Astronomy Final Review
Do you know what each layer of the Sun's interior and exterior are called?
(Layers innermost to outermost) Core | Radiation Zone | Convection Zone | Photosphere | Chromosphere | Corona
Penumbral Lunar Eclipse
A lunar eclipse during which the Moon passes only within Earth's penumbral shadow and does not fall within the umbra.
Total Lunar Eclipse
A lunar eclipse in which the Moon becomes fully covered by Earth's umbral shadow.
eccentricity
A measure of how much an ellipse deviates from a perfect circle; defined as the center-to-focus distance divided by the length of the semimajor axis.
Law of Conservation of Momentum
If two objects interact whatever total amount of momentum you had to begin with will be the same amount of momentum after the interaction
What happens in the Chromosphere?
It is the middle layer of the Sun. It is about 104-105 K. This is where the Sun's ultraviolet light originates
Kepler's Third Law
More distant planets orbit the sun at slower average speeds, obeying a precise mathematical relationship. (p^2=a^3) p= orbital perid in years | a= average distance from the sun in AUs
How did Ptolemy contribute to Astronomy?
Ptolemy attempted to explain retrograde motion using the Ptolemaic Model, which has planets and stars moving in perfect circles around the Earth while simultaniously rotating around a smaller circle. This theory was the prevailing one for around 1500 years
Waxing Cresent:
R half illuminated less than 50% Rises @ 9am- Highest @ 3pm- Sets @ 9pm
Waxing Gibbous:
R half illuminated more than 50%- Rises @ 3pm- Highest @ 9pm- Sets @ 3am
Celestial Equator
The extension of Earth's equator onto the celestial sphere.
South Celestial Pole
The point on the celestial sphere directly above Earth's South Pole.
What are sunspots and how does their appearance vary with time?
There is a pattern of every 11 years where sunspot activity increases (sunspot cycle)
Our Address in the Universe
We live on Earth, which is in the Solar System, in the Milky Way Galaxy, in the Local Group, in the Local Supercluster, in the Universe
Galaxy
a great island of stars in space, all held together by gravity and orbiting a common center
Full Moon:
completely illuminated- Rises @ 6pm- Highest @ midnight- Sets @ 6am
Totality
(eclipse) The portion of a total lunar eclipse during which the Moon is fully within Earth's umbral shadow or a total solar eclipse during which the Sun's disk is fully blocked by the Moon.
Can you summarize the "proton-proton" chain?
1. Two protons (hydrogen atoms) collide and fuse to form a nucleus consisting of one proton and one neutron (deuterium)- two gamma ray photons are emitted because two positrons collide and annihilate each other 2. A proton collides and fuses with the deuterium nucleus to form helium-3, a rare form of helium. This reaction also produces a gamma ray photon 3. Two helium-3 nuclei collide and fuse to form the more common helium-4. The two extra protons are released and are "available" for further reaction
What killed the dinosaurs, and what evidence supports the theory?
A giant impact killed everything around it and the subsequent debris that was sent in the air would have blocked out lots of sunlight causing a major change in climate that killed the dinosaurs. The evidence that proves this is the Iridium layer that spans the entire world that was laid down 65 million years ago. Iridium is very rare on Earth but is often found in meteorites, so this thin layer of Iridium was probably left by the giant meteorite that impacted Earth 65 million years ago. Also, dinosaur fossils all lay below this layer, and geologists have found a subsurface crater about 65 million years old in Mexico where the impact happened.
Annular Eclipse
A solar eclipse during which the Moon is directly in front of the Sun but its angular size is not large enough to fully block the Sun; thus, a ring (or annulus) of sunlight is still visible around the Moon's disk.
Total Solar Eclipse
A solar eclipse during which the Sun becomes fully blocked by the disk of the Moon.
Ellipse
A type of oval that happens to be the shape of bound orbits. Can be drawn by moving pencil along a string that is bound to two tacks acting as foci.
