the night skies - wildlifecampus

-WildlifeCampus Game Ranging/Field Guiding Course

This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus

1

The night skies © Copyright

Preface There are 2 reasons why astronomy is part of this course:

First, it has a definite place in science and therefore merits a brief overview. Second, the 'night skies' are an integral part of the 'African experience'.

Good field guides should be able to entertain guests on many topics and should therefore have a reasonable knowledge of astronomical features by pointing out interesting aspects of the 'Southern skies.'

Module # 11-Component # 6

The Night Skies



2


Introduction The ancient astronomy priests believed there was some link between humankind and the Universe; therefore, Astrology was born. With the later desire to formalise the Universe and the study of the stars, Astronomy evolved and became a science. Astronomers study the physical Universe. In contrast, astrologers study the more mystical aspects of the zodiac and its relevance to humankind. On a dark, clear night (in the Southern Hemisphere and away from urban areas), approximately 2500 stars and up to 5 planets are visible to the naked eye. With the use of binoculars at least 1000 times more, approximately 2.5 million stars may be seen. With a reasonable telescope, more than a million times the number is visible.



3


It is estimated that within the Milky Way (the galaxy), there are at least 100 billion stars [100 000 000 000]. If equipment as sophisticated as the Mount Palomar Telescope in the USA were used, up to 50 billion [50 000 000 000] galaxies might be seen (there are up to 100 billion known galaxies in the known Universe). Some scientists believe that it is possible to count each drop of water in every ocean and sea or every grain of sand in all the world's deserts. Still, it is almost impossible to count all the stars in the sky.

More objects in the 'cosmos' are visible from the Southern Hemisphere than from the Northern Hemisphere. From South Africa, it is possible to see all the visibly 20 brightest stars and more than 60% of the Universe's wonders. It is still unknown who first looked at the stars in a more 'serious manner', but in Russia and Europe, there are rock paintings and artefacts that date back some 30 000 years. Much of what is known about the stars was learned from ancient Babylonian scripts (Assyrians). These scripts show that the ancients also learned from previously unknown sources. Constellations (star pictures) like Scorpio, Taurus, Pisces and Orion were all identified and named long before the Babylonians existed.



4


The Universe Disclaimer: WildlifeCampus does not advocate any specific viewpoint when it comes to the Universe's origins. We do not attempt to explain or reconcile accepted scientific paradigms with established ideology. All we put forward is currently accepted scientific explanation and understanding. We emphasise that this is simply theory and not necessarily fact. The Universe appears to have started some 16 billion years ago with the big bang. In this theory, an extremely hot and dense fireball started expanding, and the Universe was born. This expansion sent unimaginably vast amounts of matter in all directions. The expanding material started arranging itself into clumps whose size and structure was dictated by gravitation and other clumps in the immediate neighbourhood. Due to the gravitational and other effects, these vast clumps would slowly have developed into protogalaxies. With the material's gravitational and rotational effects, smaller clumps in these infant galaxies would form into individual stars similarly.

Some galaxies, known as spiral galaxies, have the appearance of Saturn with its rings (or 2 fried eggs lying back to back) when viewed from the side. From above, they look like giant swirls or Catherine wheel fireworks. This effect is highlighted by the central spherical bulge of stars being packed more closely than the outer ones in the flattened disc. Galaxies can also be spherical, elliptical and irregular in shape. Galaxies tend to occur in clusters, which travel through space together, and they sometimes collide with each other. Due to the expansion of the Universe, the clusters of galaxies are moving away from each other.

NASA



5


Because space is so vast, a new unit of measurement needed to be found as the largest Earth unit (kilometre or mile) was not large enough. Scientists developed the light year. This is defined as: 'The distance travelled by light or any other Electromagnetic radiation in 1 Earth year.'

This is approximately 9.46 trillion km's [9 460 000 000 000 000 km] or 5.9 trillion miles. The Earth and Solar System are situated 30 000 light-years from the centre of the Milky Way galaxy. Astronomers know of galaxies that are 15 billion light-years away.



