Planets and Moons – Cairngorms Dark Sky Park

Blood Moon

admin Planets and Moons July 27, 2018June 22, 2018

A blood moon was a dramatic event for early civilisations. Here are some tales from long ago:

Giant Wolves

According to Viking mythology the monstrous wolf Fenrir had two sons, Sköll and Hati. Sköll

would chase the Sun whilst Hati ran after the Moon. If either the Sun or Moon were caught then there was an eclipse.

During an eclipse the Vikings used to try and rescue the Sun or Moon by making as much noise as possible to scare off the giant wolves.

A Substitute King

The ancient Mesopotamians also saw lunar eclipses as an attack on the moon. But in their stories, the assailants were seven demons.

Now the Mesopotamians regarded an attack on the Moon as an assault on their king. But being fairly good at predicting eclipses they could make preparations in advance.

So during the attack they would install someone expendable as a substitute king whilst the real king pretended to be an ordinary citizen. Afterwards the substitute would quietly disappear, possibly by poisoning, and the real king would resume his duties.

A Jaguar

The south American Inca believed that during a lunar eclipse a jaguar attacked the moon and ate it. The feline assault explained why the moon turned blood red.

During lunar eclipses the Inca would shake their spears and beat their dogs. They hoped that this would make enough noise to frighten the big cat away and stop it eating anyone.

Twenty Wives

The Hupa tribe, also in the Americas, believed that the moon had twenty wives and many pets. Most of the pets were mountain lions and snakes. When the moon didn’t bring them enough food they attacked him until he bled. However before long the moon’s wives would come to his rescue and collect his blood to restore him to health. And so the eclipse would end.

What is really going on?

A “blood moon” occurs when the Moon is in total eclipse.

The Moon takes about 27 days to orbit the Earth. Roughly once per month the Moon is directly opposite the Sun. But because the Moon’s orbit is at a slightly different angle to the Earth’s orbit the Earth does not usually get in the way of the sun and we see a full Moon.

However sometimes the orbital plane of the moon lines up with the orbital plane of the Earth and the Earth blocks the sunlight from falling on the Moon. That is what causes a lunar eclipse.

When the sunlight is only partially blocked by the Earth we get a partial eclipse and the Moon darkens slightly. As the eclipse begins a dark shadow can be seen taking a bite out of the edge of the Moon. When the Moon moves directly behind the Earth then we get a total eclipse and the moon goes very dim. The colour turns red because a small amount of light still reaches the lunar surface, refracted through Earth’s atmosphere.

So the red colour of the Blood Moon is the light of every sunrise and sunset on Earth being simultaneously reflected back at us from our Moon.

Gas and Ice Giants

admin Planets and Moons May 31, 2017June 15, 2017

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 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.

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 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 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 April 1, 2017May 12, 2017Jupiter, Moon, Planet

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 17^th 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 17^th 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.

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 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.

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 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, 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.