Category Archives: Chapter 9 – Stars and Galaxies

Asteroid, Comet and Meteors


Asteroids are made of rocky and/or iron-nickel material and most are found in an orbit between Mars and Jupiter. Most are pitted with impact craters and dust left from collisions with other objects in the solar system. A group of asteroids orbit the sun called Near-Earth Asteroids because they are somewhat close to the Earth and occasionally may cross Earth’s orbit.

Any asteroid falling from the sky would have a tremendous amount of energy. Here’s a typical example. In 2028, the asteroid 1997XF11 will come extremely close to Earth but will miss the planet. If something were to change and it did hit Earth, what you would have is a mile-wide asteroid striking the planet’s surface at about 30,000 mph. An asteroid that big traveling at that speed has the energy roughly equal to a 1 million megaton bomb. It’s very likely that an asteroid like this would wipe out most of the life on the planet.

There are obvious craters on Earth (and the moon) that show us a long history of large objects hitting the planet. The most famous asteroid ever is the one that hit Earth 65 million years ago. It’s thought that this asteroid threw so much moisture and dust in to the atmosphere that it cut off sunlight, lowering temperatures worldwide and causing the extinction of the dinosaurs.

The amount of dust and debris thrown up into the atmosphere would block out the sun and cause most living things on the planet to perish. If an asteroid that big were to land in the ocean, it would cause massive tidal waves hundreds of feet high that would completely scrub the coastlines in the vicinity.

In other words, if an asteroid strikes Earth, it will be a really, really bad day no matter how big it is. If the asteroid is a mile in diameter, it’s likely to wipe out life on the planet. Let’s hope that doesn’t happen anytime soon!


Comets are believed to be in long eliptical orbits that take them from beyond the orbit of Uranus to around the sun. These objects are found in the Kuiper Belt between Uranus and Neptune and the Oort Cloud from way out beyond Pluto.

The name “comet” comes from the Greek meaning “long-haired” because of their tails. Chinese astronomers record several observations as well. Comets throughout history have been thought to bring bad luck but these are just natural phenomena of the solar system.

The nucleus of a comet is like a ball of rock and dirty snow. As these objects get close to the sun the frozen gases and dust begin to heat and cause a long tail of vaporized gases, dust and debris to flow behind them. As it melts a cloud of gases and dust forms a coma. The head of the comet is the nucleus and coma together. Because of their orbits we can see them come back from time to time. Halley’s Comet appears about every 76 years, for example.


Meteors, known also as shooting stars, are usually sized from a grain of sand to about a softball. As the meteor enters the Earth’s atmosphere it becomes very hot due to friction like when you rub your hands together for a few moments. They become bright and seem to streak across the sky.

When the Earth enters a meteoroid stream left by a comet it produces a meteor shower. These showers can be predicted and come every year or so. They are named after the constellation that the meteors appear to be coming from.

These meteor showers can have over 100 meteors an hour and be quite spectacular. The best way to view these events are reclining or laying on the ground so you can see the whole sky without neck strain.

Meteors that survive the intense heat of friction with our atmosphere and hit the ground are called meteorites. Scientists have collected over 10,000 meteorites for study. These are made up of parts called Breccia, Carbonaceous Chondrites, Chondrites, and Chondrules.


The End Of The world ………Myth or reality????……

Nothing is forever…Like the death of a star that is really happened in times!!. …….it can also happen to the world…..still…..The reality is no one knows how its going to happen!!…so, lets be happy!!!


The Milky Way Galaxy……our home galaxy!!!!

The Milky Way Galaxy is a spiral galaxy. This type of galaxy has a center with arms of clustered stars spiraling out. The Milky Way Galaxy is estimated to have anywhere from 200 billion to 400 billion stars. If that does not give you an idea of how big it is, the Milky Way is roughly 100,000 light years in diameter. The Sun is far from the center of the Galaxy, halfway to the edge of the Galaxy along the Orion spiral arm. The Sun is revolving around the center of the Galaxy at a speed of half a million miles per hour, yet it will still take 200 million years for it to go around once.


Galaxies of the Universe


Space mysteries …………!!!!!



a) Spiral shaped galaxy

b) Elliptical Shaped galaxy

c) Irregular shaped galaxy


Death of stars in space

Several billion years after its life starts, a star will die. How the star dies, however, depends on what type of star it is. When the core runs out of hydrogen fuel, it will contract under the weight of gravity. However, some hydrogen fusion will occur in the upper layers. As the core contracts, it heats up. This heats the upper layers, causing them to expand. As the outer layers expand, the radius of the star will increase and it will become a red giant. The radius of the red giant sun will be just beyond the Earth’s orbit. At some point after this, the core will become hot enough to cause the helium to fuse into carbon. When the helium fuel runs out, the core will expand and cool. The upper layers will expand and eject material that will collect around the dying star to form a planetary nebula. Finally, the core will cool into a white dwarf and then eventually into a black dwarf. This entire process will take a few billion years.

When the core runs out of hydrogen, these stars fuse helium into carbon just like the Sun. However, after the helium is gone, their mass is enough to fuse carbon into heavier elements such as oxygen, neon, silicon, magnesium, sulfur and iron. Once the core has turned to iron, it can burn no longer. The star collapses by its own gravity and the iron core heats up. The core becomes so tightly packed that protons and electrons merge to form neutrons. In less than a second, the iron core, which is about the size of the Earth, shrinks to a neutron core with a radius of about 6 miles (10 kilometers). The outer layers of the star fall inward on the neutron core, thereby crushing it further. The core heats to billions of degrees and explodes (supernova), thereby releasing large amounts of energy and material into space. The shock wave from the supernova can initiate star formation in other interstellar clouds. The remains of the core can form a neutron star or a black hole depending upon the mass of the original star.


Characteristics of stars

A star is a massive ball of plasma that emits light throughout the universe. While there is only one star in our solar system, there are billions upon billions of stars throughout our galaxy and exponentially more in the billions of galaxies in the universe. A star can be defined by five basic characteristics: brightness, color, surface temperature, size and mass.

Two characteristics define brightness: luminosity and magnitude. Luminosity is the amount of light that a star radiates. The size of the star and its surface temperature determine its luminosity. Apparent magnitude of a star is its perceived brightness, factoring in size and distance, while absolute magnitude is its true brightness irrespective of its distance from earth.

A star’s color depends on its surface temperature. Cooler stars tend to be redder in color, while hotter stars have a bluer appearance. Stars in the mid ranges are white or yellow, such as our sun. Stars can also blend colors, such as red-orange stars or blue-white stars.

Surface Temperature
Astronomers measure a star’s temperature on the Kelvin scale. Zero degrees on the Kelvin scale is theoretically absolute and is equal to -273.15 degrees Celsius. The coolest, reddest stars are approximately 2,500 K, while the hottest stars can reach 50,000 K. Our sun is about 5,500 K.

Astronomers measure the size of a given star in terms of our own sun’s radius. Thus, a star that measure 1 solar radii would be the same size as our sun. The star Rigel, which is much larger than our sun, measures 78 solar radii. A star’s size, along with its surface temperature, will determine its luminosity.

A star’s mass is also measured in terms of our own sun, with 1 equal to the size of our sun. For instance, Rigel, which is much larger than our sun, has a mass of 3.5 solar masses. Two stars of a similar size may not necessarily have the same mass, as stars can vary greatly in density.


Black Holes, Neutron Stars, White Dwarfs, Space and Time


Life and death of stars


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