6


Rotation and light Due to the rotation of the Earth, only some of the constellations are visible at certain times of the year. Because of this movement (Earth's spinning on its own axis), in South Africa, we are travelling at 1500 kph [932 mph] around the Earth's centre. Standing at the equator, a person would be travelling at 1664 kph [1033 mph].

The Earth travels around the sun at 106 660 kph [66 275 mph]. In turn, the sun and the planets (the Solar System) are travelling through the Milky Way (the galaxy) at a speed of 1 120 000 kph [695 935 mph]. The entire galaxy travels through the Universe at 1 600 000 kph [994 193 mph]. Albert Einstein stated that… 'Light is the limiting factor on the Universe', as nothing appears to move faster than the speed of light. This limit appears to be unsurpassable at present. Einstein also stated that… 'The closer any object gets to the speed of light then the slower it will function'. The speed of light is about 300 000 km/sec or 1 079 254 200 kph [670 617 468 mph]. To make this a little more understandable: Assume that a person is standing on top of a mountain on Earth with a gun that could fire a ball of light. If they fired this gun, the ball would travel around the entire globe and pass through them 7.5 times before they had the time to step out of the way or count to 1. American physicists experimented (The Hafele-Keating experiment) to put this theory to the test. They took 2 identical atomic clocks (clocks that operate on the vibration of atomic energy). They placed 1 of the clocks in the basement of an office building. The other clock was placed in a jet fighter aircraft kept airborne and flying at top speed for 3 weeks by refuelling in mid-air. This experiment was repeated several times, and the respective clocks were compared. The clock in the fighter plane always lost a fraction of time compared to the stationary clock. Therefore, time slows down the faster an object travels than a stationary observer.



7


The Milky Way (known as the 'galaxy')

The Milky Way was formed approximately 15 billion years ago. The Milky Way is a spiral galaxy with a central spherical core and spiral arms. The centre of the galaxy is beyond the stars of the constellation Sagittarius. The Solar System rotates around the spherical centre of the galaxy. It will take

about 225 million years to complete 1 rotation (known as a Galactic year). The sun has only completed 20 revolutions since its formation. Because the Solar System and Earth are part of the Milky Way galaxy, when looking

at the night sky, we see the galaxy side on. All the stars that can be seen with the naked eye are part of the Milky Way.

The Milky Way was called Via Lactea. In ancient mythology, this referred to the milk spilt by the goddess Aphrodite nursing Hercules. Early stories of the sky always related them to highly descriptive myths and legends.

The dark areas seen in the Milky Way are dense dust clouds that block out the light from other stars.

Astronomers estimate that the Milky Way measures about 100 000 light-years in diameter.

It is estimated that between 100 billion-400 billion stars are to be found in the galaxy, and many of them are invisible from Earth.



8


The differences between planets and stars

The best way to understand the difference is to think of planets as reflecting balls and the stars as giant balls of light.

The name 'planet' comes from the Greek word meaning 'wandering star.' Planets are not stars but look like stars when seen with the naked eye Planets cannot produce their own light but reflect light from the sun. Stars produce their own energy and emit light. Stars are huge spheres of gas that, by nuclear fusion, release energy in the form of

light and other radiation. Protostars are stars in the phase of their lives before nuclear burning takes place The sun is a small star known as a G2 yellow dwarf by astronomers. Stars can occur in many forms, such as red giants, supergiants and white dwarfs Nebulae are vast gas clouds, which glow due to the presence of stars in or close

to them. Stars form out of these nebulae. Some nebulae are 100 light-years across.



9


Constellations of the southern skies Southern Cross (Crux)

The Southern Cross can be seen from all over South Africa but not always. It is unmistakable and one of the easiest constellations to identify.

The star at the base of the Cross is known as Alpha crucis (Acrux, the brightest star in Crux). Moving in a clockwise direction are Beta crucis, the top star is called Gamma, and the fourth star is called Delta. All of the brightest stars in the sky have proper names and are known by a letter of the Greek alphabet.

