The Andromeda Galaxy

The Andromeda Galaxy ( also known as Messier 31, M31, or

NGC 224; is a spiral galaxy approximately 2.5 million light-years 

^{in the constellation Andromeda. It is the nearest spiral galaxy to our}

^{own, the Milky Way. As it is visible as a faint smudge on a moonless}

^{night, it is the farthest object visible to the naked eye, and can be seen}

^{with binoculars even in urban areas.}

Andromeda is the largest galaxy of the Local Group, which consists of  the  Andromeda Galaxy, the Milky Way Galaxy, the Triangulum Galaxy, and about 30 other smaller galaxies with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. Although the largest, it may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping. In physics and cosmology, dark matter is matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxies, as well as Big Bang cosmology, dark matter accounts for the vast majority of mass in the observable universe .

Recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion (10^{12) stars, greatly exceeding the number of stars in our own galaxy. 2006 estimates put the mass of the Milky Way to be 80% of the mass of Andromeda, which is estimated to be 7.1×1011 solar masses.}

The earliest recorded observation of the Andromeda Galaxy was in 964 CE by the Persian astronomer, Abd al-Rahman al-Sufi (Azophi), who described it as a “small cloud” in his Book of Fixed Stars. Other star charts of that period have it labeled as the Little Cloud. The first description of the object based on telescopic observation was given by Simon Marius in 1612. Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi’s earlier work. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of the M31. He believed it to be the nearest of all the “great nebulae” and, based on the color and magnitude of the nebula, he estimated (incorrectly) that it was no more than 2,000 times the distance of Sirius, the brightest star in the night sky.

The first photographs of M31 were taken in 1887 by Isaac Roberts from his private observatory in Sussex. The long-duration exposure allowed the spiral structure of the galaxy to be seen for the first time. However, at the time this object was commonly believed to be a nebula within our galaxy, and Roberts mistakenly believed that M31 and similar spiral nebulae were actually solar systems being formed, with the satellites nascent planets. In 1917, Heber Curtis had observed a nova within M31. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our Galaxy. As a result he was able to come up with a distance estimate of 500,000 light-years.

In 1920 the Great Debate between Harlow Shapley and Heber Curtis took place, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that “Great Andromeda Nebula” (M31) was an external galaxy, Curtis also noted the appearance of dark lanes resembling the dust clouds in our own Galaxy. Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of M31. These were made using a 2.5 metre (100 in) reflecting telescope, and they enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our Galaxy, but an entirely separate galaxy located a significant distance from our own. In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy and The first radio maps of the Andromeda Galaxy were made in the 1950s by John Baldwin and collaborators at the Cambridge Radio Astronomy Group.

The Andromeda Galaxy is approaching the Sun at about 300 kilometers per second (186 miles/sec.). Given the motion of the Solar System inside the Milky Way, one finds that the Andromeda Galaxy and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec.). The impact is predicted to occur in about 2.5 billion years. In that case the two galaxies will likely merge to form a giant elliptical galaxy. However, Andromeda’s tangential velocity with respect to the Milky Way is only known to within about a factor of two, which creates uncertainty about the details of when the collision will take place and how it will proceed. Such events are frequent among the galaxies in galaxy groups as already scientists have found evidences of such massive collisions between galaxies in the far reaches of space.

In the great expanse of the Universe, full of mysteries and new discoveries, the discovery of our neighbouring galaxy Andromeda has indeed increased our understanding of the biggest mystery surrounding the lives of each and every indidvidual living on planet Earth. With improved technology, stronger telescopes and newer techniques, off late scientisits have been able to find remarkable facts about the Universe and as long as human life flourishes on Earth, the quest for revealing the truth will continue.

Lunar Eclipse

One of the most fascinating celestial objects which have encouraged onlookers for thousands of years is the Moon. It is the largest solar body visible to the naked eye in the night sky and it light ups the dark nights for many travelers who have lost their way. And its most fascinating feature gives a stunning picture for Earthlings to observe.

Lunar eclipse occurs when Moon comes in the shadow of the Earth, this event can occur only when Moon, Earth and Sun are exactly aligned. With Earth in the middle, it fully or partially blocks the way of sunlight reaching the Moon, hence, some portion of the Moon appears to be brownish-red. As during a lunar eclipse, all the three celestial bodies are almost exactly aligned so there is always full moon visible in the sky.

The earth’s shadow is mainly divided into two parts; Umbra and Penumbra. Umbra is the darkest part of Earth’s shadow completely concealing the source of light, while Penumbra is the region in which the light emitting body is partially obscured. When only a portion of the Moon enters Earth’s Umbra, a partial lunar eclipse occurs; whereas a total lunar eclipse occurs when Moon completely enters the Umbra.

Penumbral eclipse occurs when Moon passes through Earth’s Penumbra resulting in an unnoticeable darkening of the Moon, but total Penumbral eclipse, a special type of Penumbral eclipse, occurs when the Moon lies exclusively in the Penumbra. This rare eclipse is more noticeable than the more common eclipses.

