This site is to help you answer most of the questions about the infinite universe, here you will find information on nebulas, planets and many more. So hope you all can find what you wish to find in this website.
The Big Bang Theory -how the universe was formed
The word 'nebula' is from the days of old days when Latin
was the principal language in the western world, and is also used to define
most scientific phenomena and species, etc. In Latin, the word nebula means
"a cloud, or a mist, or a vapor". Nebulae is just the plural (more
than one) of nebula. In ancient times, before the invention of the telescope,
people would look up at the night skies and see various areas of the sky that
instead of having a star or several stars close together, they would instead
see a small faint glow or 'mist' with the naked eye. So, not being able to determine
what they were seeing, to them it looked like a cloud, a mist or a vapor. So
these objects were then called nebulae. Again, this was well before the invention
of the telescope.
1) Reflection Nebulae
(2) Emission Nebulae
(3) Dark Nebulae
(4) Planetary Nebulae
(5) Supernova Remnant
These are the 5 different types nebulas. Each of these types is covered below, just scroll over the image to see information about that nebula type.
Reflection Nebulae -This is one example of a reflection nebula. This is named
the Merope (mer-o-pe) Nebula in the constellation Taurus. It is found among
the beautiful star cluster named 'The Pleiades' (plea-ah-dees). This star cluster
is also known as M45 (Messier Object 45), and as 'The Seven Sisters'.
The dust and gas of this nebula does not emit its own light. It only REFLECTS the light from the nearby star or stars; in this case, from the star Merope. Under very dark skies, with an optically corrected moderate sized amateur style telescope, you can detect this reflection nebula, as well as additional reflection nebulae regions within the Pleiades cluster. To detect even a faint bluish hue though is quite a task, requiring larger telescopes, and fine optics. Other nebulae will, if at all, show different hues. Reflection nebulae abound in the night sky, and many that are found in concert with Emission Nebulae, next on our tour of Nebulae.
Emission Nebulae - Here is an example of an emission nebula. This is the Rosette
Nebula in the constellation Monoceros (mo-nos-er-os). The nebula surrounds a
young star cluster. This nebula is emitting its own light, due to the presence
of ultraviolet radiation from the very hot young stars that make up the cluster.
This radiation, although not visible to the eye, is strong enough to 'excite'
the atoms in the interstellar dust and gas so that they 'jump' to different
energy levels and emit their own form of radiation which can be seen in the
nebula's light spectrum. It is not simply reflecting the light from the cluster.
Emission nebulae can be found in many areas of the night sky, the most famous
being the Orion Nebula. In astronomical terms, these type of nebulae are also
referred to as H II regions (H two). This is because of the hydrogen atoms having
been ionized - gaining or losing its single electron due to the strong ultraviolet
radiation from a star or stars.
3. Dark Nebulae - Some of the most difficult, but spectacular objects to be seen at night are dark nebulae. The image to the left is called the 'Horsehead Nebula' and is located in the constellation of Orion. But believe me, you will probably never see this good of a view through a telescope. It is often an extremely difficult object to view, because the background is just barely lighter than the foreground object. Dark nebulae are clouds of gas and dust that absorbs some light from behind them. The light that is absorbed heats up the dust particles, and thus these particles re-radiate, or emit, some of the absorbed energy as infrared light (Infrared light is on the opposite side of the light spectrum from ultraviolet). Some of the background light is also scattered into the surrounding interstellar medium and thus can reduce the contrast between background and foreground, making viewing them even more difficult.
Planetary Nebulae - Using the Hubble Space Telescope to obtain visual and other
spectral data, our knowledge of the 1000+ known PN's has increased immensely.
The image shown is of the PN known as the 'Eskimo Nebula', and sometimes as
the 'Clownface Nebula'. It is in the constellation Gemini. This is just one
example of many forms that PN's take while expelling their outer layers of gas.
PN's are formed when old stars of a particular size, similar to our Sun's size, have consumed most of their hydrogen fuel after billions of years. The hydrogen has mostly been converted to helium, and the star has expanded to become a Red Giant. The star does not so much explode as much as it ejects the gases at much lower speeds and at different times. As the star evolves, the central core of the star evolves into a White Dwarf, a very hot star. The very high temperature radiation causes the ejected gases to become ionized and glow.
5. Supernova Remnant -When a star goes supernova, it is a violent and catastrophic event that more often than not outshines the parent galaxy's total light output. Stars in external galaxies that have been witnessed as supernovas have been measured to exceed the Sun's brightness by a billion times. The nebula pictured here is the remains of a star that went SN in the year 1054A.D., as witnessed on Earth. It was so bright, it was visible during the daytime for several weeks. This is the Crab Nebula, also known as M1 in Taurus. It is estimated to be at a distance of 6,500 light years. The speed of light is approximately 300,000 kilometers per second or 186,000 miles per second. It is believed that the most powerful SN's occur due to a companion star's mass being gravitationally drawn to a white dwarf star. When the dwarf's mass exceeds a certain value, it undergoes rapid Carbon burning and explodes, immediately ejecting the equivalent of 1 solar mass (The Sun's mass).
Pictures and information courtesy of www.blackskies.com , nasa.gov, http://archive.ncsa.uiuc.edu, http://oposite.stsci.edu