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Lights in the Sky
If you are outside at night for a walk or a drive and the sky is clear, it doesn't take long before you notice lights in the sky. Whether you are in the country or the city, with a clear sky you will see things in the sky that are not terrestrial in origin and the brighter they are, the greater the chance that you will notice them. The variety of objects visible to you in the night sky varies greatly depending on your location. In the city, with all the ambient light from street lamps, cars, buildings and signs, your night vision is severely limited but you will be able to spot some of the brighter planets, and a few stars, the Moon and even a shooting star if you are lucky.
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What's up there? Many wondrous things! There are many objects that might be visible and get your notice. The planets Venus, Jupiter, Saturn and maybe Mars and even Mercury may be bright enough to garner your attention.
Venus is the queen of the planets and under the right conditions can have a magnitude approaching -4.5. (Note that the more negative the magnitude, the brighter the object: the full moon has a magnitude of -12.5, which appears almost 1700 times brighter than Venus and the sun is -26.7. For more about magnitude read Magnitude and How it Works.) Jupiter, the largest of the planets and the fourth brightest object in the sky, can reach a magnitude of -2.9 with Mars next at -2.8 with a distinct reddish hue. The elusive Mercury, which when it can be seen, is always very low in the sky, near the sun at sunrise or sunset and it can reach -1.5. Saturn, the ringed planet, rounds out the list of naked-eye visible planets with a magnitude of -0.3. As a point of reference the human eye can only make out stars down to a magnitude of +6 (remember, the more negative the magnitude, the brighter the object) .
The inner planets, Mercury and Venus will always be relatively low in the sky and be visible in the evening or morning because of the geometry of their orbits and the Earth's. The outer planets, Mars, Jupiter and Saturn can be seen throughout the night from evening to morning and can appear in the sky anywhere from horizon to zenith (the point in the sky directly above you). This is also due to the geometry of their orbits and the Earth’s.
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Brightest Stars in the Sky
There are a few stars that stand out prominently in the night sky but not quite as bright as the planets, except for Sirius, the Dog Star in the constellation of Canis Major, which shines at a magnitude of -1.42—brighter than Mars but not quite as bright as Mercury. Next in brightness is Canopus, which is in the constellation of Carina and has a magnitude of -0.72. At -0.27, the Alpha Centauri star system is next in order of brightness. This system is also the closest stars to our solar system at a distance of 4.3 light-years and can be found in the constellation of Centaurus. Arcturus is fourth on the list with a magnitude of -0.04 and is in the Bootes constellation. In the constellation of Lyra resides the star Vega, which shines at a magnitude of 0.03. Capella has a magnitude of 0.08 and is the brightest star in the constellation of Auriga and is followed by Rigel at 0.12 in the constellation of the Hunter – Orion. Orion also possesses the red giant Betelgeuse, which blazes at a magnitude of 0.5.
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What Causes Twinkling Stars?
One more thing we need to consider when we see bright objects in the sky and that is the atmosphere that we are looking through. If you are seeing an object very low in the sky, its light is passing through a denser layer of the atmosphere and is prone to more refraction effects that vary as the light passes through the air, which is moving and has changing temperatures and density. This causes the twinkling effect you will see with stars (not so much with the planets because they have a larger apparent diameter, which is not as affected by the changing physical conditions in the column of air the light is passing through.) In some cases this twinkling will be seen as dramatic color changes from blue to green to red, leading one to seriously consider the possibility that UFO's do exist! As these objects move higher in the night sky they will gradually become more stable and appear as expected.
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Viewing Satellites and the International Space Station
There are a few more objects in the night sky that can catch your eye, especially when you realize that they are silently and quickly moving across the sky, and they are satellites. The largest and brightest of these is the International Space Station. Since it has been outfitted with its full complement of solar arrays the station can appear with a magnitude equal to or brighter than Venus! The brightness of the station will vary as it transits overhead and also if the space shuttle is docked with it. The space shuttle itself is easily visible in the night sky, though not as bright as the station and the two make a fascinating sight when they are about to dock or have just undocked as these two bright dots follow each other very closely across the night sky. There are other satellites visible in the night sky but none can compare with the ISS, with the possible exception of the Iridium communications satellites that can produce flashes of light or flares in brightness that can peak at about a magnitude of -9! And, don't forget the stray meteor that blazes across the sky in a brilliant flash, they are very easy to identify by the trail they leave. The above image is a composite of two photographs showing the ISS tracking overhead and two hours later the space shuttle Discovery followed on its way to rendezvous with the station. Also visible in the image is an Iridium flare and an airplane as well as Mars and Saturn. The image was captured by Jürgen Michelberger. Check out his site for more amazing images!
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Keep Looking Up!
The stars will follow a very regular, season schedule, as they have for eons, while the planets are wanderers, as their Greek name suggests, and they will move across the sky against the fixed stars. Their orbits are very predictable and there are many sources on the web that will tell you what planets, satellites, and stars are visible at any given time. So the next time you see a bright object in the sky, take note of the season and time you are seeing it, it's relative location to the horizon and to any recognizable constellation it may be in or near, it's relative brightness and you just might be able to puzzle out what you are seeing. If you can't figure it out, get on the Internet when you have a chance and check to see what's up in the night sky!.