Unit Content, Structure and Components
The Universe, Our Galaxy and Our Solar System
The Universe and Our Galaxy
The diameter of the universe “…is about 93 billion light years in diameter”.14 This means that if we think of the universe as a sphere like a soccer ball, and we calculated the distance across the whole universe would be about 900,000,000,000,000,000,000,000 (900 sextillion) miles across.15 That would be like taking the Earth and lining it up 100,000,000,000,000,000,000,000 times. These numbers are almost unfathomable to our minds. Consider that our solar system is one of more than 5,000 known solar systems just in the Milky Way galaxy alone16, this means that the Milky Way contains other planets that many people do not know much about. Just as there are many more solar systems in our Galaxy, the universe is made up of roughly 100 to 200 billion other galaxies besides ours.17 This means that these other galaxies can in turn have planets and solar systems as well. There are different types of galaxies based on their shapes: spirals, ellipticals, irregulars, interacting and active Galaxies.18 According to Astronomy Made Simple by Dr. Marvel, “The Milky Way is an average spiral galaxy with a diameter of about 100,000 light years”.19
Our Solar System
Our solar system consists of the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, and Pluto, which has been categorized as a dwarf planet. “Mercury is the planet that is closest to the sun; as a result it is often blocked from our view by the light of the sun itself” (Marvel, 72).20 This terrestrial planet has a diameter of 3,032 miles and is 35,983,605 miles from the Sun.21 Also due to its closeness to the Sun, Mercury has very different temperatures on either side of it.22 The side of Mercury that faces the Sun can reach 800 degrees Fahrenheit and the other side of Mercury can reach negative 300 degrees Fahrenheit.23 Mercury is considered to have high density, a powerful magnetic field and it is suspected that it has a core made of metal such as iron.24 Venus, the next planet, has a diameter of 7,521 miles and is 67,230,000 miles from the Sun.25 Venus has many clouds around it and has a dense atmosphere.26 Venus also gets extremely hot, at 900 degrees Fahrenheit.27 Venus has properties that are similar to earth such as mass and size, but due to the fact that Venus has an atmosphere of Carbon Dioxide that is so dense, the greenhouse effect on Venus has taken over the entire planet.28 Venus has been found to have a rocky and semi-volcanic surface.
Earth, has a radius of 3,959 miles and is 92,960,000 miles from the sun.29 “Earth is composed of large areas of land called continents and vast oceans of liquid that cover about 70% of the planet” (Marvel, 78).30 Plate tectonics (the shifting of the tectonic plates on earth’s surface), erosion (the weathering and wearing away of Earth’s surface), and the hydrologic cycle (the way that water cycles and travels through and around the earth) are the causes of constant changes to our home planet.31 Our moon is the largest of those among the terrestrial planets and is about 230,000 miles away from us.32 Mars is the next planet from the Sun, and has been the target of the largest portion of space exploration for life on other planets.33 Mars has a diameter of 4,222 miles and is 141,000,000 miles from the sun.34 Similar to Venus, the atmosphere of Mars is made up of carbon dioxide, however, the atmosphere is too thin to trap heat by the greenhouse.35 According to Astronomy made Simple by Kevin Marvel, “Mars has volcanoes, craters, canyons and polar ice caps”.36 Mars is also a cold planet, as its temperatures are usually at freezing temperatures.37
The next planet in our solar system, Jupiter, is our largest planet. Jupiter is so large that it would be possible to fit about 1000 planets the size of earth inside of it.38 The atmosphere of Jupiter has red, brown, orange and white colors.39 Jupiter is also identified by a large red spot the Great Red Spot which is the result of a disruption in Jupiter’s atmosphere and is essentially a gigantic hurricane. Jupiter has a diameter of 88,850 miles and is 483,600,000 miles from the Sun.40 Jupiter is also a fast planet, as it rotates once every ten hours, and therefore has very strong winds of over 100 miles per hour.41 Jupiter is very hot closer to the core, and below freezing above, and has a very high amount of pressure.42 Many moons (more than seventy!) orbit Jupiter, the largest being Callisto, Europa, Ganymede and Io.43 Saturn is the next planet from our sun, a diameter of 74,900 miles and is 888,200,000 miles from the Sun; Saturn is also the second largest planet in our solar system.44 The rings of Saturn are made of chunks of ice and rock, and they rotate between 30,000 and 44,000 miles per hour.45 Saturn is cold planet as it has an atmosphere that is made of helium and hydrogen and is farther from the sun; water, has a higher density than Saturn. Saturn too has many moons; the largest a large moon is called Titan and is the only moon that has an atmosphere of its own.46 Uranus and Neptune, are far out in our solar system. Uranus has a diameter of 31,760 miles and is 1,784,000,000 miles from the Sun, whereas Neptune has a diameter of 30,780 miles and is 2,799,000,000 miles away from the Sun.47 Uranus is tipped almost completely on its side, and one half of the planet will be dark and the other light for about half of a year.48 Neptune is a cold planet and has a temperature of about -350 degrees Fahrenheit.49 This information on the planets can be accessed in a reference called: Astronomy Made Simple by Kevin B. Marvel. As the main topic of this unit is stars, to give students a context, we will begin with the Sun, our closest star.
