Astronomy Midterm Review Flashcards
What is the definition of Astronomy?
Astronomy is the study of objects and their interactions with each other beyond planet Earth
What is the definition of Science? and what does it generate?
Science itself is a process, as Science is when we attempt to generate a method to create a common understanding of how nature behaves.
Science generates series of approximations of the natural world
What is the three processes of the Scientific Method?
- The first step is when you gather data, through observation
- You then create a model from your observations
- After creating the model, you test the model to see if your data agrees with your model
If the data doesn’t agree with the data, then you must change the model, however if it does, you are able to create a general theory after many steps
What is a Hypothesis?
A Hypothesis is an educated guess that is able to be tested. In other words, you try to explain why the unknown behaves the way it does
What is a Theory?
A Theory is a hypothesis that has been repeatedly tested in multiple ways by multiple scientists, which results in a general consensus of what the best current understanding/approximation of the unknown
What is a Consistent? (Hallmark of Science)
A consistent is when the results of repeated observations and experiments about a natural phenomenon are within the same range
What is an Observable? (Hallmarks of Science)
The phenomenon you are trying to explain must be observable, either through a controlled creation of an event in a lab, or by observing nature itself
What is a Natural Mechanism? (Hallmarks of Science?)
In order to be considered science, a natural mechanism must be present to explain the cause of the phenomenon
What is a Testable Prediction? (Hallmarks of Science)
Any sort of explanation of a phenomenon must have a prediction that can be observed/measured
What are the two Foundational Principles? (Hallmarks of Science)
- Our minds are changed when new data demands it because scientific explanations are always subject to revision and correction if new data arises
- Everything must be debated by multiple scientists to confirm authenticity
What is a Built-in Assumption? (Natural Law)
A built-in assumption assumes that the universe is orderly, reasonable, and testable, as the laws of nature are the same everywhere in the universe
What is the Scientific Notation
Since Astronomy frequently deals with very large numbers, a scientific notation is used to write large numbers in a more compact way
What is an example of the Scientific Notation?
Distance to the Sun: 150,000,000 km = 1.5 x 108 km
4x1015 = 4,000,000,000,000,000
What are Unit’s, and what are their purposes?
Scientists will present evidence, often in the form of measurements. Units are used to accompany a value to create a measurement.
What is the definition of a Light-Year Unit?
A Light-Year is the distance that light travels within one year
How fast does light travel?
Light travels at a speed of 300,000 km/s
How far is 1 light-year?
1 light year = 9.46 x 1012 km
In other words, almost 10 trillion kilometres
How does light-year work?
When you look at something that is one light-year away, you are actually perceiving it how it was a year ago
How does light-year correlate to looking “back in time”?
And what pros and cons arise from this?
When looking at a sky object that is a light-year away, you are perceiving it how it was a year ago. In other words, you are looking one year into the past
While it does enable us to label the distance between sky objects, it sets a limit on how quickly we can observe/learn about events within the universe
If a star that was located 4720 light-years away enters our telescopes, how long has the light been traveling through space? And what year would we have to wait until we can take a picture?
The light has been traveling through space for 4720 years. If we wanted to take a picture of the light, we would need to wait an additional 4720 years in order to take a picture
How big is planet Earth?
About 13,000 km wide
How big is the Solar System?
About 50 x 1013
or 2 light-days wide
How big is the Sun?
About 1,392,700 km wide
What is a star?
A star is an object that is mainly made of plasma which is held together by gravity, which results in a glowing ball of gas that can generate light through nuclear fusion
What is a planet?
A planet is a moderately large object that orbits a star, and shines by reflected light emitted from the star
What characteristics can planets have?
Planets can be rocky, icy, or even gaseous in their composition
What is the Milky Way Galaxy?
The Milky Way Galaxy is comprised of a collection of stars that can be seen by the unaided eye
How big is the Milky Way Galaxy?
The Milky Way Galaxy is as big as a 100,000 -light-year sphere
What are Nebulae’s?
Typically found in the Milky Way Galaxy’s
A nebula is a cloud of gas and dust within the Milky Way Galaxy
What are Globular Clusters?
Typically found in the Milky Way Galaxy’s
Are a cluster of stars within the galaxy
What is the nearest major galaxy to the Milky Way?
The Andromeda Galaxy which is 2.5 million light-years away from it
What is the Cosmic Calendar?
