SOLAR SYSTEM

Milky Way Galaxy - our celestial backyard

On dark, clear nights we can sometimes see a faint, hazy band of light studded with many stars and stretching across the sky. This is the body of the Milky Way, the galaxy in which we live. Here in the southe rn part of Australia, the centre of the Milky Way passes almost directly overhead so we can obtain an excellent view of our galaxy.

Our understanding of the Universe has changed vastly over the last 400 years. The Earth is no longer regarded as the centre of the Universe. Now we know that we are like "suburban residents" of the Milky Way, situated well away from the centre of the galaxy. Our solar system is about 30,000 light years out from the galactic centre and orbits around it at a speed of 250 kilometres per second. The astronomer Harlow Shapley, in the 1920s, was the first to realise that we are not at the centre of the Milky Way.

Containing over 100 billion stars (some of which may have planets!), and different types of interstellar gas and dust, the "body" of our galaxy is shaped like a great disc 300 light years thick and 100,000 light years across. It is a spiral galaxy, and our Sun is about two thirds of the way out from the centre along one of the spiral arms. Humans like to think they are important; but in the vastness of the Milky Way, our Earth is like a grain of sand on the beach - and the Milky Way is only one of millions of galaxies wheeling through space!

The galaxy has four main parts:

Nuclear Bulge:	The galaxy is shaped like a pancake with a bulge at the centre. This "nuclear bulge" is about 16,000 light years in radius, and contains mainly old stars and interstellar gas and dust.
Galactic Disc:	The part of the pancake outside the bulge, extending about 50,000 light years out from the centre. The disc contains all the young stars, and more interstellar gas and dust.
Halo	The spherical region surrounding the disc to a radius of about 65,000 light years. The halo contains old stars, globular star clusters, and thinly spread interstellar gas and dust.
Galactic Corona	The galactic corona is an enormous sort of outer halo that may extend as far as 300,000 light years in radius. The corona is now believed to contain most of the mass of the galaxy.

The galaxy is slowly rotating: our Sun takes about 250 million years to do one orbit of the galactic centre. Hence our solar system must have made only 20 or so orbits.

source:http://www.perthobservatory.wa.gov.au//information/milky_way.html#

SATURN

SATURN

Saturn is a gas giant. It's structure is very similar to jupiter's core is composed liquid rock. Next comes a layer of liquid hydrogen. It is under such high pressure that the nature of the hydrogen changes, and is able to conduct electricity like metal. This generates the planet's magnetic field.

The layer on top of this is ordinary liquid hydrogen. Next, the hydrogen thins out into the gaseous atmosphere. It is composed of mainly hydrogen and helium with trace amounts of methane, water, ammonia, and hydrogen sulfide.

Interestingly, Saturn creates some of its own heat, but in a much different way than Jupiter. Scientists believe that the hydrogen and helium are slowly separating out, like vinegar and oil when left to sit. In Saturn's case, the heavier helium is slowly making its way through the hydrogen, generating heat (from friction) as it goes.

Saturn has something like Jupiter's Great Red Spot, but it is a Great White Spot. Nothing is currently known about the phenomenon, but it is probably similar to the Great Red Spot in the way it has formed. Besides this, Saturn's outer atmosphere is not nearly as turbulent as Jupiter's. This is because, being about two times farther away from the sun, it receives approximately 1/4 as much as energy from it. Less energy means that there is less to power atmospheric phenomenon.

Atmosphere

Saturn is basically one big atmosphere - as far as we know, there is no real surface to the planet. Its composition is nearly all H₂; the rest is approximately:

• H₂: 96.3±2.4%
• He: 3.25±2.4%
• CH₄: 0.45±0.2%
• NH₃: 0.0125±0.075%
• HD: 0.011±0.0058%
• C₂H₆: 0.0007±0.00015%

Besides this, aerosols of ammonia ice, water ice, and ammonia hydrosulfide exist in the atmosphere.

The temperature at 1 bar is approximately 134 K, and at 0.1 bar it is 84 K. The density at 1 bar is 190 g/m³. Below 30° latitude, wind speeds range up to 400 m/s, and above that only 150 m/s. The scale height of the Saturnian atmosphere is about 59.5 km.

Unique Characteristics

Saturn has a few unique features:

• First, it is the least dense of all the planets. If there were a bathtub big enough to fit Saturn in, the planet would float.
• Second is Saturn's magnificent ring system. This system has four sections. The farthest out, F, was discovered during the Voyager mission. Moving towards Saturn, next is the A section, and this section makes up about half the diameter of the entire system. Then comes the Cassini Division, between A and B, which is the large gap visible in most photographs. Next is the B ring, which has raised parts, caused by the planet's magnetism. These appear as spokes. In-between B and C, there is a small division called Enck's Division. The C ring is transparent. Farther in, there are very small ring particles which are slowly spiraling in towards the planet.
  
