The Facts OF GALAXIES

The Facts

1) Main Types of Galaxies: 3;

• Spiral
• Elliptical
• Irregular (Ellipticals and Irregulars exist in both normal and 'dwarf' sizes)

2) Number of Galaxies Visible: 100 billion

3) Most Abundant Type of Galaxy: Dwarf Ellipticals

4) Distribution of Normal Size Galaxies in Hubble Classification: Spiral-75%; Elliptical-20%; Irregular-5% (Edwin Hubble's data was skewed because spirals are generally brighter than any other galaxies, and he found more of them. Dwarfs are dim and were not found until bigger telescopes were built.)

5) Spiral Galaxy Nearest Our Milky Way Galaxy: Andromeda - 2.6 million light years away. (The Magellanic Clouds - dwarf irregulars--are only an average 200,000 light years away, but they are more giant star clusters than galaxies.) (See - Survey of Our Nearest Galaxies)

6) Distance of Visible Galaxies Fatherest From Us: Appx. 14 billion light years.

7) Size of Typical Galaxy: 3,260 light years to 326,000 light years across.

8) Number of Stars in Average Galaxy: 40 billion

9) Number of Stars in Typical Large Galaxy (such as our Milky Way): 200 billion to 400 billion.

10) Number of Galaxies in Local Group: Appx: 40 (there may be dwarfs so dim we can't see them).

11) Largest Galaxy in Local Group: Andromeda

12) Smallest Galaxy in Local Group: Leo T, a dwarf irregular 600 light years across

13) Number of Galaxies in Average Galactic Group: <50

14) Fewest Number of Galaxies in Known Group: 4; Seyfert's Sextet in the constellation Serpens (in the photo it appears there are 6 galaxies, but closer study reveals that one is much farther way, and one is not a galaxy at all but a wisp of stars pulled from one of the other galaxies by gravitational forces).

Galaxies Amazing Facts

1) Massive black holes may be at center of large galaxies - It appears that most, perhaps all, spiral and elliptical galaxies hide a massive black hole at their core. This was suspected for years, but the Hubble telescope has given us direct evidence that it is a fact. Visual, infrared and ground based radio telescope images have produced clear images of high speed jets of electrons and gas shooting from the core of a number of galaxies. The Hubble also has shown that the core of these galaxies are rotating at extremely high rates. That could be caused only by a massive gravitational field--far greater that that of the stars in the core of the galaxy. Some theories suggest that black holes are the engine that form galaxies.

Our Milky Way contains such a black hole at its core. Our neighbor Andromeda may contain two, as it appears to have two distinct cores.

2) Galaxies like company - Galaxies invariably form groups, and groups form clusters, and clusters form superclusters. Gravity is at the core of this tendency. When a large galaxy forms, its massive gravitational field captures smaller galaxies that have formed in its vicinity. These smaller galaxies often actually become satellites of the large galaxy. Our Milky Way has several small satellite galaxies that orbit around us. Sometimes two galaxies get so close they collide.

Then our local group, which includes Andromeda (our group is fairly unusual in having two large galaxies), has a gravitational connection with several other groups that together form the Virgo Cluster, so called because they all appear in the constellation Virgo. Then the Virgo Cluster teams up with two other clusters to form the Virgo Super Cluster, a collection of 100 groups of gravitationally attached galaxies approximately 200 light years across.

Read more: http://www.brighthub.com/science/space/articles/12504.aspx#ixzz0Yb4vFPrM

The Sun II

Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy.

        diameter:    1,390,000 km.
       mass:        1.989e30 kg
       temperature: 5800 K (surface)
                    15,600,000 K (core)

The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest).

It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it. But there are many more smaller stars than larger ones; the Sun is in the top 10% by mass. The median size of stars in our galaxy is probably less than half the mass of the Sun.

The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol.

The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun but the core of the Sun rotates as a solid body.

