The Universe Handout This is an important topic, on an average, a question appears in CSE prelims, every year. Let us discuss the following concepts one by one. 1. Stars 2. Solar system 3. The Moon 4. The Earth 5. Longitudes and Latitudes 6. Motions of the Earth 7. The Universe 8. Current updates 1. Stars The sun, the moon and all objects shining in the night sky are known as Celestial bodies Some celestial bodies called stars are very big and hot. They are made up of gases. They have their own heat and light, which they emit in large amounts. The sun is a star. Countless twinkling stars in the night sky are similar to the sun. Since they are very far from us, we do not feel their heat or light, and they look so tiny. 1 www.eduscreen.in www.aasaanias.com Source of energy of the stars : The source of energy of the stars is due to Nuclear fusion (conversion of hydrogen to helium) Twinkling of Stars: Stars look like twinkling, when observed from the earth, due to the atmosphere on Earth. Different layers of atmosphere has different temperatures, hence different densities, So the light ray coming from the star, undergoes Refraction (bending of light ray when it enters from one medium to another medium of different density) Colour of Stars: The colour of a star depends on its surface temperature. Some stars looks dull and red, while others are white and others look bright blue. (More temp – towards Blue, less temp – towards Red) 2 www.eduscreen.in www.aasaanias.com Colour of the Sun: The light of the Sun would actually look very white from space. (Our Sun’s surface temperature is about 6,000 Kelvin). When we see the Sun at sunrise or sunset, when it is low in the sky, it may appear yellow, orange, or red. But that is only because its short-wavelength colors (green, blue, violet) are scattered out by the Earth's atmosphere Hence only the reds, yellows, and oranges get through the thick atmosphere to our eyes. 3 www.eduscreen.in www.aasaanias.com Why the Colour of the Sky looks Blue? The colour of sky looks blue when observed from the Earth, it is due to atmosphere on earth. (When the Sun is high in the sky, the shorter waves, primarily the blue, strike air molecules in the upper atmosphere and bounce around and scatter. Hence the sky looks blue). If there is no atmosphere on Earth, or if observed from the space, or from the moon, the sky looks dark (Black). The Sun and the Earth Comparison: The ratio of the Sun's diameter to the Earth's diameter is 1,392,000/12756 = 109.1 This means the ratio of their volumes is 109.1 x 109.1 x 109.1, which is about 1,300,000,and that means that 1,300,000 Earths should fit inside the Sun. 4 www.eduscreen.in www.aasaanias.com Imp. Units to measure distances of astronomical bodies: Astronomical unit (A.U): The distance from Earth to the sun is called an astronomical unit, or AU, which is used to measure distances throughout the solar system. 1 AU = 149,597,870,700 meters (app. 150 mn km) The Sun is the closest star to Earth, about 150 million kms away. 5 www.eduscreen.in www.aasaanias.com Light year: A light year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. Considering this, the distances the light will travel in one year is taken to be one light year. This equals to 9.461×1012 km. The mean distance between the sun and the earth is 149,598,000 km. In terms of light years, it is 8.311minutes. One light-year (ly) is 63,240 A.U Parsec (Pc): A parsec is the length of the long leg of a right triangle, whose short leg is one astronomical unit when the angle between the Sun and the Earth, as seen from an object in space (a star for example), is one arcsecond The word parsec stands for "parallax of one arc second" one parsec (pc) is equal to 3.26 light years. 6 www.eduscreen.in www.aasaanias.com Imp. Stars: Closest stars: Proxima Centauri claims the honor of being our true nearest neighbor (after Sun) at only 4.24 light years away. Alpha Centauri is a triple star system (Three stars bound together by gravity) Alpha Centauri A, Alpha Centauri B and Proxima Centauri. Pole star (Polaris): Polaris (the North Star or Pole Star) is the brightest star in the constellation Ursa Minor, and the 50th brightest star in the night sky. It is very close to the north celestial pole, making it the current northern pole star. 7 www.eduscreen.in www.aasaanias.com Many recent papers calculate the distance to Polaris at about 434 light-years. The south celestial pole lacks a bright star like Polaris to mark its position. At present, the naked-eye star nearest to this imaginary point is the faint Sigma Octantis, which is sometimes known as the South Star. Constellation of stars: Various patterns formed by different groups of stars are known as Constellations. 