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Nikola Božić

Astronomy


Hey, Mom! Can you see me?


Learn and Try series

Astronomy прво издање

Idea: Ljiljana Marinković Author: Nikola Božić • illustrator: Aleksandar Zolotić • graphic designer: Dušan Pavlić reviewer: PhD Milan Ćirković, MA Srđan Vebrić, PhD Oliver Trošković • editor: Milena Trutin proof reader: Violeta Babić • technical editor: Nebojša Mitić • for publisher: Dejan Begović, executive director Published by: KREATIVNI CENTAR, 8 Gradištanska street, Belgrade, Serbia Phone: +381 11 38 20 483, +381 11 38 20 464, +381 11 244 06 59 www.kreativnicentar.rs • e-mail: info@kreativnicentar.rs Copyright©KREATIVNI CENTAR 2012

To my parents, Who knew how to awaken in me the curiosity and spirit of an explorer and supported me astronomically


Nikola Božić

Astronomy Illustrated by

Aleksandar Zolotić


Contents 5 ...... The sky above us 6 ...... Astronomical observations 8 ...... Discoveries 10 ...... Constellations 12 ...... Find the North Star 12 ...... Asterisms 14 ...... The movement of the Earth and Moon 14 ...... Your own meridian 15 ...... Measuring latitude 16 ...... Phases of the Moon 17 ...... Planets of the solar system 18 ...... Characteristics of planets 20 ...... Small objects of the solar system 21 ...... Space travel

22 ...... Stars 23 ......

Heating water with solar energy 24 ...... Galaxies 25 ...... The beginnings of space 26 ...... Observation journal 26 ...... Measuring distances in the sky 27 ...... Astrophotography of the Moon 27 ...... Making observation notes 28 ...... If you become an astronomer 29 ...... Good sides of being an astronomer 29 ...... Troubles of being an astronomer 29 ...... Education opportunities 30 ...... Glossary 31 ...... Index


The sky above us

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hen you hear the news of a coming eclipse of the Sun or Moon, meteor rain or comet, you are likely to be eager to see it. Such phenomena, as well as many others, are studied by a science called astronomy. At night when the sky is clear, you can look up and see a multitude of stars, the Moon or even a lonely spark shooting across the celestial dome. If you would like to explore the sky with binoculars or a telescope, you will be doing what real astronomers do. You will find that Earth is nothing but a particle in the possibly infinite universe, as well as that we live on a rather small planet.

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The night sky and universe have been an endless source of inspiration for writers of science fiction stories and novels; movies and series about travelling to distant worlds are very popular.


Is it Mom’s birthday tomorrow?

Astronomical observations

stronomy studies space, its origin, evolution, the content of celestial objects and their movement. The word astronomy literA ally means the law on stars. Unlike most other sciences, in astrono-

The earliest astronomical observations were made in Egypt and Central America around 6,000 years ago. Back then priests studied the movement of celestial objects in order to keep track of the calendar, passing of years and months, season change as well as holidays.

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Radio telescopes, infrared telescopes, X-ray telescopes, gamma-ray telescopes and neutrino telescopes are instruments that detect radiation and particles from stars.

my there are no experiments. Sky phenomena can only be observed. As early as 2,500 years ago the ancient Greeks developed the first theories on the origin of space and what the world looked like away from the Earth. However, it was the invention of the telescope that made astronomy a modern science and lead to many great discoveries of up to then unknown space areas. The first telescope was made more than 400 years ago by the Italian astronomer, Galileo Galilei. We gained new knowledge of the world around us from the observations made by this instrument.

Nowadays, astronomers use modern telescopes, i.e. optical instruments that enable watchers to reach farther and see more light, which makes remote stars look bigger and clearer. A layer of air surrounding the Earth - the atmosphere – makes the observation of space phenomena difficult because it decreases the amount of light coming from stars. That is why sometimes scientists launch telescopes and other instruments into the Earth’s orbit. The most famous telescope in orbit is Hubble space telescope, which has been taking photos of celestial objects and collecting other important scientific data since 1990.


An astronomical observatory is a building where space observation instruments are. The most noticeable part of the observatory is the dome – a roof shaped like a hemisphere. The dome can rotate and open both partly and fully. There is a telescope that moves by means of the motor in all directions towards stars. In observatories there are also offices, very powerful computers, libraries with numerous books and scientific magazine, a lounge and small kitchen.

The first Serbian observatory was founded in the late 19th century by Milan Nedeljković, an astronomer and meteorologist, in Belgrade. In the beginning the observatory was located in a rented house in Vračar neighborhood. In 1891 it got its own building in Karađorđev park (today it is Meteorological station). Thanks to the efforts of Vojislav Mišković, an astronomer, Belgrade observatory got a new modern building equipped with new instruments in Veliki Vračar neighborhood in 1932. Today this part of Belgrade is called Zvezdara (zvezda means star) because it is a place where stars are watched from.

For exploring the solar system not only telescopes are used. Many interplanetary space probes have been launched: Mariner, Venera, Pioneer, Voyager, Mars Pathfinder, CassiniHuygens and so on. They enable scientists to explore celestial objects in close-up. Planets Venus, Mars, Jupiter, Saturn, Vesta the asteroid, Hailey’s comet, etc. have been explored in this way.

Observatories are usually built far from urban areas, because city lights may hinder observation. Sometimes people stay there and observe for a few days. That is why in observatories there are also rooms for rest.

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True!

Discoveries

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ll historical periods were important for the development of astronomy. Although discoveries from the past seem rather dull today, it took plenty of observation, mathematical calculations and knowledge to achieve that.

Today we know that the Earth revolves around the Sun, but long time ago people simply accepted what they saw in the sky – the Sun revolved around the Earth.

The first idea about the Sun being in the centre around which the Earth revolved was conceived almost 2,000 years ago by an astronomer and mathematician, Claudius Ptolemy (100 – 170). However, this idea was widely ignored in Europe until a Polish astronomer, Nicolaus Copernicus (1473 – 1543), explained that the Earth rotates around its axis and, like other planets, revolves around the Sun. The church dismissed Copernicus’s theory. As a consequence, his book On the Movement of Celestial Objects was banned for a few centuries. His idea was thought to be so peculiar that an expression Copernican’s turn was coined. Meanwhile, the Arabs translated the knowledge of the ancient Greeks into their language and enhanced it with new discoveries. That is why many stars have Arabic names (Aldebaran, Alnitak, Algol, just to name a few).

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When Italian scientist Galileo Galilei (1564 – 1642) invented the telescope in 1609, it was the beginning of a new era in astronomical observations. The first telescope observations discovered up to then invisible objects – four biggest satellites of Jupiter, details in the surface of the Moon and its craters as well as sunspots. He found that Venus had phases just like the Moon, which was the proof of Venus revolving around the Sun like the Earth.

The observations of positions of planets and 700 stars made by Danish astronomer Tycho Brahe (1546 – 1601) shed some light on the movement of planets in relation to the Sun. Brahe’s observations of planet Mars helped his student, Johannes Kepler (1572 – 1630) to establish three laws on the movement of planets. According to Kepler’s laws, planets move along their ellipses around the Sun, which is in one of the focal points of en ellipse.


Observing orbits of celestial objects lead British scientist Isaac Newton (1643 – 1727) to the conclusion that there is a force of attraction among celestial objects that holds them in place. This force (gravitation) acts on any spot and on any object – from an apple falling off the tree to the Moon staying in its orbit around the Earth. The theory of gravitation inspired British scientist Edmund Hailey (1656 – 1742) to mathematically prove that comets move around the Sun along elongated ellipses. He calculated that a comet, today called Hailey’s comet after him, would return in 1758. It appeared in the year when it was expected confirming Hailey’s claims as well Newton’s theories on the movement of celestial objects. American scientist Henrietta Leavitt (1868 – 1921) studied Cepheid variable stars. She discovered a direct relationship between a time needed for a Cepheid variable star’s luminosity to change and its distance from the Earth. This helped Edwin Hubble (1889 – 1953) to bring a revolution in science. These are his findings: the universe is expanding, it is much bigger than previously thought and all galaxies are moving away from each other – the ones that are close move away slowly, while those that are apart move away faster and faster. This rule known as Hubble’s law was the beginning of the theory of the origin The universe is expanding! of the universe. Serbian astronomy became famous thanks to Milutin Milanković (1879 – 1958). He was a construction engineer, geophysicist, mathematician and astronomer famous for his theory of ice ages, which explains this phenomenon by the Earth’s revolution around the Sun and the change in its path. He was the author of Canon of the Earth’s Insolation.

The key to great discoveries is in imagination!

In the early 20th century Albert Einstein (1879 – 1955) and his general and special theory of relativity introduced an innovation in the theory of gravity and explanation of the movement of celestial objects. His theories brought a revolution in physics by proving the similarity between the force of gravity and some other physical forces.

Ready for reduced insolation!

Milanković estimated climate change for the Earth, as well as for other planets of the solar system.

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