In the sky with the naked eye, a planet has the same size as a star (a single light point) but it is brighter than a star because a lot closer. As the planet shines with a constant brightness, the stars themselves, twinkle because of the currents of hot and cold air from the atmosphere. To identify planets you should be familiar with the stars of the zodiac because they follow the ecliptic. Compared with a planet, stars are gigantic. Sun has a diameter of ≈1,5 million km and some stars as Antares or Betelgeuse have a diameter 800 times greater than our sun. The Earth has a diameter of ≈12 756 km. Most stars appear white to the naked eye. But if we look carefully at the stars, we can notice a color: blue, white, red and even gold. When two stellar objects shine with the same brilliance, how can we recognize them? Why do stars twinkle? On 4 June 2010, Regulus, the brightest star of the constellation Leo, and Mars shone at about the same brightness. They were very close to each other, separated by 1.5 ° of arc in the sky. A pose of 10 seconds was sufficient to differentiate them. An ingenious device made it possible to achieve these artificially colored spirals, two stars. Why the planet shines with a fixed brightness?
What is the spiral of the star and of the planet? Atmospheric turbulence makes the stars twinkle, that is to say, it seems to change color rapidly and brilliance. By cons, color and brightness of the planet remain fixed. The flickering is much more pronounced in the case of the star because the light beam that reaches us is extremely thin. The star's beam is broken by the atmosphere which acts as a prism and different primary colors are observable. The atmosphere of the refractive index varies continuously as a result of turbulence. Thus the light rays composed of different colors, are deflected differently depending on their wavelength and substitute very quickly with each other, causing the apparent flicker. In other words, atmospheric disturbances break the light wavefront and gives this sparkling impression. Mars is much closer and the light beam that is seen is much wider and therefore less disturbed by turbulence. The difference between the luminous flux from a planet and a star is shown in this image. We obtain a trail in the colors of the rainbow in the case of the star Regulus (left) and a reddish streak, to the fixed color, in the case of Mars.
Image: Difference between the brightness of a star and that of a planet. We obtain a trail in the colors of the rainbow, in the case of the star (Regulus left), and a trail of fixed color, (red for Mars).
The ecliptic is the great circle of the celestial sphere crossed by the Sun in its apparent movement around the Earth.
Earth describes around the Sun, an orbit whose plane makes an angle of ≈23° 26' with the celestial equator (the equator projection).
The Sun appears to move in and traversing the twelve signs: Aries, bull, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces.