Study Guide for Astronomy
The History and the Details
Ptolemy – developed the Earth-centered theory of universe (called Geocentric)
Copernicus – developed the Sun-centered theory of universe (called Heliocentric)
Day – length of time it takes Earth to rotate once on its axis, approximately 24 hours
Month – length of time it takes the moon to orbit once around Earth, approximately 28 days
Year – length of time it takes Earth to make one full revolution around the sun – 365 and ¼ days
Revolution – Earth’s pathway around the sun – takes 365 and ¼ days (we have Leap Year every 4 years for this purpose)
Rotation – Earth spinning on its axis – takes approximately 24 hours for one rotation
Brahe – first to make detailed observations of the sky
Kepler – assisted Brahe with observations, eventually published findings and developed the 3 laws of planetary motion
Galileo – first to use telescopes to study sky
Newton – developed the Laws of gravity and motion
Hubble – developed the idea that there was more to the universe than our Milky Way Galaxy. The Hubble Space Telescope is named for him.
Refracting Telescopes – uses lenses so that light is bent and magnified into the eyepiece
Reflecting Telescopes – uses mirrors so that light is reflected and magnified, #1 choice of professional astronomers!!
Electromagnetic Spectrum – organized based on wavelengths. Longest to shortest. Longest are Radio Waves, next Microwaves, then Infrared Waves (detects heat), Visible Light (ROY G BIV), Ultraviolet waves (Sunlight), then X-Rays, lastly the shortest – Gamma Rays!
The electromagnetic spectrum is used in combination with telescopes to identify the composition of distant objects!
Constellations are patterns that stars create in the sky. It takes a LOT of imagination and patience to find them. Constellations were originally used for telling the seasons so that farmers would know when to plant crops. Eventually, it became a type of entertainment in an age where stories were passed down, not read from books. Most of the early civilizations have their own twist to the mythological creatures in the sky.
As far as locating constellations, you need a few pieces of information. The ZENITH is the sky right over your head. The horizon is where the land meets the sky. Lastly, the altitude is the degree mark ABOVE the horizon. Given these factors, you should be able to locate a constellation. Please remember that you cannot see all of the constellations all of the time. It depends on your location as well as the time of year.
Light year – the distance that light can travel in ONE year. This is 9.46 TRILLION kilometers!
Classification of Stars
The closer to Blue or White a star is the HOTTER it is (like the term White Hot). As the star ages, it cools and the color changes and eventually progresses toward Red. Stars go from White to Blue to Yellow to Red in their life span. This allows astronomers to use temperature to classify stars.
Spectroscopes can be used to help identify the composition of stars – what type of gases they are made up of. Depending on the type of gas, some colors are absorbed and others are reflected. The colors reflected are the ONLY colors we see. If an object looks YELLOW, the YELLOW is reflected and all the other colors are absorbed. If the color is white, ALL colors are REFLECTED. If the color is black, ALL colors are absorbed! Each individual gas emits (gives off) a particular color, so this helps us classify stars as well.
Brightness is also used to classify stars. Apparent Magnitude is how bright a star appears to be based on your location. Absolute Magnitude is the actual brightness. On the magnitude scales, the higher the number, the dimmer the star. Very bright stars will have magnitudes that are negative!
Parallax – the apparent shift in position. We practiced this by putting a thumb up at arm’s-length and alternated closing each eye. This is an example of parallax!
Doppler Effect – used to identify stars… Identification of RED SHIFT and BLUE SHIFT. When observing electromagnetic waves. If the waves are RED, they are moving away from your location. If they are BLUE they are getting closes. This comes back to the fact that RED waves have MUCH longer wavelengths than BLUE waves.
Life Cycle of a Star
Stars begin as areas of gas and dust – gravity pulls them together. Nuclear fusion changes hydrogen into helium. They are extremely hot (white or blue) and dense at this point. As a star goes through its life cycle, it will change in color and in size. Most stars spend the majority of their life in a stage called Main Sequence. Before a star’s death, it will be extremely large and red in color. These are called red giants or supergiants, depending on their size. The stars eventually go supernova and explode. Sometimes, red dwarf stars are left behind after a star goes supernova. These are the oldest stars in the universe!
Hertzsprung-Russell Diagram (H-R Diagram) – shows the relationship between a stars brightness and temperature. Stars are plotted all along the diagram for comparison.
Neutron stars are stars that have collapsed and the only particles left are neutrons (particles that carry no charge). A PULSAR is a neutron star that is spinning.
Black Holes – objects in the universe that are so massive that not even light can escape their gravitational pull. Astronomers believe that black holes may form when a star goes supernova.
Galaxies
Collection of stars, gases, and dust held together by gravity.
3 types:
Spiral – bulge at center and have spiral arms. Our galaxy, The Milky Way is a spiral galaxy.