What is an eclipse and what conditions are necessary for it to occur?
An eclipse is an event in which one astronomical object casts a shadow on another or crosses our line of sight to the other object. For a solar eclipse the moon needs to pass directly in between the S and E at a node, for a lunar eclipse the moon needs to pass through a node and the E must be directly in front of the S
Kepler's Second Law
As a planet moves around its orbit, it sweeps out equal areas in equal times. (planets travel faster the closer they are to the sun and slower the farther they are)
How were asteroids formed and where do most of them reside?
Asteroids were formed from the giant cloud of gas (the nebula) that contracted and flattened resulting in collisions between particles that eventually solidified and accreted into planetesimals. Asteroids are the leftover planetesimals that formed inside the frost line- most reside in the Asteroid Belt.
Why are they pointing in the observed directions?
Because it is the solar wind and photons from the Sun that push against these tails meaning that no matter the direction the comet itself is traveling the tails will be facing away from the Sun.
Why does the Sun shine?
Because of nuclear fusion
How do scientists know so much about comets and asteroids?
Because they have landed on Earth before and can be studied, they can be viewed through telescopes and other data gathering technology that is used to better understand their characteristics. Also, the Nebular Theory goes a long way to describe their origins and thus how they were created and what they are made of.
Vernal Equinox (Spring)
Both the point in Pisces on the celestial sphere where the ecliptic crosses the celestial equator and the moment in time when the Sun appears at that point each year (around March 21). Start of spring in NH- fall in SH
Autumnal Equinox (Fall)
Both the point in Virgo on the celestial sphere where the ecliptic crosses the celestial equator and the moment in time when the Sun appears at that point each year (around September 21). Start of fall in NH- spring in SH
Summer Solctice
Both the point on the celestial sphere where the ecliptic is farthest north of the celestial equator and the moment in time when the Sun appears at that point each year (around June 21). Longest day in NH- shortest day in SH
Winter Solctice
Both the point on the celestial sphere where the ecliptic is farthest south of the celestial equator and the moment in time when the Sun appears at that point each year (around December 21). Shortest day in NH- longest day in SH)
What is the difference between comets, asteroids, meteors, and meteorites?
Comets are made up of hydrogen molecules and other materials and are located beyond the frost line. Asteroids are made up of rocks and minerals and are located inside the frost line. Meteorites are rocks from space that land on Earth. Meteors are the bright trail left by a meteorite.
How were comets formed and where do they reside?
Comets were formed the same way asteroids were (formed from the giant cloud of gas (the nebula) that contracted and flattened resulting in collisions between particles that eventually solidified and accreted into planetesimals), except that they formed outside of the frost line, where it was cold enough for hydrogen to solidify (ice). They are mostly located in the Oort Cloud and Kuiper Belt.
Do you know primarily what category of light comes from each layer of the exterior?
Corona is not visible unless during an eclipse, chromosphere ultraviolet light, photosphere visible light
What causes a meteor shower and why do they occur at about the same time each year?
Earth crosses the debris-filled orbit of a comet at regular intervals every year, which causes tons of material left over from the comet to enter our atmosphere and plummet towards Earth.
Geocentric Model (Theory)
Earth is the center of the universe and stationary. Everything else rotated around Earth in perfect circles
Describe all the motion of the universe
Earth rotates around axis once per day (synodic day) Earth orbits around the Sun once per year Moving relative to local stars around 70,000 km/hr Entire solar system is moving around the Milky Way Galaxy at 800,000 km/hr (takes about 230 million years to complete orbit) Milky Way Galaxy is moving throughout space, about 300,000 km/hr towards Andromeda Galaxy All galaxies are moving away from us (expansion of the universe)
What happens in the Radiation Zone?
Energy is transported upwards by photons (absorbed and readmitted)
What happens in the Convection Zone?
Energy is transported upwards by rising hot gas, while cooler surface material drops down
What conditions are necessary for fusion to occur in the Sun's core?
