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Gas and Ice Giants

admin Planets and Moons

A gas giant is a large planet made mainly out of hydrogen and helium. Jupiter and Saturn are the gas giants of the solar system. The outermost parts of their atmospheres have many layers of visible clouds that are mostly made out of water and ammonia.

Jupiter has been covered in some detail elsewhere, so here we will concentrate on the other three giant planets.

Saturn
Saturn and it's rings
Hubble view of Saturn and it’s rings

Saturn is the sixth planet from the Sun and the second-largest in the solar system after Jupiter. It’s diameter is about nine times that of earth and it takes twenty nine and a half years to orbit the Sun. Binoculars will show an odd shaped disc. However even a modest telescope, such as a spotter scope, will reveal it’s rings.

Saturn was the ancient Roman god of agriculture. He was remembered in December during the most famous Roman festival of all – the Saturnalia. The Saturnalia was a time of feasting, free speech, gift-giving, role reversal, and revelry. Saturn the planet and Saturday are both named after him.

Saturn’s atmosphere usually appears bland and lacking in contrast. Ammonia crystals in it’s upper atmosphere give it a pale yellow hue. Wind speeds on Saturn can reach 1,800 km/h.

Saturn’s best known feature are it’s rings. These consist mainly of ice particles with a small amount of rocky debris and dust. Saturn also has sixty-two moons not including the hundreds of moonlets within it’s ring system. The largest moon is Titan. Bigger than the planet Mercury, Titan is the only moon in the Solar System to have a substantial atmosphere. One of Saturn’s most interesting moons is Enceladus. This moon is regarded as a potential habitat for life. In 2015 the Cassini probe flew through a plume on Enceladus and detected most of the ingredients needed to sustain some forms of primitive microbes.

Enceladus
Enceladus
The Ice Giants

An ice giant is a large planet made mainly out water, ammonia and methane, along with traces of other hydrocarbons.There are two ice giants in the solar system – Uranus and Neptune.

Uranus

Uranus is the coldest planet in the solar system, with a minimum temperature of −224°C. It is the seventh planet from the Sun and it’s diameter is about four times the size of earth’s. It is the most distant planet that can be seen with the naked eye.

Uranus is the only planet whose name is derived from a figure in Greek mythology. Uranus or “Father Sky” was the husband of Gaia, “Mother Earth”. Together they were the ancestors of most of the other Greek gods.

Uranus
Uranus

Uranus takes 84 years to complete one orbit. It is also unique because it’s axis of rotation is tilted over at almost 900 compared to the other planets. This means that it’s seasonal changes are completely different to any other planet. Each pole gets 42 years of continuous sunlight, followed by 42 years of darkness. Around the equinoxes the rest of the planet has a normal day – night cycle, but around the solstices only a narrow strip round the equator experiences that normal rhythm.

Neptune
Neptune
Neptune

Neptune is the eighth and farthest known planet from the Sun. It’s diameter is about 3.9 times that of earth and it takes a hundred and sixty five years to orbit the Sun. Although Neptune is not visible to the unaided eye it may be seen with binoculars.

Neptune was the god of freshwater and sea in Roman mythology. He was also the creator of horses as well as the owner of a powerful weapon, his Trident.

Neptune is the only planet in the Solar System that was found by mathematical prediction. During the first half of the nineteenth century Alexis Bouvard discovered unexpected changes in the orbit of Uranus that led him to realise that it was being affected by an unknown planet. From 1843, John Adams, and later from 1845, Urbain Le Verrier began work to calculate the position of the new planet. Johann Galle was the first person to see it through a telescope on 23 September 1846, within a degree of the position predicted by Le Verrier.

Image credits: NASA

Jupiter – King of Planets

admin Planets and Moons , ,

The planet Jupiter has been known since ancient times. It is visible to the naked eye in the night sky and can occasionally be seen in the daytime when the Sun is low. To the Babylonians, this planet represented their god Marduk. The Romans named the planet after Jupiter, the principal god of Roman mythology. The Greek equivalent of the Roman Jupiter was Zeus.

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass two and a half times that of all the other planets in the Solar System combined. Jupiter can be bright enough for its light to cast shadows, making it the third-brightest object in the night sky after the Moon and Venus.

Through modern binoculars you should be able to see what Galileo spotted with his first telescope in the 17th century. The planet appears as a disc and if you hold your binoculars steady enough you should be able to see the four Galilean moons orbiting the planet.

This discovery was dynamite in the 17th century. In those days people believed that everything in God’s perfect universe rotated around the earth. But Galileo had spotted moons going round Jupiter. This was one of the observations that persuaded him to support the Copernican theory that the planets orbited the sun rather than the earth. Eventually Galileo was convicted of heresy for these views. Forced to recant by the Inquisition he spent the rest of his life under house arrest.

