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August 2 - October 8, 2021
Astronomy is the scientific study of objects in the universe and the events that shape them.
Astronomers use the term astronomical unit (shortened to AU) to define the distance between Earth and the Sun. It’s equivalent to 149 million kilometers (93 million miles).
In interstellar space, we use other units. The light-year (shortened to ly) comes from multiplying the speed of light, 300,000 kilometers per second, by the total seconds in a year. The result is the distance light travels in a year: 9.5 trillion kilometers.
The speed of light is the fastest velocity that anything can move in the universe. It is generally stated as 299,792,458 meters (186,282 miles) per second, in a vacuum.
The light from the next closest star, called Proxima Centauri, shows us how it looked just over four years ago.
When you look out in space, you’re looking back into time. The farther across space you look, the further back in time you see. This means the telescopes and instruments we use to study the cosmos are really time machines.
Spectroscopy gives information about how fast or slow an object is moving, and helps astronomers figure out how far away it is. An object moving toward us shows lines in its spectrum that are blueshifted, or shifted to the blue end of the spectrum. If it moves away from us, then the lines are redshifted —shifted toward the red end of the spectrum. The term redshift is often used to indicate an object’s distance, say a redshift of 0.5. Astronomers notate that as z = 0.5.
The entire solar system is surrounded by a shell of frozen bits of ice and rock called the Oort Cloud.
The bubble’s inner edge is called the heliopause. Beyond that lies interstellar space, where other stars go through the process of nuclear fusion just as our Sun does.
The Sun constantly emits a stream of charged particles called the solar wind.
The charged particles energize molecules of gas in our upper atmosphere, called the ionosphere. This causes them to glow. That glow is called the aurora. If it appears over the north pole, it’s called the aurora borealis; over the south pole it is called the aurora australis. Most of the time it glows white or green. However, if the solar storm is fairly energetic, more and different gases are energized and we can see reds and purples in spectacular auroral displays.
How aurora's are created!
Mercury Facts Closest point to Sun: 46 million kilometers (28.5 million miles) Most distant point from Sun: 69.8 million kilometers (43.3 million miles) Length of year: 88 Earth days Length of day: 59 Earth days Tilt of axis: 0.0 degrees Gravity: 0.38 Earth’s gravity
protosolar nebula (the solar system’s birth cloud)
Our birth nebula
The surface is covered with a thick layer of dusty material called regolith. Below that is the crust, and it’s made mostly of a mineral called plagioclase, which is also found on Earth. The crust ranges in thickness from 60 to 150 kilometers (37 to 93 miles). Beneath it is the mantle, which is made of such iron-rich minerals as olivine, which is also plentiful on Earth. The central part of the Moon—the core—may be partially molten and is probably made of iron-rich materials. The central part of the core is almost certainly pure iron. The Moon experiences “moonquakes” fairly often. They are
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When the Voyager 2 spacecraft swept past Uranus in 1986, it caught a quick image of a most unusual feature on the little moon Miranda: a cliff 5 kilometers (3.1 miles) high. It’s surrounded by what looks like cracks in the ground, suggesting that something powerful shook up this moon. This jagged scar on Miranda is named Verona Rupes, and it is the tallest known cliff in the solar system.
Biggest cliff in the solar system
January: Quadrantids April: Lyrids May: Eta Aquarids June: Arietids and Bootids July: Southern Delta Aquarids August: Perseids October: Orionids November: Leonids December: Geminids
Meteor Showers that occur every year!
Types of Stars Astronomers classify stars by their color, which reveals the temperature at the star’s photosphere (the visible “surface”). They pass starlight through a spectroscope, an instrument that splits light into its component wavelengths (creating a spectrum). Each element that exists in the star leaves distinctive fingerprints in that spectrum in the form of dark dropouts called absorption lines. Those lines show that the temperature of the star is just right for that element to exist there. Stellar spectra are incredible tools. They tell us: How fast a star is rotating What chemical
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The Milky Way has its very own central black hole called Sagittarius A*. It’s about 26,000 light-years away from us in the direction of the constellation Sagittarius. It’s a very bright radio source and also gives off x-rays. The mass of this black hole is just over 4 million solar masses.
Galaxies are huge collections of stars, gas, dust, and dark matter all bound together by gravity.
Defintion of a Galaxy
There are only three galaxies that can be seen with the naked eye from Earth (besides our own). These are the Andromeda Galaxy and the two satellite galaxies of the Milky Way called the Large and Small Magellanic Clouds.
The evolution of galaxies is a constant work in progress. For example, the Milky Way and Andromeda are bound together by a common pull of gravity. They’re approaching each other at 110 kilometers (68 miles) per second. In about 5 billion years, they will actually pass through each other. They’ll mingle stars, but more importantly, they’ll draw some of each other’s gas and dust out into long, intergalactic, star-forming streamers. Over several billion years, the two will perform a delicate cosmic dance—passing through each other several times before ending up as a giant elliptical galaxy.
The central region of the Milky Way is densely populated with stars and a black hole called Sagittarius A*.
This inverse-square law says that something looks dimmer the farther away you are. If you know the object’s luminosity you can calculate the distance.
