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tags: stars yellow dwarf Betelguese Mizar



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The stars at night are amazing. Even if you know very little about them, you can still appreciate them. They are such a beautiful backdrop to our horizon. Stars are the stuff of poems, lullabies, oil paintings, and romance and mystery and magic. They are beautiful in how they twinkle, and how they are whitish, but with hints of other colors, too, and the way that they fleck the night sky with a perfect randomness. There is so much beauty in the stars, and there is so much to appreciate about them, visually and artistically. But stars become even more magnificent if you bolster their aesthetic with some scientific understanding.

When you look up into the night sky, the average person, on a cloudless night, can see somewhere between 2000 to 5000 twinkling stars. If they are far away from a light source, that is. If you live in a city, you will be lucky to see more than a handful of stars, even on the clearest of nights. Light pollution is the bane of stargazing for laypersons and astronomers alike. Yet there is something special about those stars which can be seen with the naked eye. They are accessible to everyone; no special equipment is needed. In fact, the telescope was not invented and pointed skyward until the early 1600s¹; historically, the vast majority of stargazing has been done with the eyes alone. Furthermore, the sky and the stars that sprinkle it appear very much as they did to our ancestors, many thousands of years ago. We see what they saw, for the most part. Gazing at the heavens connects us with the past, and affirms our own infinitesimal place in the cosmos at large.

When you look upon the night sky, every one of those little sparkling points you see is a star in our own Milky Way galaxy. It is estimated that our Milky Way has between 100 and 400 billion stars, so with our eyes alone we can see only a small fraction of all that there is; less than even 0.000001% of the total. Individual stars in other galaxies are much, much too far away to see with the naked eye. Imagine this: If somehow we could turn up the dial and see all of the stars in our own galaxy the entire sky would be lit up without any darkness at all.

Here is an interesting fact: It turns out that most of the twinkling stars that we see in the sky are more than one star². This is because over half of what we perceive as "stars" are binary systems or larger. To our eyes, over the vast distances between earth and the stars, these multi-star systems often appear as singles. A good example of this is Polaris, better known as the North Star. Polaris is actually a triple-star system, with all 3 stars combining into a brighter yet solitary sparkle in the sky. Furthermore, in some instances we see two or more stars clumped as one even though they are not remotely close to one another, and may in fact be many, many light years away. From our vantage point, they get lined up and appear as a single star. When stars line up like this they are called "optical binaries", but alignments like this are temporary. After some weeks they will tease out and appear slightly separated, because they are usually travelling in different directions and at tremendous speeds.

Besides our sun, stars seem very far away, and they are. The closest star is Proxima Centauri, and it is just over 4 light years away. A light year is 6 trillion miles, so our closest solar neighbors are over 24 trillion miles from us. If Elon Musk piloted his Falcon 9 rocket towards Proxima Centauri it would take many tens of thousands of years to get anywhere close to it. However, some of the flecks in the sky are not stars at all, but rather planets in our own solar system. In fact, the 5 brightest things in our sky, in order, are: The sun, the moon, Venus, Jupiter, Mars, Mercury, and finally at number 7 is the star Sirius, the brightest star in the sky, which is twice as luminous as the next brightest star, Canopus. Stars generate their own light, and twinkle, while planets, and our moon, reflect light from the sun, and twinkle much less.

Stars generate light because each one of them is a powerful nuclear reactor. All stars spend most of their lifetime -- which is millions, sometimes billions, and for some, what will eventually be trillions! -- of years fusing hydrogen into helium. When a star is fusing hydrogen into helium it is said to be on the "main sequence." When the hydrogen is used up, any star we can see with the naked eye will undergo other types of nuclear fusion, burning elements heavier than hydrogen. Nuclear fusion produces an unimaginable amount of energy in the form of electromagnetic radiation, made up of infrared radiation, ultraviolet light, X-rays, and especially visible light. This light radiates outward in every direction from the star, and when we see a star at night we are seeing photons that meet our eyes after traveling for trillions of miles.

To the eye, a star is whitish with a colored lilt according to how hot it is. Counter-intuitively, blue stars run hot, while red stars are cooler. All of the stars we see in the sky are different sizes, temperatures, and colors according to how old they are, and how massive they were when they formed. Our own sun is a Yellow Dwarf that formed about 4.5 billion years ago. In billions of years, when it burns through its hydrogen, it will become a Red Giant, several times bigger than it is now, and after that it will shrink into a White Dwarf, much smaller than it currently is. Oddly, astronomers classify stars as either Dwarfs or Giants (or Supergiants); there are no "normal-sized" stars. "Dwarfs" are smaller/dimmer, whereas "Giants" and "Supergiants" are bigger/brighter. The color qualifier, like "Red" in Red Giant, is tied to how these stars appear when viewed through the Earth's atmosphere³.

Stars that we see with the naked eye are not an accurate cross section of the myriad of star-types that are out there. The most common type of star in the Milky Way is a Red Dwarf, and in fact it is a star of this type that is our nearest stellar neighbour, Proxima Centauri, mentioned earlier. However, Red Dwarfs are weak stars, that live a long time, but radiate relatively little light, so even though they compose 75% of the stars in the Milky Way we can't see them with the naked eye. Conversely, most of what we do see with the naked eye is overrepresented. For instance, about 35% of what we see are Giants, yet they make up only 0.4% of stars in the Milky Way. Giants are so massive and radiate so much light, they are easy to spot. There is also a class of star, mentioned earlier, called a Supergiant, which make up 5% of what we see in the sky, yet they compose only 0.0001% of stars in the Milky Way. So about 40% of stars we see in the night sky are made up of rare stars that occur far less than 1% in the wild. Interestingly, our own sun's star type, a Yellow Dwarf, makes up about 10% of stars in the Milky Way, yet we can hardly see any at all. Besides our sun, there are only a handful of Yellow Dwarfs visible to the naked eye; they are just too small and feeble.

Continue to Lauding the Stars: Part 2.

  1. In 1608 a patent application for a telescope was recorded in the Netherlands, and in 1609 Galileo Galilei is said to be the first person to turn a telescope skyward (after improving upon the design of the day).
  2. Giants and Supergiants tend to be part of multi-star systems. That fact, coupled with the fact that some Dwarfs are also multi-star systems, means most of what we observe with the naked eye are likely binary systems or larger.
  3. Particulate matter in the Earth's atmosphere "scatters" the lights and shifts the color of stars. Furthermore, the chemical composition of a star may change over time, meaning the color of the light it emits may also change. (As was mentioned, our own sun will be a Yellow Dwarf, a Red Giant, and a White Dwarf as it ages.)

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This writing above is from the article "Lauding the Stars." It is a two-part article dedicated to my love of starry nights.
Want to read about what motivated me to write this article? Check out: "About 'Lauding the Stars'"
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