Astronomy Part1

Astronomy An introduction to Astronomy for the BSA Astronomy Badge

Part 1: The inner Solar System

Our Sun, Sol, is a star at the center of a planetary system we call the Solar system. So as the Sun slowly sets in the valley, burning everything, let us begin our odyssey.

If you took a photograph of the Sun from the same location at noon every day for a year, remembering not to look directly at it, you would see it trace a path in the sky. It reaches the very top on the summer solstice in June and the very bottom at the winter solstice in December. This bowling pin shape is called an Analemma. The Sun is on the rise in this graphic.

The Sun is ¾ hydrogen, ¼ helium and a trace of other elements. With properly filtered telescopes, we can see sunspots, yellow in this photo, magnetic storms on the Sun that we see as dark spots, because they are cooler than the rest of the Sun. In this photo we can see a solar prominence jumping from one sunspot to another.

The core of the sun is where the nuclear reactions take place. The energy leaves through the radiative zone. This energy is carried by rising and falling hot gases in the convection zone to the photosphere, the visible layer from which the radiation and light escapes through the hot gases of the chromosphere.

Here we can see just how much larger than the Earth and Jupiter, the largest planet in the Solar System, the Sun is. You could fit 100 Earths across the Sun.

The Sun is just an average sized middle aged, 4 billion years old, star. Here we see how the Sun compares to some of the larger and younger and hotter stars we see in the night sky. Sirius is the brightest star, other than the Sun, that we can see from Earth.

Here we see Spica, the largest star from the previous slide and with Earth’s orbit for comparison, next to some of the largest stars. Our Sun may someday grow to the size of Betegeuse ( yes, it’s pronounced “Beetlejuice”) but don’t pack your bags just yet. This will not happen for a few billion years, so we have plenty of time. The Sun is too small to become an exploding nova or supernova. Notice how it is mostly the older and cooler red stars than the younger and hotter blue stars that grow to the super large sizes.

What happens when a star goes supernova? Here is a Hubble image of the supernova remnant that we saw explode in 1987. The debris that is forming a circle in the center of this image is what was blown off by the exploding star. This will eventually form a nebula, a cloud of gas and dust.

A solar eclipse occurs when our moon crosses in front of the Sun. Eclipse are so awe inspiring that battles have stopped because of them. During an eclipse is the only time we can look at the Sun without severely damaging our eyes. Here we can see some of the flares that can disrupt our communication and power grids. The Sun’s energy controls our weather by heating our atmosphere, evaporating our water and driving the winds.

Here we see the shadow of a solar eclipse crossing the surface of the Earth. Eclipses can last from a under a minute to up to 5 minutes, depending on the orbit of the Moon and your position on the Earth.

In this graphic we can see the Umbra, the shadow of a total eclipse and the Penumbra, the shadow of a partial eclipse. A solar eclipse will occur every year somewhere on the Earth but the next total solar eclipse for North America will not occur until August of 2017.

Here we can see the paths of solar eclipses until 2025. Notice that in April of 2024 that an eclipse will occur in this area and last several minutes.

The inner planets of the Solar System are the rocky planets of Mercury, Venus, Earth and Mars. The word planet is from the Greek word for wanderer. Only Mercury and Venus show phases like our Moon because they orbit the Sun inside of Earth’s orbit.

Mercury, the closest planet to the Sun looks very much like our moon. It circles the Sun in 88 days at a distance between 28.6 and 43.3 million miles.

This is one of the latest images of Mercury, taken by the Messenger space probe in October of 2008. The crater in the center of the image is called Kuiper.

Venus is nearly a twin of the Earth except it is only 67 million miles from the Sun. It takes Venus 243 days to circle the Sun. It’s surface is often compared to the Bible’s Hell. The temperature is 475°C and the air pressure is almost 100 times that of Earth.

These photos of the surface of Venus where taken by a probe that was crushed and melted soon afterwards by Venus’s atmosphere.

The Earth is the third planet from the Sun. It’s average distance from the Sun is 93 million miles or 1 Astronomical Unit (AU). The Earth revolves around the Sun in 365.24 days. This photo of the Earth was taken from Apollo 17.

When a strong solar wind from the Sun hits the Earth’s protective magnetosphere we get the Aurora Borealis and Aurora Australius, the northern and southern lights.

