Exploring The Universe
Astronomy, the scientific study of stars, planets, satellites, comets, meteors, meteorites, and asteroids, collectively called celestial or heavenly bodies, has developed considerably in recent years. Today, our knowledge of the universe, the vast limitless space that contains celestial bodies, is far more accurate than it was in the older days. Now we know far more about the universe and celestial bodies that exist in the universe. In addition to celestial bodies, the universe also contains gas and dust particles.
Nebulae:
The universe is full of glowing clouds of gas and dust between stars. Some give out their own light, while others reflect light from nearby stars. Some clouds are dark or black. This is because they blot out the light of stars behind them. These clouds of gas and dust particles, floating in space, are called nebulae. Often the force of gravity pulls the particles of gas and dust closer into a mass. If the mass is heavy enough, the spinning cloud starts to glow. This is a protostar or an early stage in the formation of a star.
Grade-4
The universe is made up of everything that exists, including galaxies, stars, planets, space, all matter, and energy. There are billions of galaxies in the universe.
The sun and the celestial bodies that revolve around it form the solar system.
It is a long way indeed to the moon, but man has made that historical trip. The first men to land on the moon were the crew of the American space mission, Apollo 11. It was launched from the Kennedy Space Center in Florida, on July 16, 1969. The rocket that carried it into space was Saturn 5. Apollo 11 carried three American astronauts - Neil Armstrong, Edwin Aldrin and Michael Collins.
Astronomy is the study of the universe such as stars, planets and space. Scientists use different technologies such as telescopes to study the universe. Galileo invented an improved telescope that allowed him to see far into space.
Galaxies:
There are millions of stars scattered throughout the univerwse.They form enormous clusters called galaxies. The earth is a part of the Milky Way galaxy, also called the Akash Ganga in Hindi. It appears as a hazy band stretching across the night sky, when observed away from city lights.
Constellations:
For centuries people - poets, farmers, navigators, and astronomers - have imagined the stars to form different patterns in the night sky. A named group of stars forming a pattern is called a constellation. Some constellations resemble animals or objects. Some commonly known constellations are the Great Bear, Pisces, Scorpio, and Cassiopeia's Chair.
Differences Between Stars and Planets:
Stars Planets
1. Stars are self-luminous bodies that produce their own light.
1. Planets are non-luminous bodies that reflect the light of the sun.
2. They are huge.
2. They are very small, compared to stars.
3. Stars are made up of hot, burning gases.
3. Planets are made up of solid materials like rocks and stones, while some comprise cool gases.
4. They are very hot.
4. The temperature of planets depends on their distance from the sun,
5. Stars twinkle.
5. They do not twinkle.
6. There are millions of stars.
6. There are eight known planets.
7. The sun is an example of a star.
7. The earth is an example of a planet.
Satellites:
The word satellite means a 'follower' and refers to the small heavenly bodies that revolve around the planets in their journey around the sun. Satellites do not have light of their own and reflect the light of the sun. All planets do not have satellites, for example, Mercury and Venus. The moon is the only satellite of the earth. The number of known natural satellites has increased in recent years due to advances in space exploration. There are 146 known sastellites in our solar wsystem.
Besides natural satellites, there are man-made or artificial satellites that orbit the earth. These satellites are mainly used for telecommunication, weather forcasts
The distance from the Moon to the Earth is 3,84, 400 km.
Light can travel at approximately 3,00,000 km a second.
The distance from the Sun to the Earth is about 15,00,00,000 km.
Light takes about 8 minutes to travel from the Sun to the Earth.
Chapter- 8
Grade-5
Q.2. Short Answered Questions:
a) What are two motions of the Earth?
Ans: The motions of the Earth are -i) rotationii) revolution or annual motion
b) What causes day and night?
Ans: The earth’s rotation causes day and night.
c) Why do the phases of the Moon take place?