The Sun: Our Star
The Sun is the star closest to us and is the center of our Solar System. Instruments on the Solar Dynamics Observatory allow us to image and view the Sun in many wavelengths.50 Other space missions, like the Solar and Heliospheric Observatory (SoHO) have coronagraphs that can produce a virtual eclipse of the Sun through technology and image its outermost layers that are generally hidden by the glare of sunlight.51 Astronomers use these very powerful telescopes to try to observe the sun, stars and other stellar objects.52
Prior to our technical age, many cultures that have studied and worshipped the Sun for hundreds of years, and many of these cultures set their calendars by the Sun as well. Cultures such as ancient Egypt worshipped the Sun God Ra, and other indigenous cultures represented as Father Sun and Mother Earth.53 In addition to these cultures, we will learn about the Sun mythology of Hinduism with the Sun God Surya,54 as well as the mythology of the god Anansi in Africa.55 Once we discuss this history of the Sun as well as its place in our solar system, we will transition into the basics of its composition.
The diameter of the Sun is roughly 864,938 miles, and therefore the circumference is roughly 2,713,406 miles.56 This is quite astounding when we consider the size and diameter of the earth and the other planets. “You could line up 109 earths across the face of the Sun”.57 The Sun is not only large in comparison to our earth and other planets but is composed of things that we should discuss as we educate about its solar power and materials. The Sun is made of mostly hydrogen.58 This is important to explaining the fact that the sun is a low mass star, but the mass of the sun is over 700 times the mass of the earth and all the planets put together.59 The Sun is composed of varying layers and elements. According to NASA, the Sun can be divided into about seven different layers and/or zones. These layers and zones are made up into the inner layers which are: the core, the radiative zone and the convection zone;60 and the outer layers which are: photosphere, chromosphere, transition region and the corona.61 The core of the Sun is the center and inner-most region, which, like the rest of the Sun is made of hydrogen, helium and small amounts of other materials.62 This is where energy is produced through nuclear fusion which change the hydrogen to helium.63 The radiative zone is where energy from the core is transferred through radiation.64 This region of the Sun is about two to seven million Fahrenheit depending on where you are in this zone, the temperature drops and pressure drops too.65 Above the radiative zone is the convection zone where heat is transported by the movement of gas ¾ gas closest to the radiative zone gets heated and rises and as it rises it gives off heat and cools down, the cooler gas then sinks back down and gets heated again and so on.66 This convection brings heat to the photosphere, from where it leaves the Sun.67 As for the outer layers of the Sun, the photosphere (literally “sphere of light”) emits light we can see, and is the layer which is the “surface of the Sun” and on which we can view phenomena such as sunspots.68 The next layer, the chromosphere, is the layer in which the Sun emits a red light.69 The transition region connects the chromosphere to the corona and is a layer where temperature increases dramatically. The corona, is the outer atmosphere of the sun.70 Sun’s light can also be studies through spectroscopy, which means that the different wavelengths of light are separated out and studied by themselves, thus is how we determine what the Sun is composed of.71
We can see with our eyes that the Sun is incredibly bright. While the Sun does emit a lot of energy, the brightness that we see from the Sun can be attributed to how close the Sun is to the earth. According to astronomical studies, there are 149,597,870,700 meters between the earth and the Sun.72 While these numbers are high, we know that the sun is not the only star of its kind. We know that the Sun is not the largest star in our universe.73 The Sun is considered mid-sized in comparison to most other stars in our Galaxy.74 According to NASA, “There are stars that are 100 times bigger in diameter than our star”.75 This is difficult to fathom, as our Sun seems so large to us. For example, the star UY Scuti is also in our Galaxy, and has been found to be 1,700 times larger than the Sun.76 The Sun powers our planet, but how do we know just how much power we are receiving from the Sun as a whole? We know that the Sun is producing 380 quintillion (380,000,000,000,000,000,000) megawatts in measures of energy.77 In thinking about our modern times and energy, trying to fathom the amount of energy the Sun emits can be difficult. We can however, put this into simpler terms now. “…the Sun emits enough energy every second to provide for all the world’s current energy needs for 5,000 years” (Golub, Pasachoff, 12).78 We have not mastered how to collect and utilize all the power from the Sun that we can. As many people in our world convert to solar power for the planet, this could be researched. Knowing how much power the Sun emits also allows us to understand its temperature. The Sun is about 10,000 degrees Fahrenheit on its surface.79
The Sun is not only a mid-sized star, but it is also a middle-aged star.80 The Sun is about 4.6 billion years old at middle age,81 and is a yellow dwarf that will eventually become a red giant, and will end its life as a white dwarf.82 The Sun’s age is important, when we analyze its energy, as well as the length of time that it can sustain the earth. Our Sun does not have any other large stars around it.83 According to NASA, “…solar systems can have more than one Sun; In fact, that is often the case”.84 Our Sun is unique because it is the only one, we have.85 As the Sun is a star, all of these aspects of our Sun are vital to understanding stars themselves and their characteristics, formation and phases.
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