A countless number of stars and satellites and even a few planets can be seen in sky at night. The planets will most likely be brighter and they will be the closet planets to Earth. Some planets that can been seen at certain times are Mars, Saturn, Jupiter and/or Venus. They appear to shift positions in the sky from time to time. However, we know that they stay stationary. An illusion is created when the Earth orbits the Sun. It seems like the stars are moving, but, we are the ones moving. We cannot feel the Earth move while we are on the ground, but it does move. We can use this movement to determine the distance between stars and the Earth. The closer the stars are to Earth, the more they seem to move or shift positions. It would take us four years to reach the closest star, Proxima Centauri, which is 23 million miles away. Our star (the sun) is only 8 light- minutes away from Earth! The brightness of the star depends on its luminosity (light it radiates) and its distance from the earth.
The existence of the Milky Way galaxy has been acknowledged since 1750. The existence of other galaxies was not known until 1924, when Edwin Hubble proposed the theory. Hubble said that if stars in another galaxy were close enough to be measured, we would be able to calculate the distance between that galaxy and ours. Different types of stars can be distinguished by observing the color light they give off. It is hard to determine this difference with the naked eye, so telescopes are used to determine the spectrum of the light from the star. Different types of stars have different visible spectra. Certain colors are absent from the star's spectrum, and different stars have different colors missing.
I watched the video you had and one of the related videos on the side bar of youtube about the size of objects in the sky. I'll say that the term "supergiant" really fits those stars well.
ReplyDeleteI think it is amazing how there are so many stars in the sky and how we can even see planets at times.
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