Dantes Astronomy

Front 1

One of the most famous of the Greek philosophers was ________________.

Back 1

Aristotle. He wrote encyclopedic treatises on nearly every field of human endeavor during his time. Unfortunately, his expositions in astronomy were less sound than some of his other work. The greatest of the Greek accomplishments in the fields of physics and astronomy came post-Aristotle.

Front 2

The shape of the _________ in the sky depends simply on how much of its daylight hemisphere is turned to our view.

Back 2

Moon. The phases of the moon and of eclipses are the results of illumination by sunlight. The moon itself is not luminous (it does not emit its own light). Below is a diagram of the phases of the moon; take a minute to note the position of the moon relative to the earth and the sun for the various phases:

Front 3

_______________ of Samos was the first astronomer of the Alexandrian school and devised an ingenious method to find the relative distances from the Earth to the sun and moon.

Back 3

Aristarchus. His procedure rests on the three assumptions that the moon goes about the Earth in a perfectly circular orbit, that the moon's orbital velocity is perfectly uniform, and that the sun is near enough that its rays travel along diverging paths to different parts of the moon's orbit. Although all three of these assumptions are incorrect, he pioneered a scientific approach that could be used to determine the distances from the Earth to the sun and moon.

Front 4

Aristarchus also devised an ingenious technique to determine the relative ___________ of the sun, moon, and Earth.

Back 4

Sizes. Although the data obtained and used by him were inaccurate and his results somewhat far from the truth, at least they were better than any available before and the first objective measures of astronomical dimensions based on logical reasoning.

Front 5

The _________________ hypothesis states that the Earth orbits the sun and the Earth is not the center of the universe.

Back 5

Heliocentric. Aristarchus was the first to profess this belief. This is opposed to the geocentric model of the universe, which states that the Earth is at the center of the universe and all objects revolve around it. Aristotle and Ptolemy were believers in the geocentric model.

Front 6

The greatest astronomer of ancient times was _________________.

Back 6

Hipparchus. His studies are credited with the development of both plane and spherical trigonometry, highly accurate observations, the use of old observations to determine changes, and the invention of a geometrical representation describing the motions of the sun and moon more precisely than ever before.

Front 7

Another Greek astronomer, Cladius ______________, compiled a series of thirteen volumes on astronomy known as the Almagest.

Back 7

Ptolemy or Ptolemeus. Most of the Almagest is a compilation of the astronomical achievements of the past, especially Hipparchus. However, it does contain some of his own contributions including the measurement of the distance to the moon by a technique essentially identical to the one used today.

Front 8

Nicolas _______________ was born in Thorn on the Vistula in Poland. His forte was mathematics.

Back 8

Copernicus. His great contribution to science was a critical reappraisal of the existing theories of cosmology and the development of a new model of the solar system.

Front 9

Copernicus's excellence as a mathematician and astronomer gave him the information to determine values for the distances of the various ____________ from the sun.

Back 9

Planets. He lived from 1473 – 1543, yet his calculations (as shown by the table below) compared to modern calculations show how advanced he was in his observations and mathematical genius.

Front 10

After beginning training for a medical career, ______________ found that he had little interest in the subject and later switched to mathematics.

Back 10

Galileo. His refusal to accept dogmatic statements without proof allowed his mathematic abilities to proliferate. In 1589, he became professor of mathematics and astronomy at the university at Pisa.

Front 11

Galileo's greatest contributions were in the field of ______________.

Back 11

Mechanics. Galileo experimented with pendulums, with balls rolling down inclined planes, with light and mirrors, with falling bodies, and many other objects. Galileo showed that if a heavy and light object were dropped together, even from a great height, both would hit the ground at practically the same time.

Front 12

Galileo has often been called the ___________ of modern astronomy

Back 12

Father. Galileo probably has been the person most widely recognized as the "father of modern astronomy", although there are many historians that have given the title to Nicholas Copernicus or Johannes Kepler.

