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GS Paper: GS1-15.Geographical features and their location- Changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

  • Africa’s splitting plates could give birth to a new Ocean: Study

    africa

    Central idea

    • Scientists predict a new ocean will be created as Africa splits into two separate parts connected to the East African Rift
    • This geological process will inevitably divide the continent resulting in new coastlines and sub-sea internet infrastructure but also will have significant repercussions

    What is Rifting?

    • The Earth’s lithosphere, comprising the crust and upper part of the mantle, is divided into tectonic plates that move in relation to each other at varying speeds.
    • Tectonic forces move the plates and can cause them to rupture, resulting in the formation of a rift and potentially leading to the creation of new plate boundaries.
    • Rifting refers to the geological process in which a single tectonic plate is split into two or more plates separated by divergent plate boundaries.
    • In the present day, the gradual separation of the Somali and Nubian tectonic plates is leading to the formation of a rift that could eventually lead to the creation of a new ocean basin.
    • The movement of tectonic plates is a fascinating geological phenomenon.

    Rifting in African Continent

    • The African continent is located on the African Plate, which is one of the Earth’s major tectonic plates.
    • The continent is characterized by a number of geological features, including rift valleys.

    Most profound feature: The East African Rift System

    • The East African Rift System is the most prominent example of rifting in Africa.
    • It stretches for over 6,000 kilometers from the Red Sea in the north to the Zambezi River in the south.
    • The rift system includes a series of interconnected rift valleys, volcanoes, and lakes.

    Causes of the East African Rift System

    • The rift system is caused by the movement of the African Plate away from the Arabian Plate and the Somalian Plate.
    • This movement creates tension in the Earth’s crust, causing it to pull apart and form a rift.

    Impact: Lakes Formed by Rifting

    • Over time, the rifting process has led to the formation of several large lakes in the region.
    • These lakes include Lake Victoria, Lake Tanganyika, and Lake Malawi.
    • They are believed to have formed as a result of the sinking of the land between the rift valleys.

    Future of Rifting in Africa

    • The rifting process is ongoing and may eventually lead to the splitting of the African continent into two or more separate land masses.
    • However, this process is expected to take millions of years and is not likely to have a significant impact on human populations in the near future.
    • The necessary evacuation of people and potential loss of lives will be an unfortunate cost of this natural phenomenon.
    • The emergence of new coastlines will unlock opportunities for economic growth
    • As the plates continue to split in the future, this phenomenon will result in the displacement of communities, settlements, and various flora and fauna.

    Conclusion

    • The movement of tectonic plates has significant implications for the continent’s future.
    • It is important to study and monitor these changes while remembering the power of the Earth’s natural forces and the impact they can have over time.
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  • Earth’s inner core rotating slower than surface: Study

    earth

    Earth’s inner core, a hot iron ball the size of Pluto, has stopped spinning faster than the planet’s surface and might now be rotating slower than it, research suggested.

    A quick recap of Earth’s Interior

    earth

    Structure of earth’s interior is fundamentally divided into three layers – crust, mantle and core.

    [A] Crust

    • It is the outermost solid part of the earth, normally about 8-40 kms thick.
    • It is brittle in nature.
    • Nearly 1% of the earth’s volume and 0.5% of earth’s mass are made of the crust.
    • The thickness of the crust under the oceanic and continental areas are different. Oceanic crust is thinner (about 5kms) as compared to the continental crust (about 30kms).
    • Major constituent elements of crust are Silica (Si) and Aluminium (Al) and thus, it is often termed as SIAL(Sometimes SIAL is used to refer Lithosphere, which is the region comprising the crust and uppermost solid mantle, also).
    • The mean density of the materials in the crust is 3g/cm3.
    • The discontinuity between the hydrosphere and crustis termed as the Conrad Discontinuity.

     [B] Mantle

    • The portion of the interior beyond the crust is called as the mantle.
    • The discontinuity between the crust and mantleis called as the Mohorovich Discontinuity or Moho discontinuity.
    • The mantle is about 2900kms in thickness.
    • Nearly 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle.
    • The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA.
    • The density of the layer is higher than the crust and varies from 3.3 – 5.4g/cm3.
    • The uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
    • The asthenosphere (in between 80-200km) is a highly viscous, mechanically weak and ductile, deforming region of the upper mantle which lies just below the lithosphere.
    • The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
    • The discontinuity between the upper mantle and the lower mantleis known as Repetti Discontinuity.
    • The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.