Conditions at the Sun's core (approximately the inner 25% of its radius) are extreme. The temperature is 15.6 million Kelvin and the pressure is 250 billion atmospheres. At the center of the core the Sun's density is more than 150 times that of water.

The Sun's power (about 386 billion billion megaWatts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.

The surface of the Sun, called the photosphere, is at a temperature of about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 km in diameter. Sunspots are caused by complicated and not very well understood interactions with the Sun's magnetic field.

A small region known as the chromosphere lies above the photosphere.

The highly rarefied region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during a total solar eclipse (left). Temperatures in the corona are over 1,000,000 K.

It just happens that the Moon and the Sun appear the same size in the sky as viewed from the Earth. And since the Moon orbits the Earth in approximately the same plane as the Earth's orbit around the Sun sometimes the Moon comes directly between the Earth and the Sun. This is called a solar eclipse; if the alignment is slighly imperfect then the Moon covers only part of the Sun's disk and the event is called a partial eclipse. When it lines up perfectly the entire solar disk is blocked and it is called a total eclipse of the Sun. Partial eclipses are visible over a wide area of the Earth but the region from which a total eclipse is visible, called the path of totality, is very narrow, just a few kilometers (though it is usually thousands of kilometers long). Eclipses of the Sun happen once or twice a year. If you stay home, you're likely to see a partial eclipse several times per decade. But since the path of totality is so small it is very unlikely that it will cross you home. So people often travel half way around the world just to see a total solar eclipse. To stand in the shadow of the Moon is an awesome experience. For a few precious minutes it gets dark in the middle of the day. The stars come out. The animals and birds think it's time to sleep. And you can see the solar corona. It is well worth a major journey.

The Sun's magnetic field is very strong (by terrestrial standards) and very complicated. Its magnetosphere (also known as the heliosphere) extends well beyond Pluto.

In addition to heat and light, the Sun also emits a low density stream of charged particles (mostly electrons and protons) known as the solar wind which propagates throughout the solar system at about 450 km/sec. The solar wind and the much higher energy particles ejected by solar flares can have dramatic effects on the Earth ranging from power line surges to radio interference to the beautiful aurora borealis.

Recent data from the spacecraft Ulysses show that during the minimum of the solar cycle the solar wind emanating from the polar regions flows at nearly double the rate, 750 kilometers per second, than it does at lower latitudes. The composition of the solar wind also appears to differ in the polar regions. During the solar maximum, however, the solar wind moves at an intermediate speed.

Further study of the solar wind will be done by the recently launched Wind, ACE and SOHO spacecraft from the dynamically stable vantage point directly between the Earth and the Sun about 1.6 million km from Earth.

The solar wind has large effects on the tails of comets and even has measurable effects on the trajectories of spacecraft.

Spectacular loops and prominences are often visible on the Sun's limb (left).

The Sun's output is not entirely constant. Nor is the amount of sunspot activity. There was a period of very low sunspot activity in the latter half of the 17th century called the Maunder Minimum. It coincides with an abnormally cold period in northern Europe sometimes known as the Little Ice Age. Since the formation of the solar system the Sun's output has increased by about 40%.

The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards, will result in the total destruction of the Earth (and probably the creation of a planetary nebula).

The Sun's satellites

There are eight 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 the source of some controversy, but in the end it is really only a matter of definition. Pluto is no longer officially a planet but we'll keep it here for history's sake.)

http://nineplanets.org/sol.html

Fact About Pluto

Pluto is the farthest planet from the Sun (usually) and by far the smallest. Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton).

orbit: 5,913,520,000 km (39.5 AU) from the Sun (average)
diameter: 2274 km
mass: 1.27e22 kg

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.

After the discovery of Pluto, it was quickly determined that Pluto was too small to account for the discrepancies in the orbits of the other planets. The search for Planet X continued but nothing was found. Nor is it likely that it ever will be: the discrepancies vanish if the mass of Neptune determined from the Voyager 2 encounter with Neptune is used. There is no tenth planet.