Elliptical – massive globs of stars – about 1/3 of all stars are in elliptical galaxies
Irregular – galaxies that do not fit in the other categories!
Nebula – massive clouds of gas and dust in the universe
Star Clusters – 2 types
Globular – a tight group of stars that looks like a ball
Open Clusters – stars that are close relative to their surroundings (they are more spread apart)
Quasars – very bright, star-like objects that generate a lot of energy. ..believed to be the center of young galaxies that are forming!
Where Did It All Begin?
Cosmology - the study of the origin, properties, processes, and evolution of the universe
The expansion of the universe uses the movement of galaxies as its basis. Most scientists today believe the universe is continually expanding like bread dough when it is baked.
Big Bang Theory – the theory that considers that the universe began with a huge explosion. Cosmic radiation is a supporting factor in this theory.
Age of the Universe – still unknown, however it must be at least as old as the oldest stars it contains…
Solar Systems
Are formed from nebulas combined with gravity. Our solar system was formed by the solar nebula! Scientists believe that it took about 10 BILLION years for the formation to occur. Planets begin very small are called planetesimals.
The outer planets are believed to have formed first since they are much less dense and contain mostly gases. The gases on the outer planets could not have survived the temperature closer to the sun. The rocky planets are closer to the sun because of the gravitational attraction of the sun. A combination of fusion, gravity, and gases eventually developed our sun.
The Sun
Is made of hydrogen and helium, driven by fusion, and held together by gravity.
The sun has several layers:
Core – the inner most later – where the energy is generated
Radiative zone – very dense and thick
Convective zone – where gases circulate
Photosphere – visible part of the sun we can see from Earth
Chromosphere – very thin layer
Corona – forms the sun’s outermost atmosphere
Our sun is very average in size, temperature and color. It has been burning for approximately 4.6 billion years and scientists believe it will last about 10 million years total.
Nuclear Fusion – developed by Einstein is signified by the equation E = mc2. Where E is energy, m is mass, and c is the speed of light. In the process, 4 hydrogen atoms fuse to form one nuclei of helium.
Solar winds – constant flow of magnetic fields from the sun. They can develop into SOLAR STORMS and cause interference with satellite technology.
Sunspots – cooler spots on the surface of the sun
Solar Flares – eruptions on the surface of the sun
Earth
4.6 billion years old
Made mostly of rock and approximately ¾ covered in water
Earth is still cooling – earthquakes, volcanoes, and hot springs allow the Earth to release heat.
The layers of the Earth are caused by the drastic differences in density of the particles on the planet. The core is primarily iron and nickel.
As the Earth has continued to cool, there was no breathable oxygen present – only toxic gases. Eventually water vapor condensed and fell as rain. It is also possible that comets brought frozen water and added to the process. Ultraviolet light is potentially one of the pieces of the puzzle that allowed life to form on the planet. According to scientists, the first life-forms did not require oxygen. Somewhere around 3.4 billion years ago, breathable oxygen began to form on the planet.
Orbit –the path an object follows as travels around another body in space
Kelper’s Laws of Motion
1st – the orbit of planets is elliptical – between a circle and an oval (like an egg)
2nd – planets seem to move faster when they are closer to the sun
3rd – distant planets take longer to orbit the sun
Universal Law of Gravitation: 2 parts
- Gravitational attraction increases as mass increases
- Gravitational attraction decreases as distance increases
Gravitational attraction keeps planets in their orbits, but INERTIA keeps them moving. INERTIA is an objects resistance to change speed or direction.
Our Solar System
Astronomical Unit (AU) – the distance from Earth to the Sun. This is how we measure distance in our Solar System. One AU is about 150 MILLION kilometers!
The inner planets: Mercury, Venus, Earth, Mars
The outer planets: Jupiter, Saturn, Uranus, Neptune
The inner planets are called the TERRESTRIAL planets and the outer planets are called the JOVIAN or GASEOUS planets.
Use the acronym: My Very Energetic Mother Just Served Us Noodles!
Mercury: smallest planet – revolution is 88 days
Venus: has the densest atmosphere – revolution 224 days – surface temps average 900 degrees
Earth: liquid water and supports life – revolution 365 days
Mars: thin atmosphere, may have once had liquid water – has the largest mountain in the solar system - revolution 1 year and 322 days
Jupiter: largest planet, recognized by giant red spot that is a storm – revolution 11 years and 313 days
Saturn: is believed to still be forming, recognized by its rings (although all the gas giants have rings) – Saturn’s rings are very large, has a very low density – so much that it could actually float in a bathtub if we had one large enough– revolution 29 years and 155 days
Uranus: made of hydrogen and methane which is where it gets its blue color, is tilted to 90 degrees on its axis, so it lays on its side and rotates – revolution 83 years and 273 days
Neptune: very similar to Uranus in composition and size, clouds are visible on Neptune, has a storm like Jupiter – called the great dark spot – revolution 163 years and 263 days
Pluto: a dwarf planet that is half the size of Mercury, has a rocky surface – revolution 248 years and 4 days
Moons
Satellites – objects that orbit other objects in space
Moons are most likely left over material from the formation of the planets
Luna – earths Moon – normally called “The Moon”
The phases of the moon: appearance of a shadow caused by the movement and position of the moon
Waxing – lit part of the moon is getting larger
Waning – lit part of the moon is getting smaller
Eclipses: when shadows fall on other celestial bodies
Solar: Moon moves between the sun and Earth and casts a shadow on the sun, blocking out the light.