Ans: The moon has no light of its own. The moon shines because the sun gives it light. Half of the moon is always lighted by the sun. But as the moon orbits around the earth, the area of the lighter side is facing the earth changes. These changes cause the phases of the moon.
d) What is the difference between planet and satellite?
Ans: i) A planet moves around the sun.ii) A planet is bigger than satellite.
iii) Ex. Earth is a planet.
i) A satellite moves round the planet to which it belongs.
ii) A satellite is smaller than planet.
iii) Ex. Moon is a satellite.
e) Why does the temperature rises in the Summer?
Ans: When the northern hemisphere tilts toward the Sun, it is summer there. In summer, the sunlight shines more directly on the northern half of the Earth giving more energy. This causes the temperatures to rise.
A lunar eclipse occurs when the moon passes directly behind Earth into its umbra( shadow).
A solar Eclipse happens when the moon moves in front of the sun.
During an annular solar eclipse, the Moon is too far from Earth for its shadow to fully reach the surface, creating a dazzling halo effect around the Sun's disc. Whereas a total solar eclipse is when the Moon completely blocks the Sun, casting an eerie darkness over the path of totality.
3. Descriptive Questions:
a) Explain the causes of seasons.
Ans: The tilt of the Earth’s axis and its orbit around the Sun causes seasons. As the Earth revolves around the Sun, different parts of the Earth tilt towards or away from the Sun.
When the northern hemisphere tilts towards the Sun, it is summer there. In summer, the sunlight shines more directly on the northern half of the Earth giving more energy. This causes the temperatures to rise and the period of daytime to be longer. Opposite season occurs in the southern hemisphere and it is winter there.
b) The sun does not move around the Earth, but it seems to move from east to west across the sky. Explain why.
Ans: The Sun rises in the morning and sets in the evening everyday. One side of the Earth is facing the Sun, whereas the other side of the earth is not facing the Sun. The part of the Earth that is facing the Sun has daytime. On the other hand, the part of the Earth that is facing away from the Sun has night. But the Sun does not move at all, it only seems to move because the Earth is rotating.
c) When the northern half of the Earth tilts toward the sun, what happens to the length of day and night?
Ans: When the northern hemisphere tilts towards the Sun, it is summer there. In summer, sunlight shines more directly on the northern half of the Earth giving more energy. This causes the temperatures to rise and the period of daytime to be longer.
d) How are the solar system, the milky Way Galaxy, and the Universe related?
Ans: Our Earth orbits the Sun in our Solar System. Our Sun is one star among the billions in the Milky Way Galaxy. Our Milky Way Galaxy is one among the billions of galaxies in our Universe.e) Look at the pictures below. Both of the pictures were taken at the same time and same place, but they look different. Why does it happen?
Ans: Both of the pictures were taken at the same time and same place, but they look different because In June, when the Northern Hemisphere is tilted toward the sun, the sun's rays hit it for a greater part of the day than in winter. This means it gets more hours of daylight. In December, when the Northern Hemisphere is tilted away from the sun, with fewer hours of daylight.
Q/A1. What is phases of the Moon?Ans: The changing shapes of the bright part of the Moon that we see are called the phases of the Moon.2. What is orbit?Ans: The path that Earth and other planets move around the Sun is called orbit.3. What is revolution?Ans: The orbital motion of the Earth around the Sun is called revolution. It takes 365 days and 6 hours for the Earth to complete one trip around the Sun.4. What is axis?Ans: An axis is the imaginary line through the centre of an object. Earth's axis goes through the North and South Poles. Earth's axis is tilted at some degree.
Put a tick mark on the correct answer.
1. Which one is correct?
a) the Moon gives off its own lightb) the Moon is a satellitec) the Moon is a planetd) the Moon moves around Sun
2. How many days does the Earth take to complete one trip around the Sun?
a) 24 daysb) 28 daysc) 365 daysd) 7 days
Important Terms:
orbit= the fixed path of a planet around the sun
interior planets = the planets whose orbits are closer to the sun than the earth's orbit is
superior planets = the planets whose orbits are farther away from the sun than the earth's orbit is
fusion = the act or process of combining the nuclei of atoms to form a heavier nucleus, with energy being released
There are eight known planets in the solar system.
