Our Solar System Dr. G. M. Ballabh The Sun THE SOLAR FAMILY Nine Planets? Many many satellites of the planets Many Comets and asteroids In short anything that goes about Sun is its member
The Rig-Veda describes the Sun as follows: This clearly indicates that our ancients have realized the importance of Sun much before the Vedic period. In the modern times Solar System studies have played an important role in our understanding of the physics of the diverse phenomena of the universe. It is the study of the motion of the planets which has laid the foundations of celestial mechanics. Sun being the nearest star it is possible to investigate, in greater detail, the complex processes occurring in its interior and surface which helps us to understand the phenomena in other stars. Studies of the solar system have acquired new importance over the past fifty years because of our exploration of planets and their satellites through space probes.
The Sun The Sun plays very important role in our lives, but for the Sun the life could not survive on Earth. It is also the nearest star. Hence its study not only helps in understanding its various effects on life but also helps in unraveling the mysteries of other stars. The Sun is a very big ball of mostly hydrogen gas (75%) and produces heat and light by nuclear fusion process. To produce the current rate of radiation the Sun converts 70,00,00,000 tons of hydrogen into Helium per second and in the process losses about 50,00,000 tons of mass per second. When observed in the white light it shows features like limb darkening, granulation and sun spots. In monochromatic lights (H-alfa, UV, x-ray etc.) we observe many other features like prominences, flares etc. The outer most atmosphere of the Sun called the corona can be seen only during a total solar eclipse. In order to study the interior of the Sun, techniques similar to seismology on Earth are used. This new branch of study is called helioseismology. Limb darkening: The visible disk of the Sun does not appear uniformly bright, with the radiation from the edge or limb being less intense than that from the center. The solar radiation reaching the observer from the solar centre comes in the vertical direction while from the limb it comes at a large angle to the vertical. Radiation moving in the vertical direction is more intense than radiation moving at an angle to the vertical and as a result, the edge of the disk appears darker than the center.
Granulation : A pattern of small cells seen on the surface of the Sun caused by the convective motions of the hot solar gas. Granules Sun spots : Dark areas having high magnetic fields and lower temperature than the surrounding photosphere. Show 11 year cycle of increasing and decreasing number of spots, called the solar sun spot cycle.
Sun s view in H-alfa wavelength : showing bright active regions Solar fountains (prominences : hot gases forming an arc over its surface)
Sun in X-Ray : showing active centres Solar corona seen at the time of a total solar eclipse. The shape is related to solar sun sopt cycle.
Helioseismology The Sun is found to oscillate (pulsate) every 5 minutes. These oscillations are caused by pressure waves which are generated by the turbulence in the convection zone, near the surface of the Sun. The study of the propagation of these pressure waves in the Sun is called Helioseismology. Certain frequencies are amplified by constructive interference. The acoustic oscillations are detectable on almost any time series of solar images, but are best observed by measuring the doppler shift of photospheric emission lines. Changes in the propagation of pressure waves through the Sun reveal inner structures and allows astrophysicists to develop extremely detailed profiles of the interior conditions of the Sun. Sun s motion through the zodiac. It traverses one sign in about a month. Other solar System Objects So far we have known nine planets from Mercury to Pluto. However after the discovery from 2002 AD onwards of more Pluto size planets lying beyond Pluto, a controversy arose as to which is the tenth planet, eleventh planet and so on. To settle this controversy, the International Astronomical Union (IAU) has adopted the following resolution on August 24, 2006. According to which all objects in the Solar System (other than the sun) have been divided into the following three distinct categories.
(1) Classical planets (2) Dwarf planets and (3) Small solar system bodies. The definition of each category is : (1) A classical planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) Has cleared the neighbourhood around its orbit. (2) A dwarf planet is celestial body that : (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. (3) All other objects orbiting the Sun shall be referred to collectively as Small Solar System Bodies. Resolution about Pluto : Pluto is a dwarf planet by the above definition and is recognized as a prototype of a new category of trans- Neptunian objects. This category is to be called plutonian objects. (1) Classical planets. They are now eight in number. Mercury : has no atmosphere, shows craters, the most interesting thing is that it has spin-orbit synchronization ( 2 revolutions = 3 rotations ). Being closer to Sun it is difficult to observe. Fafourable time to observe it when it reaches its maximum elongation (angular separation) from the Sun. Has very small magnetic field. Venus : has very thick atmosphere and hence its surface features are not visible. Has no magnetic field, shows phases like Moon, which were first observed by Galileo. Copernicus used the data to develop heliocentric theory.