Gamma

Delta

Beta

Alpha



10


If the long axis of the Cross is extended down, 4.5 times its length, the South Pole (celestial south) of the sky is reached. A line 'perpendicular' to the horizon from this point will indicate due south on the Earth.

The 2nd method used to determine south by using the Southern Cross requires you also to identify the 2 pointers to the Cross. Once you have identified the 2 pointers, draw an imaginary line between them, and find the mid-way mark. From here, draw a perpendicular line sideways. Then take the long axis of the Southern Cross and extend it. Where these 2 lines meet will be the celestial South Pole. From here, you will drop a perpendicular line straight down to the horizon – this is south.

The South Celestial Pole is where all the stars in the Southern Hemisphere rotate. The height of this point above the horizon measured in degrees always corresponds

to the observer's latitude.



11


The Jewel Box (Also known as the Kappa Crucis Cluster, NGC 4755, or Caldwell 94)

This can be found close to the second star of the Cross (Beta Crucis and looks like a 'fuzzy' star).

Using binoculars, the star becomes an open cluster of multi-coloured stars named the Jewel Box by Sir John Herschel when he was in the Cape.

NASA



12


Jewel Box

Coalsack Nebula (Southern Coalsack, or simply the Coalsack) Between Alpha and Beta Crucis, there is an area of the sky where virtually no stars are visible. It was once thought that there were no stars in this area of sky and a 'hole' in the Milky Way. This, however, is not true. The reason for the apparent 'hole' is actually a huge cloud of dust and gas in this area, preventing the light from the stars behind it from being visible.

Below is a diagram of some of the constellations and stars near the Southern Cross

East South West

Alpha Centauri

Beta Centauri

Omega Centauri

Coal Sac

Southern Cross

False Cross Canopus

Cape Clouds South

Celestial Pole

Achernar



13


Omega Centauri

A 'fists width' (10 degrees) from Beta Crucis and forming a triangle with Beta Centauri is another 'fuzzy' star named Omega Centauri. With a pair of binoculars, this star resolves itself into a large ball of stars. This globular cluster is estimated to contain around 1 million stars and is 180 light-years in diameter. The cluster is 17 000 light-years away and is the most luminous known. It is also one of the closest to Earth.

European Southern Observatory (ESO)



14


Beta Centauri

It is the 10th brightest star in the sky and is estimated to be 10 000 times brighter than the sun. It is also named Hadar or Agena and is the closer of the 2 pointers to the Southern Cross. Beta Centauri is 320 light-years away from Earth, and due to its distance, it appears less bright than Alpha Centauri. It is, in fact, much brighter and larger than Alpha Centauri as it is classified as a B1 giant. It has a small close companion and is therefore also a double star.

Alpha and Beta Centauri help identify one of the easiest' constellations' in the night sky. These stars are lined up in such a way as to point directly towards the apex star of the Southern Cross. Therefore, they have become known as the pointer stars.

This NASA/ESA Hubble Space Telescope has given us this stunning view of the bright Alpha Centauri A (on the left) and Alpha Centauri B (on the right), shining like huge cosmic headlamps in the dark. Alpha Centauri

This is the 2nd closest star to the Southern Cross. Alpha Centauri is also named Rigel Kentaurus and is the 3rd brightest star in the Earth's sky. This is not only 1 star but 3 stars revolving around each other. 2 of these stars can be seen with binoculars. The 3rd is too small and can only be seen with a high-powered telescope. Alpha Centauri (the 3rd star Proxima Centauri) is the closest star to Earth (excluding the sun), a mere 4.3 light-years away.

