As the Sun Rushes Through Space at a Speed of 150 Miles

8/6/2019 As the Sun Rushes Through Space at a Speed of 150 Miles

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The Milky Way Galaxy

The Milky Way Galaxy is a spiral system consisting of several billion stars, one of whichis the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and

gas clouds that stretches across the sky. Although the Earth lies well within the Galaxy,

astronomers do not have as clear an understanding of its nature as they do of someexternal star systems. A thick layer of interstellar dust obscures much of the Galaxy from

scrutiny by optical telescopes, and astronomers can determine its large-scale structure

only with the aid of radio and infrared telescopes, which can detect the forms of radiationthat penetrate the obscuring matter.

The Milky Way


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The Solar System

As the sun rushes through space at a speed of 150 miles (240 kilometers) per second, it

takes many smaller bodies along with it. The sun and its smaller companions together are

known as the solar system. Together, these bodies are making a revolution around theMilky Way that takes 225 million years. These other members of the solar system range

in size from the giant planet Jupiter to microscopic particles called micrometeorites and

even smaller particlesatoms and molecules of the interplanetary gas. Earth is one of thelarger bodies of the solar system, though it is quite small when compared with the sun or

Jupiter.

The inner solar system contains the Sun, Mercury, Venus, Earth and Mars:


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The main asteroid belt (not shown) lies between the orbits of Mars and Jupiter. The

planets of the outer solar system are Jupiter, Saturn, Uranus, Neptune and Pluto:

Astronomers do not know exactly how far out the solar system extends. When it is at itsfarthest point from the sun, some 4.5 billion miles (7.2 billion kilometers)a point called

the aphelionPluto is the most distant known planet. Many comets, however, have orbits

that take them even farther out, upto several hundred times the distance of Pluto. Even at

that distance the sun's gravitational force can pull the comet back. Some hundred billioncomets form a tenuous halo in the outer parts of the solar system. Each is like a giant

snowball, 1,000 to 10,000 feet (300 to 3,000 meters) in diameter.

The solar system centers on the sun, one of a huge group of stars swirling around in a

huge pinwheel-shaped mass called the Milky Way galaxy. There are more than 100billion stars in the galaxy. Astronomical distances are so huge that astronomers often use

the light-year as the unit of distance. One light-year is equal to the distance light travels

in a year, or 5,880,000,000,000miles (9,463,000,000,000 kilometers).

The galaxy is about 100,000 light-years across. The solar system's nearest neighbor in the

galaxy is the triple star system Alpha and Proxima Centauri, which is 4.3 light-years

away from our sun. Outside the Milky Way there are billions more galaxies stretching outthrough space. Evidence suggests that there are also at least two planets orbiting a pulsar

outside the solar system and more than 50 planets orbiting extra solar stars.


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Astronomers cannot see to the end of the universe, which is the vast space that contains

the galaxies and all other matter and energy that anyone knows to exist. However,

galaxies and other objects have been detected that are thought to be between 5 billion and15 billion light-years away from the sun. Compared with such distances, our solar system

occupies a very tiny amount of space.


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The Sun's satellites

There are nine planets and a large number of smaller objects orbiting the Sun. (Exactly

which bodies should be classified as planets and which as "smaller objects" has been thesource of some controversy, but in the end it is really only a matter of definition.)

Distance Radius Mass

Planet (000 km) (km) (kg) Discoverer Date

--------- --------- ------ ------- ---------- -----

Mercury 57,910 2439 3.30e23

Venus 108,200 6052 4.87e24

Earth 149,600 6378 5.98e24

Mars 227,940 3397 6.42e23

Jupiter 778,330 71492 1.90e27

Saturn 1,426,940 60268 5.69e26

Uranus 2,870,990 25559 8.69e25 Herschel 1781

Neptune 4,497,070 24764 1.02e26 Galle 1846

Pluto 5,913,520 1160 1.31e22 Tombaugh 1930


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The Planets.

The largest and most massive members of the solar system, after thesun, are the nineknown planets. Even so, their combined mass is less than 0.2 percent of the total mass of

the solar system.

The planets travel around the sun in regular orbits that are nearly circular in shape.