Lunar : moon passes through Earth’s shadow. This is NOT a new moon! You don’t see a solar and lunar eclipse every month because the moon’s orbit around the Earth is tilted.
Mars’s two moons, Phobos and Deimos, are small, oddly shaped satellites
Jupiter has dozens of moons. Liquid water may be beneath the surface of the moon Europa.
Like Jupiter, Saturn has dozens of moons. Most of these moons are small bodies of mostly frozen water but some contain rocky material.
Uranus has several moons. Uranus’s largest moons are made of ice and rock and are heavily cratered.
Neptune has several known moons, only one of which is large. The large moon has a thin atmosphere of nitrogen.
Pluto’s only known moon is Charon. Charon’s orbit is tilted relative to Pluto’s orbit.
Other Celestial Bodies
Comet - A small body of ice, rock, and cosmic dust loosely packed together is called a comet.
Comets have tails. When a comet passes close enough to the sun, solar radiation heats the ice so that the comet gives off gas and dust in the form of a long tail.The orbits of all bodies that move around the sun are ellipses. A comet’s ion tail always points AWAY from the sun. Many scientists think that comets come from the Oort could, a spherical region that surrounds the solar system.
Asteroids- Small, rocky bodies that revolve around the sun are called asteroids.Most asteroids are located between the orbits of Mars and Jupiter in the asteroid belt.
Meteoroids- A meteoroid is a small, rocky body that revolves around the sun.
Meteorite – a meteoroid that strikes Earth’s surface
Meteor – a meteoroid that burns up in Earth’s atmosphere (shooting star)
Rocket Science and the Great Race for Space
A rocket is a machine that uses escaping gas from burning fuel to move.Tsiolkovsky is known as the father of rocket theory.American physicist and inventor Robert Goddard launched the first successful liquid-fuel rocket in 1926. The military soon took notice and Germany developed the V2 rocket. The team was lead by Werner von Braun. He later defected to the U.S. Rocket research and development boomed in the 1950’s.
NASA - National Aeronautics and Space Administration – created by the government in 1958. Rocket development was the main task at the time.
Newton’s 3rd Law – for every action, there is an equal and opposite reaction. This is the basis of rocket propulsion.
Thrust-is the pushing or pulling force exerted by the engine of an aircraft or rocket.
The gravitational pull of the Earth is the main factor a rocket must overcome. A rocket must reach a certain velocity, or speed and direction, to orbit or escape the Earth.
Orbital velocity- is the speed and direction a rocket must travel in order to orbit a planet or moon.
Escape velocity- is the speed and direction a rocket must travel to completely break away from a planet’s gravitational pull.
Artificial satellite-any human-made object placed in orbit around a body in space…communication and weather satellites are examples.
•In 1957, the Soviets launched the first artificial satellite, Sputnik 1. It orbited for 57 days before it fell back to Earth and burned up in the atmosphere.
• Two months later, Sputnik 2 carried the first living being into space—a dog named Laika.
*This was the driving force behind the creation of NASA!*
The United States launched its first satellite, Explorer 1, in 1958.
Geosynchronous orbit – a satellite orbits at the same speed as the Earth rotates
Space probe- an uncrewed vehicle that carries scientific instruments to planets or other bodies in space.
The first space probe, Luna 1, was launched by the Soviets in 1959 to fly past the moon. In 1966, Luna 9 made the first soft landing on the moon’s surface.
In 1983, Pioneer 10 became the first probe to travel past the orbit of Pluto.
In 1961, Yuri Gargarin became the first human to orbit Earth. The Soviets were the first once again, and the Americans were concerned that their rivals were winning the space race.
In 1962, John Glenn became the first American to orbit the Earth.
On July 20, 1969, Neil Armstrong became the first human to set foot on a world other than Earth.
Apollo 11 returned moon rocks to the Earth for study. Its crew also put devices on the moon to study moon-quakes and the solar wind.
Space shuttle- a reusable space vehicle that takes off like a rocket and lands like an airplane.
Columbia, the first space shuttle, was launched in 1981.