Category Astronomy

The rings around Saturn were first identified by astronomer Galileo Galilei in 1610. It was, however, Dutch Physicist Christian Huygens, who in 1659, recognized them as a broad, flat, thin ring, separated from the body of the plant.

In 1675, the Italian Astronomer G.D. Cassini identified two rings around it. Until 1969, it was believed that there were just three rings around Saturn “A”, “B”, and “C” and 151; “A” being the outermost and “C”, close to the planet. In 1969, the fourth ring was discovered by Pierre Guoria and soon, another one was also identified.

Pioneer satellite Data (1971) had indicated that was one more ring (“F”). French Astronomer, Edourd Albert Roche in 1849 postulated that the rings were the remnants of satellite that strayed too close to Saturn and due to which reason, disintegrated. His theory was that, if a satellite approaches, it’s primary, closer than a certain distance (known as “Roche Limit’ & 151; 2.44 times the radius of the planet), the satellite would break up and the broken pieces would gradually get distributed around the planet in a circular path.

The distances of the rings of Saturn are within the “Roche limit”. This would suggest that the rings are the remnants of a disintegrated satellite only.

The present thinking is that the rings are made up of countless small objects (varying in size from very small grains to small chunks of rocky material, covered by ice) and that each revolves around Saturn in its own orbit like a satellite.

That the rings contain particulate matter has been confirmed by  the fact that Rings “A” and “C” exhibit certain transparency due to which, the body of Saturn could he seen through them, as also the light from the stars.

 Furthermore, the satellites of Saturn are not completely eclipsed too, when they pass into the shadow of the rings. Very little information is available as to the precise composition of the matter in the rings. As per the observations of C.P. Kupier (1952), the Infra Red Spectrum is similar to the reflection spectrum of hoar-frost.

It is quite likely that these particles must have been of much bigger size earlier (even some metres in diameter), but these might have been a continuous reduction in their sizes due to their abrasion with objects like the meteoroids. Scientists are of the view that the continuous erosion may ultimately (at a far distant future) result in the rings slowly vanishing forever!

 

 

 

 

 

 

 

 

 

 

The overall appearance of the Moon is bright ash grey caused by the dark and bright barren rocky land, where there is no atmosphere. When viewed in a naked eye or through a telescope, there are vast basins called seas, which were filled with molten lava millions of years ago. These are the low land plains appearing dark or dusky for the naked eyes. During the final ending phase of volcanism on the Moon, numerous crators had liberated enormous quantity of glowing gases and mineral vapours through their vents, which had blown in all directions over the surface, depositing the mineral condensates in the form of micron-size glassy spherules, tear drops and other powdery forms.

The Lunar surface is full of these bright rays like deposits, which scatter-reflect the sunlight quite effectively giving it a bright appearance on surface. The combined effect of rocks and soil along with the crators and minerals like calcium, aluminum and titanium therefore give a silvery appearance to the naked eye.

 

 

 

 

 

 

 

 

 

The Moon revolves around the Earth in a period of about 27 days; it also rotates once on its axis in the same time and so it always keeps the same face towards the Earth. This phenomenon is known as captured rotation.

Inspite of the fact that the Moon’s axial rotation is equal to its period of revolution round the Earth, we can actually examine more than the half of the total surface. The reason is that Moon travels round the Earth in an ellipse, not in a circle since it takes elliptical path, the rate of axial spin remains constant, whereas orbital velocity changes and moves fastest when closest to us.

We can thus see a little round alternate edges of the Moon. Also, the lunar orbit is tilted with reference to ours, so that the Moon is sometimes north and sometimes south of the mean plane, enabling us see some way beyond alternate poles. These minor shifts, known as Librations, allow us to examine four-sevenths of the total surface. The remaining three-sevenths of the Moon is permanently hidden from our inquiring eyes.

The time taken for the moon to turn on its axis once and the time taken for it to revolve once around the earth are the same. Hence the moon shows us the same face every night. This is called synchronisis rotation or captured rotation. 

 

 

 

 

 

The angular diameter of the sun and moon is about half a degree each. The celestial objects are seen with two eyes (binocular vision). When we observe the horizon, the terrestrial surface with all its objects, such as tree, houses, roads or ground give us a perspective view (geometrical phenomenon), i.e., farther the objects smaller they appear, as they subtend smaller and smaller angles at the retina.  Through this long distance perspective, which some time extends to several kilometres, our vision is able to realize a long perceptual distance. At the end of this perspective we locate the celestial objects and realize a particular size.

On the other hand, when we view these objects in the sky, the most important perspective is absent and consequently the two eyes are left with their own power to discern a distance. This binocular distance limit in the absence of the perspective has been found to be about 500 feet, which vary slightly from person to person. This can be checked by the absence of parallax shifts of objects beyond the distance when we view with alternate eyes. Therefore the sun and moon are located at short distance. Naturally a half degree object located at a distance of about 500 feet must appear much smaller  than  a similar half degree object at a considerably long, perceptual distance realized by the sense of vision with the help of perspective.

 In order to illustrate this phenomenon, we place a large ball at a distance from the eye and a much smaller ball closer to the eye in order that the smaller one just covers the angular dimension of the larger ball. Now both the balls subtend the same angle at the eye, but to our binocular vision the larger ball at that distance appears decidedly larger and it is physically larger. Through a telescope or a camera, the sun and moon appear of the same sizes either at the horizon or over the high sky. This view also applies to star constellations at the horizon and at the high sky. Monocular vision by one-eyed people has no illusion of this nature, because they have no perceptual depth.