Mercury Venus Phases of Venus
Earth : Most important of all planets as it supports the existence of life which so far has not been found anywhere else. Sun and its various activities have great influence on Earth s environment. The tree rings have been found to be in phase with 11 year sun spot cycle. Auroral lights, produced by charged particles from the sun, and the midnight Sun are seen at high latitudes. Auroral light The midnight sun
Nature of Life Living organisms are distinguished from inorganic matter by the following properties: (i) They have a life cycle of birth, growth and death. (ii) During the course of living, they undergo the process of metabolism, i.e. taking in nutrition in the form of food, digesting and converting it into energy and eliminating the waste products. (iii) They respond to stimuli through sense organs, are controlled by the brain and the central nervous system. (iv) They undergo reproduction On the basis of this, vegetation, bacteria, animals and human beings are living, while matter and energy are non-living. Coditions for life Congenial temp. : Organic compounds are efficient in a limited temp. range of 10-40 deg. Cent. In extreme conditions they can survive temp. between -10 to 100 deg. Cent. Atmosphere: Most organisms require oxygen for producing energy by burning the food consumed by them.hoever there are some bacteria which can survive without oxygen. In fact it is known that there was no oxygen in the Earth s atmos. when life originated. Water: Water is absolute necessary for existance of life as it a universal solvent for organic compounds of life as well as the material of food. So far these conditions are met only on the Earth and hence we have life only here. However there is a possibility of similar conditions to be there on some exoplanets (planets around other stars) Moon : is a natural satellite of Earth. Apart from being a beautiful sight at night and inspirer of poets, Moon along with the Sun help us to keep time. In the Indian calendar a complete cycle of Moon s phases (new moon to new moon or full moon to full moon) constitutes a month, while a complete circle of the zodiac by the Sun constitutes a year. The length of twelve lunar months is 12 x 29.5306=354.3672 days, while one sidereal year is 365.2564 days. This results in a difference of 10.8892 days in a year, which will become equal to one lunar month in about 2.7 years or in about 32 months. Hence an extra month is added at about every two and half year s interval to keep the two measures in phase.
The Moon : showing craters and maria Mars : also known as a red planet because of its reddish appearance. It has been explored by many space probes. So far no life form has been detected.
Mars Probe Jupiter, Saturn, Uranus and Neptune are gaseous planets and have rings of icy particles around them. However these rings are not visible through the telescope except for the Saturn. Jupiter : bands and red spot Jupiter s four large moon s
Saturn : rings can be seen even through a small telescope Detail structure of Saturn s rings which are made of icy rocks, some as small as dust particles.
Uranus rotates on its side. The ring around Uranus was found by Vainu Bapu,J C Bhattacharya and Kuppusamy from India Uranus Neptune (2) Dwarf planets With the new definition of planets Pluto has come under the category of Dwarf Planets. Also the newly discovered objects of the sizes comparable to Pluto like Sedna etc. come under this category. ( Pluto : dia. 2300 km, P: 248 yrs, Minor Planet catalogue No. 134340) Newly discovered Plutonians Quaoar : June, 2002, dia. 1250 km, 42 AU, p: 266 yrs, a KBO Sedna : March, 2004, dia. 1770 km, 86 AU, P: 780 yrs, (Oort cloud?) Xena (2003 UB313) : Oct. 2003, dia. 2400 km, 67 AU, P:560 yrs, a KBO Eris (Goddess in Greek Mythology) ; Satellite: Dysnomia (Daughter of Eris) 2003 EL61 : dia. 1750, 44 AU, P: 285 yrs, a KBO Orcus (2004 DW) : dia. 1600 km, 2005 FY9 : dia. 1750 km, 46 AU, P: 307 yrs, a KBO (KBO is Kuiper Belt Object : a ring of icy debris beyond Neptune)
(3) Small Solar System Objects Asteroids and comets come under this category. Asteroid are the small objects which form a belt between Mars and Jupiter. These are rocks of different sizes and irregular shape which fly through their domain. Comets are visitors from outer regions of the solar system. When near the Sun they get heated up and develop a tail of evaporated dust and gas. They are made up of what is called dirty ice. Small particles left by comet tails are attracted by the Earth and when they enter the earths atmosphere they get heated and burn out. These appear as shooting stars or meteors. Space probes are planned to study the cometary material in detail as it is thought that the comets have the clue for the origin of life on Earth.