Front 13

The actual first telescope that attracted much notice was built by the Dutch spectacle maker ______ _____________ in 1608, but was only about three power.

Back 13

Hans Lippershey. Historians generally credit Lippershey with the invention of the telescope, as he was the first to apply for a patent for a design. There is uncertainty about whether others had built telescopes earlier in the past.

Lippershey's telescope was a simple refracting telescope which involved two lenses:

Front 14

Galileo was the first known astronomer to build a telescope for the specific purpose of observing and recording celestial bodies. His telescope was about __________ power.

Back 14

Thirty. Hans Lippershey invented the telescope in 1608, intending it for use as a military device. Having heard of the discovery of Hans Lippershey, it was in 1609 that Galileo constructed a much improved refracting telescope of his own. He is the first person credited with using the telescope for looking at the stars. With the aid of his telescope, he was able to make keen observations that were recorded in his book Message from the Stars.

Front 15

It was Isaac ____________ who formulated the basic laws of modern mechanics and showed them to be universal throughout the solar system, applying to the motions of the celestial objects as well as to objects on the Earth.

Back 15

Newton. His greatest contributions in the fields of astronomy, mechanics, optics, and mathematics were conceived by the time he had reached the age of 24.

Front 16

Newton is also often credited with developing the next big development in telescopes in 1668 (about sixty years after Galileo's first telescope), the ______________ telescope.

Back 16

Reflecting. The reflecting telescope (also called a newtonian telescope) uses a curved mirror instead of a lens. Netwon's development of the use of mirrors instead of lenses opened the door to development of telescopes of millions of times magnification--far beyond what could ever be achieved with a lens.

Front 17

Newton's entire system is based on three laws of ____________.

Back 17

Motion. These three laws are: 1. In the absence of outside forces, the momentum of a system remains constant. 2. If a force acts upon a body, the body accelerates in the direction of the force, its momentum changing at a rate numerically equal to that force. 3. Forces are always mutual, thus if a force is exerted upon a body, that body reacts with an equal and opposite force upon whatever exerts the force upon it.

Front 18

In 1905, Albert Einstein published a paper in which he outlined his theory of ______________.

Back 18

Relativity. Einstein's theory was based on two postulates: 1. There is no absolute reference system with which we can measure absolute motions in space. The best we can hope to measure is the relative motion of one object with respect to another. 2. The speed of light, with respect to all observers, is always the same.

Front 19

The equatorial circumference of the Earth is ____________ statute miles.

Back 19

24,900. The Earth is not quite perfectly spherical. Along the Earth's equator one degree is about 60 nautical miles and a nautical mile is 1.1516 statute miles. The formula for figuring the circumference is 360 (degrees in a circle) x 60 (nautical miles in a degree) x 1.1516 (nautical miles in a statute mile).

Front 20

The study of stresses that build up gradually in the crust of the Earth and cause earthquakes is called ______________

Back 20

Seismology. Energy is often released by slippages along fissures or faults resulting in earthquakes. Some of these vibrations travel along the surface and others pass directly through the interior of the Earth. Seismology is studied through the use of instruments that pick up vibrations and record the activity.

Front 21

The ______________ increases about one degree Celsius for every one hundred feet you go downward into the crust of the Earth.

Back 21

Temperature. As the core slowly cools, conduction gradually transmits heat from the Earth's interior out through the crust. Cooling of the hot core occurs at a very slow rate.

Front 22

The chemical composition of the Earth's atmosphere is mostly _____________.

Back 22

Nitrogen. At the Earth's surface, the constituent gases are found to be 78 percent nitrogen, 21 percent oxygen, and 1 percent argon, with traces of water, carbon dioxide, and other gases. At lower elevations, variable amounts of dust particles and water droplets are also found suspended in the air.

Front 23

The Earth has a ______________ field similar to that produced by a bar magnet.

