the nippy side. Crisp, clear winter evenings make the stars twinkle like a cosmic
light show. One of the best of these “twinklers” is Arcturus, the fourth brightest star in the sky. Look for it
low in the northeast once the sky is fully dark. As one of the brightest stars in the sky and clearly visible
from both hemispheres, Arcturus has been significant
to observers since antiquity. In Ancient Greece, the
star's celestial activity was supposed to portend
tempestuous weather. Greek mythology portrays
Arcturus as the guardian of the two bears Ursa Major
and Ursa Minor. Prehistoric Polynesian navigators
knew Arcturus as Hōkūleʻa, the "Star of Joy".
Scientifically, Arcturus is a type K1.5 IIIpe orange
giant star—the letters "pe" stand for "peculiar
emission," which indicates that the spectrum of light
given off by the star is unusual and full of emission
lines. This is one of the main reasons for its twinkling
appearance. The diagram at left shows why it is called
a giant star.
Our Sun seems tiny in comparison and it is.
That doesn’t mean that it isn’t active, although its
recent activities have astronomers scratching their
heads. As perplexing as it may sound, solar researchers are predicting the sun is about to fall into the
doldrums, again. Despite all the incredible solar flare action we've seen in recent months as our nearest star
ramps up toward solar maximum, which is expected to occur in 2013, scientists are predicting the next solar
cycle (Cycle 25) will be notable in that it might not even happen. Researchers from the National Solar
Observatory (NSO) and the Air Force Research Laboratory have collected a number of observations of the
solar interior, visible surface and corona (the sun's atmosphere), and all the data points to an incredibly lazy
sun in the near future. This conclusion is based on three separate, but related, fields of solar study. All these
factors appear to converge on a common conclusion: Something weird is going on inside the sun, and
theorists are currently at a loss to explain the phenomenon. But one thing is for certain, the sun is slowing
down and magnetic activity is growing weaker. Could the next solar cycle be the weakest in modern
history? Might Cycle 25 not start at all? Are sunspots a thing of the past? Although it might be a mystery,
we have possibly experienced this phenomenon before. Beginning in 1645, astronomers monitoring the sun
observed no sunspots for 70 years. This period is known as the "Maunder Minimum," and is thought to be
tied into a long-term cycle where the sun's magnetic activity shuts down. On Earth the "Little Ice Age" froze
Europe around the same time, and a growing body of evidence suggests the Sun's slowdown may have
caused the climate to cool. Over the coming months and years, solar physicists will be watching the Sun
very closely, waiting to see if sunspot activity picks up or shuts down completely. So enjoy the current rash
of solar flares and beautiful coronal mass ejections, not to mention some good auroral displays, because it
might be some time before we see a solar cycle like this again.
In planetary news, Mercury is putting in an appearance in the evening sky in July. Towards the end of July,
Mercury will be within 3 or 4 degrees of the 1.4 magnitude star Regulus, the brightest star in the
constellation Leo. The planet will be to the left of the star, starting below it, but climbing past it on the 25th
and 26th. Scientists are elated with the wealth of information that is coming to us from the Messenger
spacecraft, now in its third month of orbit around Mercury. Among the eight experiments aboard is a
camera, of course. This one is equipped not only with wide and telephoto lenses but also with 11 filters
optimized to isolate key aspects of the planet's geologic history and surface composition.
The innermost planet has many broad lava plains that are miles thick in places. Also highlighted at a recent
NASA briefing were important new compositional results from two lesser-known instruments: a
spectrometer that records solar X rays bouncing off the surface, and a gamma ray and neutron spectrometer.
The latter "works" only because Mercury is constantly bombarded by galactic cosmic rays; these slam into
atomic nuclei, freeing up high-speed neutrons that, in turn, strike other atomic nuclei. These collisions
create gamma rays of varying energy, depending on the elements that release them. Over time, the XRS
creates a global map of elements with high atomic weights such as silicon, magnesium, and aluminum,
precisely the ones that form rocks. Mercury
is nicknamed the Iron Planet because its
high overall density implies that it's hiding
a very large metallic core, an iron-rich
cannonball that takes up three-fourths of its
diameter and half its volume. So how did it
get that way?
The most likely among the major formation
theories is the "big splat" scenario. That is,
Mercury was initially somewhat bigger, but
early on the planet suffered a massive hit
that stripped away most of its early crust
and mantle, leaving behind its core and not
much else. This spectacular view of the
crater Degas was obtained as a highresolution targeted observation (90
m/pixel). Impact melt coats its floor, and as
the melt cooled and shrank, it formed the cracks observed across the crater. For context, Mariner 10’s view
of Degas is shown at left. Degas is 52 km in diameter.
Astronomers, including Victoria astrophysicist Professor Denis Sullivan and researchers from Massey,
Auckland, Canterbury and Victoria universities, have discovered a new class of Jupiter-sized planets
floating alone in the dark of space, away from the light of a star. The team believes these lone worlds were
probably ejected from developing planetary systems. The discovery is based on a joint Japan-New
Zealand survey that scanned the center of the Milky Way galaxy, revealing evidence for up to 10 freefloating planets roughly the mass of Jupiter. The isolated orbs, also known as orphan planets, are difficult to
spot, and had gone undetected until now. The newfound planets are located at an average approximate
distance of 10,000 to 20,000 light-years from Earth. The discovery indicates there are many more freefloating Jupiter-mass planets that can't be seen. The team estimates there are about twice as many of them as
stars. In addition, these worlds are thought to be at least as common as planets that orbit stars. This would
add up to hundreds of billions of lone planets in our Milky Way galaxy alone. It’s getting to be a busy place
This is the time of the year when we ask our supporters to renew their membership in Friends of the
Planetarium. The Planetarium receives no government or local body funding. We rely on donations and
patronage for our survival. If you receive this newsletter by email then please download a membership
renewal form from our website http://www.holtplanetarium.org.nz/. For postal members, a renewal form is
enclosed for your convenience. Please feel free to photocopy this and give one or two to your friends so that
they can become our Friends. Remember that your membership fee is tax deductible.