(TU) Stars Lesson
Stars
There are billions of galaxies in the Universe and billions of stars in our galaxy. If you could travel at the speed of light you could make it to the Sun in about 8 minutes. To get to the closest star after our Sun would take 4.2 years and to get to the center of our galaxy it would take 25,000 years.
What is a star?
In space, light travels at a speed of 300,000 kilometers per second. A light-year is the distance that light travels in one year. Typically when we talk about a year we are thinking about an amount of time. However, when you read or write "light-year" you are referring to a measurement of distance.
Light-Year Calculation
60 seconds per minute (x) 60 minutes per hour = 3,600 seconds per hour.
3600 seconds per hour (x) 24 hours per day = 86,400 seconds per day.
86,400 seconds per day (x) 365 days a year = 31,536,000 seconds per year.
31,536,000 seconds per year (x) 186,000 miles per second =
5, 865,696,000,000 miles per year = 1 light-year in miles.
or
31,536,000 seconds per year (x) 300,000 kilometers per second =
9,469,800,000 kilometers per year = 1 light-year in kilometers.
Astronomers often use parallax to measure distances to nearby stars. Parallax is the apparent change in position of an object when you look at it from different places. The less the star appears to have moved the farther away the star is.
Stars are huge spheres of glowing gas. Stars make energy by nuclear fusion and they are made up of mostly hydrogen. The energy a star makes causes it to shine very brightly. We see our Sun and it seems to shine like the brightest star in the Universe. In reality our Sun is neither the brightest star or the largest star in the Universe. In fact the Sun is sort of an average star but Earth is so close to the Sun it feels and looks big. Compared to Earth of course it is bigger than big.
Classifying Stars
There are three main physical characteristics used to classify stars:
- size,
- temperature
- and brightness
| Class | Color | Prominent Spectral Lines | Surface Temp (K) |
|---|---|---|---|
| O | Blue | Ionized helium, hydrogen | > 25,000 K |
| B | Blue-White | Neutral helium, hydrogen | 11,000-25,000 K |
| A | White | Hydrogen, ionized sodium and calcium | 7,500 -11,000 K |
| F | White | Hydrogen, ionized and neutral sodium and calcium | 6,000-7,500 K |
| G | Yellow | Neutral sodium and calcium, ionized calcium, iron, magnesium | 5,000-6,000 K |
| K | Orange | Neutral calcium, iron, magnesium | 3,500-5,000 K |
| M | Red | Neutral iron, magnesium, and neutral titanium oxide | < 3,500 K |
Size - Stars range in size from little tiny neutron stars, up to really large stars called giant stars, and even bigger absolutely huge stars called supergiants. White dwarfs are stars about the size of Earth and the neutron stars are only about 20 kilometers in diameter.
From large to small: Supergiants, giants, medium-sized stars, white dwarfs and neutrons
Temperature - Astronmers can tell the temperature of a star by its color. Stars around 3,200 degrees Celsius will tend to be reddish in color. These are cooler stars. Stars that are about 5,500 degrees Celsius will glow white hot. Hot, hot stars around 10,000 degrees Celsius will have a slight blue hint of color and the hottest stars at 15,000 degrees Celsius will glow blue-white.
Brightness - Size and temperature will determine a stars brightness but the distance a star is from Earth will determine how bright we perceive a star to be. To account for the difference we use two different terms.
Apparent Magnitude - the brightness of a star as seen from Earth and
Absolute Magnitude - is the brightness of a star if we were determining it from a standard distance.
Our Shining Star: The Sun
The Sun, our star, is at the center of the solar system. We need its warmth and light to survive. Without the energy supplied by the Sun, Earth would be a cold and inhospitable planet. The Sun is our primary source of energy. Our world would have no liquid water, no weather, and no life without the Sun's energy. The Sun's light is not the only reason we should be thankful. It's gravity also holds our solar system together. Watch the presentation below to learn more about the Sun. Be patient it may take a few moments to load the video.
The Sun is a big ball of plasma or heated gases but the Sun does have layers. The Sun contains extreme amounts of energy that will at times come to the surface and burst outward.
What are the layers of the Sun?
Core - Also called the Solar Core, is considered to extend from the center to about 0.2 to 0.25 solar radius. It is the hottest part of the Sun and of the Solar System. It is approx. 15,000,000°C if we convert that to Farhenheit that would be 27,000,000°F.
Photosphere - The visible surface of the Sun; the upper surface of a convecting layer of gases in the outer portion of the sun whose temperature causes it to radiate light at visible wavelengths; sunspots and faculae are observed in the photosphere.
Corona - The outer atmosphere of the Sun made up of thin gases and can only be seen during a solar eclipse without telescopes its temperature is 1 - 2,000,000°C.
Chromosphere - The lower level of the solar atmosphere between the photosphere and the corona.
Solar Wind - streams of charged particles constantly given off by the Sun.
See description of diagram Links to an external site.
Recall that, up until Galileo challenged Ptolemy's geocentric model, most people believed that Earth was at the center of the universe. Although Earth seems big, when compared to our Sun, the size of our planet seems less than impressive. However, as big as our Sun seems, there are even bigger objects in the universe.
Diagram of the Sun
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