Mercury is closest to the sun and is also the smallest planet;
Venus is the brightest and hottest planet; the earth is the only planet that has water and supports life;
Mars has a very thin atmosphere;
Jupiter is the biggest planet;
Saturn has several rings around it;
Uranus' axis is inclined at 98 degree
Neptune is the farthest from the sun.
Q. a) What is the temperature at the surface of the sun? What is the temperature in its interior?
b) What are sunspots? In which layer of the sun are they likely to be found?
c) What makes the sun so hot?
d) Name the planets in order of their distances from the sun.
e) Name the largest satellite of Jupiter.
Ans: Titania is the largest satellite of Uranus while Ganymede is the largest satellite of Jupiter.
Q1. Describe the structure of the sun.
2. Which is the hottest planet in the solar system? What are the reasons behind this?
3. What are the reasons that make the earth a unique planet?
4. What are satellites? How are they different from planets? Name any three prominent satellites.
Ans: Satellites are heavenly bodies that revolve around a planet. They do not have the light of their own but reflect the light of the sun. Not all planets have satellites, for example, Mercury and Venus do not have any. The Earth has only one satellite called the Moon. Mars has two satellites - Deimos and Phobos. Nepture has 14 satellites, the largest of which is Triton. Uranus and Jupiter have 27 and 67 known satellites respectively. Titania is the largest satellite of Uranus while Ganymede is the largest satellite of Jupiter.
5. Write a note on asteroids, comets, and meteors.
Asteroids: thousands of irregular, small celestial bodies revolve around the sun. They lie between the orbits of Mars and Jupiter. They are called asteroids or planetoids as they are presumed to be the shattered fragments of previously existing planets that lay between Mars and Jupiter.
Comets are small heavenly bodies that have a head called the coma and a long tail. They move across the sky and can be seen only when they travel close to the sun. The head is made of dust, ice, and frozen gases, when the ice melts, the gases and dust get blown back to form the tail, which is always away from the sun. Halley's Comet is the best-known example of a comet.
Meteors or shooting stars are small heavenly bodies. The earth's gravity pulls meteors towards the planet's surface. On entering the earth's atmosphere, they start burning. This is why they are visible as fast-moving bright lights in the sky that die out in a few seconds. Very large meteors do not get surface as meteorites. Some meteorites are very large and their impact may result in the formation of huge but shallow depressions on the earth's surface called craters.
PTK-Exams
Tools of the Astronomer
The basic tool that astronomers use to study celestial objects is the telescope. People tend to be most familiar with optical telescopes, but astronomers use telescopes that span the entire electromagnetic spectrum.
Light-gathering power
Think about trying to fill a canteen with water during a rain shower by allowing rain to fall into the opening of the canteen. Inserting a funnel into the opening of the canteen will allow you to fill it more quickly. The funnel increases the water-gathering power of the canteen. A funnel with a larger area will have more water-gathering power. Analogously, telescopes act as light funnels to gather light from a larger area down to the smaller area of the eyepiece or instrument on the telescope.
The light-gathering power of a telescope then allows astronomers to observe fainter stars or galaxies than would be possible with less light-gathering power. The light-gathering power of a telescope depends on the area, or the square of the diameter, of the primary mirror or lens. The primary purpose of most large astronomical telescopes is increased light-gathering power.
Resolving Power
The resolving power of a telescope is the ability to see sharp detail. A telescope with good resolving power allows us to see smaller details than a telescope with poor resolving power. The resolving power depends on the diameter of the primary mirror or lens.
However, turbulence in Earth’s atmosphere limits the resolving power of large telescopes. The reason that images from the Hubble Space Telescope are so sharp is that the resolving power is not limited by the atmosphere.