From the Small to the Large Matter in the universe is clustered in a hierarchy. Here’s a list of cosmic objects, ranging from small to large. Planets Stars Galaxies Groups of galaxies Galaxy clusters Superclusters (clusters of galaxy clusters) Voids between clusters and superclusters Filaments of galaxies outlining the voids
The origin of the universe and how it has evolved to the complex and large structures we see today are the subject of a science called cosmology.
However, there are hypothetical particles called tachyons that always move faster than light.
The Kepler mission is on the hunt for Earth-like planets around other stars, called exoplanets, and has found many planet candidates, not all of them suitable for life as we know it.
Aristotle (384 B.C.–322 B.C.), who observed and charted the sky. He suggested that Earth was the center of the universe.
Kepler’s Laws of Planetary Motion Kepler applied Brahe’s observations in an effort to solve the problem of Mars’s peculiar-looking orbit. He reasoned that Mars followed an elliptically shaped orbit. This led to his first law of planetary motion: A planet moves in an ellipse around the Sun and the Sun is at one focus of the ellipse. By applying some geometry to the problem, Kepler then devised his second law of orbital motion: A line connected between a planet and the Sun sweeps out equal areas in equal times as the planet orbits the Sun. Kepler then applied his mathematics to calculate orbital
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Newton’s Three Laws of Motion Isaac Newton carefully worked out the math describing an object’s motion in space. On the basis of this, he postulated three laws: An object at rest will stay at rest. If it’s in motion, it will stay in motion unless it’s acted upon by another object or force. Acceleration occurs when a force acts on a mass. The greater the mass, the more force is needed to accelerate the object. Physics and astronomy students learn this as F = ma, where m stands for the amount of mass and a stands for acceleration. In the case of an apple falling to the ground, you plug in the
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He proved that some distant clouds of light in the sky are actually distant galaxies that lie well beyond the boundaries of our own home galaxy, the Milky Way.
Hubble’s discovery showed, for the first time, that the universe was much larger than anyone thought.
Hubble also discovered that objects in the universe seem to be moving apart, thus showing that the universe is expanding. He determined that the velocity of this so-called “recession” is faster the farther away an object lies from us.
That expansion rate came to be called the Hubble Constant, often noted in astronomy literature as Ho (pronounced “H-naught”).
His most famous equation is E=mc2, which established that if you take the mass of an object and multiply that by the speed of light squared, you get its energy content.
Observational astronomy, which is concerned with gathering as much information about objects in the universe as possible. Think of it as the data-gathering part of astronomy.
Astrophysics, which applies physics to explain the properties, interactions, and evolution of planets, stars, the interstellar medium, nebulae, galaxies, and other objects in the distant reaches of the cosmos. Astrophysicists also apply aspects of chemistry, electromagnetism, particle physics, and other disciplines to explore and explain objects and processes in the universe.
Theoretical astrophysics uses models, statistics, and simulations to explain objects in the universe and predict what they might do in the future.
Light can act as a particle, called a photon, or it can travel through space as a wave. This dual nature of light is central to how we detect objects in the universe. We can collect photons using cameras, but we can also measure wavelengths of light.
tectonism. This affects the outer layer of a planet or a moon, and it happens very slowly. It’s caused by heat escaping from under the crust of the planet. As it does, it warps the surface, causing it to fold or create faults (fractures).
As with volcanoes elsewhere, heat from within the world is melting subsurface ices and forcing them to erupt through what are called cryovolcanoes.
Today’s modern optical (visible-light) telescopes are computer-guided creations that can be steered quickly to view an object or event occurring in the sky. Among the better known are: Mauna Kea in Hawaii, including the twin Keck telescopes, the Subaru Telescope, and the Gemini North telescope The European Southern Observatory in Chile The Australian Astronomical Observatory in Coonabarabran Palomar Mountain Observatory, Mount Wilson, and Lick Observatory in California The Kitt Peak National Observatory in Arizona
Famous telescopes to review later
The Hubble Space Telescope is controlled by engineers at the NASA Goddard Space Flight Center, while the Space Telescope Science Institute (STScI) is in charge of all science operations.
The Kepler website at www.kepler.nasa.gov has instructions for obtaining the data.
How to access Kepler data
Fermi and the Sun The Sun can release incredible amounts of energy during outbursts called solar flares. On March 7, 2012, it unleased a powerful X5.4-class solar flare. Not only did this flare produce huge amounts of x-rays, but astronomers using Fermi detected so much gamma radiation from this one flare that for a short time the Sun was the brightest gamma-ray object in the sky.
Star charts can help you find your way around the sky. These are maps that show what’s up in the sky in the month or season you’re observing. There are many sources of star charts online as well as in such magazines as Sky & Telescope and Astronomy.
The Stars: A New Way to See Them, also by Rey, has more details and is written for older children and adults.
Book to read in the future
Easy Targets to Observe If you have binoculars or a small telescope, check out these sky sights: The Moon—you can see individual craters and other surface features Mars—through a small telescope, you can spot its dark and bright areas and its polar caps Jupiter—through binoculars you can look for its four brightest moons Saturn—look for its rings through binoculars and the bright moon Titan through a telescope The Andromeda Galaxy—near the W-shaped constellation Cassiopeia. It’s most visible from August through part of March; it is just barely visible to the naked eye The Orion Nebula—best
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