The motions of the earth and the moon are used to measure the time. Motions of Earth. But months are related to moon s motion around the earth.

Transcription

1 [Std 4 Geo Notes] [Ch-1] [Measurement of Time] The motions of the earth and the moon are used to measure the time. Motions of Earth Diurnal motion: The rotation of the earth around itself is called the diurnal motion. The time taken is called a day. Annual motion: The revolution of the earth around the sun is annual motion. The time taken is called a year. But months are related to moon s motion around the earth. One Day One Year One Month Earth's Rotation around itself Earth's Diurnal Motion Earth's Revolution around Sun Earth's Annual Motion Moon's Revolution around Earth 1 Mahaedutechnet.org

2 [Std 4 Geo Notes] [Ch-1] The Moon [Measurement of Time] Moon is a satellite of the earth. It revolves around the earth at the same time it also rotates around itself. Time taken by moon to rotate around itself is almost same as that taken by it to revolve around the earth. Hence only a specific part of the moon is seen from the earth. Phases of the moon 2 Mahaedutechnet.org

3 [Std 4 Geo Notes] [Ch-1] [Measurement of Time] Part of the moon which faces the sun gets illuminated, The moon revolves around the earth, As a result the position of the moon and its shape as observed from the earth keeps on changing. The changes seen in the shapes of the illuminated portion of the moon are called the phases of the moon. Phases of Moon Full Moon New Moon When the illuminated portion of the moon appears as a full circle, it is called a full moon and the night is called as full moon night. When the illuminated portion of the moon remains totally invisible to us,it is called a new moon and the night is called new moon night. 3 Mahaedutechnet.org

4 [Std 4 Geo Notes] [Ch-1] [Measurement of Time] Waxing: The visible part of the moon keeps on increasing from the new moon day to the full moon day. It is called as waxing. Waning: The visible part of the moon keeps on reducing from the full moon day to the new moon day. This is called as waning. Month: The time taken by the moon to complete one revolution around the earth is called a month. It extends from one new moon to the next. Fortnight: A month is divided into two halves, each half comprising of 15 days. These halves (periods) are called as Fortnights. Week : It is not related to the motion of the moon or the earth. It is comprised of seven days. 4 Mahaedutechnet.org

5 [Std 4 Geo Notes] [Ch-1] [Measurement of Time] Different types of time measurements Lunar time measurement Solar time measurement Luni - solar time measurement Only the motion of the moon is used. Only the motion of the earth around the sun is used. In this system, for measuring the year, the earth s annual motion is used. 12 lunar months It has 12 months While for measuring the month, the moon's motion around the earth is used. The months have 29 or 30 days It has approximately 365 days in a year. Hindu calendars are luni-solar. It has 355days in a year Islamic calendar is based on the lunar time measurement. The Gregorian(January to December) calendar and the Indian national calendar arebased on Solar time measurement. For uniformity,the Indian national calendar is designed by the Government of India. The year starts from 22 nd march. The names of the months are same as that of the Hindu calendar. In this calendar the five months from Vaishakh to Bhadra have 31 days and rest have 30 days. 5 Mahaedutechnet.org

6 [Std 4 Geo Notes] [Ch-1] [Measurement of Time] Leap year 365 days and 6 hours is the time taken by the earth to complete its revolution around the sun. There is a difference of 6 hours in the measurement of each year. Hence to make up for this difference, every fourth year, the year is considered to be of 366 days. And such a year is called a Leap year. A year is a leap year if that number is completely divisible by 4. In Gregorian calendar, in the Leap year,the month of February has 29 day instead 28 days In the Indian national calendar, in a leap year, the year starts on 21 march instead of 22 nd March. And the month of Chaitra has 31 day instead of 30 days. THE SEASONS ARE RELATED TO THE ANNUAL MOTION OF THE EARTH. SO IN SOLAR AND LUNISOLAR CALENDAR, FESTIVALS FALL IN SPECIFIC SEASONS. & IN LUNAR CALENDAR FESTIVALS DO NOT RELATE TO SEASONS. 6 Mahaedutechnet.org