Extremely high temperatures need to be present for the nuclear fusion of hydrogen to occur in its core
Newton's Third Law
For every force, there is an equal and opposite reaction force
Newton's Second Law
Force = Mass x Acceleration (F=ma) | a net force causes causes things to accelerate (i.e., dump truck and bike standing still on a road, if you hit both with 10 lbs of force, the truck will not move but the bike will take odd because it is less massive)
Third Quarter:
Half illuminated on L side- Rises @ midnight- Highest @ 6am- Sets @ noon
First Quarter:
Half illuminated on R side- Rises @ noon- Highest @ 6pm- Sets @ midnight
semimajor axis
Half the distance across the long axis of an ellipse; in this text, it is usually referred to as the average distance of an orbiting object, abbreviated a in the formula for Kepler's third law.
How did Copernicus contribute to Astronomy?
He believed in a heliocentic model of the universe, but because he also believed that all planets rotated in perfect circles, his model was just as complex as Ptolemy's and was therefore not widely excepted
How did Tycho Brahe contribute to Astronomy?
He commpiled a huge collection of data using the best equipment of his time. He supported the geocentric model because he could not detect stellar parallax. His apprentice was Johannes Kepler
How did Johannes Kepler contribute to Astronomy?
He inherited all of Tycho's data, and he tired to develop a more accurate description of orbits. HIs model was off by 8 arcminutes from Tycho's, which led him to the idea of ellipses. Challenging the idea that planets orbit in perfect circles. He developed the 1st, 2nd, and 3rd Kepler's Laws
What does the brightness of a star depend on, and in what way?
It depends on distance and luminosity (the amount of power a star radiates | energy/second = watts). The farther a star is the dimmer it will appear even if its luminosity is the same.
What happens in the Corona?
It is the outermost layer of the solar atmosphere. It is about 1 million K and cannot be seen unless a solar eclipse occurs
What is the significance of the Main Sequence on the H-R diagram?
It is where stars spend the majority of their lives and can tell us things like how old a galaxy is.
What happens in the Photosphere?
It· is the visible surface of the Sun. It is about 6,000K, and it is where we get our visible light from
Waning Gibbous:
L half illuminated more than 50%- Rises @ 9pm- Highest @ 3am- Sets @ 9am
Waning Cresent:
L half illuminted less than 50%- Rises @ 3am- Highest @ 9am- Sets @ 3pm
If I gave you the apparent magnitudes of several stars, would you be able to tell me which is the brightest and which is the faintest?
Lower apparent magnitudes signify higher luminosities
New Moon:
New Moon: not illuminated Rises @ 6am- Highest @ noon- Sets @ 6pm
If you were given the spectral type of a star, would you be capable of making a statement regarding its temperature?
OBAFGKM (Temperature highest-lowest)
Could you tell a fellow student how parallax is used to measure distances?
Parallax of stars are when apparent positions of the nearest star shifts by about an arcsecond as Earth orbits the sun. p= parallax angle | equation: d(in parsecs) = 1/p(in arcseconds) OR d(in lightyears) = 3.26 x 1/p(in arcseconds)
What is the real cause of the seasons?
Seasons are dictated by two things: 1- number of daylight hours during the course of the year (average daylight is 12 hours, but in NH most daylight is in July (22nd) @ summer solstice & least daylight is in December (21-22nd) @ winter solstice- opposite in SH) (Autumnal and Vernal equinoxes get exactly 12 hours of day and night) 2- Directness of sunlight (this is controlled by the tilt of E's axis- 23.5 degrees offset frim the plane of E's orbit around S- the tilt remains constant, but the direction of the tilt will change throughout the year sometimes towards sometimes away every 6 months. On equinoxes, neither NH or SH is pointed towards Sun, so daylight is the same in both hemispheres) NOTE: if live on the equator angle of sunlight does not change much, and so it is warm year-round without seasons. Could have rainy and dry seasons though.
Could you explain to someone the different types of "solar weather" and how they might affect people on Earth?
Sunspots: are cooler than other parts of the sun's surface (4000 K) and are regions with strong magnetic fields that "pop out" from the Sun. Loops of gas often connect sunspot pairs (S and N poles). The magnetic activity causes solar flares that send out bursts of x-rays and charged particles into space. Magnetic activity also causes solar prominences that erupt high above the Sun. Charged particles streaming from the Sun can disrupt electrical power grids and disable communications satellites because it distorts the Earth's magnetic field.
Ecliptic
The Sun's apparent annual path among the constellations.
Retrograde Motion
The apparent motion of the planets when they appear to move backwards (westward) with respect to the stars from the direction that they move ordinarily (eastward). This occurs during the period in Earth's orbit where it catches up to and passes another planet, it makes it appear like that planet is moving backwards.
Do you know what happens to a comet as it gets closer to the Sun?
The comet gets hotter and a gas coma begins to form around 5 AU | Its tail forms about 1 AU from the Sun | and as solar heating diminishes, coma and tail disappear between 3-5 AU
Local Group
The group of galaxies to which the Milky Way Galaxy belongs. The Local Group has at least 70 members, most relatively small compared to the Milky Way.
Celestial Sphere
The imaginary sphere on which objects in the sky appear to reside when observed from Earth. It is a useful tool used to map the sky as seen from Earth. Two points and two circles are used as reference markers
Kepler's First Law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
Comet tails......what are they all about?
The plasma tail is the gas that is escaping from the coma that is pushed by solar wind (trails in the opposite direction of the Sun). The Dust tail is pushed by photons, which makes it a bit curved (it also trails in the opposite direction of the Sun)
North Celestial Pole
The point on the celestial sphere directly above Earth's North Pole.
Why do we see phases of the moon?
The revolution of the Moon around the Earth allows us to see different amounts of the Moon being illuminated by the Sun. Like if a person is holding a ball at arm's length in front of them with a source of light pointing at them. They can then turn, and they will see the ball go through phases like the moon.
Can you describe what is meant by the solar thermostat?
The solar thermostat is like a thermostat at home: it works to maintain a constant temperature. If the solar core were to increase in temperature, the nuclear fusion rate would soar, generating excess energy that increases the pressure and pushes the core outwards. This cools down the core's internal temperature, which in turn lowers nuclear fusion rates until it reaches equilibrium
Local Supercluster
The supercluster of galaxies to which the Local Group belongs
What determines the time of day for someone on Earth?
The term 'one day' is determined by the time the Earth takes to rotate once on its axis and includes both day time and night time
Ancient Greeks contobution to Astronomy?
They were one of the first civilizations to study the sky and understand astronomy. They realized the Earth was a sphere, or a three-dimensional circular object, and tried to measure its size. They also created an idea of a geocentric solar system in which everything orbits around the Earth.
Partial Lunar Eclipes
a lunar eclipse during which the Moon becomes only paritally covered by the E's umbral shadow
Partial Solar Eclipse
a solar eclipse in which the Sun only becomes paritally blocked by the disk of the Moon
Solar System
a star and all the material that orbits it, including its planets and moons
Lunar Eclipse
an event that occur when the moon passes through E's shadow, which can occur only at a full moon
Solar Eclipse
an event that occurs when the Moon's shadow falls on Earth, which can only occur at a new moon
Newton's First Law
an object retains its stateof rest, or constant velocity, unless acted upon by a net force
Conservation of Energy
energy can not be created or destroyed only change form
Momentum
equal to mass x velocity (p=mv) | a force acting for a given time will change an object's momentum
Conservation of Angular Momentum
equal to mass x velocity x radius | angular momentum is conserved as Earth orbits the Sun as long as Earth does not exchange angular momentum with something else it's momentum will stay the same (ex. ice skater will speed up as she spins if she draws her arms in)
Nulcear Fusion
fuels the Sun | reaction energy in which atomic nuclei of low atomic # fuse to form a heavier nucleous with a release of energy
How would you recreate the scale model of the solar system in which the Sun is the size of a grapefruit?
