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Monday, 23 May 2011

SPA Bulletin No. 311

Electronic News Bulletin No. 311 2011 May 22

Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by

By Andrew Robertson, SPA Planetary Section Director

Note: altitudes and timings are given for 52°.5 N, 1°W, near the
centre of England (about Leicester). There will be slight variations
depending on where you live in the UK. Times are BST.

SATURN crosses the meridian about 21:50, 45 minutes after sunset, at
an altitude of 35°. It is now only half a degree from Porrima (Gamma
Virginis), a fine double star with components of equal magnitudes of
3.5, currently only 1".5 apart. As the nights get shorter Saturn will
soon start sinking in the west, so make the most of this apparition --
for the next dozen years it will be at a lower altitude.

As you may be aware from Bulletin 309 and other sources, there is
currently a grouping of planets in the morning sky: Venus, Mars and
Mercury are all within 3° of each other, with Jupiter 10° to the west
of them. At sunrise (5:00) on May 22 the three are only 5° above the
eastern horizon with Jupiter only 4° higher. To be honest I think
that the only way you will see that grouping of planets is if you have
a totally unobscured horizon such as over the sea on the east coast
and you use a large pair of binoculars on a tripod before sunrise.
I say before sunrise as it would be dangerous to scan the horizon once
the Sun has risen, and in any event the grouping probably would not be
visible in binoculars with the Sun above the horizon. I would be
interested to hear if any SPA member manages to observe the grouping.

Any reports of observations would be most welcome at

BBC News

Jupiter's innermost satellite Io, which is slightly larger than our
Moon, is the most actively volcanic body in the Solar System. It
erupts about 100 times more lava each year than the Earth does. In
principle Io's rotation is locked to its orbital revolution, so that
it keeps one face permanently towards Jupiter, as the Moon does
towards the Earth. Interaction between the orbits of Io and the other
Galilean satellites, however, causes the orbits to be slightly
off-circular, so Io would appear to an observer on Jupiter to librate
slightly in longitude. Although the actual rotation of the satellite
with respect to the Jupiter-Io line is very small, owing to the great
mass and proximity of Jupiter it results in heavy tidal squeezing that
dissipates enough energy to keep much of Io's interior molten. Data
from the Galileo probe suggest that under a 50-km crust there is a
magma ocean at least 50 km thick and probably much thicker.
Readings from a magnetometer on Galileo indicated that Io was
dramatically distorting Jupiter's magnetic field -- but it has taken
several years to conclude that the reason is related to the nature of
Io's rocks and how they behave when molten. Experiments found that
when certain types of rock are melted, their electrical conductivity
increases by orders or magnitude. It is the very high conductivity
that can create the type of signature seen by Galileo, which is
consistent with Io's being made of rocks like lherzolite, an igneous
rock rich in silicates of magnesium and iron.

The magma layer, whose temperature probably exceeds 1,200C, is thought
to make up at least 10% of Io's mantle by volume. The mantle -- the
moon's interior mid-layer -- probably extends down a further 700-800
kilometres. Gravity measurements suggest that the core is made of
iron and may be liquid, just like that of the Earth. Although Io is
so much smaller than the Earth, tidal heating seems to have given it
an internal structure quite similar to the Earth's.


It is 14 years since Comet Hale-Bopp (C/1995 01) lit up the skies
during the first months of 1997, becoming one of the most spectacular
comets of the last century. As always happens, once the comet was no
longer visible to the naked eye it slipped out of the attention of the
media, and the general public heard no more of it. However, some
researchers continued to follow it in its 2,500-year orbit. They
imaged the comet at red wavelengths last December, when it was 30.7
astronomical units away (about the same distance as Neptune) with the
ESO 2.2-m telescope at La Silla. The comet appeared star-like, with
an angular diameter less than 1.9 seconds,and had a magnitude of 23.3.
There was no clear evidence of any coma or tail. It seems as though
there is no longer any cometary activity, as is not surprising for an
object so far from the Sun. However, some doubt remains, because,
according to an estimate of the size of the nucleus, the comet is
about three times as bright as would be expected if it had the
albedo of 4% that is thought to be typical of an inactive nucleus.


Haumea, whose existence was confirmed in 2005, is the fifth dwarf
planet in the Solar System after Pluto, Ceres, Eris and Makemake. It
moves beyond the orbit of Neptune and has two satellites, Hi'iaka and
Namaka, has the shape of a flattened rugby ball, is around 2,000 km
long, and rotates in less than four hours. Now an international
research team has confirmed that 75% of the surface of Haumea and 100%
of that ofHi'iaka (which is about 400 km in diameter) are covered with
crystallised water-ice (with an ordered structure), and not, as would
have been expected, with amorphous ice disorganised as a result of
solar radiation. The study suggests that the planet is made up of a
frozen outer layer and an internal volume made up of between 88% and
97% rock with a density of 3.5 g/cm3. Since solar radiation
constantly destroys the crystalline structure of ice on the surface,
energy sources are required to keep it organised. Possible sources
are internal heat from radioactive elements, and tidal forces between
Haumea and its satellites. The research also highlights other
peculiarities of Haumea. Its orbital plane is inclined at 28ยบ to the
orbital planes of most of the other planets in the Solar System, and
the orbits of its satellites are not in the same plane either.
According to the scientists, the two satellites might have been
created by the collision of another object with Haumea, which could
also have given it its rapid rotation and moulded it into its
rugby-ball shape.


Scientists from the Max Planck Institute for Extraterrestrial Physics
in Germany, using the Herschel infrared space observatory, have
detected winds of molecular gas streaming away from galaxies.
Suspected for years, such outflows may be able to strip galaxies of
gas and halt star formation in its tracks. The winds that Herschel
has detected are extraordinary: the fastest is blowing at more than
1,000 km/s. They could be generated by the intense emission of light
and particles from young stars or by shock waves from the explosion of
old stars. Alternatively, they might be triggered by the radiation
given off as matter swirls around a black hole at the centre of the
galaxy. The discovery is important because stars form from molecular
gas, and the outflows are robbing the galaxies concerned of the raw
material needed to make new stars. If the outflows are powerful
enough, they could even halt star-formation altogether. The research
team studied 50 galaxies, and inferred that 1,200 times the mass of
the Sun is being lost each year from the galaxies with the most
vigorous outflows. That is enough to strip them of their entire
reserves of star-forming gas within 1 million to 100 million years.
The fastest winds appear to be coming from the galaxies that contain
the brightest 'active galactic nuclei', in which massive black holes
are thought to be feeding from their surroundings. The class of red
and almost structureless 'elliptical galaxies might owe its existence
to the absence of star-formation, owing to the removal of molecular
gas from the original galaxies by powerful outflowing winds.


The Dawn spacecraft has obtained its first image of its destination,
the asteroid Vesta. The image was taken on May 3 when the spacecraft
was approximately 1.2 million kilometres from Vesta. Vesta is 530 km
in diameter and is the second-most-massive object in the asteroid
belt. It has been known for about 200 years, but its angular diameter
is too small for appreciable surface detail to be seen on it from the
Earth. Dawn is expected to enter orbit around Vesta on July 16, when
the asteroid is about 188 million kilometres from the Earth. To enter
orbit, Dawn must match the asteroid's path around the Sun, which
requires very precise knowledge of the body's location and speed. By
analyzing where Vesta appears relative to stars in images taken by the
spacecraft, navigators will determine its location and refine the
spacecraft's trajectory. Dawn is intended to start collecting
scientific data in early August from approximately 2,700 km above the
asteroid's surface. As the spacecraft gets closer, it will take
multi-angle images, allowing scientists to produce topographic maps;
it is intended ultimately to lower its orbit to about 200 km. Dawn
will remain in orbit around Vesta for one year; then, after another
long cruise phase, it should arrive in 2015 at its second destination,

Bulletin compiled by Clive Down

Owing to holidays, the next bulletin will be issued on June 19.

(c) 2011 the Society for Popular Astronomy

Good Clear Skies
Colin James Watling
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
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