c. the solar system

The Solar System

Theories about the Origin of the Solar System

• The Planetisimal Theory – proposed by Count Georges Comte de Buffon.

• A passing star collided with our sun and the collision caused large chunks of material from the two stars to be thrown off into space. These streamers then presumably broke into small chunks called "planetesimals."

• The Companion Star Theory – was proposed by Fred Hoyle.

• According to these theory the sun had a companion star. And these star exploded when it collided with one another due sun’s gravitation. The materials from these collision became the planets and other bodies found in the solar system.

Nebular Theory

• Marquis de Laplace in 1796 first suggested that the Sun and the planets formed in a rotating nebula which cooled and collapsed. It condensed into rings which eventually formed the planets, and a central mass which became the Sun.

The Sun

• The sun consist of four layers:

• Photosphere• Chromosphere• Corona• Reversing Layer

Photosphere

• The light and main body of the sun.

• The photosphere is the visible surface of the Sun that we are most familiar with. Since the Sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick

• It is characterized by various disturbances like:

• 1. Granules• 2. Facula• 3. Sunspots

Granules

• These are small (about 1000 km across) cellular features that cover the entire Sun except for those areas covered by sunspots.

• These features are the tops of convection cells where hot fluid rises up from the interior in the bright areas, spreads out across the surface, cools and then sinks inward along the dark lanes. Individual granules last for only about 20 minutes

Faculae

• These are bright areas that are usually most easily seen near the limb, or edge, of the solar disk.

• These are also magnetic areas but the magnetic field is concentrated in much smaller bundles than in sunspots.

• While the sunspots tend to make the Sun look darker, the faculae make it look brighter

Sunspots

• Sunspots appear as dark spots on the surface of the Sun.

• Temperatures in the dark centers of sunspots drop to about 3700 K (compared to 5700 K for the surrounding photosphere).

• They typically last for several days, although very large ones may live for several weeks.

• They follow an eleven year cycle.

Chromosphere

• The chromosphere is an irregular layer above the photosphere where the temperature rises from 6000° C to about 20,000° C.

• At these higher temperatures hydrogen emits light that gives off a reddish color (H-alpha emission).

• This colorful emission can be seen in prominences that project above the limb of the sun during total solar eclipses.

• This is what gives the chromosphere its name (color-sphere)

Prominences

• Prominences are dense clouds of material suspended above the surface of the Sun by loops of magnetic field.

• Prominences and filaments are actually the same things except that prominences are seen projecting out above the limb, or edge, of the Sun.

• Both filaments and prominences can remain in a quiet or quiescent state for days or weeks.

Solar Flares

• Outbursts or flares of high energy radiation and atomic particles from the photosphere pass through the corona and can affect radio and telecommunications on Earth.

Corona

• Corona is the hot, outermost layer of the Sun which extends for millions of kilometres into space where it gradually becomes the solar wind.

• It is visible during total eclipses of the Sun as a pearly white crown surrounding the Sun.

Internal Structure of the Sun

• The interior of the sun is composed of three layers:

• 1. The core• 2. The Radiative

zone• 3. Convective

Envelope.

• The Sun's core is the central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light.

• The radiative zone is characterized by the method of energy transport - radiation.

• The convection zone is the outer-most layer of the solar interior. It extends from a depth of about 200,000 km right up to the visible surface.

Internal Structure of the Sun

PLANETS OF THE SOLAR SYSTEM

• Planets are grouped according to size.

• A. Terrestrial planetsA. Terrestrial planets are small, have high densities due to their bodies that are made up of rocks and heavy elements.

• 1. Mercury, • 2. Venus• 3. Earth• 4. Mars• 5. Pluto

• B. Jovian planetsB. Jovian planets are large and massive, they have low densities and dense atmosphere.

• 1. Jupiter• 2. Saturn• 3. Uranus• 4. Neptune

Mercury

• Mercury is the closest planet to the Sun and the eighth largest. Mercury is slightly smaller in diameter than the moons Ganymede and Titan but more than twice as massive.

• Transit – the phenomenon where mercury passes directly between sun and earth on rare occasion.

• No atmosphere due to weak gravity.• The surface is poked with thousands of craters.• No satellite

VENUS• Venus is known as the veiled

and twin planet of the earth.• Venus' orbit is the most nearly

circular of that of any planet, with an eccentricity of less than 1%.

• Like Mercury, it was popularly thought to be two separate bodies: as the morning star and as the evening star.

• Its dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun

• Venus atmosphere is composed of 96% CO2

• It has high albedo of 77%• Considered to be the brightest due to the

chemical fires on the cloud layers that appear as a halo.

MARS

• The Red planet due to iron oxide (rust) and carbon dioxide

• Polar caps – the most prominent sight during winter.