A scale that compresses the history of the universe into 1 year
What is the timeline within the Cosmic Calendar?
Major months: January, May, September, October, November, & December
January: The Big Bang Occurs
May: The Milky Way Galaxy Forms
September: Our Solar System Forms, beginning life on Earth
October: Earth’s atmosphere becomes oxygenated
November: First complex life forms appear
December: Leads up to the presence of humans
What is the December Timeline in the Cosmic Calendar?
Major dates: 19th, 20th, 25th, 26th, 30th, 31st
19th: Vertebrates appear
20th: Land plants appear
25th: Dinosaurs appear
26th: Mammals appear
30th: Dinosaurs become extinct
31st: Humans appear
What is science, and what is not science?
Science is not only a body of facts, but rather a process that attempts to explain how something in nature works
Why can Astronomy be considered as Observational Science and Historical Science?
Observational Science b/c: Astronomers create tests from observing many samples of the certain object of study, while also noting down important information on how each sample differs
Historical Science b/c: Anything that was observed had already happened in the universe, and cannot can be changed
What is the main fundamental assumption made about the universe? and why must we make this assumption?
The same laws apply everywhere in the universe. For example, the law that determines the motions of stars in space are the same exact laws that determines the arc of a baseball after being hit by a batter
The reason why we make this assumption is that astronomers would not make much progress since the laws are inconsistent. Astronomers would not be able to determine what happened in other “neighborhoods”
How far is the nearest star?
The nearest star to us is a system called Alpha Centauri which is about 4.3 light-years away
Why is travel time (light-years) such a tremendous benefit to astronomers/scientists?
If astronomers wanted to learn about how the universe came to be, they need to find the evidence about each period of time of the past
What is the distance from the Sun to the Earth?
150 million kilometers away
What is in our solar system?
Our solar system is comprised of eight planets, along with their moons and smaller bodies such as dwarf planets
What is dark matter?
Dark matter that cannot be currently observed with our instruments, however we know that dark matter is present because of the pull it exerts onto the stars and raw material we CAN observe
Everything else about dark matter are unfortunately unknown
What is the closest galaxy outside of the Milky Way?
Two dwarf galaxies that lie 200,000 light-years away
What is the Magellanic Clouds?
The Magellanic Clouds are two other galaxies that lie beyond the Sagittarius dwarf galaxy
What is the Local Group?
The local group is a certain part of a supercluster of galaxies, which were called the Virgo Supercluster
What is the Virgo Supercluster?
A supercluster of galaxies that stretches over a diameter of 110 light years
What is the most abundant element within the Universe?
Hydrogen
What is the structure of an atom?
The structure of an atom consists of a central, positively charged nucleus which is surrounded by negatively charged electrons
Bulk of the matter of atoms are found in the nucleus, which consist of positive protons and electrically neutral neutrons which are bounded tightly together in a small space
How many stars can be seen with the naked eye? and do they all belong to the Milky Way Galaxy?
Looking up, the naked eye can see 3000 stars, as well as the Milky Way Galaxy. All stars we see in the sky are part of the Milky Way Galaxy
What is the Celestial Sphere?
Whenever we look up at the sky, we fall under the impression that the sky is a dome shape that stretches from horizon to horizon
What are the characteristics of a Celestial Sphere?
What is the North & South Celestial Pole, Celestial Equator, & Ecliptic?
North Celestial Pole: The point directly above Earth’s North Pole
South Celestial Pole: The point directly above Earth’s South Pole
Celestial Equator: An extension of Earth’s equator onto the sphere
The Ecliptic: Is a pathway the Sun takes on the Celestial Sphere throughout the year
What is the Zenith point?
The point that is directly over your head
What is the Horizon?
A point where the ‘sky dome’ meets the Earth in all directions
What are Latitude and Longitude?
and what are their Zero points?
Latitude: Position North or South of Equator (Up or down)
Zero point = The Equator
Longitude: Position East or West of Prime Meridian which runs through Greenwich, England (Right or left)
Zero point = The Prime Meridian
How does Latitude affect the Sky visible to you?
It determines what part of the encircling star you are able to see
What happens to stars near the North Celestial Pole?
They never set
What happens to stars near the South Celestial Pole?
We cannot see them
What is the relationship between the altitude on the sky of the celestial pole to a local observer, and the local observer’s latitude on the planet?