Mercury's orbit lies nearest the sun. Next is Venus, then Earth, Mars, Jupiter, Saturn,

Uranus, Neptune, and finally Pluto. Pluto's orbit is the most elliptical of any of theplanets. When Pluto is nearest to the sun (at perihelion), it is nearer to the sun than is

Neptune.

The above composite shows the nine planets with approximately correct relative sizes

The motions of the planets are similar in significant ways. All the planets orbit the sun in

very nearly the same plane, which is the plane of the sun's equator. Pluto is the most

divergent; its orbital plane makes an angle of about 17 to theplane of Earth's orbit


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around the sun. Mercury is next, making a 7 angle to Earth's orbital plane. The planes of

all the other planetary orbits lie within 3.5 of Earth's orbit.

The planets may be grouped according to their nearness to the sun or according to their

physical properties. For example, Mercury and Venus, whoseorbits lie between the sun

and Earth, are called inferior planets. The planets whose orbits lie beyond Earth's orbitare the superior planets. Alternatively, theplanets may be divided by location into inner

planets (Mercury, Venus, Earth, and Mars) and outer planets (Jupiter, Saturn, Uranus,

Neptune, and Pluto).

The reason for this division is that the four inner planets are similar in composition

mostly silicate rock and iron in varying proportionswhile the four major outer planets,

Jupiter to Neptune, are huge, not very dense, and have deep gaseous atmospheres. SinceJupiter is the outstanding representative of this group, these four planets are also known

as the Jovian planets. These planetsare composed mostly of hydrogen and helium in

liquid and gaseous form. Pluto is an exception. It is much smaller than the other planets

and is composed mostly of nitrogen.

Seven of the planets have smaller bodiestheir natural satellitescircling them. Jupiter,Saturn, and Uranus have more than 20 moons each. Earth and Pluto each have one moon.

These moons are so large with respect to the planets they orbit that each of the two

planet-moon systems is sometimes considered a double planet system. Jupiter's

Ganymede and Saturn's Titan are larger than the planet Mercury. The planetary ringsaround Jupiter, Saturn, Uranus, and Neptune are made up of innumerable tiny satellites.


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The Earth.

Earth is the third planet from the Sun and the fifth largest:

orbit: 149,600,000 km (1.00 AU) from Sun

diameter: 12,756.3 km

mass: 5.972e24 kg

Earth is the only planet whose English name does not derive from Greek/Roman

mythology. The name derives from Old English and Germanic. There are, of course,

hundreds of other names for the planet in other languages. In Roman Mythology, the

goddess of the Earth was Tellus - the fertile soil (Greek: Gaia, terra mater - MotherEarth).

It was not until the time of Copernicus (the sixteenth century) that it was understood thatthe Earth is just another planet.

Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was notuntil the twentieth century that we had maps of the entire planet. Pictures of the planet

taken from space are of considerable importance; for example, they are an enormous help

in weather prediction and especially in tracking and predicting hurricanes. And they are

extraordinarily beautiful.

The Earth is divided into several layers which have distinct chemical and seismic

properties (depths in km):

0- 40 Crust40- 400 Upper mantle

400- 650 Transition region


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650-2700 Lower mantle

2700-2890 D'' layer

2890-5150 Outer core5150-6378 Inner core

The crust varies considerably in thickness, it is thinner under the oceans, thicker underthe continents. The inner core and crust are solid; the outer core and mantle layers are

plastic or semi-fluid. The various layers are separated by discontinuities which are

evident in seismic data; the best known of these is the Mohorovicic discontinuity betweenthe crust and upper mantle.

Most of the mass of the Earth is in the mantle, most of the rest in the core; the part we

inhabit is a tiny fraction of the whole (values below x10^24 kilograms):

atmosphere = 0.0000051

oceans = 0.0014

crust = 0.026mantle = 4.043

outer core = 1.835inner core = 0.09675

The core is probably composed mostly of iron (or nickel/iron) though it is possible that

some lighter elements may be present, too. Temperatures at the center of the core may beas high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably

mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The

upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium andaluminum. We know most of this only from seismic techniques; samples from the upper

mantle arrive at the surface as lava from volcanoes but the majority of the Earth is

inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates likefeldspar. Taken as a whole, the Earth's chemical composition (by mass) is:

34.6% Iron29.5% Oxygen

15.2% Silicon

12.7% Magnesium

2.4% Nickel1.9% Sulfur

0.05% Titanium

The Earth is the densest major body in the solar system.