Pluto is the only planet that has not been visited by a spacecraft. Even the Hubble Space Telescope can resolve only the largest features on its surface.

Fact About The SUN

The Sun is one out of billions of stars. The Sun is the closest star to Earth. The Sun rotates once every 27 days. The Sun is now a middle-aged star, meaning it is at about the middle of its life. The Sun formed over four and a half billion years ago. You may think the Sun will die soon, but it will keep shining for at least another five billion years.

The Sun’s surface is called the photosphere. The temperature of the photosphere is about 10,000° Fahrenheit. Its core is under its atmosphere. The temperature at the core, or very middle, of the Sun, is about 27 million° Fahrenheit. That’s pretty hot!

The Sun’s diameter is about 870,000 miles wide. The Sun is 109 times wider than Earth, and is 333,000 times heavier. That means if you put the Sun on a scale, you would need 333,000 objects that weigh as much as the Earth on the other side to make it balance.

The Sun is only one of over 100 billion stars. In ancient times, the people believed the Sun was a burning ball of fire created by the gods. Later, people thought it was a solid object, or a liquid ball. Over one million Earths could fit inside the Sun. Looking directly at the Sun can permanently damage your eyes because it is so bright. A star mostly gives off light and heat. The larger the star, the hotter its temperature. A super giant star can get to be 400 times larger than our Sun, which is almost a million miles in diameter. The Sun is tilted.

Without the Sun, Earth could not support life. The Sun gives off heat and light that the Earth needs to support life (us). If you lived on the Sun, and you built a spacecraft, it would have to go over 618.2 kilometers per second to escape the Sun’s gravitational pull. The Sun is 695,000 kilometers at its equator. The Sun is the largest mass in our Solar System.

Sun loops are large loops caused by the Sun’s magma (molten rock) shooting off of the Sun’s surface. These loops can fly millions of miles into space. Our Sun is approximately 25,000 light-years from the galactic core of our galaxy (the Milky Way). It is like a really big star. It is a million times bigger than the biggest.

Did you know that the Sun is made out of 92% hydrogen, 7% helium and the rest is other low number gasses? The Sun’s core is the hottest part of its matter. It is 27 billion° Fahrenheit. The Sun does not rise or set. It just looks like it does because the Earth is moving. The Earth orbits the Sun every 365 space days. Can you believe that the Sun can burn over seven million tons of natural gas every second? A star can live for over three billion years. If the Sun was hollow, you could fit 333,000 Earths inside! The Sun rotates, too. It rotates every 25-36 days. It seems as if stars always stay in the same position night after night, year after year, but they actually do move over time. They helped scientists to develop a reference system for charting a planet’s movement.

The moon does not give off light of its own. It is the Sun that gives light to the Moon. The Moon reflects the Sun’s light. A star is the only body in space that emits its own light; everything else reflects light from the closest star. Can you believe that it is over 4.24 light-years to the nearest star? Did you know that about 65% of all “stars” are actually double stars? They are stars that look like one, but when viewed through a telescope, they are actually two stars. Stars vary in sizes. They can be as small as 7,000 miles in diameters, or as large as 900 billion miles in diameter. Some stars change in brightness over a period of time. They do this when the star’s temperature dramatically drops. These stars are called Variable Stars.

A star has many different characteristics, such as their position, motion, size, mass, chemical ingredients and temperature. No two stars are exactly alike. The number of stars in the known Universe exceeds one billion.

http://library.thinkquest.org/J002231F/Sun/factsaboutthesun.htm

Moon Facts

How did the moon form? Why do we always see only one side of it? Why does the lunar day last one Earth month? Scroll down for the answers—and other facts about our moon. • How did the moon form? According to the "giant impact" theory, the young Earth had no moon. At some point in Earth's early history, a rogue planet, larger than Mars, struck the Earth in a great, glancing blow. Instantly, most of the rogue body and a sizable chunk of Earth were vaporized. The cloud rose to above 13,700 miles (22,000 kilometers) altitude, where it condensed into innumerable solid particles that orbited the Earth as they aggregated into ever larger moon lets, which eventually combined to form the moon.