More can be seen through a modest telescope. At even a low magnification of x50, two dark bands of clouds can be seen circling the middle of the planet. If you are lucky you may even catch a glimpse of the great red spot, a giant storm that is known to have existed since at least the 17th century.

Jupiter
Jupiter with Europa’s shadow and the great red spot
The Galilean Moons

Jupiter has 67 known moons. The four largest were discovered by Galileo. These moons were named after lovers of the god Zeus: Io, Europa, Ganymede and Callisto.

Io
Io was one of Hera’s priestesses

Io is the closest moon to Jupiter and orbits the planet in less than two earth days. This proximity sets up huge tidal stresses in Io’s surface which heat the rocks and melts them. As a result Io is the most geologically active object in the solar system, with over 400 live volcanoes.

Europa
Europa was a mythical Phoenician noblewoman, who became queen of Crete

The second Galilean moon, Europa, is one of the smoothest objects in the solar system. The surface is made of ice and it is thought that an ocean of liquid water exists underneath the ice. Like Io, it is heated by tidal flexing in Jupiter’s immense gravitational field. Some scientists think that extra-terrestrial life could exist in Europa’s ocean.

Ganymede
Ganymede was the cup bearer of the Greek gods

Ganymede is the third Galilean moon. It is bigger than the planet Mercury and is the largest natural satellite in the solar system. This moon is primarily composed of rock and water ice. There may be an ocean at a depth of 200km, sandwiched between layers of ice.

Callisto
Callisto was a hunting companion of the goddess Artemis

Callisto, the fourth Galilean moon, is one of the most heavily cratered satellites in the solar system. It has long been considered the most suitable base for future exploration of the Jovian system because it is the furthest large moon from Jupiter’s intense radiation.

Of course not even the Hubble space telescope can take pictures like the ones above. You need to get close up for images like that! The picture of Jupiter is from NASA’s Cassini mission and the moon’s are from their Galileo mission.

The Hunter and the Seven Sisters

admin Constellations, Nebulae, Star Clusters

Orion is one of the most recognizable constellations in the winter sky.

The easiest way to find Orion is to go outside in the evening this winter and look to the south east. You are looking for three bright stars close together in almost a straight line. These three stars represent Orion’s belt. The two bright stars to the north are his shoulders and the two to the south are his feet.

Orion
Orion

Orion the Hunter could walk on water because he was the son of the sea-god Poseidon. After many adventures Orion walked to the island of Crete where he hunted with the goddess Artemis. During the hunt, he threatened to kill every beast on Earth. But Mother Earth objected and sent a giant scorpion to kill him. After Orion’s death, Zeus placed him among the constellations adding the Scorpion as well, to commemorate the hero’s death.

One of the show pieces of Orion is the Great Nebula. To find it first locate Orion’s Belt, which contains the row of three bright stars. Next, look below his belt for a vertical row of fainter stars marking the Hunter’s Sword. Look for the fuzzy “star” in the middle of the Sword. That’s the Orion Nebula. Binoculars will give you a better view.

The Great Nebula
The Great Nebula

The Orion Nebula is a stellar nursery where new stars are being born. Stars form when clumps of hydrogen and other gases contract under their own gravity. As the gas collapses, the central clump grows stronger and the gas heats to extreme temperatures. When the temperature gets high enough, nuclear fusion ignites the gas to form a star. The star is ‘born’ when it begins to emit enough radiative energy to halt it’s gravitational collapse. Detailed observations have revealed approximately 700 stars in various stages of formation within this nebula.

The Pleiades – The Seven Sisters

Start by looking for the three stars in a diagonal row that make up Orion’s belt. Draw an imaginary line between those stars up and to the right. Continue your line, and you should come to a group of stars that looks like the letter “V”. That is the face of Taurus – The Bull. A little to the right of Taurus is a small clump of stars. They are the Pleiades, looking almost like a tiny dipper. Once again binoculars will give you a better view.

The Pleiades were the seven daughters of Atlas and the sea-nymph Pleione. After Atlas was forced to carry the heavens on his shoulders, Orion began to pursue all of the Pleiades. To comfort their father, Zeus transformed them first into doves, and then into stars. The constellation of Orion is said to still pursue The Pleiades across the night sky.

The Pleaides
The Pleaides

The Pleiades is an open star cluster containing hot middle-aged stars. It is one of the nearest star clusters to Earth. Probably formed from a nebula similar to the Orion Nebula around 100 million years ago, the cluster is dominated by hot blue and extremely luminous stars.

The faint reflection nebulosity around the brightest stars was at first thought to be left over from the formation of the cluster, but is now known to be an unrelated dust cloud in interstellar space, through which the stars are currently passing. Astronomers estimate that the cluster will survive for about another 250 million years, after which it’s stars will disperse.

