Special features: Situated directly above Earth's North Pole.
Navigating by the Star
Because the North Star is brighter than neighboring stars and always visible above the horizon, it helps sailors, navigators, and explorers find their way. Long before the invention of the compass, the North Star was used to find directions. When you face it, you're facing north. Accordingly, south is behind you, east is to your right, and west is to your left.
How to Find the North Star
The North Star is part of the constellation Ursa Minor (the Little Bear). It is usually easy to find with the help of the stars of the Big Bear and Cassiopeia. Even though it isn't as bright as Sirius or Vega, it stands out because there aren't many bright stars in its vicinity.
"Oh, great king, Ramses, I've come to tell you the star of Isis has risen in the heavens of your majestic kingdom. Hence, the hour has come: The great tide of the River Nile will arrive in a few days. So say the priests to the kings of thunder."
With these words, the ancient kings of Egypt would herald the rising of Sirius, the brightest star in the night sky.
QUICK FACTS
Name: Sirius (The Dog Star)
Type: Star, in the Milky Way Galaxy, in the constellation Canis
Major
Color: Bluish-white
Distance from Sun: 8.8 light-years
Diameter: 2 times larger than our sun
Long Journey to a Bright Star
Sirius is almost 9 light-years away from us. A trip to Sirius in a spacecraft traveling as fast as Voyager would take more than one hundred thousand years!
Sirius is the brightest star in the nighttime heavens. Measurements show that it is 25 times brighter than our sun. Due to its close proximity and its intensity, Sirius is the brightest star in the night skies.
Learn from the Light
Like our sun, Sirius is a star. Like every star, it emits light and radiation. From this light, we can learn quite a bit about the star. Observations have shown that the temperature on the face of Sirius is approximately 18,000°F (10,000°C). This is much hotter than the face of our sun.
We know that temperature dictates the color of the stars. The hotter they are, the bluer they appear. The colder they are, the more orange-red they appear. Sirius appears blue, while our sun appears yellow.
The Pup Star
In 1844, the German astronomer Friedrich Bessel found that Sirius has an unusually wavy orbit. Bessel concluded that the gravity of another star, unseen but very close to Sirius, was causing it to shift slightly from its orbit. Indeed, in 1862, using a telescope, astronomers were able to detect the missing star. They called it "the Pup Star" because it was like a small puppy following its mother, Sirius, the Dog Star. Its scientific name is Sirius B.
Sirius B is almost 10,000 times dimmer than Sirius. It orbits Sirius in a very elliptical orbit approximately once every 50 years.
Today, we know that Sirius B is in the white dwarf stage of its life cycle. A white dwarf is a small, very dense star whose hydrogen has completely burned up in the core.
White dwarfs are special, because they are exceptionally dense. Sirius B, for example, is only 3 times larger than Earth, but it weighs more than 300,000 times as much. If we could fill a matchbox full of matter from Sirius B, it would weigh 20 tons on Earth!
For its size, Sirius B is a real heavyweight. Its gravity is correspondingly tremendous. This immense gravity causes the motion of Sirius to be wavy.
A Hunter and His Dog
Sirius, the brightest star in the nighttime heavens, is also known as the Dog Star. It was given this name, because it belongs to the constellation Canis Major - the Big Dog. Like a devoted hunting dog, this constellation faithfully follows the constellation Orion, the Hunter.
How do we find Sirius in the heavens?
Sirius is visible in the autumn and winter months. The best time to observe it is during the middle of winter, in January and February.
To observe Sirius, go out on a clear night at around nine o'clock. The constellation Orion will be high in the southern sky. Sirius will be visible to the left of Orion, glowing very brightly.
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