1. The sky at night

2. What can we see in the night sky
When the moon is bright we can not see many other objects in the sky. At a clear night with young moon, and from a place without any light pollution, we can see more than 4000 stars just with our naked eyes.
The image of the sky at night changes every few months.

3. The planets
Like the Sun and the Moon, all the planets are moving on a belt we call ecliptic.
This belt is passing through the 13 zodiac constellations.

4. The ecliptic in the sky

5. The planets in the night sky
We can see 5 planets in the sky (Mercury, Venus, Mars, Jupiter and Saturn).
We can not see all the planets every night. It depends on the positions of the planets on their orbits around the sun.

6. The constellations
A constellation contains random stars that happens to appear at the same area in the sky. They don’t have any relation to each other, and the distances of the stars from Earth are different. Because the stars are very far away, we can see only 2 dimensions in the night sky. We can not see which star is closer and which is more far away.

7. The night sky at winter

8. The origin of constellations
The constellations we use today comes from mythology, mostly from the ancient Greeks. The ancient people recognized shapes from mythical animals and heroes in the sky. Only a few constellations resemble what they call.
There are 88 constellations in the sky. About 30 are visible only from the southern hemisphere. Some constellation are visible throughout the year.
The Dolphin constellation looks like a fish, but Eagle constellation does not look like a bird!

9. About stars
The stars, like the Sun, are shining because they burn hydrogen into helium (thermonuclear fusion).
Some stars are reddish. We call them red giants and they are old stars.
Stars are born (in big clusters) and die, like we people do. The massive stars have a shorter lifetime.

10. Open star cluster (Pleiades)

11. The names of the stars- Betelgeuse
The ancient Greeks gives us the names of the constellations, but they did give name only to a few stars. So the names of the stars come from the Arabic people. Betelgeuse is also called the α Orionis star, the brightest star of Orion constellation.
إبط الجوزاء Ibṭ al-Jauzā’, meaning "the underarm of Orion", or يد الجوزاء Yad al-Jauzā’, meaning "the hand of Orion"
This star is a red giant, 1000 times larger than our Sun.

12. The sizes of the stars
Stars have a range of sizes. The most of them are red dwarfs, and they are invisible with the naked eye.
The Sun is a medium size star, but it is 1000 times bigger than the Earth!

13. The stars we can see in the night sky
The brightest stars we can see are the closest and the more massive, like Sirius in the winter sky and Vega (wāqi‘ meaning "falling" or "landing", via the phrase an-nasr al-wāqi‘, "the falling eagle) in the summer sky.

14. The apparent movements of the constellations
The Earth is in orbit around the Sun, so we see different constellations each season. During the night we see the stars moving in the sky, because the Earth is turning.
All the stars appear to move around the polar star

15. The real movements of the stars
The stars are very far away. So we can not see the real movements of the stars.
Our Sun needs 240 millions years to orbit the Galaxy's center!

16. How can we found the polar star
Concern we put a giant needle through the south pole to the north pole. This needle would point the polar star. It is the only star what we can see all night and every night on the same position in the sky.
We can found it easily extending 4 times the (unreal) line between the 2 stars in the body of the Big Dipper that are far from the tail, and not to the direction what the tail is pointing.

17. The polar star in the sky

18. The constellations next to the polar star
The constellations next to Polaris are visible all year around (circumpolar constellations).
Us more far from Polaris (south) a constellation is located in the sky, it appears for a shorter period of time. So we can observe Scorpion only during the summer and Orion during the winter.

19. What else can we observe in the night sky
We can see a few star clusters. They contain many young stars what are all formed at the same period of time. The most famous is Pleiades in the Taurus constellation. We can see 7 stars of Pleiades but there are more than 3000 stars in this cluster.

20. The <falling stars>
We can see meteors burning in the atmosphere.
They are small stones and not stars. Stars are very big, a million times more massive than Earth is!

21. The milky way
We can see a piece of our Galaxy's spiral. The spiral is an area in our Galaxy where stars and gas are more dense.
In the spiral are many beautiful object that we can observe with a telescope.

22. The milky way in the night sky

23. The most distance object we can see
Andromeda galaxy is the most distance object we can see with naked eye. It is times more distance than the stars we see in the sky (2,3 million light years).

25. From the southern hemisphere
The southern night sky is amazing. We can look at the center of the Galaxy, but we also can easily see our 2 big satellite galaxies, the Big and the Small Magellanic clouds.
They appear like small clouds in the sky!

26. But we can see only very little
Astronomy has to do with very distant and faint objects, like nebulas, globular clusters, galaxies and double stars. We can observe these objects only with a telescope.
And we are not able to follow the evolution of these objects, because it takes millions ore milliards of years!

27. More <invisible> objects in the sky

28. Looking at the night sky gives us the opportunity to image the size of the universe