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Descriptive Astronomy Exam 1
Terms in this set (90)
What is an astronomical unit?
93 million miles - the distance of the Sun from Earth
What is a light year?
6 trillion miles - the distance that light travels in a vacuum in one earth year.
What is the Milky Way?
It is the galaxy that contains our solar system. "Milky" is derived from its appearance as a dim glowing band arching over the night sky.
What is scientific notation, and why is it useful?
It is an easy way to easily handle very large numbers or very small numbers without having to fully write them out.
Convert this to scientific notation: 0.0000000056
5.6 x 10^-9
Convert this to scientific notation: 5600000000
5.6 x 10^9
What are the typical units of length, time, and mass that are used by scientists?
Length is meters, Time is seconds, Mass is Kilograms
What is the Scientific Method?
a method of procedure that has characterized natural science since the 17th century, consisting in systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.
What is a hypothesis?
proposed explanation made on the basis of limited evidence as a starting point for further investigation.
What is a theory?
a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.
What is a law?
a statement of fact, deduced from observation, to the effect that a particular natural or scientific phenomenon always occurs if certain conditions are present.
What is a sidereal day?
the time it takes for the Earth to rotate about its axis so that the distant stars appear in the same position in the sky.
How is a sidereal day different from a solar day?
A sidereal day is different because it is measured by earths position relative to the stars in the distant background and the Solar day is the time it takes for the earth to rotate on its axis so the sun appears in the same position in the sky. Also the sidereal day is shorter than a solar day by four mintues.
Looking down on Earth's north pole, which way does the Earth rotate?
The earth rotates counterclockwise.
What is a solar day?
the time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky.
Which way does the Earth revolve around the sun?
What is the difference between a planets rotation and its revolution?
rotation is how it spins itself and revolution is is how it goes around the sun
How is the Earth's year defined?
The earth's year is defined by the amount of time it takes for earth to make one complete revolution around the sun.
Why does Earth have seasons?
Earth has seasons because of how earths tilt of it's axis is based on its relative position to the sun. If your location on earth is tilted further away from the sun it will be winter and if it is tilted towards the sun it will be summer.
Where are the seasonal variations most/least dramatic?
During winter and summer
What characteristics are associated with summer?
The earth's axis is tilted toward the sun in respect to its rotation
What characteristics are associated with winter?
The earth's axis is tilted away the sun in respect to its roation
Why do the northern and southern hemispheres experience opposing seasons?
Because when one pole is pointed toward the sun the other is away from the sun.
What are solstices?
either of the two times in the year, the summer solstice and the winter solstice, when the sun reaches its highest or lowest point in the sky at noon, marked by the longest and shortest days.
What are equinoxes?
the time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of equal length (about September 22 and March 20).
Why does the moon go through phases?
The half that is facing the Sun.) The reason that we do not always see a Moon which is half lit is because of our position relative to the Moon and the Sun. As the Moon moves in its orbit, different portions of it appear (to us!) to be lit up as we look at it from Earth. This is why we see lunar phases.
How is the cycle of phases related to the month?
Because it is the length of time it takes for the moon to orbit the earth and the cycle of phases tell its location in relation to its position in orbit.
Could you point out to me the approximate position of the Moon on its orbit around the Earth for each lunar phase?
If you think of the moons orbit around earth like the face of a clock with earth at the center going clockwise the order is as followed from 12: 12- first quarter (halfway illuminated on the right side), between 1 and 2: waxing crescent (only a sliver illuminated on the right side), at 3 - new moon ( no parts of the moon are illuminated), between 4 and 5- waning crescent (only a sliver is illuminated on the left side), at 6: third quarter (half of the moon is illuminated on the left half), between 7 and 8: Waning gibbous (3 quarters of the moon is illuminated on the left side) at 9: Full moon (the whole moon is illuminated), between 10 and 11: Waxing gibbous (three quarters of the moon is illuminated on the right side)
What is the difference between waxing and waning moons?
Waxing means "growing" or expanding in illumination and waning means "shrinking" or decreasing in illumination
What ways can you tell if the moon is going through the waxing or waning portions of the lunar phase cycle?
Waxing moon illumination is on the right side of the moon, waning moon illumination is on the left side of the moon.
What is a solar eclipse?
an eclipse in which the sun is obscured by the moon.