Getting the best view

Discovering a dark place shouldn’t be too difficult on the Glenlivet Estate. I find my garden is as good a place as any. Switch off any outdoor lights and allow your eyes to acclimatise to the dark. In the dark your sensitive night time black and white vision will allow to you see more in the night sky, but it does take a while to kick in.

Avoid looking directly at any visible lighting. That will destroy your night vision almost instantly and you will have to wait another ten minutes before your dark adapted eyes are beginning to work again.

Because you are using your night vision you will only be seeing in black and white so don’t expect to see the Orion Nebula in full colour. Colour images can only be produced with long photographic exposures. Nevertheless witnessing the wonders of the night sky for yourself is an altogether different level of experience compared to admiring pictures by the Hubble space telescope from the comfort of your armchair.

Get out there and look up at our glorious dark skies!

Tomintoul Street Light Replacement

admin Dark Skies Project

Street lighting replacement in Tomintoul is well under way. Old sodium units are being replaced with new full cut off LED lighting and making a huge difference to the levels of light pollution and energy wastage. Over half of all the outside lighting in the Landscape Partnership area is now dark sky friendly.

In the picture of Tomnabat Lane below there are four of the old street lights in the foreground and seven of the new LED’s in the background.

Replacement street lighting - Tomintoul
Street lighting is now being replaced in Tomintoul

Andromeda and The Milky Way

admin Galaxies ,
The Milky Way

The Milky Way is one of the highlights of our late autumn and early winter skies. A glorious soft band of light curves across the evening sky from south west to north east after dark. In ancient times it was thought to be just that – a band of light. It wasn’t until 1610, with the invention of the telescope, that Galileo discovered the Milky Way was really composed of a huge number of distant stars.

The Milky Way
The Milky Way
Dust and Dark Nebulae

Once you have allowed your eyes adapt to the night sky, you will begin to see dark patches within the arc of the Milky Way. These are regions of dust and cold gas that may eventually turn into new stars. But these clouds also obscure our view of our galaxy beyond them making it difficult for early observers to understand the shape of the Milky Way.

By the mid 1700’s Immanuel Kant and others were suggesting that the Milky Way might be a huge, flattened swarm of stars. But it was only in the twentieth century that the true spiral nature of the Milky Way emerged, with the discovery of other galaxies.

The Milky Way is a vast spinning disc of over 100 billion stars with a diameter of 100,000 light years. (A light year is the distance that light travels in one year. Light takes about eight minutes to go from the Sun to the Earth).

Our nearest significant galactic neighbour is in the constellation of Andromeda. Although it is 2,500,000 light years away you can see it with your naked eye on clear nights. It is visible in the picture above, appearing like a nebulous bright star in the top left hand corner of the image.

Andromeda

Andromeda is known as “the Chained Lady”. That name refers to Andromeda’s role in the Greco-Roman myth of Perseus: Cassiopeia, the queen of Ethiopia, boasted that her daughter was better looking than the Nereids, sea nymphs favoured with exceptional beauty. Offended by her remark, the nymphs asked Poseidon to punish Cassiopeia for her impudence and Poseidon ordered the sea monster Cetus to attack Ethiopia. Concerned for his kingdom, Andromeda’s father Cepheus consulted the Oracle of Ammon, only to be told to sacrifice his daughter to the monster. So Andromeda was chained to a rock by the sea. However the hero, Perseus appeared in a nick of time and used the head of the gorgon, Medusa to turn the monster into stone.

Star Hopping

To find the Andromeda galaxy in the night sky we will have to go star hopping. First of all find the Great Square of Pegasus. Andromeda is the constellation to the north east of the Square. Starting at the north eastern corner move three stars to the north east counting the corner of the Square as the first star. The star you have landed on is the first in a line of three pointing to the north west. Go to the third star in line. Just to the west of it is the faint glow of the core of the Andromeda galaxy.

The view is improved through binoculars if you have them to hand. The scale of this galaxy is vast. Although the disc and spiral arms are not visible with the naked eye, their diameter extends to six times the width of the full moon!

The Andromeda Galaxy
The Andromeda Galaxy (M31)

In the picture above the core and spiral arms of M31 can clearly be seen. In between the spiral arms are dark lanes of dust and gas. You can clearly see that stars of our galaxy are in the foreground and that M31 itself lies beyond the Milky Way.

As a bonus we get two other smaller galaxies in the picture. Both M32 (above) and M110 (below left) are dwarf elliptical galaxies, satellites of the larger M31.

Measurements indicate that we are on a collision course with M31, which will be due in around 3.75 billion years time. But I guess that there will be other things to worry about before that happens!