Pedro Castle, 1st August, 2011, 7.30

The Dawn probe has successfully entered orbit around the asteroid Vesta. Pictured above is the asteroid’s southern polar region, seen from a distance of about 10,500km
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones. They are grouped with the outer bodies as minor planets, which is the term preferred in astronomical circles
A meteoroid is a suggested term for a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are called a meteor shower.
A comet is an icy, small Solar System body which, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. Comets have been observed since ancient times and have traditionally been considered bad omens.
The probe has taken four years to get to Vesta and will spend the next year studying the huge rock before moving on to the "dwarf planet" Ceres.
Asteroid Vesta looks like a punctured football, the result of a colossal collision sometime in its past that knocked off its south polar region.
Vesta was discovered in 1807, the fourth asteroid to be identified in the great belt of rocky debris orbiting between Mars and Jupiter.
At the time, its great scale meant it was designated as another planet but it later lost this status as researchers learnt more about the diversity of objects in the Solar System.
Asteroids can tell us about the earliest days of the Solar System. These wandering rocks are often described as the rubble that was left over after the planets proper had formed.
Vesta and Ceres should make for interesting subjects. They are both evolved bodies - objects that have heated up and started to separate into distinct layers.
Vesta is thought to have a metal core in the centre - an iron core - and then silicate rock around it. Sometime in its history, it got banged on the bottom and a lot of material was liberated. Some of this material was pulled into the Earth's atmosphere. One in 20 meteorites seen to fall to Earth has been identified with Vesta.
Ceres, which, at 950km in diameter, is by far the largest and most massive body in the asteroid belt, probably did not evolve as much as Vesta.
Scientists think it likely that it retains a lot of water, perhaps in a band of ice deep below the surface.
Dawn's quest at Vesta over the coming months will be to map the asteroid's surface.
We will not be able to observe these small, dark objects, but Saturn is still visible, as are some distinctive asterisms. Scorpius is in the south, Ursa Major in the north, and the Summer Triangle is rising in the east.

Pedro Castle, 3rd July 2011 7.30

The constellation illustrated above, Virgo, is high in the south at the meeting time.
Though a large constellation, Virgo, the Virgin, does not have much of any prominent stellar pattern, relying on Spica to tell us where it is. Also shining brightly in the faint asterism is the planet Saturn, which is very close to Porrima at the moment.
With 26 known exoplanets orbiting around 20 stars in this constellation, Virgo has more confirmed exoplanets than any other constellation. 8 planets in this constellation were discovered in 2009, which is the most planets discovered in a single constellation in a single year.
The star 70 Virginis has one of the first known extrasolar planetary systems with one confirmed planet 7.5 times the mass of Jupiter. Chi Virginis has one of the most massive planets ever detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets: one is a super-Earth and two are Neptune-mass planets.
Because of the presence of a galaxy cluster (consequently called the Virgo cluster) within its borders 5° to 10° west of Vindemiatrix (which can be seen at the “top” on the cart above) this constellation is especially rich in galaxies.
A noted galaxy that is not part of the cluster is the Sombrero Galaxy (M104), an unusual spiral galaxy. It is located about 10° due west of Spica
Though at a distance of 250 light years Spica is still first magnitude (1.04), showing its absolute brilliance, the star visually 1900 times more luminous than the Sun. The apparent brightness is deceptive, however, as Spica actually consists of two stars very close together (a mere 0.12 Astronomical Units apart) that orbit each other in slightly elliptical paths with a period of only 4.0145 four days, which makes them difficult to study individually. Both are blue class B (B1 and B4) hydrogen-fusing dwarfs (the brighter nearing the end of its stable lifetime), making Spica one of the hottest of the first magnitude stars. The high temperature produces a great deal of radiation in the ultraviolet, which renders Spica vastly brighter than visually indicated.
The brighter primary star has a temperature 22,400 Kelvin, a true luminosity of 12,100 Suns, a radius 7 solar, and a mass 10.5 times solar, which may be enough to send it someday into a supernova explosion.
Just up and to the right of Spica lies dimmer, third magnitude Porrima, Virgo's Gamma star (or Gamma Virginis). Unlike most star names, which are Arabic, this one is Latin and honors a Roman goddess of prophecy. A telescope shows a remarkable sight, one of the finest double stars in the sky. The components are almost perfect identical twins, both white class F (F0) dwarf stars with surface temperatures of about 7100 degrees Kelvin, significantly warmer than the Sun. They orbit each other on highly elliptical paths in only 169 years. Thirty-eight light years away, the stars average 43 Astronomical Units from each other, about the distance between the Sun and Pluto, the orbital eccentricity taking them between 81 and 5 AU.
The best Saturn viewing window is nearing its end, just as the ring tilt begins to widen. Saturn moves away from Porrima, and on July 3, it will look more three dimensional as the shadows of the rings and the globe are visible.