Back 23

Magnetic. The magnetic poles of the Earth are located about 1200 miles from its geographical poles: the north magnetic pole is in Northeast Canada. The origin of this magnetic field is unknown, although it may be connected with the Earth's rotation and possibly with electrical currents in the interior.

Front 24

In 1851, a French physicist named Jean Foucault proved that the Earth rotates through the use of a ______________.

Back 24

Pendulum. Foucault suspended a 200 feet pendulum weighing 60 pounds from the domed ceiling of the Pantheon in Paris. He started the pendulum swinging evenly and the direction of swing of the pendulum was recorded on a ring of sand placed on a table beneath its point of suspension. At the end of each swing, a pointed stylus attached to the bottom cut a notch in the sand. After a few moments, the plane of oscillation of the pendulum was slowly changing with respect to the ring of sand, and hence, with respect to the Earth.

Front 25

The _____________ effect is any apparent deflection in the motion of a body resulting from the Earth's rotation.

Back 25

Coriolis. Any object moving freely over the surface of the Earth appears to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere because of the rotation of the Earth beneath it. The graphic below illustrates the Coriolis effect on a projectile launched from the North Pole towards the equator:


The Coriolis effect can be seen in weather, where it affects the movement of winds (causing them to take curved paths instead of going straight) and its effects can be most obviously seen in large systems such as hurricanes.

Front 26

The Earth's ____________ is a great circle on the Earth's surface halfway between the North and South Poles.

Back 26

Equator. A great circle is any circle on the surface of a sphere whose center is at the center of the sphere. The equator is such a circle.

Front 27

There is also a series of imaginary great circles that pass through the North and South Poles called _____________.

Back 27

Meridians. These circles intersect the equator at right angles and can be used to specifiy the east-west location of that place.

Front 28

The ______________ of a place is the number of degrees, minutes, and seconds of arc along the equator between the meridian passing through the place and the one passing through Greenwich, England (the Prime Meridian), the site of the old Royal Observatory.

Back 28

Longitude. The measurement for longitude is either to the east or west of the Greenwich meridian from 0° to 180°

Front 29

The ____________ of a specific location is the number of degrees, minutes, and seconds of arc measured along its meridian starting at the equator.

Back 29

As you can see in the image above, latitude lines are horizontal; they measure how far a location is north or south of the equator. Longitude lines are vertical; they measure how far a location is east or west of the prime meridian in Greenwich, England.

Front 30

In denoting positions of objects in the sky, it is often convenient to make use of the fictitious _____________ sphere, a concept that earlier observers accepted literally.

Back 30

Celestial. The celestial sphere can be thought to be a hollow shell of extremely large radius centered on the observer. Coordinate systems, analogous to latitude and longitude can be devised to designate the positions of objects in the sky.

Front 31

By imagining that the meridian of the observer on the Earth is projected upward and outward until it reaches the celestial sphere, it then becomes the observer's celestial _________________.

Back 31

Meridian. As you can see in the figure below, the reference points we use on the earth are projected outward onto the celestial sphere, so the Earth's equator is projected outward to form the celestial equator, the north and south poles project outward to form the north and south celestial poles, and the meridians on earth are projected outward to form celestial meridians:


The celestial sphere stays still; it's the Earth that rotates. As the Earth turns, the observer's terrestrial meridian moves under the celestial sphere and the stars pass by the observer's stationary celestial meridian.

Front 32

The _____________ is the overhead point along the extension of a line from the center of the Earth up through the observer.

Back 32

Zenith. The zenith is the point on the celestial sphere that's directly over our heads at any given time. Together with the horizon, the zenith is used to denote the position of objects in the sky.

Front 33

The ____________ is a great circle on the celestial sphere 90° from the zenith.

Back 33

Horizon. The horizon passes through the center of the Earth and is parallel to the sensible horizon of a given position or the plane of such a circle. Keep in mind that the zenith and horizon are relative to where on Earth a person is standing; the zenith for a person in Seattle, Washington will not be the same as the zenith for someone in Seoul, Korea:

Front 34

A system that is relative to the observer for specifying the position of a star is the ______________ coordinate system.