Magnifying power
The magnifying power of a telescope is simply how many times bigger the image appears than it actually is. Magnification does nothing to improve the quality of the image; hence it is less important than the other two functions of a telescope. The amount of magnification is determined by the eyepiece. Changing eyepieces changes the amount of magnification.
Many people incorrectly think that magnifying power is the most important function of a telescope. However, magnifying a blurry image will simply produce a bigger blurry image; the other two functions that improve the image quality are more important.
How Do Telescopes Work?
There are two basic types of telescopes. Reflecting telescopes use mirrors as the main light-gathering element; refracting telescopes use lenses. Because there are engineering limitations on how large a lens can be made, most large astronomical telescopes are reflecting telescopes.
What about the Rest of the Electromagnetic Spectrum?
Astronomers use telescopes that cover the entire electromagnetic spectrum because celestial objects emit radiation throughout the entire spectrum. At infrared wavelengths, ground-based optical telescopes with minor modifications and special instrumentations are used as infrared telescopes. Some infrared wavelengths are absorbed by the atmosphere and require telescopes launched by satellites.
Most ultraviolet, X-ray, and gamma-ray wavelengths are absorbed by the atmosphere. At these wavelengths, astronomers must use satellite-borne telescopes. X-ray and gamma-ray telescopes borrow detection techniques from high-energy elementary particle physics and bear little resemblance to optical telescopes.
Radio telescopes are basically large concave radio antennas that look similar to the antennas for satellite TV reception. Radio telescopes can be as large as hundreds of feet in diameter.
Contrary to popular belief, astronomers seldom look through telescopes. Rather, they mount various types of instruments on the end of telescopes. Digital cameras have largely replaced traditional photography. To study the chemical compositions of celestial objects, astronomers mount a spectroscope on the end of the telescope. Other types of instruments have more specialized functions, but generally, data is recorded digitally and analyzed by computers.
The Solar System
Jupiter
Our solar system consists of the Sun, a star named Sol, and eight planets orbiting it. In addition, there are numerous moons, comets, asteroids, and other smaller bodies in the solar system.
According to the International Astronomical Union’s (IAU) latest definition (2006), a 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 and (c) has cleared the neighborhood around its orbit.” The planets in order out from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There are two basic classifications of planets in the solar system. The inner planets, which are Mercury, Venus, Earth, and Mars, are all roughly similar in size and composition. Being somewhat like Earth, the inner planets are classified as the terrestrial planets. Earth’s Moon is also classified as a terrestrial planet, and many astronomers consider the Earth and Moon system as a double planet system. Terrestrial planets are basically small balls of rock. Jupiter, Saturn, Uranus, and Neptune form the other major group of planets. Being similar to Jupiter, they are called Jovian planets. They are basically big balls of gas, so they are often referred to as gas giants. Pluto does not fit into this classification scheme. Pluto has properties more like the major moons of the Jovian planets, and in 2006 was reclassified as a dwarf planet.
Astronomers think that the solar system formed when a large cloud of gas and dust began to collapse. Such a cloud is called a nebula, so this theory is called the nebular theory. Once the collapse starts, gravity pulls the cloud particles closer together and toward the center. As it collapses, it begins to spin faster and flatten. Most of the matter was used to form the Sun, and a small amount of the material in the flattened disk spun into eddies and formed the planets. In the inner part of the solar system, the Sun’s heat evaporated most of the hydrogen and helium and other gases. Hence these inner planets are mostly metal and rock, while the outer planets are mostly gases such as hydrogen, helium, ammonia, and methane. Because planets are natural byproducts of the formation of stars, most stars should have planets orbiting them.
As large as it may seem to us, our solar system is on a cosmic scale quite small. Our Sun is one of hundreds of billion stars in our Milky Way galaxy. Our galaxy is only one of an unknown number of billions of galaxies in the universe.
Question
1. Which best describes the relative size and composition of terrestrial planets compared to Jovian planets?
a) Larger, composed of rock and metal
b) Smaller, composed of rock and metal
c) Larger, composed of gas
d) Smaller, composed of gas
The Earth Makes Its Closest Approach to the Sun in Mid-January, So Why Is That the Coldest Time of the Year?