7 [Std 4 Geo Notes] [Ch-2] [Earth s Spheres] On the earth we find land,water,air and living organisms, forming separately four different spheres of the earth. Lithosphere Hydrosphere Atmosphere Biosphere The land and a portion below it Area occupied by water The cover of air around the earth All the living organisms found in these spheres on the earth Mountains, plateaus,plains, different types of rocks Oceans, Seas, Lakes, reservoirs,rivers, etc. Various gases,water vapour, and dust particles Plants, animals, birds, Micro-organisms The portion of the earth up to the depth of about 100 km from the land surface is called the Lithosphere. Land is composed of different types of rocks. Rock is a mixture of various minerals and is classified on the basis of how it is formed. Igneous Metamorphic Types of Rocks Sedimentary 1 Mahaedutechnet.org

8 [Std 4 Geo Notes] [Ch-2] [Earth s Spheres] Continents:- Extensive and continuous portions of land There are seven continents on the earth There are oceans between these continents Australia Antarctica North America Africa Seven Continents South America Europe Asia 2 Mahaedutechnet.org

9 [Std 4 Geo Notes] [Ch-2] [Earth s Spheres] Oceans are the largest storages of water. Oceans All the oceans are connected and hence continuous. Extensive and huge storages of salty water There are four oceans The Pacific Atlantic Indian Arctic Salt water bodies smaller than ocean. Seas Most seas are part of oceans Arabian sea - part of the Indian ocean Enclosed seas:- The seas not connected to oceans but totally or largely enclosed by land Caspian sea, the Mediterranean sea,etc 3 Mahaedutechnet.org

10 [Std 4 Geo Notes] [Ch-2] [Earth s Spheres] Bays Salt water storages having land on three sides. Smaller than seas. E.g. The Bay of Bengal Gulf: Narrow portion of sea or ocean projecting into land. e.g.- the Gulf of Khambhat. Strait A narrow water body that joins two seas. E.g.Palk Strait - joining the Bay of Bengal and the Arabian Sea. Atmosphere It is the cover of air around the earth. Consists of various gases,water vapour, and dust particles. Close to the earth s surface, the air is dense and becomes thin as we go higher. With height, the temperature of the air changes. from the atmosphere, we get oxygen which is necessary for all living bodies to live. Ozone gas which is at high altitude, protects the living world from the harmful rays of the sun, by not allowing them to reach the earth. 4 Mahaedutechnet.org

11 [Std 4 Geo Notes] [Ch-2] [Earth s Spheres] Biosphere: Life forms like plants, animals, birds, micro-organisms which are found in the lithosphere, hydrosphere, and atmosphere are called biosphere. Plants,animals and micro-organisms are the major components of the biosphere. Proper quantities of oxygen, heat, water, and food are the important things on which the living world thrives. Closer to the earths surface,number of living bodies are quite large. Biosphere is found under the ground and in the water bodies up to a certain depth. In the atmosphere, up to the altitude to which oxygen is available, the biosphere exists. Growing industrialization Hunting of wildlife by man Unnecessary cutting of forests Factors causing major changes in all spheres of the earth Growing number of vehicles 5 Mahaedutechnet.org

12 [Std 4 Geo Notes] [Ch-3] [Natural Environment] The natural environment is formed by the natural conditions that surround and affect the living world on the earth The lithosphere, the hydrosphere, the atmosphere and the biosphere, all these four spheres are a part of the natural environment. Components of Natural Environment are classified in two groups All living things called Biotic Factors All non-living things called Abiotic Factors Human beings, animals,birds, plants, insects, micro-organisms,etc. Air,water,sunlight, clouds, hills,etc. 1 Mahaedutechnet.org

13 [Std 4 Geo Notes] [Ch-3] [Natural Environment] The biotic and abiotic factors depend on one onether. And through this dependency the cohesion in the nature is maintained. Usefulness of abiotic factors to biotic factors Air:-Oxygen for respiration Air:-Plants make food using carbon dioxide Water:- For drinking,etc. Formation of abiotic factors from biotic factors excreta of living things Remains of plants, animals,etc decompose and mixi n the soil,etc. Examples of biotic factors:- Examples of abiotic factors:- all living things Tiger,cow,lion,fox,butterfly,earthworm, tree,grass,dog,farmer,fish,lion,elephant, duck,snake,ant,crow,amoeba,etc. All non-living things Water,hills,river,air,cloud,sunlight,kite, road,factory,bus,car,house,cycle,purse, steemer,bullock-cart,lantern,etc. 2 Mahaedutechnet.org

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