    [C] Core

    • It is the innermost layer surrounding the earth’s centre.
    • The core is separated from the mantle by Guttenberg’s Discontinuity.
    • It is composed mainly of iron (Fe) and nickel (Ni) and hence it is also called as NIFE.
    • It constitutes nearly 15% of earth’s volume and 32.5% of earth’s mass.
    • It is the densest layer of the earth with its density ranges between 9.5-14.5g/cm3.
    • It spins independently because it floats in the liquid metal outer core. One cycle of the swing is about seven decades approximately.
    • It consists of two sub-layers: the inner core and the outer core.
    • The inner core is in solid state and the outer core is in the liquid state (or semi-liquid).
    • The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.
    • Barysphere is sometimes used to refer the core of the earth or sometimes the whole interior.

    What should one understand about the interior of the earth?

    • It is not possible to know about the earth’s interior by direct observations because of the huge size and the changing nature of its interior composition.
    • It is an almost impossible distance for the humans to reach till the centre of the earth (The earth’s radius is 6,370 km).
    • The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.

    Sources of Information about the interior of the earth

    Direct Sources:

    1. Rocks from mining area
    2. Volcanic eruptions

    Indirect Sources

    1. By analyzing the rate of change of temperature and pressurefrom the surface towards the interior.
    2. Meteors, as they belong to the same type of materials earth is made of.
    3. Gravitation, which is greater near poles and less at the equator.
    4. Gravity anomaly, which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
    5. Magnetic sources.
    6. Seismic Waves: the shadow zones of body waves (Primary and secondary waves) give us information about the state of materials in the interior.

    What is the new study about?

    • Exactly how the inner core rotates has been a matter of debate between scientists— and the latest research is expected to prove controversial.
    • A new research has analyzed seismic waves from repeating earthquakes over the last six decades.
    • It shows that- the inner core started rotating slightly faster than the rest of the planet in the early 1970s, the study said.
    • But it had been slowing down before coming in sync with Earth’s rotation around 2009.

    What made the core spin slower?

    • So far there is little to indicate that what the inner core does has many effects on surface dwellers.
    • The researchers said this rotation timeline roughly lines up with changes in what is called the “length of day”— small variations in the exact time it takes Earth to rotate on its axis.
    • But the researchers said they believed there were physical links between all of Earth’s layers, from the inner core to the surface.

     

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  • What is Winter Solstice?

    solstice

    Today, December 21, is Winter Solstice, the shortest day of the year in the Northern Hemisphere. In the Southern Hemisphere, conversely, it was Summer Solstice, the year’s longest day.

    What is Winter Solstice?

    • The winter solstice, also called the hibernal solstice, occurs when either of Earth’s poles reaches its maximum tilt away from the Sun.
    • This happens twice yearly, once in each hemisphere.

    What are Solstices?

    • Solstices occur because Earth’s axis of rotation is tilted about 23.4 degrees relative to Earth’s orbit around the sun.
    • This tilt drives our planet’s seasons, as the Northern and Southern Hemispheres get unequal amounts of sunlight over the course of a year.
    • From March to September, the Northern Hemisphere is tilted more toward the sun, driving its spring and summer.
    • From September to March, the Northern Hemisphere is tilted away, so it feels like autumn and winter.
    • The Southern Hemisphere’s seasons are reversed.
    • On two moments each year—what are called solstices—Earth’s axis is tilted most closely toward the sun.

    Impact on day-time

    • The hemisphere tilted most toward our home star sees its longest day, while the hemisphere tilted away from the sun sees its longest night.
    • During the Northern Hemisphere’s summer solstice—which always falls around June 21—the Southern Hemisphere gets its winter solstice.
    • Likewise, during the Northern Hemisphere’s winter solstice—which always falls around December 22—the Southern Hemisphere gets its summer solstice.

    Impact of the tilted axis

    • The Northern Hemisphere spends half the year tilted in the direction of the Sun, getting direct sunlight during long summer days.
    • During the other half of the year, it tilts away from the Sun, and the days are shorter.
    • Winter Solstice, December 21, is the day when the North Pole is most tilted away from the Sun.
    • The tilt is also responsible for the different seasons that we see on Earth.
    • The side facing the Sun experiences day, which changes to night as Earth continues to spin on its axis.

    Un-impacted regions

    • On the Equator, day and night are equal. The closer one moves towards the poles, the more extreme the variation.
    • During summer in either hemisphere, that pole is tilted towards the Sun and the polar region receives 24 hours of daylight for months.
    • Likewise, during winter, the region is in total darkness for months.

    Celebrations associated with the Winter Solstice

    • For centuries, this day has had a special place in several communities due to its astronomical significance and is celebrated in many ways across the world.
    • Jewish people call the Winter Solstice ‘Tekufat Tevet’, which marks the start of winter.
    • Ancient Egyptians celebrated the birth of Horus, the son of Isis (divine mother goddess) for 12 days during mid-winter.
    • In China, the day is celebrated by families coming together for a special meal.
    • In the Persian region, it is celebrated as Yalda or Shab-e-Yalda. The festival marks the last day of the Persian month of Azar and is seen as the victory of light over darkness.
    • Families celebrate Yalda late into the night with special foods such as ajeel nuts, pomegranates and watermelon, and recite works of the 14th-century Sufi poet Hafiz Shirazi.

    In Vedic tradition

    • In Vedic tradition, the northern movement of the Earth on the celestial sphere is implicitly acknowledged in the Surya Siddhanta.
    • It outlines the Uttarayana (the period between Makar Sankranti and Karka Sankranti). Hence, Winter Solstice is the first day of Uttarayana.

     

    Try this MCQ:

    Q. On 21st June, the Sun

    (a) Does not set below the horizon at the Arctic Circle

    (b) Does not set below the horizon at Antarctic Circle

    (c) Shines vertically overhead at noon on the Equator

    (d) Shines vertically overhead at the Tropic of Capricorn

     

    [wpdiscuz-feedback id=”g83sek2y9c” question=”Please leave a feedback on this” opened=”1″]Post your answers here.[/wpdiscuz-feedback]

     

     

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  • Cyclone Mandous makes landfall in Tamil Nadu

    mandous

    Cyclone Mandous crossed the north Tamil Nadu coast with fierce winds and heavy downpour.

    Cyclone Mandous

    • ‘Mandous’ was a name submitted by WMO member United Arab Emirates and is pronounced as ‘Man-Dous.’
    • It means ‘treasure box’ in Arabic.

    What are Tropical Cyclones?

    • A tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
    • Cyclones are formed over slightly warm ocean waters. The temperature of the top layer of the sea, up to a depth of about 60 meters, need to be at least 28°C to support the formation of a cyclone.
    • This explains why the April-May and October-December periods are conducive for cyclones.
    • Then, the low level of air above the waters needs to have an ‘anticlockwise’ rotation (in the northern hemisphere; clockwise in the southern hemisphere).
    • During these periods, there is an ITCZ in the Bay of Bengal whose southern boundary experiences winds from west to east, while the northern boundary has winds flowing east to west.
    • Once formed, cyclones in this area usually move northwest. As it travels over the sea, the cyclone gathers more moist air from the warm sea which adds to its heft.

    Requirements for a Cyclone to form

    There are six main requirements for tropical cyclogenesis:

    • Sufficiently warm sea surface temperatures
    • Atmospheric instability
    • High humidity in the lower to middle levels of the troposphere
    • Enough Coriolis force to develop a low-pressure centre
    • A pre-existing low-level focus or disturbance
    • Low vertical wind shear

    How are the cyclones named?

    • In 2000, a group of nations called WMO/ESCAP (World Meteorological Organisation/United Nations Economic and Social Commission for Asia and the Pacific) decided to name cyclones.
    • It comprised Bangladesh, India, the Maldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand, decided to start naming cyclones in the region.
    • After each country sent in suggestions, the WMO/ESCAP Panel on Tropical Cyclones (PTC) finalized the list.
    • The WMO/ESCAP expanded to include five more countries in 2018 — Iran, Qatar, Saudi Arabia, United Arab Emirates and Yemen.

    Basics

    Cyclones

    • The atmospheric disturbances which involve a closed circulation of air around a low pressure at the center and high pressure at the periphery, rotating anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere (due to the Coriolis force) are called “cyclones”.

    Cyclones are broadly classified into two types based on the latitudes of their origin-

    • Tropical cyclones
    • Temperate/Extra-tropical cyclones

    Tropical Cyclones

    • Tropical cyclones develop in the region between the tropics of Capricorn and Cancer. These are violent storms that originate over oceans in tropical areas and move on to the coastal regions bringing large-scale destruction caused by violent winds, very heavy rainfall and storm surges. These cyclones are one of the most devastating natural calamities.
    • Tropical cyclones mostly move along with the direction of trade winds, so they travel from east to west and make landfall on the eastern coasts of the continents.
    • Tropical cyclones are known by different names depending on the regions of the world. They are known as Hurricanes in the Atlantic, Typhoons in the Western Pacific and South China Sea, Willy-willies in Western Australia and Cyclones in the Indian Ocean.

    Temperate Cyclones/Extra-Tropical Cyclones

    • It occurs between 30°-60° latitude in both hemispheres (in between the Tropic of Cancer and the Arctic circle in the northern hemisphere and in between the Tropic of Capricorn and the Antarctic Circle in the southern hemisphere).
    • These cyclones move with the westerlies and are therefore oriented from west to east.

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  • Mauna Loa: Hawaii’s biggest Volcano set to erupt

    mauna

    Mauna Loa, the world’s largest active volcano has erupted after 38 years, spewing ash and debris, and covering the sky of Hawaii’s Big Island.

    Where is Mauna Loa?

    mauna

    • Mauna Loa is one of five volcanoes that together make up the Big Island of Hawaii (biggest being the Mauna Kea).
    • It is the southernmost island in the Hawaiian archipelago.
    • It’s not the tallest (that title goes to) but it’s the largest and makes up about half of the island’s land mass.
    • It sits immediately north of Kilauea volcano, which is currently erupting from its summit crater.

    Do you know?

    Any volcano that has erupted within the Holocene period (in the last 11,650 years) is considered to be “active” by scientists. “Dormant” volcanoes are those active volcanoes which are not in the process of erupting currently, but have the potential to do so in the future.

    Why do volcanoes erupt?

    • The deeper one goes under the surface of the Earth towards its core, the hotter it gets.
    • The geothermal gradient, the amount that the Earth’s temperature increases with depth, indicates heat flowing from the Earth’s warm interior to its surface.
    • At a certain depth, the heat is such that it melts rocks and creates what geologists call ‘magma’.
    • Magma is lighter than solid rock and hence it rises, collecting in magma chambers.
    • Chambers that have the potential to cause volcanic eruptions are found at a relatively shallow depth, between six to ten km under the surface.
    • As magma builds up in these chambers, it forces its way up through cracks and fissures in Earth’s crust. This is what we call a volcanic eruption.
    • The magma that surfaces on the Earth’s crust is referred to as lava.

    Why is the eruption of Mauna Loa so explosive?

    • Eruptions vary in intensity and explosiveness, depending on the composition of the magma.
    • In simple terms, runny magma makes for less explosive volcanic eruptions that typically are less dangerous.
    • Since the magma is runny, gasses are able to escape, leading to a steady but relatively gentle flow of lava out of the mouth of the volcano.
    • The eruption at Mauna Loa is of this kind. Since the lava flows out at a slow pace, people typically have enough time to move out of the way
    • . Geologists are also able to predict the flow of the lava depending on the incline and exact consistency it has.

    How is vulcanism measured?

    • The Volcanic Explosivity Index (VEI) is a scale used to measure the explosivity of a volcano.
    • It has a range of 1 to 8 with a higher VEI indicating more explosivity.
    • While the VEI of the current eruption at Mauna Loa is not known yet, the previous eruption in 1984 was deemed to have a VEI of 0.

     

    Also read about the Pacific Ring of Fire.

     

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  • Places in news: Shiveluch Volcano

    shiveluch

    The Shiveluch volcano on the Kamchatka Peninsula in the Russian Far East has increased its activity and is now in danger of erupting violently.

    About Shiveluch

    • Shiveluch is one of the largest and most active volcanoes in Kamchatka, having erupted at least 60 times in the past 10,000 years.
    • Kamchatka is home to 29 active volcanoes, part of a vast belt of Earth known as the “Ring of Fire” which circles the Pacific Ocean and is prone to eruptions and frequent earthquakes.
    • It has two main parts: Old Shiveluch, which tops 3,283 metres (10,771 ft), and Young Shiveluch – a smaller, 2,800-metre peak protruding from its side.
    • Young Shiveluch lies within an ancient caldera – a large crater-like basin that likely formed when the older part underwent a catastrophic eruption at least 10,000 years ago.
    • It is this part that has become extremely active; the lava dome continues to grow and that stronger “fumarole activity” has been observed.

     

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  • Places in news: Sahel Region

    sahel

    French President Emmanuel Macron announced the end of the decade-long Operation Barkhane in Africa’s Sahel Region.

    Note the nations falling in Sahel Region.

    Sahel Region

    • The Sahel is the ecoclimatic and biogeographic realm of transition in Africa between the Sahara to the north and the Sudanian savanna to the south.
    • Having a semi-arid climate, it stretches across the south-central latitudes of Northern Africa between the Atlantic Ocean and the Red Sea.
    • The name is derived from the Arabic term for “coast, shore”; this is explained as being used in a figurative sense in reference to the southern edge of the vast Sahara.
    • The Sahel part includes from west to east parts of northern Senegal, southern Mauritania, central Mali, northern Burkina Faso, the extreme south of Algeria, Niger, the extreme north of Nigeria, the extreme north of Cameroon and the Central African Republic, central Chad, central and southern Sudan, the extreme north of South Sudan, Eritrea and the extreme north of Ethiopia.

    What is Operation Barkhane?

    • France began its military operations in Sahel in January 2013.
    • Titled Operation Serval, it was limited to targeting Islamic extremists linked to al-Qaeda who took control of northern Mali.
    • However, in 2014, the mission was scaled up, renamed Operation Barkhane and was aimed at counter-terrorism.
    • The objective was to assist local armed forces to prevent the resurgence of non-state armed groups across the Sahel region.
    • Around 4,500 French personnel were deployed with the local joint counter-terrorism force.

     

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  • Groundwater Extraction Lowest in 18 years

    groundwater

    Groundwater extraction in India saw an 18-year decline, according to an assessment by the Central Ground Water Board (CGWB).

    What is Groundwater?

    groundwater

    • Groundwater is the water found underground in the cracks and spaces in soil, sand and rock.
    • It is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers.
    • Aquifers are typically made up of gravel, sand, sandstone, or fractured rock, like limestone.
    • Water can move through these materials because they have large connected spaces that make them permeable.
    • Aquifers, hand-dug wells, and artesian wells are different types of sources of groundwater.

    Declining trend of groundwater extraction

    • The total annual groundwater recharge for the entire country is 437.6 billion cubic metres (bcm) in 2022.
    • However the extraction for entire country is only 239.16 bcm, according to the 2022 CGWB report.
    • By comparison, an assessment in 2020 found that the annual groundwater recharge was 436 bcm and extraction 245 bcm.
    • The 2022 assessment suggests that groundwater extraction is the lowest since 2004, when it was 231 bcm.

    Implications of the CGWB report

    • A detailed analysis of the assessment indicates increase in ground water recharge.
    • This is mainly attributed to:
    1. Increase in recharge from canal seepage,
    2. Return flow of irrigation water and
    3. Recharges from water bodies/tanks & water conservation structures.

    Significance of groundwater

    • Groundwater supplies drinking water to a sizeable population in India and almost 99% of the rural population.
    • It helps grow our food. 64% of groundwater is used for irrigation to grow crops.
    • It is an important component in many industrial processes.
    • It is a source of recharge for lakes, rivers, and wetlands.

    Why discuss this?

    • Depletion: People face serious water shortages because groundwater is used faster than it is naturally replenished.
    • Contamination: In other areas groundwater is polluted by human activities.

    Reasons for Depletion

    • Increased demand for water for domestic, industrial and agricultural needs and limited surface water resources lead to the over-exploitation of groundwater resources.
    • Limited storage facilities owing to the hard rock terrain, along with the added disadvantage of lack of rainfall, especially in central Indian states.
    • Green Revolution enabled water-intensive crops to be grown in drought-prone/ water deficit regions, leading to over-extraction of groundwater.
    • Frequent pumping of water from the ground without waiting for its replenishment leads to quick depletion.
    • Subsidies on electricity and high MSP for water-intensive crops is also leading reasons for depletion.
    • Inadequate regulation of groundwater laws encourages the exhaustion of groundwater resources without any penalty.
    • Deforestation, unscientific methods of agriculture, chemical effluents from industries, and lack of sanitation also lead to pollution of groundwater, making it unusable.
    • Natural causes include uneven rainfall and climate change that are hindering the process of groundwater recharge.