The northern lights have been seen as far south as southern Florida on rare occasions. One of the strongest Aurora in this area was on the night of March 13, 1989. In this film you can see how an aurora appears to dance across the sky.

The Moon is Earth’s only natural satellite. It is roughly ¼ the size of the Earth. In this view of a ‘Full Moon” we can see not only “The man in the Moon” but also the “Victorian lady reading a book” and “The rabbit”.

The Moon is kept in orbit around the Earth by two forces. The Moon’s inertia and the Earth’s gravity. If there was no gravity from the Earth, the Moon would move away from the Earth and orbit the Sun. If there was no inertia, the Earth’s gravity would pull the Moon into the Earth.

The Moon orbits the Earth in 27.3 days but goes from full moon to full moon (a synodic month) in 29.53 days at a distance roughly between 221,000 and 253,000 miles. In this graphic, the outer circle is the Moon’s orbit and shows each phase. Inside the squares is what we see from Earth.

Here we see some of the more noticeable features of the Moon, such as Mare Crisium, the 340 mile wide right eye of “The Man in the Moon”. Mare Tranquillitatis, the Sea of Tranquility, is where humans first walked on the Moon. Copernicus is an 57 mile wide, 800 million year old impact crater.

Mars the “Red Planet” has long been of interest to the people of the Earth. It ‘s surface has a great abundance of oxidized iron, rust, giving it the red color it is famous for. Mars’s core has solidified, weakening it’s magnetosphere to the point that the solar winds have blown it’s atmosphere away into space, leaving it uninhabitable for humans.

This series of photos shows how Mars seems to go backwards in the sky. This is called “retrograde motion”. This caused astronomers many problems in trying to find Mars’s orbit.

It was not until German mathematician Johannes Kepler discovered that Mars had a highly elliptical orbit that the problem of Mars orbit was solved. Mars orbits the Sun in 687 days at a distance between 128 and 155 million miles. It’s day last 24.6 hours. The diagram above shows Kepler’s 2nd Law: that a planet in a elliptical orbit sweeps out areas of equal size in equal time. The shaded areas are of equal size and it takes the planet the same amount of time to move from A to B as it does from C to D.

This photo of Mars, taken by one of the orbiter’s, shows a dust cloud from an avalanche of ice and dust along sheer cliffs near the north pole. The cloud is about 590 feet across, and about 625 feet from the base of the cliff.

These graphics show the uniqueness of Mars. The left photo shows how Olympus Mons a extinct volcano on Mars that is 15 miles high, nearly three times taller than Mount Everest, would fill the entire state of Arizona. On the globe to the right you can see Mars with Olympus Mons on the far left. On the lower central section of Mars is Valles Marinaris, a valley that would stretch from New York to California if it was on Earth.

Mars has two moons, Deimos and Phobos. These moons are actually captured asteroids that happened to get too close to Mars. Phobos speeds around Mars in only 7 hours and 39 minutes. While the smaller Deimos takes 30 hours and 18 minutes to orbit Mars.

Asteroids mainly are located in a belt between Mars and Jupiter. In this graphic we see the orbit of the asteroid Ceres as the gray ellipse. All of the unlabeled white dots in this graphic are also asteroids.

If we view the orbits of many of these other asteroids, we now see that most of these do orbit between Mars and Jupiter. These are only some of the thousands of asteroids in the Solar System.

Credits: Photo of sunset, Kepler’s Law graphic, star size graphics, and Moon phases graphic (graphics created with AutoCAD, Autodesk Inc.): Steve Smith, Waynesville, Ohio, USA . Photo of solar eclipse courtesy of Luc Viatour, Brussels, Belgium. Film of the Aurora courtesy of Dick Hutchinson, Circle, Alaska, USA. Graphics of Solar System and asteroid orbits, Mars globe view, solar analemma, Moon globe, solar eclipse and intro page created with Starry Night software, Simulation Curriculum Corp. Mercury Graphic courtesy of ESA. Mercury image courtesy of NASA, John Hopkins University Applied Physics Laboratory, Carnegie Institution of Washington. Other photos and graphics courtesy of NASA/JPL-Caltech or NASA/JPL/University of Arizona (avalanche photo).