grapefruit-sized Sun 50 feet away is Earth, which is smaller than the head of a pin. The entire orbit of Earth's Moon fits comfortably in the palm of your hand. (you have already passed Mercury and Venus) You fly by Mars and arrive at a marble-sized Jupiter, now 250 feet from the model Sun. Looking down at the model Jupiter, the cloud bands on the largest planet are visible in great detail, as is the Great Red Spot—a hurricane-like storm the size of three Earths. A system of rings surrounds the planet, and Jupiter's 4 largest moons can be seen, with the largest—Ganymede—bigger than the planet Mercury. Your next destination is nearly twice as far from the Sun as Jupiter. You are now 470 feet from the model Sun, when you encounter the planet Saturn, appearing slightly smaller than Jupiter. Four of Saturn's moons are clearly seen. The largest, Titan—also bigger than the planet Mercury—has an atmosphere thicker than Earth's. After a comfortable 20-minute walk, stopping along the way to visit Uranus and Neptune, you arrive at the Smithsonian Castle Building, 6.5 football fields west of the model Sun (2000 ft). Here, just visible is tiny Pluto—far smaller than the head of a pin, and its moon Charon. Looking back at the model Sun, across over 6 football fields of empty space, you realize that Earth is no more than a small speck of dust orbiting close to the Sun. If you could continue your walk westward, you wouldn't find the nearest star to our Sun—Proxima Centauri, and the size of a grape—until you had reached the California coast. (roughly 4,000 km)
Acceleration
is equal to the rate of change in velocity divided by the change in time
Velocity
is the speed plus direction (ex. 10 m/h south)
Speed
magnitude of the velocity of an object | speed= distance/time (m/s)
What us E=mc(squared)
mass energy (E) = speed of light squared (c) x mass (m) | mass itself is a form of potential energy. A small amount of mass can release huge amounts of energy | consentrated energy cab spontaneously turn into particles
Aphelion
point in a planet's orbit that is farthest from the sun
Perihelion
point in a planet's orbit where it is closest to the sun
umbra
the dark central region of a shadow
What is a Light Year?
the distance light travels in one year (about 10 tillion kilometers or 6 trillion miles). It is equal to the time of how many years in the past an object is to us (ex. Andomeda Galaxy is 2.5 million ly awat, so we see today what it looked like 2.5 million years ago)
Heliocentric Model (Theory)
the idea that the sun is at the center of the solar system (but not universe)
penumbra
the lighter, outlying regions of a shadow
What is the difference between the Universe and the Visible Universe?
the space between things, on a multi galactic scale, is getting larger. The universe as a whole is infinite in size and age. The part of it we can see is called the visible universe.
Universe
the sum total of all matter and energy
Foci (Focus)
two points inside an ellipse; one being a focus
How did Galileo contribute to Astronomy?
used telescopes to overcome objections rooted in Aristotelian view: 1: Earth could not be moved bc objects in the air would be left behind- objects will stay in motion unless a force acts to slow them dow. Shown with experiements using balls 2: Non-circular oribits are not "perfect" as heavens should be- used telescope to spot sunspots and mountains/valleys on Moon proving that the Sun and Moon are not perfect 3: If Earth were really orbiting the Sun, we would see stellar paralax- showed that stars must be way farther than Tycho thought (in part by using his telescope to see the Milky Way is countless individual stars) if stars are far away, then stellar paralax was hard to detects with the current equipment of the time.
What happens in the Core?
· Energy is generated here by nuclear fusion. It is about 15 million K, and it takes the light generated here 100s of thousands of years to make it out of the Sun and into space.