    Impact of groundwater depletion

    • Lowering of the water table: Groundwater depletion may lower the water table leading to difficulty in extracting groundwater for usage.
    • Reduction of water in streams and lakes: A substantial amount of the water flowing in rivers comes from seepage of groundwater into the streambed. Depletion of groundwater levels may reduce water flow in such streams.
    • Subsidence of land: Groundwater often provides support to the soil. When this balance is altered by taking out the water, the soil collapses, compacts, and drops leading to subsidence of land.
    • Increased cost for water extraction: As the depleting groundwater levels lower the water table, the user has to delve deep to extract water. This will increase the cost of water extraction.

    Regulation of Groundwater in India

    (1) Central Ground Water Authority (CGWA)

    • It has the mandate of regulating ground water development and management in the country.
    • It is constituted under the Environment (Protection) Act of 1986.
    • CGWA issues advisories, public notices and grant No Objection Certificates (NOC) for ground water withdrawal.

    (2) National Aquifer Mapping and Management Programme (NAQUIM)

    • The NAQUIM is an initiative of the Ministry of Jal Shakti for mapping and managing the entire aquifer systems in the country.
    • It maintains the Hydrological Map of India.

    (3) Atal Bhujal Yojana 

    • It is a Central Sector Scheme, for sustainable management of groundwater resources with community participation in water-stressed blocks.

    Way Forward

    • Routine survey: There should be regular assessment of groundwater levels to ensure that adequate data is available for formulating policies and devising new techniques.
    • Assessment of land use pattern: Studies should be carried out to assess land use and the proportion of agricultural land falling under overt-exploited units.
    • Changes in farming methods: To improve the water table in those areas where it is being overused, on-farm water management techniques and improved irrigation methods should be adopted.
    • Reforms in power supply subsidies: The agricultural power-pricing structure needs to be revamped as the flat rate of electricity adversely affects the use of groundwater.
    • Monitoring extraction: There should be a policy in place to monitor the excessive exploitation of groundwater resources to ensure long-term sustainability.

     

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  • What are Eclipses?

    eclipse

    India recently witnessed a partial solar eclipse. Let’s take a look over all dynamics of Eclipses.

    What are Eclipses?

    • An eclipse takes place when one heavenly body such as a moon or planet moves into the shadow of another heavenly body.
    • There are two types of eclipses on Earth: an eclipse of the Moon and an eclipse of the Sun.

    [I] A Lunar Eclipse

    eclipse

    • The moon moves in an orbit around Earth, and at the same time, Earth orbits the sun. Sometimes Earth moves between the sun and the moon.
    • When this happens, Earth blocks the sunlight that normally is reflected by the moon. (This sunlight is what causes the moon to shine.)
    • Instead of light hitting the moon’s surface, Earth’s shadow falls on it. This is an eclipse of the moon — a lunar eclipse.
    • A lunar eclipse can occur only when the moon is full. (But not every full moon is also a lunar eclipse. Can you guess why?)

    Observing a Lunar Eclipse

    • A lunar eclipse can be seen from Earth at night.
    • A lunar eclipse usually lasts for a few hours.
    • At least two partial lunar eclipses happen every year, but total lunar eclipses are rare.

    There are two types of lunar eclipses: total lunar eclipses and partial lunar eclipses.

    • A total lunar eclipse occurs when the moon and the sun are on exact opposite sides of Earth. Although the moon is in Earth’s shadow, some sunlight reaches the moon.  The sunlight passes through Earth’s atmosphere, which causes Earth’s atmosphere to filter out most of the blue light. This makes the moon appear red to people on Earth.
    • A partial lunar eclipse happens when only a part of the moon enters Earth’s shadow. In a partial eclipse, Earth’s shadow appears very dark on the side of the moon facing Earth. What people see from Earth during a partial lunar eclipse depends on how the sun, Earth and moon are lined up.
    • In a penumbral lunar eclipse, only the more diffuse outer shadow of Earth – the penumbra – falls on the moon’s face. This third kind of lunar eclipse is much more subtle, and much more difficult to observe than either a total or partial eclipse of the moon.

    [II] A Solar Eclipse

    eclipse

    • Sometimes when the moon orbits Earth, it moves between the sun and Earth.
    • When this happens, the moon blocks the light of the sun from reaching Earth.
    • This causes an eclipse of the sun or solar eclipse.
    • During a solar eclipse, the moon casts a shadow onto Earth.

