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4. Further Away

Polaris Star Circle
Ian Parker

Astronomy is an old science. It probably started with shepherds, herding their flocks. They noticed the regular behaviour of the stars, discovered that some stars were wanderers (planets) and saw in the sky the action of their gods. In our days, with increasing light pollution, there will be more and more people who have never experienced the amazing beauty of the sky at night. They do not know that stars exist in many colors from reddish to blue-white, and they have never seen the Milky Way or the spark of a colliding meteorite.
What a pity.

The Milky Way Over Ontario
Kerry-Ann Lecky Hepburn

On a clear, dark night it should be possible to see a few thousand stars with the naked eye. The nearest star is Proxima Centauri, at 4.2 ly. Like many stars it is actually a star system, in this case it forms a binary system with the much brighter Alpha Centauri, the third brightest star in the night sky.

Sirius, the brightest star (again a binary system) at the firmament, is another close neighbor, at 8.6 ly. But Canopus, the third-brightest star has a distance to the Sun of 310 ly. And Polaris, the Pole Star (a triple system!) is 430 ly away.

All these stars belong to our "home" galaxy, the Milky Way. The name comes from the band of light, visible on a clear night along the sky. Several Greek philosophers thought already that this light was coming from distant stars, and Galilei confirmed it with his telescope. The picture below is a composite image of the Milky Way, combining images from both hemispheres.

The Milky Way contains at least 200 billion stars, has a diameter of 100.000 ly and a thickness of 1000 ly. Our Sun orbits the galactic center at a distance of ~26.000 ly in ~220 million year.

The life of stars is counted in millions or even billions of years, but they do not have eternal life. They are born and they die. We will come back to it later, here are a few examples.

The Orion Nebula

The Orion Nebula, part of the Hunter's "sword", is a region of massive star formation, at a distance of 1350 ly. It is a stellar nursery with ~700 stars in various stages of development.
Another example of such a nursery is the Eagle Nebula at 6500 ly. Star formation takes place inside the columns of interstellar dust. Later the new-born stars will blow away the remaining dust and become visible. The beautiful Hubble image is often nicknamed "Pillars of Creation"

Part of the Eagle Nebula

The Pleiades

The famous Pleiades is an open star cluster, at a distance of 440 ly from the Earth. It consist of more than 1000 stars, formed less than 100 million year ago. Seven stars are bright and has given the cluster its popular name, The Seven Sisters.
Globular clusters like M80 belong to the oldest objects in the Universe. They can be found in the halo surrounding the Milky Way and contain several hundred thousand stars. This one has a distance of ~ 32.000 ly.

Globular cluster M80

The Crab Nebula

Almost all stars die in a violent way. The Crab Nebula is the result of a so-called supernova event. In 1054 a massive star at 6500 ly distance "exploded", a big part of the star's mass was expelled and the rest forms now a pulsar in the center. More details later.
Our Sun will end its life in a different, slightly less violent way. It will also expel a part of its mass in the form of what is called a planetary nebula, and then cool down to a "white dwarf". No need to worry, it will take another 5 billion year. The planetary Helix nebula (distance 700 ly, only 10.000 year old ) has been nicknamed "The Eye of God"

The Helix Nebula

Until the beginning of the 20th century, most astronomers thought that the Milky Way was the Universe. That was a mistake. The Universe is much, much bigger. So in the next page we are going to look even further away!

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