What are the relative positions of the Sun, moon, and Earth during a solar eclipse?
Sun --- Moon --- Earth
What lunar phase is the moon in during a solar eclipse?
a new moon
What is a lunar eclipse?
an eclipse in which the moon appears darkened as it passes into the earth's shadow.
What are the relative positions of the sun, moon, and earth during a lunar eclipse?
Sun --- Earth --- Moon
What is the lunar phase of the moon during a lunar eclipse?
a full moon
What is the tidal activity on Earth during a lunar eclipse?
The tides are greater because of the gravitational pull between the earth and moon. This is due to the tidal bulge on either side of earth, spring tides occur during a new and full moon and neap tides occur during third quarter and first quarter moon.
What is the umbra?
the region of a shadow that is totally shaded (completely black)
What is the penumbra?
The portion of a shadow that is partially shaded
Why is the moon rust-colored during a lunar eclipse?
The light through Earth's atmosphere then falls onto the moon. NASA notes that the red light seen during a lunar eclipse is much dimmer than a typical moon's light. That happens because the red light is reflected back to Earth, and it is much dimmer than the white light the sun usually shines onto the moon's surface
Why do we not see eclipses every month?
A lunar eclipse occurs when the Moon enters the Earth's shadow. A solar eclipse occurs when the Moon's shadow falls on the Earth. They do not happen every month because the Earth's orbit around the sun is not in the same plane as the Moon's orbit around the Earth.
What is the celestial sphere?
an imaginary sphere of very large radius surrounding earth to which the planets, stars, sun, and moon seem to be attached
Why is the celestial sphere useful?
It is still used today to map out the constellations and measure distances and sizes between two objects that appear fixed because they are so far away from us
What is the ecliptic?
a great circle on the celestial sphere representing the sun's apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it.
What is the significance of the zodiac?
Because it is the band centered on the ecliptic and encircling the sky, it marks the center and motion of the sun, moon, mercury, venus, mars, jupiter, and saturn (the visible planets) and it is the basis of astrology.
What is your meridian?
is the great circle passing through the celestial poles, the zenith, and the nadir of a particular location.
What is your zenith?
The point in the sky that is directly above the observer.
What is your horizon?
The circular boundary between the sky and the earth.
What is your nadir?
The point on the celestial sphere that is directly below the observer: opposite of the zenith.
How do you measure altitude?
By measuring its distance in relation from the horizon.
What is a constellation?
one of the stellar patterns identified by name, usually of mythical gods, people, animals, or objects. Also the region of the sky containing that star pattern
How is an asterism different from a constellation?
A named grouping of stars that is not one of the recognized constellations. (Big dipper is an asterism and is part of Ursa Major)
What is the astronomical magnitude scale?
the astronomical brightness scale. The larger the number the fainter the star is.
How does the astronomical magnitude scale work?
The larger the number the fainter the star is, the higher the number the lower the number is.
What is precession and what causes it to occur?
It is the slow change in orientation of the earths axis of rotation. One cycle takes 26,000 years. It occurs because: Earth is bulged in the middle, the sun and moon gravity pull on earth, and the dramatic effects as a result is that the poles moves.
What effects does precession have on Earth?
It moves the poles, the earth bulges in the middle.
Where does the term "planet" come from?
They seem to wander about among the fixed stars. The ancient Greek name for such a heavenly body was plan s, which means "wanderer." The English word planet comes from the Greek plan s.
Which objects in the solar system did ancient greeks consider to be planets?
The sun and some stars
What is retrograde motion and when and how does it occur according to our understanding of the solar system today?
Retrograde motion refers to the occasional backwards motion of the planets. It is entirely an illusion caused by the moving Earth passing the outer planets in their orbits.
What is a parallax?
The apparent change in position of an object due to a change in the location of the observer. Astronomical parallax is measured in seconds of arc.
Why was a parallax such a problem for the heliocentric model until the 19th century?
The problem here is that even the closest star (apart from the Sun) are so far away that their parallax is less than one arc-second - i.e., less than 1/3600 of a degree, and therefore hard to measure.
Why did the geocentric model win more support in ancient greece?
It had an "halo effect" and surrounded some dominant philosophers (ptolemy and aristotle) and there was lack of evidence that the earth moves through space back then because they were not able to accurately see the change of stars in the night sky.