Although it’s counter-intuitive, the changing distance between the Sun and Earth does not cause the seasons. The Earth does follow an elliptical orbit around the Sun, but it is close enough to being circular that the difference in distance cannot cause the seasons.
The tilt of the Earth’s axis and the revolution of the earth around the sun causes the seasons. As the Earth orbits the Sun, the tilt of Earth’s rotational axis causes an apparent north-south movement of the Sun in the sky. On the summer solstice, June 21, Earth’s northern hemisphere is tilted 23.5° towards the Sun and the Sun is in its northernmost position in the sky. Hence in the northern hemisphere, we see the sun higher in the sky, the Sun’s rays strike the northern hemisphere more directly, the daylight periods are longer, and it gets hot.
On the winter solstice, December 21, the reverse is true. The northern hemisphere is tilted 23.5° away from the Sun. Hence we see the Sun lower in the sky, the Sun’s rays strike the northern hemisphere less directly, the daylight periods are shorter, and it gets cold out. On the spring and autumn equinoxes, March 21 and Sept 21, the Sun is directly over the equator. Clearly, it is the tilt of the Earth’s axis and the revolution of the Earth around the sun that causes the seasons and also causes the seasons to be reversed between the northern hemisphere and the southern hemisphere. The changing distance between the Earth and the Sun does not cause the seasons.
What Causes Lunar Phases?
As the Moon orbits the Earth every month, its position in the sky changes. It rises about forty-eight minutes later every day. Hence depending on where it is in its orbit, the Moon might be seen at any time of the day or night. At any given time, half the Moon is lighted by the Sun and half can be seen from the Earth. But these are not always the same parts of the Moon. If the Moon is directly opposite the Sun in the sky, we see the daylight side of the Moon and call it a full Moon.
If the Moon is between the Sun and Earth, we see only the nighttime side of the Moon and call it a new Moon. If the Moon is at a ninety-degree angle from the Sun in the sky, we see one of the quarter phases. Less than ninety degrees gives us the crescent phases, and more than ninety degrees gives us the gibbous phases. The lunar phases are not caused by the Earth’s shadow falling on the Moon. That is an eclipse.
What Causes Eclipses?
When the Moon passes between the Sun and Earth and blocks the sun from view, the Moon’s shadow falls on the Earth. That is a solar eclipse. A solar eclipse can only occur during the new Moon, but not during every new moon. The Moon’s shadow may fall above the north pole or below the south pole.
During the full Moon, when the Moon is opposite the Sun in the sky, Earth’s shadow might fall on the Moon. This is a lunar eclipse. We don’t have a lunar eclipse during every full Moon because the shadow may fall above the Moon’s north pole or below its south pole.
Question
Which moon phase is most likely to cause a solar eclipse?
a) Crescent
b) Quarter
c) Gibbous
d) None of the above
Newton’s Laws
When Copernicus suggested that the planets orbit the Sun, he did not have any idea why. The Copernican model at this point was not a very good scientific model because it lacked a physical explanation. Galileo recognized this fact and began to work on the physics of motion. Newton put it all together with his three laws of motion and his law of gravity.
You can find the words stating these laws in most textbooks, but many people recite the words without understanding them. Don’t be one of those people. Concentrate on the physical meaning of these laws.
In physics, speed and velocity are not the same thing. Velocity includes direction; speed does not. Acceleration is any change in velocity. Note the distinction here; a change in direction at a constant speed is also an acceleration.
The meaning of Newton’s first law, the inertial law, is that any change in velocity requires an external force. An object will move at a constant velocity—rest is a constant velocity of zero—until an external force acts on it. As long as there are no external forces acting on an object, its velocity will not change. If something is slowing down, when no force seems to be acting on it, friction is the external force acting on it.
The second law provides a formula for telling how much force is needed to get a given amount of acceleration. Force equals the mass times the acceleration: