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Counting stars

By: Juliana Rocha

During the day, we can’t look into the sun, against a blue sky. But at night, we can see dots shining in the dark. Isn’t it beautiful? Stars have always fascinated people, who, even since primitive times, have been trying to observe and understand them. What are they made of? How were they formed? Can they affect what happens down here on Earth?

Stonehenge / Wikipedia

Stonehenge / Wikipedia

The basic principles of astronomy - a science that studies the formation and movement of celestial bodies - have been known by man for six thousand years. The science was important for earlier civilizations because it helped planning the crops. By observing stars, man was able to change the sky into a big clock: now that they knew when seasons would change, they could determine when to plant and when to harvest. It is believed that Stonehenge, for example, was a prehistorical observatory in England.

If we had to choose which of the celestial bodies most fascinate people, we would certainly have to choose stars. Ok, then. We call “stars” all celestial bodies that produce their own light. By the way, do you have any idea why stars emit light? Inside stars, chemical reactions that release a huge amount of energy take place. This energy is released in the form of light and can be seen by us, even though we’re millions of miles away. Did you know that the closest start to the Earth, after the Sun is more than 25 trillion miles away from us?

Sunset over the Atlantic Ocean/NOAA

Sunset over the Atlantic Ocean/NOAA

The light a stars emits is our greatest source of information about it. With the help of modern satellites and telescopes (which are capable of detecting, not only light, but other forms of radiation of energy, such as infrared and radio waves), we can find out about a star’s chemical content, temperature and age.

Astronomers classified stars according to their size and surface temperature. Depending on their size, stars can be considered supergiants, bright giants, giants, subgiants, dwarfs (or normal) and subdwarfs. To make the communication easier, each one of these names can be substituted by a Roman number, from I to VI. By temperature, starts are classified as O, B, A, F, G, K, M, R, N and S. Each letter represents a range of temperature: the surface temperature of some stars is around 2,500o C (or around 4,500o F), but other stars can reach up to 50,000o C (or around 90,000o F)!

Since there is a huge diversity of stars in the universe, astronomers still use arabic numbers from zero to nine to identify variations in brightness and temperature between stars classified as in the same class. The sun, for instance, is a G2V, that is, a normal star with a surface temperature of around 6,000o C (or around 10,800o F).

Do you want to go out now and watch the stars? With the help of a sky map, you’ll be able to find all constellations!

Find out a little more about stars:

The life cycle of a star


Fundação Planetário da Cidade do Rio de Janeiro

Imagine the Universe – National Aeronautics and Space Administration (NASA)

The Goddard Library Homer E. Newell Memorial Library (NASA)

NASA Image Gallery

NOAA Photo Library

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