ESA/Hubble & NASA



15


Orion

Orion is one of the best-known and easily recognised constellations. It is easily seen from both hemispheres of the Earth. It represents Orion, the hunter from myth and legend. Betelgeuse (Alpha Orion), the star in Orion's right shoulder, is a red supergiant star. If it were placed in the sun's position, the planets Mercury, Venus, Earth and Mars would orbit inside this vast star. Orion's belt (the 3 stars in a line) and sword/dagger are easily visible. The fuzzy patch in the sword is a nebula 20 light-years in diameter and 1500 light-years away. Viewed through binoculars, the nebula can be seen to contain stars and gas. Through a telescope, a 'trapezium' of stars can be seen that highlight the gas that they evolved from. The myth of Orion the hunter and Scorpio Orion was once a very mighty hunter who roamed the Earth searching for animals to kill. The goddess of Earth, Gaia, got upset with Orion because he was killing so many of her pure and innocent creatures that she decided to do something about it. She sent a very small animal, the scorpion, to sting Orion on his heel. The scorpion found Orion and stung him on his heel, injecting him with venom. Orion fell. But, luckily for him, there was a witch doctor named Ophiuchus who gave him an antidote for the venom so that he could rise again. However, Orion and Scorpio would never be seen in the same night skies again.

Orion’s belt

Betelgeuse

Orion Nebula



16


Scorpius, or Scorpio

One of the largest and most 'lifelike' of the constellations. From the Southern Hemisphere, it is viewed upside down. Antares is the brightest star in the constellation and is the 15th brightest star in the sky. Antares is another red supergiant. Antares is Greek and means' rival to Mars' or 'like Mars' and is so named due to its similarity to the red planet when viewed with the naked eye.

Antares



17


Taurus (the Bull)

This constellation can be seen quite close to Orion and is part of the 'great hunting group', including Orion, Canis Major and Minor, Taurus and Auriga. One of the bull's eyes, Aldebaran, is also a red giant star.

Aldebaran



18


Pleiades or Seven Sisters

This beautiful 'asterism' (distinctive pattern) of stars is sometimes erroneously referred to as a constellation. It forms part of Taurus and consists of 7 or more bright stars seen with the naked eye. When viewed through binoculars, however, there are many more to be seen, and up to 300 stars have been counted in the group.

IsiLimela or the Pleiades were the 'digging stars', whose appearance in southern Africa warned of the coming need to begin hoeing the ground. All over Africa, these stars were used as a marker of the growing season. 'And we say IsiLimela is renewed, and the year is renewed, and so we begin to dig'. (Callaway 1970). Xhosa men counted their years of manhood from the time in June when IsiLimela first became visible.

NASA



19


The Solar System

On the grand scale of the Universe or even in comparison to a galaxy, the Solar System is infinitesimally minute. However, from a human on Earth's point of view, it is spectacularly massive. To put the scale into perspective, we have reproduced a popular analogy.

In this model, the entire solar is reduced 1 billion times. An orange sphere 1.5 m [4.9 ft] in diameter represents the sun. The Earth is positioned 1 city block [500 ft] away and is the size of a grape. The moon is the size of a grape pip and orbits one foot away from Earth. Jupiter (grapefruit-sized) is 5 blocks away from the sun, with an orange-sized Saturn 5 blocks further still. Uranus and Neptune (lemon sized) are 20 and 30 blocks respectively away from the sun. A human being placed in this model would be approximately the size of an atom.

In total, the Solar System consists of 1 star (the sun), 8 planets and the 67 or more different moons that orbit the planets, uncountable asteroids, comets and a vast amount of dust and gas.



20


The Sun

The sun is classified as an ordinary G2 yellow dwarf star. It is one of more than 100 billion in the Milky Way galaxy. It was named Helios by the Greeks and Sol by the Romans (hence Solar System).

Diameter 1 390 000 km [863705.95 mi] Mass 1.9 x 10 30 kg (330 000 times the mass of the Earth) Temperature 5527C [9981F] at the surface

15 600 000C [28 080 000F] at the core The sun is an enormous sphere of burning gases (75% hydrogen, 25% helium and other gases).

NASA



21


Every second the following occurs:

700 million tonnes of hydrogen are converted into 695 million tonnes of helium by nuclear fusion.

5 million tonnes of energy in the form of light and other radiation is released. The sun loses 5 million tonnes in mass.

The amount of energy released from the sun does not remain constant. Since the formation of the Solar System has increased in output by some 40%. Therefore, the sun's time is running out, although not for a considerable period on the human scale. In approximately 5 billion years' hydrogen will be depleted, and helium will start to burn. An enormous expansion of the sun will occur. The sun will expand to its red giant stage like Aldebaran in Taurus. When this occurs, the Earth will be destroyed along with the other inner planets.

Warning: never look directly at the sun with or without binoculars. It is extremely bright and can result in permanent eye damage.



22


Mercury The second smallest planet after Pluto and closest to the sun. Mercury derives its name from Roman mythology and is named after the ancient god of commerce, travel and thievery. Diameter 4880 km [3030 mi] Mass 0.055 x Earth (3.3 x 10 23 kg) Temperature -180° to + 430°C [- 292°F to 806°F] Orbit (average) 58 million km [36 million mi] from the sun Mercury day 58 'days'-turns on its axis

176 'days'-sunrise to sunrise Mercury year 88 'days'

NB. Earth days have been shown as 'days' to avoid confusion with the days of the other planets.

Water ice (yellow) at Mercury's north polar region

NASA



23


Due to its small size, it would take 18 Mercury's to make 1 Earth. Mercury's orbit around the sun is not circular, and it varies from 46-70 million km. As can be seen from the above table, Mercury's day is longer than its year. Because it is so close to the sun, it is only seen from Earth in the morning or evening twilight. Many people, including astronomers, have never seen Mercury. To find Mercury look for a small pinkish 'star' close to the sun. In binoculars, it would show phases like the moon. It has a rocky surface that is heavily pockmarked with craters, although it has some relatively smooth regions. It looks remarkably like the moon.

NASA



24


Venus Venus's orbit is the most circular of any planet, varying less than 1% in the distance between its closest orbit (perihelion) and furthermost orbit (aphelion)

Diameter 12 100 km [7562 mi] Mass 0.81 x Earth (4.8 x 10 24 kg) Temperature 465°C [869°F] Orbit (average) 108 million-km [67 million mi] from the sun Venus day 243 'days'-turns on its axis

117 'days'-sunrise to sunrise Venus year 224 'days'

This is the closest planet to Earth and is the brightest celestial body after the sun and the moon. It is often referred to as the Evening or Morning Star. It is seen either in the evening just after sunset or in the morning just before sunrise.

Size comparison of Venus (using a false-colour, radar-based image of the surface) and Earth.

NASA



25


It can only be viewed for a maximum of 2 hours in the dark sky before it sets in the evening or is no longer visible in the morning. Venus can be seen with the naked eye during the day if its position is known. Venus is known as the sister planet to Earth as it is similar in size. However, its atmosphere is very different as it is composed mostly of carbon dioxide with a sulphuric acid haze. These account for the planet's extreme temperature and caught in a runaway greenhouse effect. The planet was named after the goddess of beauty and love.

NASA



26


Earth It might be unusual to learn that the Earth was only discovered in the 16th century. This was accomplished by the renowned astronomer Copernicus who was the first to put forward the idea that the Earth was just another planet-not the centre of the Universe.

Diameter 12 756 km [7972 mi] Mass 1 Earth (5.9 x 1024 kg) Temperature -70°C to +55°C [-94°F to +131°F] Orbit (average) 149.6 million-km [93 million mi.] from the sun Earth day 23 hours 56 min-turns on its axis

24 hours-sunrise to sunrise Earth year 365 'days'

The Earth is the only planet that does not derive its name from Greek or Roman mythology but rather from Old English and German.

NASA



27


Moon

The moon is the closest celestial body to the Earth, being only 385 000 km [240 000 mi] away. The Amazon Jungle would cover one whole face of the moon. The moon's movement gives rise to the tides, solar and lunar eclipses. Diameter 3 476 km [7972 mi] Mass 0.012 x Earth (81 moons to make one Earth) Temperature -155°C to +105°C [-247°F to +221°F] Orbit (average) 27.3 days Lunar day 27.3 days-turns on its axis

29.5 days-new moon to new moon Due to its orbital period and day being the same length, the moon always shows the same face towards the Earth. Because the orbit is elliptical, up to 59% of the moon's surface can be seen simultaneously.



28


Mars

Named from the Greek god of war, this distinctive red planet varies in brightness due to its orbit and is therefore difficult to locate. Of all the planets, Mars is the one that most resembles Earth, and its day is almost the same length.

Diameter 6 786 km [4241mi] Mass 0.11 x Earth (6.4 x 1023kg) Temperature -120°C to +25°C [-184°F to 77°F] Orbit (average) 227.9 million-km [142.5 million mi] from the sun Mars day 24 hours 37 min-turns on its axis

24 hours 38 min-sunrise to sunrise Mars year 687 'days'

NASA



29


Mars's surface is very rugged and is covered in red dust. Global dust storms often buffet the entire planet. There are polar ice caps composed mainly of frozen carbon dioxide (dry ice). There is clear evidence of past erosion of the Martian surface, so at one time, Mars appears to have had large amounts of free-flowing surface water either in large lakes or oceans. Mars has the largest known volcano in the Solar System, Olympus Mons that is 3 times higher than Mount Everest.

The thin atmosphere (less than 1% of the Earth) on this planet consists of 95% carbon dioxide, 3% nitrogen, 1.5% argon, and trace amounts of oxygen and water vapour.

Mars has 2 moons (Phobos and Deimos), but these are not visible without a telescope.

Comparison of Earth and Mars

NASA



30


Jupiter

This is the largest planet in the Solar System and equals 2.5 times all the other planets together. Had it been 50 times larger, it would have been hot enough to fuse hydrogen and become a star.

Diameter 142 984 km [89 365 mi] (equatorial)

133 708 km [83 567 mi] (polar) Mass 318 x Earth (1.9 x 10 27 kg) Temperature -150 °C at cloud tops [- 238°F] Orbit (average) 778.3 million-km [486 million mi] from the sun Jupiter day 9 hours 55 min-turns on its axis/ sunrise to sunrise Jupiter year 11.86 Earth 'years'

NASA



31


Jupiter is the first of the giant gas planets moving outward from the sun. It is composed of 90% hydrogen and 10% helium and has no solid surface. What is seen in photographs (or actual views) of the planet is its outermost cloud layers. It may possess some form of a rocky core, although there is no proof yet. The planet's core temperature may be as high as 35 000C [63 000F], and the planet gives off twice as much heat as it receives from the sun.

The Great Red Spot seen on most Jupiter photographs is a region of high pressure, effectively a massive storm (3 times the diameter of the Earth) where its clouds are higher than surrounding areas. Galileo first saw the storm in 1609.

This giant planet has 80 known moons and possibly many more and a fine dust ring. 4 of Jupiter's moons (Io, Europa, Ganymede, and Callisto) may occasionally be seen with binoculars. They are known as the Galilean moons because Galileo first saw them. The planet was named after a Roman god.

Jupiter viewed by the Juno spacecraft (February 12, 2019)

NASA



32


Saturn

Although all the gas giants have rings, Saturn is known as the 'Ringed planet'. It is the name of this planet that gives us 'Saturday'. Named for the Roman god of agriculture.


108 728 km [67 955 mi] (polar) Mass 95 x Earth (5.6 x 10 26 kg) Temperature -180 °C at cloud tops [- 356°F] Orbit (average) 1.4 billion-km [875 million mi] from the sun Saturn day 10 hours 40 min-turns on its axis/ sunrise to sunrise Saturn year 29.46 Earth 'years'

Saturn is another gas giant with a consistency of 95% hydrogen and 5% helium. Like Jupiter, it radiates more energy than it receives from the sun. Its core temperature is likely to be around 12 000C [21 632F]. Also, like Jupiter, this energy is not generated by nuclear fusion (as in the sun) but rather due to gravitational compression.

Saturn's most obvious features are its rings. These consist primarily of ice particles and small amounts of rock. Although the rings look quite uniform and solid, they are made up of billions of individual particles ranging from several inches to several feet across. Each particle has its own individual orbit. Moving outward from the planet, the rings measure a massive 274 000 km [149 12.9 mi] in diameter but are only a maximum of 1.5 km [0.93 mi] deep.

Astronomers have identified 7 individual rings. In addition, this planet has 31 named moons. Titan, one of its moons, is the second-largest in the Solar System.

NASA



33


Uranus

This recently discovered planet (1781) was named after the Greek god of the Heavens. Diameter 51 118 km [31 948 mi] (equatorial)

49 946 km [31 216 mi] (polar) Mass 14.5 x Earth (8.7 x 1025 kg) Temperature -210 °C at cloud tops [- 410°F] Orbit (average) 2.87 billion-km [1.79 billion mi] from the sun Uranus day 17 hours 14 min-turns on its axis/ sunrise to sunrise Uranus year 84 Earth 'years'

Unlike the other gas giants, Uranus generates little heat of its own. Its atmosphere is 83% hydrogen, 15% helium and 2% methane. One of the most remarkable things about Uranus is that it is tilted almost at 90 to its axis: it effectively orbits the sun on its side. This planet has 11 known rings (made up of some of the blackest material known in the Solar System), 15 named moons and 6 yet un-named moons discovered in 1999.

NASA



34


Neptune

Neptune was 'discovered' some time before it was seen. This was because discrepancies were found in the orbit of Uranus that inferred that there was a large mass (a planet) nearby. Working on this premise and mathematical inferences from Uranus's eccentricities, the planet was duly found.


48 600 km [30 375 mi] (polar) Mass 17 x Earth (1.0 x 1026 kg) Temperature unknown Orbit (average) 4.5 billion-km [2.8 billion mi] from the sun Neptune day 16 hours 7 min-turns on its axis/ sunrise to sunrise Neptune year 164.79 Earth 'years'

NASA



35


This planet has a similar structure to Uranus. Like a typical gas planet, it harbours an atmosphere dominated by incredible winds. Neptune's winds reach speeds of up to 2000 kph [1250 mph]. Neptune has 4 rings and 11 moons, one of which, Triton, is the largest moon in our Solar System.

A Voyager 2 mosaic of Triton

NASA



36


Pluto Pluto was traditionally recognised as the 9th planet of the Solar System. Many Astronomers and planetary scientists believe that it is a minor body of the Solar System and should be reclassified as an asteroid. Pluto was officially declassified in August 2006 as a true planet due to its small size and overlapping orbit. It is now considered a dwarf planet. Diameter 2284 km [1427 mi] Mass 0.0022 x Earth (1.3 x 10 22 kg)-smaller than the moon Temperature -220°C [ -364°F] Orbit (average) 5.9 billion km [3.68 billion mi] from the sun Pluto day 6 days 9 hours-turns on its axis/sunrise to sunrise Pluto year 248 Earth 'years'

NASA



37


Hades was the Greek god of the underworld and Lord of the Dead. He was not Death himself, whom the Greeks called Thanatos and the Romans Orcus. He was the 3rd brother of the Olympians Zeus and Poseidon. The Greeks and the Romans also called him Pluto, the god of wealth and precious metals found under the Earth. The Romans never referred to him as Hades. He had a cap or helmet, which made him invisible. It was most unusual for him to leave the underworld to visit Olympus, nor was he invited, as he was not a welcome visitor. He was terrifying and unpitying in his dealings with humans but just, although he was not an evil god. His wife was Persephone (Proserpine), the daughter of Demeter (Ceres), goddess of the Corn. He carried her away from Earth to become Queen of the Lower World (see also the story of spring and Demeter). Charon was the boatman who ferried souls of the dead across the River Styx to their destination in the underworld. Charon demanded payment for his service, and the Greeks placed coins in the mouths of the dead before burial for this reason. The Cypress and Beech trees are associated with Pluto and immortality.

Size comparisons: Earth, the Moon, and Pluto

NASA

the night skies - wildlifecampus

Documents