• By measuring the ages of lunar rocks, we know that the moon is about 4.6 billion years old, or about the same age as Earth.

• The distance between the Earth and its moon averages about 238,900 miles (384,000 kilometers). The diameter of the moon is 2,160 miles (3,476 kilometers). The moon's mass—the amount of material that makes up the moon—is about one-eightieth of the Earth's mass.

• Because the force of gravity at the surface of an object is the result of the object's mass and size, the surface gravity of the moon is only one-sixth that of the Earth. The force gravity exerts on a person determines the person's weight. Even though your mass would be the same on Earth and the moon, if you weigh 132 pounds (60 kilograms) on Earth, you would weigh about 22 pounds (10 kilograms) on the moon.

• The rotation of the moon—the time it takes to spin once around on its own axis—takes the same amount of time as the moon takes to complete one orbit of the Earth, about 27.3 days. This means the moon's rotation is synchronized in a way that causes the moon to show the same face to the Earth at all times. One hemisphere always faces us, while the other always faces away. The lunar far side (aka the dark side) has been photographed only from spacecraft.

• The shape of the moon appears to change in a repeating cycle when viewed from the Earth because the amount of illuminated moon we see varies, depending on the moon's position in relation to the Earth and the sun. We see the full moon when the sun is directly behind us, illuminating a full hemisphere of the moon when it is directly in front of us. The new moon, when the moon is darkened, occurs when the moon is almost directly between Earth and the sun—the sun's light illuminates only the far side of the moon (the side we can't see from Earth).

• The moon orbits the Earth at an average speed of 2,300 miles an hour (3,700 kilometers an hour).

• The moon's gravitational pull on the Earth is the main cause of the rise and fall of ocean tides. The moon's gravitational pull causes two bulges of water on the Earth's oceans—one where ocean waters face the moon and the pull is strongest and one where ocean waters face away from the moon and the pull is weakest. Both bulges cause high tides. These are high tides. As the Earth rotates, the bulges move around it, one always facing the moon, the other directly opposite. The combined forces of gravity, the Earth's rotation, and other factors usually cause two high tides and two low tides each day.

• The airless lunar surface bakes in the sun at up to 243 degrees Fahrenheit (117 degrees Celsius) for two weeks at a time (the lunar day lasts about a month). Then, for an equal period, the same spot is in the dark. The dark side cools to about -272 degrees Fahrenheit (-169 degrees Celsius).

• The rocks and soil brought back by Apollo missions are extremely dry; the moon has no indigenous water. However, the moon is bombarded by water-laden comets and meteoroids. Most of this water is lost to space, but some is trapped in permanently shadowed areas near both poles of the moon.

• To the unaided eye, the bright lunar highlands and the dark maria (Latin for "seas") make up the "man in the moon." A telescope shows that they consist of a great variety of round impact features—scars left by objects that struck the moon long ago. The largest scars are the impact basins, ranging up to about 1,500 miles (2,500 kilometers) across. The basins were flooded with lava some time after the titanic collisions that formed them. The dark lava flows are what the eye discerns as maria.

• On the moon there are no mountains like the Himalaya, produced by one tectonic plate bumping into another. There is no continental drift on the moon. Everywhere, the moon is sheathed by rocky rubble created by constant bombardment by meteoroids, asteroids, and comets. • No cheese has ever been found on the moon.

Adapted from the National Geographic Atlas of the World (Seventh Edition) and Exploring Your World: The Adventure of Geography, both published by the National Geographic Society.

From : http://news.nationalgeographic.com/news/2004/07/0714_040714_moonfacts.html