Space Science & Exploration

Statement A is incorrect: The distance between stellar bodies does change, but often very slowly or in predictable orbits. Planets orbit stars, stars orbit galactic centers, and galaxies orbit each other, all causing continuous changes in distance. And this statement is not related to why distance is measured in light years. Statement B is incorrect: While the gravitational constant is fundamental, the effective gravity of stellar bodies changes due to shifts in their mass (e.g., fusion, stellar winds), changes in their radius/size (expanding into red giants, collapsing into white dwarfs/neutron stars), and changes in the distance between them as they orbit. And this statement is not related to why distance is measured in light years. Statement C is incorrect: Though mostly light travels in a straight line, it can be bent by Gravity- phenomenon known as Gravitational Lensing. Statement D is correct: the speed of light does not change in a vacuum. So, it is a constant that can be used for measurement.

The description mentions three spacecraft in an equilateral triangle formation with million-kilometre sides using lasers for measurement.
This matches the design of the Evolved Laser Interferometer Space Antenna (eLISA) mission.
eLISA is a proposed space observatory aiming to detect gravitational waves using precisely positioned spacecraft. Voyager-2 and New Horizons are single spacecraft on exploration missions, not designed for gravitational wave detection. LISA Pathfinder was a precursor mission to test technologies for eLISA, not the full mission itself. Therefore, based on the details provided, the experiment refers to the Evolved LISA mission.

Remote sensing is the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance from the targeted area. Statement 1 is correct. Satellite images and remote sensing data can indeed be used to estimate the chlorophyll content in vegetation. This is done by measuring the reflectance of light from the vegetation. The chlorophyll in plants absorbs light for photosynthesis, and the amount of light reflected back can give an estimate of the chlorophyll content. Statement 2 is correct. Satellite images and remote sensing data can also be used to estimate greenhouse gas emissions. This is done by detecting the radiations emitted by the substances in the rice paddies. Statement 3 is correct. Satellite images and remote sensing data can be used to measure land surface temperatures as well. This is done by detecting the infrared radiation emitted by the land surface. Therefore, all three parameters can be measured or estimated using satellite images or remote sensing data.

The merger of black holes is expected to generate powerful gravitational waves. Gravitational waves are ripples in spacetime caused by accelerating massive objects. Detecting these waves with instruments like LIGO (Laser Interferometer Gravitational-Wave Observatory) allows us to study these events even when they are too far away or obscured to observe directly. This opens a new window for astronomical observations.

IRNSS is an independent regional navigation satellite system being developed by India. Statement 1 is correct: The Indian Regional Navigation Satellite System (IRNSS) indeed has three satellites in geostationary orbits and four satellites in geosynchronous orbits. Statement 2 is incorrect: It is designed to provide accurate position information service to users in India as well as the region extending up to 1500 km from its boundary, which is its primary service area. An Extended Service Area lies between primary service area and area enclosed by the rectangle from Latitude 30 deg South to 50 deg North, Longitude 30 deg East to 130 deg East. Statement 3 is incorrect: While India has been working on enhancing the coverage of its navigation system, as of the given timeframe (2019), it does not have full global coverage. The system is primarily regional, although there are plans for augmentation and expansion.

GPS, or Global Positioning System, is a satellite-based navigation system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth. It has a wide range of applications. Statement 1 is correct. GPS is used in mobile phones for various purposes such as location tracking, navigation, and location-based services. Statement 2 is correct. GPS is used in banking operations for ATM location services and for time-stamping transactions, which is crucial for maintaining accurate records. Statement 3 is correct. GPS is used for time-stamping power system measurements, which is vital for grid stability and synchronization. Therefore, GPS technology can be used in all the three areas mentioned.

Statement 1 is correct: According to Einstein's General Theory of Relativity, gravity can bend light. This phenomenon is known as gravitational lensing. Statement 2 is correct: The General Theory of Relativity led to the prediction of an expanding universe, which has been confirmed by observational evidence. Statement 3 is correct: According to the General Theory of Relativity, the presence of matter and energy warps the fabric of space and time around it, which is the underlying cause of the gravitational force. So, all three statements are correct.

Statement 1 is correct. PSLV (Polar Satellite Launch Vehicle) is primarily used to launch Earth observation/monitoring satellites, while GSLV (Geosynchronous Satellite Launch Vehicle) is designed to launch communication satellites into geosynchronous transfer orbits. Statement 2 is incorrect. Satellites launched by PSLV are typically placed in polar or sun-synchronous orbits, which are not geosynchronous. These satellites appear to move across the sky as viewed from a particular location on Earth. Statement 3 is incorrect. The GSLV Mk III is a three-stage launch vehicle, not a four-stage one. The first stage uses solid rocket motors, the second stage uses liquid rocket engines, and the third stage uses a cryogenic rocket engine.

Gravitational waves are ripples in the fabric of spacetime, predicted by Einstein's theory of general relativity. eLISA is a space-based gravitational wave observatory that can detect and study these gravitational waves. It is a joint project of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). eLISA is designed to detect gravitational waves from astronomical sources such as merging black holes and neutron stars. It would use laser interferometry to measure the tiny distortions in spacetime caused by passing gravitational waves. Detecting gravitational waves would provide important insights into the nature of gravity and the evolution of the universe.

* The terms 'Event Horizon', 'Singularity', 'String Theory' and 'Standard Model' are associated with the observation and understanding of the Universe, particularly in the field of cosmology and astrophysics. * Event Horizon refers to the boundary around a black hole, beyond which nothing, not even light, can escape the black hole's gravitational pull. * Singularity refers to a point in spacetime where the gravitational field becomes infinite, such as at the center of a black hole, where the laws of physics as we know them break down. * String Theory is a theoretical framework in particle physics that attempts to unify all the fundamental forces of nature, including gravity, into a single coherent model. * Standard Model is the most comprehensive and well-tested theory in particle physics, which describes the fundamental particles and their interactions, except for gravity.