The other terrestrial planets probably have similar structures and compositions with somedifferences: the Moon has at most a small core; Mercury has an extra large core (relative

to its diameter); the mantles of Mars and the Moon are much thicker; the Moon and

Mercury may not have chemically distinct crusts; Earth may be the only one with distinct


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inner and outer cores. Note, however, that our knowledge of planetary interiors is mostly

theoretical even for the Earth.

Unlike the other terrestrial planets, Earth's crust is divided into several separate solid

plates which float around independently on top of the hot mantle below. The theory that

describes this is known as plate tectonics. It is characterized by two major processes:spreading and subduction. Spreading occurs when two plates move away from each other

and new crust is created by upwelling magma from below. Subduction occurs when two

plates collide and the edge of one dives beneath the other and ends up being destroyed inthe mantle. There is also transverse motion at some plate boundaries (i.e. the San Andreas

Fault in California) and collisions between continental plates (i.e. India/Eurasia). There

are (at present) eight major plates:

North American Plate - North America, western North Atlantic and Greenland

South American Plate - South America and western South Atlantic

Antarctic Plate - Antarctica and the "Southern Ocean"

Eurasian Plate - eastern North Atlantic, Europe and Asia except for India African Plate - Africa, eastern South Atlantic and western Indian Ocean

Indian-Australian Plate - India, Australia, New Zealand and most of Indian Ocean

Nazca Plate - eastern Pacific Ocean adjacent to South America

Pacific Plate - most of the Pacific Ocean (and the southern coast of California!)

There are also twenty or more small plates such as the Arabian, Cocos, and Philippine

Plates. Earthquakes are much more common at the plate boundaries. Plotting theirlocations makes it easy to see the plate boundaries.

Earth's Plate Boundaries delineated by earthquake epicenters


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The Earth's surface is very young. In the relatively short (by astronomical standards)

period of 500,000,000 years or so erosion and tectonic processes destroy and recreate

most of the Earth's surface and thereby eliminate almost all traces of earlier geologicsurface history (such as impact craters). Thus the very early history of the Earth has

mostly been erased. The Earth is 4.5 to 4.6 billion years old, but the oldest known rocks

are about 4 billion years old and rocks older than 3 billion years are rare. The oldestfossils of living organisms are less than 3.9 billion years old. There is no record of the

critical period when life was first getting started.

71 Percent of the Earth's surface is covered with water. Earth is the only planet on which

water can exist in liquid form on the surface (though there may be liquid ethane or

methane on Titan's surface and liquid water beneath the surface of Europa). Liquid wateris, of course, essential for life as we know it. The heat capacity of the oceans is also very

important in keeping the Earth's temperature relatively stable. Liquid water is also

responsible for most of the erosion and weathering of the Earth's continents, a process

unique in the solar system today (though it may have occurred on Mars in the past).

Earth's atmosphere seen at the limb The Earth's atmosphere is 77% nitrogen, 21%oxygen, with traces of argon, carbon dioxide and water. There was probably a very much

larger amount of carbon dioxide in the Earth's atmosphere when the Earth was first

formed, but it has since been almost all incorporated into carbonate rocks and to a lesser

extent dissolved into the oceans and consumed by living plants. Plate tectonics andbiological processes now maintain a continual flow of carbon dioxide from the

atmosphere to these various "sinks" and back again. The tiny amount of carbon dioxide

resident in the atmosphere at any time is extremely important to the maintenance of theEarth's surface temperature via the greenhouse effect. The greenhouse effect raises the

average surface temperature about 35 degrees C above what it would otherwise be (from

a frigid -21 C to a comfortable +14 C); without it the oceans would freeze and life as weknow it would be impossible.

The presence of free oxygen is quite remarkable from a chemical point of view. Oxygenis a very reactive gas and under "normal" circumstances would quickly combine with

other elements. The oxygen in Earth's atmosphere is produced and maintained by

biological processes. Without life there would be no free oxygen.