    There are three types of solar eclipses.

    The first is a Total Solar Eclipse

    • A total solar eclipse is only visible from a small area on Earth.
    • The people who see the total eclipse are in the centre of the moon’s shadow when it hits Earth.
    • The sky becomes very dark as if it were night. For a total eclipse to take place, the sun, moon and Earth must be in a direct line.

    The second type is a Partial Solar Eclipse

    • This happens when the sun, moon and Earth are not exactly lined up.
    • The sun appears to have a dark shadow on only a small part of its surface.

    The third type is an Annular Solar Eclipse

    • An annular eclipse happens when the moon is farthest from Earth. Because the moon is farther away from Earth, it seems smaller. It does not block the entire view of the sun. The moon in front of the sun looks like a dark disk on top of a larger sun-coloured disk. This creates what looks like a ring around the moon.
    • During a solar eclipse, the moon casts two shadows on Earth. The first shadow is called the Umbra. This shadow gets smaller as it reaches Earth. It is the dark centre of the moon’s shadow.
    • The second shadow is called the Penumbra. The penumbra gets larger as it reaches Earth. People standing in the penumbra will see a partial eclipse. People standing in the umbra will see a total eclipse.

    Observing a Solar Eclipse

    • Solar eclipses happen once every 18 months.
    • Unlike lunar eclipses, solar eclipses only last for a few minutes.

    Why don’t solar eclipses happen at every New Moon?

    • The reason is that the Moon’s orbit tilts 5° to Earth’s orbit around the Sun.
    • Astronomers call the two intersections of these paths nodes.
    • Eclipses only occur when the Sun lies at one node and the Moon is at its New (for solar eclipses) or Full (for lunar eclipses) phase.
    • During most (lunar) months, the Sun lies either above or below one of the nodes, and no eclipse happens.

    [III] Planet Transits

    • When a planet comes between Earth and the Sun, it is called a transit.
    • The only 2 planets that can be seen transiting the Sun from Earth are Venus and Mercury because they are the only planets that orbit inside Earth’s orbit.
    • From 2000–2199, there will be 14 transits of Mercury.
    • However, Venus transits are even rarer with only 2 this century, in 2004 and 2012.

     

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  • Southwest Monsoon begins early Withdrawal/Retreat

    The southwest monsoon rainfall, 7% more than normal, has started to withdraw.

    What is Monsoon Withdrawal/Retreat?

    • In India, retreating monsoon is the withdrawal of south-west monsoon winds from North India.
    • The withdrawal is gradual and takes about three months.
    • With the retreat of the monsoons, the clouds disappear and the sky becomes clear. The day temperature starts falling steeply.
    • Monsoon rains weaken all over India except few southeastern states.
    • It is helpful in Rabi crop cultivation.

    Factors affecting the retreat

    Two predominant factors cause the phenomenon:

    (1) Land topography

    • First, the low mountain range in each region runs from north to south, shielding it from west-bound winds that trigger summer monsoon.
    • After summer, the range aids in the ‘orographic lift’ or rising of east-bound air mass from a lower to higher elevation, forming clouds and resulting in rain.

    (2) Atmospheric convection

    • The second factor is atmospheric convection or vertical movement of air.
    • As the earth is heated by the sun, different surfaces absorb different amounts of energy and convection may occur where the surface heats up very rapidly.
    • As the surface warms, it heats the overlying air, which gradually becomes less dense than the surrounding air and begins to rise.
    • This condition is more favorable from September to February because of the role played by sea surface temperature or water temperature.

    Immediate factors influencing withdrawal

    • The withdrawal of the monsoon is based on meteorological conditions such as-
    1. Anti-cyclonic circulation (dry air that is the opposite of a cyclone)
    2. Absence of rain in the past five days and
    3. Dry weather conditions over the region

    When does it occur?

    • The monsoon withdrawal is a long-drawn process and extends into mid-October, though the IMD considers September 30 to be the final day of the season over India.
    • The rain after that is categorised as “post-monsoon” rainfall.

    Try this PYQ:

    Q.The seasonal reversal of winds is the typical characteristic of:

    (a) Equatorial climate

    (b) Mediterranean climate

    (c) Monsoon climate

    (d) All of the above climates

     

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    Also read:

    Various terms related to Indian Monsoon

     

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