8 www.eduscreen.in www.aasaanias.com Some important constellations are Ursa major (also known as Big Bear/ Big Dipper/Plough), Saptarishi, Ursa minor (also known as Little Bear / Little Dipper) etc. Dubhe and Merak are important stars of Ursa major constellation Ursa minor is the most northern constellation. Polaris (North Pole star) is a part of Ursa minor and infact, it is the brightest star in the constellation. 9 www.eduscreen.in www.aasaanias.com Zodiac: Zodiac is the Imaginary region that encompass the path of the Sun and Planets. the zodiac is divided into twelve signs, each occupying 30° of celestial longitude and roughly corresponding to the constellations (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces) Neutron stars: 10 www.eduscreen.in www.aasaanias.com Neutron stars are city-size stellar objects with a mass about 1.4 to 3 times that of the sun. Born from the explosive death of another larger stars, these tiny objects pack quite a punch. Neutron stars pack their mass inside a 20-kilometer diameter. They are so dense that a single teaspoon would weigh a billion tons When stars four to eight times as massive as the sun explode in a violent supernova, their outer layers can blow off in an often-spectacular display, leaving behind a small, dense core that continues to collapse. Gravity presses the material in on itself so tightly that protons and electrons combine to make neutrons, yielding the name "neutron star Types of neutron stars: Magnetar – Neutron star with powerful magnetic field: Magnetars have magnetic fields a thousand times stronger than the average neutron star. The resulting drag causes the star to take longer to rotate 11 www.eduscreen.in www.aasaanias.com PULSAR – A flashing Neutron star: Some neutron stars have jets of materials streaming out of them at nearly the speed of light. As these beams pan past Earth, they flash like the bulb of a lighthouse. This pulsing appearance led them to be called pulsars. 2. Solar system 12 www.eduscreen.in www.aasaanias.com Our solar system consists of the sun, eight planets, moons, many dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The sun is the center of our solar system. the planets, their moons, a belt of asteroids, comets, orbit the sun. Planets: Planets do not have their own heat and light. They are lit by the light of the stars. If we look at the Earth from a great distance, say the moon, it will appear to be shining just as the moon. (The word ‘planet’ comes from the Greek word “Planetai” which means ‘wanderers’). The eight planets that orbit the sun are (in order from the Sun) are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Another large body is Pluto, now classified as a dwarf planet or plutoid. All the eight planets of the solar system move around the sun in fixed paths called orbits. These paths are elongated. 13 www.eduscreen.in www.aasaanias.com (Easy ways to remember the order of the planets (plus Pluto) are the mnemonics: "My Very Excellent Mother Just Served Us Nuts") A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. Inner Planets or Terrestrial planets: The first four planets, i.e. Mercury, Venus, Earth, and Mars are known as the inner planets These planets are, in terms of composition, "Earth-like. (that is composed primarily of silicate rocks or metals). So they are also known as terrestrial planets, telluric planets, or rocky planets 14 www.eduscreen.in www.aasaanias.com Giant Planets: A giant planet is any massive planet. They are usually primarily composed of low-boiling-point materials (gases or ices), rather than rock or other solid matter, but massive solid planets can also exist. There are four known giant planets in the Solar System: Jupiter, Saturn, Uranus and Neptune. planets such as Jupiter and Saturn are called the gas giants, hydrogen and helium constitute most of the mass of the planet, whereas they only make up an outer envelope on Uranus and Neptune, which are instead mostly composed of water, ammonia, and methane and therefore increasingly referred to as "ice giants". Ice giants consist of only about 20% hydrogen and helium in mass, as opposed to the Solar System's gas giants (Jupiter and Saturn), which are both more than 90% hydrogen and helium in mass Size of the Planets: The largest planet is Jupiter.