The interaction of the Earth and the Moon slows the Earth's rotation by about 2milliseconds per century. Current research indicates that about 900 million years ago

there were 481 18-hour days in a year.

Earth has a modest magnetic field produced by electric currents in the outer core. The

interaction of the solar wind, the Earth's magnetic field and the Earth's upper atmosphere

causes the auroras (see the Interplanetary Medium). Irregularities in these factors causethe magnetic poles to move and even reverse relative to the surface; the geomagnetic

north pole is currently located in northern Canada. (The "geomagnetic north pole" is the

position on the Earth's surface directly above the south pole of the Earth's field; see this

diagram.)


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The Earth's magnetic field and its interaction with the solar wind also produce the Van

Allen radiation belts, a pair of doughnut shaped rings of ionized gas (or plasma) trappedin orbit around the Earth. The outer belt stretches from 19,000 km in altitude to 41,000

km; the inner belt lies between 13,000 km and 7,600 km in altitude.


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Earth's Satellite

Earth has only one natural satellite, the Moon. But thousands of small artificial satellites

have also been placed in orbit around the Earth. Asteroids 3753 Cruithne and 2002 AA29

have complicated orbital relationships with the Earth; they're not really moons, the term"companion" is being used. It is somewhat similar to the situation with Saturn's moons

Janus and Epimetheus. Lilith doesn't exist but it's an interesting story.

Distance Radius Mass

Satellite (000 km) (km) (kg)

--------- -------- ------ -------Moon 384 1738 7.35e22


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Asteroids or Minor Planets.

There are many smaller bodies that circle the sun in orbits that lie, for the most part,between Mars and Jupiter. These are the asteroids, sometimes called minor planets. Ceres

is the largest, with a diameter of more than 600 miles (965 kilometers). Few asteroids

have diameters larger than 100 miles (160 kilometers). Most are probably no larger than1 mile (1.6 kilometers) across. It is estimated that millions of asteroids of boulder size

exist in the solar system.

The total mass of all asteroids in the solar system adds up to only about three times that

of Ceres. Many of the smaller asteroids are thought to be fragments caused by collisions

between the larger asteroids. Some of the fragments may collide with Earth as meteorites.

Scientists are then able to determine their compositions and ages. Some asteroids arethought to contain samples of the first materials to coalesce out of the great cloud from

which the solar system itself is believed to have formed.


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Asteroid table

A few asteroids and comets are listed below for comparison. (distance is the meandistance to the Sun in thousands of kilometers; masses in kilograms).No. Name Distance Radius Mass Discoverer Date

---- --------- -------- ------ ------- ---------- -----2062 Aten 144514 0.5 ? Helin 1976

3554 Amun 145710 ? ? Shoemaker 1986

1566 Icarus 161269 0.7 ? Baade 1949

433 Eros 172800 33x13x13 Witt 1989

1862 Apollo 220061 0.7 ? Reinmuth 1932

2212 Hephaistos 323884 4.4 ? Chernykh 1978

951 Gaspra 330000 8 ? Neujmin 1916

4 Vesta 353400 265 3.0e20 Olbers 1807

3 Juno 399400 123 ? Harding 1804

15 Eunomia 395500 136 8.3e18 De Gasparis 1851

1 Ceres 413900 466 8.7e20 Piazzi 1801

2 Pallas 414500 261 3.18e20 Olbers 1802

243 Ida 428000 35 ? ? 1880?

52 Europa 463300 156 ? Goldschmidt 185810 Hygiea 470300 215 9.3e19 De Gasparis 1849

511 Davida 475400 168 ? Dugan 1903

911 Agamemnon 778100 88 ? Reinmuth 1919

2060 Chiron 2051900 85 ? Kowal 1977
http://www.nineplanets.org/help.html#asteroidnumhttp://www.nineplanets.org/eros.htmlhttp://www.nineplanets.org/gaspra.htmlhttp://www.nineplanets.org/ida.htmlhttp://www.nineplanets.org/help.html#asteroidnumhttp://www.nineplanets.org/eros.htmlhttp://www.nineplanets.org/gaspra.htmlhttp://www.nineplanets.org/ida.html

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As the Sun Rushes Through Space at a Speed of 150 Miles

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