  The rings were probably formed relatively recently - several thousand years ago - when two of Saturn's satellites crashed together. The ring systems of the other gas giants probably formed the same way, only much earlier, which is why they are mostly gone; most of their rings have fallen into their planet's atmosphere. In about 100,000,000 years, Saturn's rings will probably be gone, too. See the table below for data on its rings.
• Another interesting property of Saturn is how it generates heat. As seen in the table below, the average temperature of Saturn is approximately 130 K. However, due to the equation for thermal equilibrium (below), it should only be about 80 K. This extra heat is generated due to its gas slowly separating. Like an oily salad dressing, the gases in Saturn's atmosphere are very slowly separating, with the lighter gas rising up and the heavier gas falling down. As this happens, friction between the molecules heats the gas, accounting for the extra heat.

source:http://burro.astr.cwru.edu/stu/advanced/saturn.html

JUPITER

JUPITER


Jupiter is the fifth planet from the Sun and is the largest planet in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains two and a half times the mass of all the other planets combined. It has a mass of 1.9 x 10²⁷ kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 62 known satellites. The four largest are CALLISTO, EUROPA, GANYMEDE and IO, and were named after GALILEO GALILIE who observed them as long ago as 1610. The German astronomer Simon Marius claimed to have seen the moons around the same time, but he did not publish his observations and so Galileo is given the credit for their discovery.

Jupiter has a very faint ring system, but is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager 1.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen becomes metallic.

Colorful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The GREAT RED SPOT is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the center, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found through out the banded clouds.

AURORAL emissions, similar to Earth's NORTHENLIGHTS, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from IO, that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed.

Jupiter's Ring

Unlike Saturn's intricate and complex ring patterns, Jupiter has a simple ring system that is composed of an inner halo, a main ring and a Gossamer ring. To the Voyager spacecraft, the Gossamer ring appeared to be a single ring, but Galileo imagery provided the unexpected discovery that Gossamer is really two rings. One ring is embedded within the other. The rings are very tenuous and are composed of dust particles kicked up as interplanetary meteoroids smash into Jupiter's four small inner moons METIS, ADRASTEA,THEBE, and AMALTHEA. Many of the particles are microscopic in size.

The innermost halo ring is toroidal in shape and extends radially from about 92,000 kilometers (57,000 miles) to about 122,500 kilometers (76,000 miles) from Jupiter's center. It is formed as fine particles of dust from the main ring's inner boundary 'bloom' outward as they fall toward the planet. The main and brightest ring extends from the halo boundary out to about 128,940 kilometers (80,000 miles) or just inside the orbit of Adrastea. Close to the orbit of Metis, the main ring's brightness decreases.

The two faint Gossamer rings are fairly uniform in nature. The innermost Amalthea Gossamer ring extends from the orbit of Adrastea out to the orbit of Amalthea at 181,000 kilometers (112,000 miles) from Jupiter's center. The fainter Thebe Gossamer ring extends from Amalthea's orbit out to about Thebe's orbit at 221,000 kilometers (136,000 miles).

Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the jovian MAGNETOSPHERE, magnetic environment, which extends 3 to 7 million kilometers (1.9 to 4.3 million miles) toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit - a distance of 750 million kilometers (466 million miles).

source:http://www.solarviews.com/eng/jupiter.htm

MERCURY

MERCURY

MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters. As the spacecraft receded from Mercury after making its closest approach on January 14, 2008, the WAC recorded a 3x3 mosaic covering part of the planet not previously seen by spacecraft. The color image shown here was generated by combining the mosaics taken through the WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet). These three images were placed in the red, green, and blue channels, respectively, to create the visualization presented here. The human eye is sensitive only across the wavelength range from about 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in black-and-white (single-color) images. Color differences on Mercury are subtle, but they reveal important information about the nature of the planet's surface material. A number of bright spots with a bluish tinge are visible in this image. These are relatively recent impact craters. Some of the bright craters have bright streaks (called "rays" by planetary scientists) emanating from them. Bright features such as these are caused by the presence of freshly crushed rock material that was excavated and deposited during the highly energetic collision of a meteoroid with Mercury to form an impact crater. The large circular light-colored area in the upper right of the image is the interior of the Caloris basin. Mariner 10 viewed only the eastern (right) portion of this enormous impact basin, under lighting conditions that emphasized shadows and elevation differences rather than brightness and color differences. MESSENGER has revealed that Caloris is filled with smooth plains that are brighter than the surrounding terrain, hinting at a compositional contrast between these geologic units. The interior of Caloris also harbors several unusual dark-rimmed craters, which are visible in this image. The MESSENGER science team is working with the 11-color images in order to gain a better understanding of what minerals are present in these rocks of Mercury's crust. (Courtesy NASA/JHUAPL)
SOURCEhttp://www.solarviews.com/eng/mercury.htm

SUN

SUN

The Sun is the most prominent feature in our solar system. It is the largest object and contains approximately 98% of the total solar system mass. One hundred and nine Earths would be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). This layer has a mottled appearance due to the turbulent eruptions of energy at the surface.

Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level) is so intense that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about .7 percent less massive than the four protons. The difference in mass is expelled as energy and is carried to the surface of the Sun, through a process known as CONVEXTION., where it is released as light and heat. Energy generated in the Sun's core takes a million years to reach its surface. Every second 700 million tons of hydrogen are converted into helium ashes. In the process 5 million tons of pure energy is released; therefore, as time goes on the Sun is becoming lighter.

The chromosphere is above the photosphere. Solar energy passes through this region on its way out from the center of the Sun. Faculae and flares arise in the chromosphere. Faculae are bright luminous hydrogen clouds which form above regions where sunspots are about to form. Flares are bright filaments of hot gas emerging from sunspot regions. Sunspots are dark depressions on the photosphere with a typical temperature of 4,000°C (7,000°F).

The corona is the outer part of the Sun's atmosphere. It is in this region that prominences appears. Prominences are immense clouds of glowing gas that erupt from the upper chromosphere. The outer region of the corona stretches far into space and consists of particles traveling slowly away from the Sun. The corona can only be seen during total solar eclipses.

SOURCE:http://www.solarviews.com/eng/sun.htm

s

Planets take center stage in July

One of the comforting things about the night sky is that it remains constant over the average human lifetime. While different constellations are visible from one season to the next, the overall shape of the constellations remains the same year after year.

However, the fact that Earth resides in a constantly moving solar system means that occasionally the sky puts on a show worthy of more than just casual observance. July 2010 is one of those times.

Over the course of the month observers will be able to see four of the five naked-eye planets and possibly a comet, all visible in the sunset sky.

The stage for the July sky show is set early in the month with Venus, Mars and Saturn being visible in the late evening sky. These three planets will be spread between the Stars Regulus in Leo and Spica in Virgo. Venus will be the most obvious, being clearly visible even before the sky is completely dark. Mars will be 23 degrees above and to the left of Venus with Saturn just 15 degrees beyond.

By July 10 Mercury will have joined the scene, but it will be fairly low on the horizon and may be lost in the glare of the setting sun. Binoculars will help locate the tiny inner planet.

Even if you can’t spot Mercury, do not despair. Also on the evening of the 10th Venus is just 1 degree from the star Regulus in Leo. In addition, Venus will have moved to within 18 degrees of Mars, and Mars will be just 10 degrees from Saturn.

On the evening of the 13th a slim crescent moon appears on the stage just 15 degrees from Mercury. This may make finding Mercury a little easier even though it is still fairly low on the horizon.

Now the show really takes off. The moon will be just 7 degrees from Venus on the evening of the 14th, 6 degrees from Mars and on the evening of the 16th and 10 degrees from Saturn on the 15th. After the evening of the 17th the moon slowly slides off stage and away from the planetary show.

On the evening of July 27th we find Mercury less than 1 degree from the star Regulus in Leo. Yet the best part of the show is on the evening of the 28th when Venus, Mars and Saturn form a neat little triangle in the constellation Virgo. Venus will be below and to the right of the two fainter planets. Venus will be less than 8 degrees from Mars, but the closest conjunction occurs between Mars and Saturn. The two planets will be less than 2 degrees from each other. Mars will appear red-orange and closer to the horizon, while Saturn will appear yellow or cream colored.

As impressive as this show sounds, it has the potential to gets even better. While the planets and the moon are doing their orbital dance, a rare object from the outer reaches of the solar system makes a brief cameo appearance early in the month. Comet McNaught (C/2009R1) will be present in the evening sky from the 1st through the 12th. Whether the comet will be visible is somewhat unpredictable. The “tail” of a comet is ionized gas streaming back from the comet as the solar wind turns the frozen material into gas. Hopefully comet McNaught will develop a long, clearly visible tail that can be seen with the naked eye. Comet McNaught will be just 3 degrees from Mercury on July 9.

In ancient times planetary conjunctions were seen as omens from the sky. The close gathering of the “wandering stars” was special enough to warrant special consideration. Today fewer people believe in the implications of such close conjunctions, yet the fact that they occur so rarely means that the event itself deserves our attention.

Whether you observe with just your eyes or a wide field telescope, take advantage of the July 2010 conjunction of planets before the players are ushered off stage.

SOURCE: http://trib.com/news/state-and-regional/article_ba8f4369-af77-5da4-90a4-6108f8f2e0c3.html