What problems did the geocentric model have that caused Copernicus to formulate a heliocentric model?
The night sky observations did not coincide with the modle and he felt that epicycles were not necessary to explain retrograde motions of planets
What was the major problem with Copernicus's model?
retrograde motion occurs, the orbits are not perfectly circular
Who was Tycho Brahe and what did he do?
danish astronomer who made the most accurate celestial observation of his time and challenged the prevailing belief in how the universe was organized.
What other famous astronomer was associated with Tycho Brahe and why was his association so important?
Johannes Kepler, he developed the planetary laws of motion
Who was Johannes Kepler?
He was who Brahe hired to work with him to map out the celestial observation
What is Kepler's law of planetary motion?
There are three laws: One- Planets move around the sun along elliptical orbits with the sun at one focus, Two- Planets move faster along the portions of their orbits that are closer to the sun, Three - planets whose orbits have semi-major axes take longer to revolve around the sun.
What is an ellipse?
a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane that does not intersect the base.
What are the foci of the ellipse?
Two fixed points on the interior of an ellipse used in the formal definition of the curve. An ellipse is defined as follows: For two given points, the foci, an ellipse is the locus of points such that the sum of the distance to each focus is constant.
What is the semi-major axis of an ellipse?
The semi-major axis is one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter. Essentially, it is the radius of an orbit at the orbit's two most distant points. For the special case of a circle, the semi-major axis is the radius.
Who was Galileo Galilei?
He was an italian astronomer
What key observations did Galileo make that were problematic for the geocentric model?
He was able to see the universe and how it moved and used a telescope and math to figure out the earths rotation around the sun.
Who was Hans Lippershey?
He is the inventor of the Telescope, he applied for the patent in 1608 but he was denied. Dutch spectral maker by trade.
Why did Galileo have to appear before the inquisition?
Because they were upset with him for challenging earth as the center of the universe because they were adamant that the sun revolved around the earth.
What contributions did Newton make to physics?
Besides his work on universal gravitation (gravity), Newton developed the three laws of motion which form the basic principles of modern physics. His discovery of calculus led the way to more powerful methods of solving mathematical problems.
Why was Isaac Newton's work so important to the heliocentric model?
Because it explained why some planets moved faster than others in relation to its position to the sun.
When was the parallax phenomenon finally observed?
Which planets are terrestrial planets?
Mercury, venus, earth, and mars.... they are small, rocky, dense, earthlike worlds and are closer to the sun, have no rings and few moons.
Which planets are Jovian Planets?
Jupiter, Saturn, Uranus, and neptune... these are jupiter like planets and are described as gas giants. They are large and have low-density, have ring systems and large families of moons.
What is the order of the planets?
Where are the two classes of planets located with respect to the Sun?
The terrestrial planets are closer to the sun and the Jovian planets are further away from the sun.
What features do planets of each type tend to have in common?
terrestrial are small, rocky, dense, and earthlike, Jovians are huge, gaseous low density planets with rings and large families of moons.
What is the Kuiper Belt?
a region of the solar system beyond the orbit of Neptune, believed to contain many comets, asteroids, and other small bodies made largely of ice.
What is the Oort cloud?
is an extended shell of icy objects that exist in the outermost reaches of the solar system. It is named after astronomer Jan Oort, who first theorised its existence. The Oort Cloud is roughly spherical, and is thought to be the origin of most of the long-period comets that have been observed.
Have either the Kuiper Belt or the Oort cloud been observed?
no direct observations have ever been made.
What is the Solar Nebula Theory?
The solar nebular hypothesis describes the formation of our solar system from a nebula cloud made from a collection of dust and gas. It is believed that the sun, planets, moons, and asteroids were formed around the same time around 4.5 billion years ago from a nebula.
What observations are explained by Solar Nebula Theory?
The planets orbit the sun in the same direction with most of their moons orbiting the same. Most planets also have the right characteristics to have formed from a disk of mainly hydrogen around a young hot sun.
What is accretion and how does it work?
it ids the sticking together of solid particles to produce a larger particle and it works with rapid acceleration in a circular orbit
What was the Late Heavy Bombardment?
(abbreviated LHB and also known as the lunar cataclysm) is an event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, corresponding to the Neohadean and Eoarchean eras on Earth. and it is when asteroids battered the young earth and moon.
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