 

Another amazing and rare spectacle occurs when the lunar eclipse and the Sun are both visible at the same time, known as Selenelion or Selenehelion. It occurs when the sun is rising or setting and the Sun and Moon can be seen on opposite sides of the horizon. Such an astounding setting is very uncommon while a normal lunar eclipse occurs at least every two years. From ancient times Moon has aroused curiosity of man and continues to help us not only to get more knowledge about the Universe but when ever we look up at the night sky we marvel at this masterwork of nature.

The Moon

Everyday when we look upwards at the night sky we see this celestial body known as the “Moon”, which is a Germanic word derived from the Latin word “Mensis”. It is the only natural satellite that Earth has and is the fifth largest in the whole Solar System. From ancient times man has had fascination with this solar body hanging over their heads in darkness emitting light. Some started worshipping it, while others started using it to measure time, but no civilization in human history has overlooked it.

 

The Moon, according to some scientists was at one time part of the Earth’s mass and formed after a huge body roughly the size of a planet collided with the Earth, ever since Moon has been revolving around Earth in an orbit. The Moon completes an orbit around the Earth every 27.3 days. The Moon’s diameter is about quarter of the earth which means that Moon’s volume is about 2 percent that of Earth and the pull of gravity is about 17 percent that of Earth. Although we look at the Moon almost every night yet few have noticed that we always look at the same side it, with a lot of craters and scars, (some even see a face of a man in it).The reason is that the Moon is revolving around its axis almost the same speed as the Earth spins so we are unable to see the other side of the Moon, often referred to as the “Dark side” of the Moon, but as a matter of fact “Dark side” of the Moon is also illuminated by the Sun. The far side of the Moon was first photographed by Soviet Union probe Luna 3 in 1959. As opposed to the side that we see the, other side is far smoother and without craters and scars.

 

The surface of the Moon is full of Impact Craters, a result of collisions with asteroids and comets, about a half a million of these craters can be found on its surface. Unlike the Earth, Moon has no atmosphere and therefore these craters have been well preserved in comparison with craters on Earth. Moon also has the distinction of containing one of the largest known craters in the Solar System, known as the “South Pole-Aitken Basin”, which is roughly 2240 km in diameter and about 13 km in depth.

 

Moon seemingly a dead solar body orbiting Earth also affects earth in many ways. It is believed by scientists that Moon has played a vital part in forming the right atmosphere and environment for life to exist and flourish on the Earth. Because of the gravitational pull of the Moon the cycle of seasons has remained stable on Earth. A big impact that Moon has on Earth’s oceans can be seen even with the naked eye. High and low tides occur on the seas due to the gravitational pull of the Moon, resulting in cyclic rise and fall in ocean’s surface. Many people believe that sometimes the Moon seems to be bigger in size when it is close to the horizon, but this is nothing but an optical illusion. A theory known as the “Relative Size Hypothesis” states that the size of an object not only depends upon its retinal size but also on the size of objects close to it. Thus, as we have the facility to compare the Moon with buildings and structures when it is on the horizon, it seems bigger.

 

The Moon

Although Moon may create an illusion to us about its size but there is most definitely no illusion when we see the color of the Moon changing to reddish brown, a phenomenon known as the Lunar Eclipse. It is widely known that the light of the Sun is reflected from Moon but when Earth comes in the path of sunrays reaching the Moon, lunar eclipse occurs. This can occur only when the Sun, The Earth and the Moon are aligned exactly with Earth in the middle, hence there will always be a full moon the night of the lunar eclipse.

 

 

Latest reports suggest that the Moon is slowly moving away from the Earth as it continues to move in its orbit. This development has been followed by scientists by many years and the distance between the two is increasing. Scientists say that as the Moon is moving farther out in the space, a time will come when it will liberate it self from the Earth’s orbit and will be thrown into the space. Without the Moon there will be utter chaos on Earth as the continuous cycle of seasons will be disrupted. But this is no fact over which we should lose our sleep because although the Moon is moving away from Earth but it is happening at a very slow rate and it may take millions of years before earth loses its only natural satellite.

 

On 20 July, 1969 the Apollo 11 Mission commanded by Neil Armstrong reached the surface of the Moon. Neil Armstrong accompanied by Edwin Aldrin landed on the Moon; this was one of the biggest achievements in scientific history and one of the most significant events in the history of mankind. Armstrong and Aldrin spent a day on the surface of the Moon before returning to Earth. An estimated 500 million people worldwide watched this event live, the largest television audience for a live broadcast at that time.

 

Scientists so far have not been able to find any traces of Extra Terrestrial life on the Moon as samples from the moon showed no indications of presence of water. But the scientists have continued the quest for new Stars, Planets, Galaxies and above all the traces for life outside Earth in the vast Universe. The Moon has not only helped us understand the mysteries of the Universe but its presence has helped life on Earth to survive and in this lonely place called the Universe it has accompanied us for quite some time and will continue to do so.