• The two satellites are• 1. Phobos - bigger• 2. Deimos

JUPITER

• The most prominent feature is the Great Red Great Red SpotSpot. (a huge and violent storm)

• There are 19 known satellites. The first 4 was discovered by Galileo.

• 1. Io• 2. Ganymede – biggest in

Jupiter, 2nd to the entire solar system

• 3. Europa• 4. Callisto

Saturn

• Saturn is the second largest.• Has 23 known satellites.• Titan the largest satellite in the

entire solar system• The major rings are

designated by letters: • A-ring – outermost and 2nd

brightest• B-ring – the brightest• C or Crepe ring – composed of

frozen ringlets that are transparent and eccentric

• D-ring least brightest and near Saturn’s atmosphere

URANUS

• Discovered by William Herschel.

• Bluish green• Five known satellites

namely:• 1. Ariel• 2. Umbriel• 3. Miranda• 4. Titania• 5. Oberon• Inclination is 98o

NEPTUNE

• Twin planet of Uranus• Discovered by

Johann Galle• Bluish green• Two satellites:• 1. Triton• 2. Negreid

Pluto• In Roman mythology, Pluto (Greek:

Hades) is the god of the underworld. The planet received this name (after many other suggestions) perhaps because it's so far from the Sun that it is in perpetual darkness and perhaps because "PL" are the initials of Percival Lowell.

• Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.

• Lone satellite – Charon discovered by James Christy

Asteroids• On the first day of January

1801, Giuseppe Piazzi discovered an object which he first thought was a new comet. But after its orbit was better determined it was clear that it was not a comet but more like a small planet.

• Piazzi named it Ceres, after the Sicilian goddess of grain. Three other small bodies were discovered in the next few years (Pallas, Vesta, and Juno). By the end of the 19th century there were several hundred.

BODE’S LAW• Bode's 'law' takes the form of a

series in which the first term is 0, the second is 3, and each term is then double the previous one, to each term add 4 and divide the result by 10. This yields the series of numbers:

• 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10.0, 19.6, 38.8

• which may be compared to the mean distances of the planets from the Sun in AU:

• 0.39, 0.72, 1.0, 1.52, 5.2, 9.52, 19.26, 30.1, 39.8

• The agreement for all but Neptune and Pluto is remarkable.The lack of a planet at 2.8 led to the discovery of the asteroids.

Types of Asteroids• Asteroids are classified into a

number of types according to their spectra (and hence their chemical composition) and albedo:

• 1. C-type, includes more than 75% of known asteroids: extremely dark (albedo 0.03); similar to carbonaceous chondrite meteorites; approximately the same chemical composition as the Sun minus hydrogen, helium and other volatiles;

• 2. S-type, 17%: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates;

• 3. M-type, most of the rest: bright (albedo .10-.18); pure nickel-iron.

• There are also a dozen or so other rare types.

Habitable Zone:

• One of the main ingredients for life as we know it is liquid water. Water exists as a liquid between 273K and 373K (unless the pressure is too low, in which case the water sublimates into gaseous water vapor). The region on the solar system (or any planetary system) where the temperature is in this range, is called the habitable zone.

• Nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids;

• Coma: dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus;

• Hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;

• Dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;

• Ion tail: as much as several hundred million km long composed of plasma and laced with rays and streamers caused by interactions with the solar wind.

When they are near the Sun and active, comets have several distinct

parts:

• When they are near the Sun and active, comets have several distinct parts:

Comet orbiting the sun

Meteor, Meteorite, Meteoroid

• Asteroids that are on a collision course with Earth are called meteoroids.

• When a meteoroid strikes our atmosphere at high velocity, friction causes this chunk of space matter to incinerate in a streak of light known as a meteor.

• If the meteoroid does not burn up completely, what's left strikes Earth's surface and is called a meteorite.

• A meteorite is a meteoroid that reaches the surface of the Earth without being completely vaporized.

• A meteor is a meteoroid that has entered the Earth's atmosphere, usually making a fiery trail as it falls. It is sometimes called a shooting star or a falling star.

• The friction between the fast-moving meteor and the gas in the Earth's atmosphere causes intense heat; the meteor glows with heat and then burns. This glowing phase usually happens 50 to 68 miles (80 to 110 kilometers) above the Earth

• Most meteors burn up before hitting the Earth. Only large meteors can survive the trip through our atmosphere. Most meteors glow for only a few seconds before they burn up.

Meteoroids, Meteors, and Meteorites

• What's the Difference?

• MeteoroidsSpace Debris

• MeteorsFalling through the Atmosphere

• MeteoritesOn Earth

Meteor Shower

• Thank you!

• EXAM next meeting.

• GOOD LUCK!