Back 34

Horizontal. The horizontal coordinate system uses measurements relative to the observer's horizon, therefore two people standing in two different parts of the world will have different measurements for the same star. The system consists of two measurements--the azimuth and the altitude. The azimuth runs from 0° to 360° and tells the observer what direction to look in, while the altitude tells the observer how high to look.

Front 35

The plane in which the Earth revolves is 23.5° different than the plane of the equator and this is called the ____________ of the ecliptic.

Back 35

Obliquity. The ecliptic plane is the imaginary plane defined by the projection of Earth's orbit (the path the Earth follows around the sun) onto the celestial sphere. As you know, the Earth is tilted; as shown in the graphic below, the difference between the plane that the equator is in and the ecliptic plane is 23.5 degrees:


While the Earth’s orbit around the sun varies by about 3% (about 91.5 million miles from the Sun at the closest point and 94.5 million miles at the furthest point of the orbit), it is the obliquity of the ecliptic that causes the variance in the seasons on Earth.

Front 36

The ______________ of the Earth result because the plane in which the Earth revolves does not coincide with the plane of the Earth's equator.

Back 36

Seasons. The Earth's axis is tilted from the vertical by 23.5° as it makes its orbit around the sun. The result of this tilt (or obliquity of the ecliptic) is that the Northern Hemisphere is inclined toward the sun in June and away from it in December, thus varying temperatures in the seasons:

Front 37

The measurement of _________ is based on the rotation of the Earth.

Back 37

Time. As the Earth turns, objects in the sky appear to move around us, crossing the meridian each day. Time is determined by the position in the sky, with respect to the local meridian, of some reference object on the celestial sphere. The interval between successive meridian crossings or transits of that object is defined as a day and each day is divided into 24 equal parts called hours.

Front 38

The __________ day is the period of the Earth's rotation with respect to the sun.

Back 38

Solar. A solar day is one complete rotation of the Earth. There are about 365 days in a year (the time it takes to make one complete revolution around the sun) and 360° in a circle. Therefore, the daily motion of the Earth in its orbit is about one degree.

Front 39

With the development of railroads and the telegraph, it became necessary to establish time _________ for the standardization of time within the nation.

Back 39

Zones. In 1883, the continental United States was divided into four time zones; Eastern Standard Time (EST), Central Standard Time (CST), Mountain Standard Time (MST), and Pacific Standard Time (PST). In 1884, an international conference was held in Washington, D.C. in which 26 nations were represented. At that conference it was agreed to establish a system of 24 international time zones around the world.

Front 40

To take advantage of the maximum amount of sunlight during waking hours, ___________ ____________ time was established during the spring and summer.

Back 40

Daylight Saving. Daylight saving time is simply the local standard or zone time of the place plus one hour. Thus, on a summer evening, when it would ordinarily get dark at about 8:00 p.m. standard time, it does not get dark until 9:00 p.m. daylight saving time. The practice of having a daylight saving time is not universal--it varies from country to country.

Front 41

The natural units of the calendar are the ______, based on the period of rotation of the Earth.

Back 41

Day.

Front 42

The __________ is based on the period of revolution of the moon around the Earth.

Back 42

Month.

Front 43

The _________ is based on the period of revolution of the Earth around the sun.

Back 43

Year. The three units of calendar measure--day, month, year--do not divide evenly into any of the others. The period of revolution of the moon around the Earth is about 27 1/3 days. The period of revolution of the Earth around the sun is 365 days, 6 hours, 9 minutes, and 10 seconds. Those extra 6 hours in our orbit around the sun account for why we have a leap year every four years--to accommodate for the extra day that has accumulated.

Front 44

The _________ is an independent unit probably invented by man, although its length may have been based on the interval between the quarter phases of the moon.

Back 44

Week. The seven days of the week are named for the seven planets including the sun and moon as recognized by the ancients.