The altitude of the Celestial Pole equals the observer’s Earthly Latitude
What are the Zodiac Constellations tracing the motion of?
Tracing the motion of stars throughout the sky
What is Altitude and Azimuth? How do we define them in the sky
Altitude: The height of the object in relation to sea/ground level
Azimuth: The direction of a celestial object from the observer
What is the Meridian
The line that passes through the Zenith point, connecting the North and South points on the Horizon
How can you use hands to measure angular size in the sky?
Holding your pinky= 1 degree
Holding three fingers up = 5 degrees
Holding a closed fist = 10 degrees
Holding index and pinky up = 15 degrees
Holding pinky and thumb up = 25 degrees
What is the angular size of a full circle? (What is that in Arcminutes?, and in Arcseconds?)
A full circle is 360 degrees
If:
1 degree = 60 arcminutes
1 arcminute = 60 arcseconds
A full circle would have 21,600 arcminutes, and 1,296,000 arcseconds
What’s the difference between angular size, and physical size of an object?
Angular Size: is the ‘apparent size’ of an object. Since objects far away appear smaller, you’re measuring the angle it takes up in your vision
Physical Size: Is the actual true size of the object, however it is hard to find the actual size of far away objects.
Why do Constellations depend on Both the Observer’s Latitude, and the Time of year?
Your position on Earth determines which constellations stay below the horizon
Time also matters because the Earth’s orbit changes the location of the constellations
What is the definition of a Constellation?
A constellation is a region of the sky with specified boundaries
What is the difference between the ‘classic’ and modern definitions of constellations?
The modern definition states that a constellation is only a region of the sky with specified boundaries
Whereas a classic definition of a constellation consists of the pattern the stars create
How many official constellations are there?
88 official constellations
What is Right Ascension? (and zero point)
Similar to longitude, it measures ‘around’ the celestial sphere (left to right)
The zero point is at the Vernal Equinox
What is Declination? (and zero point)
The same as latitude, it measures the distance from the celestial equator towards either pole
Zero point is at the celestial equator
What is the declination of both North, South, Celestial Pole, and the Celestial Equator?
North Celestial pole = 90 degrees
South Celestial pole = -90 degrees
Celestial Equator = 0 degrees
How much is the Earth’s axis tilted from the Ecliptic plane Around the Sun?
The Earth’s axis is tilted about 23.5o from the Ecliptic Plane around the sun
Where is the Axial Tilt pointed at?
Always pointed in the same direction (which is towards Polaris in the North, and Sigma Octantis in the South)
Where is the Earth’s North & South Pole pointed in the sky?
Earth’s North Pole is pointed towards the North Celestial Pole in the sky, while the South Pole is pointed towards the South Celestial Pole in the sky
What are two reasons that explains why Earth’s rotation cause temperature differences?
1st: It changes the concentration of light as higher concentration means hotter temperatures and vice versa
2nd: The time the sun spends above the horizon also depends on the tilt
Why do we have seasons? and how does it work?
Season’s occur due to the Earth’s axial tilt (23.5 degrees)
As the Earth travels around the Sun, in June, the Northern Hemisphere ‘leans into’ the Sun more, which exposes the sunlight more directly.
The situation becomes the opposite during December, as the Southern Hemisphere leans into the sun, and the Northern Hemisphere leans away
How do seasons work in the Northern Hemisphere, compared to the Southern Hemisphere?
Say if the Northern Hemisphere points towards the sun, that hemisphere is now summer, and the southern hemisphere is assumingly winter since there’s no sun
This can also be applied vice versa
What can we use to mark the changing of the seasons?
And what are the signifances of these days throughout the year?
We can indicate the change of seasons from Solstices, and Equinoxes
When is the Summer Solstice and what happens on this day?
The Summer Solstice occurs around June 21st, which is when the Sun shines down most directly on the Northern Hemisphere, and is the longest day of the year
When is the Winter Solstice? and what happens on this day?
The Winter Solstice happens around December 21st, which is a day where the Sun shines on the Northern Hemisphere it’s most indirect, and is one of the shortest nights
When are both Equinoxes and what do they do?
Equinoxes typically happen during March 21st, and September 21st. This is typically when the Sun equally shines on both hemispheres. Giving equal amounts of light and darkness.
What is the Perihelion? And what is the Aphelion?
The Perihelion: means that the object is closest to the sun
The Aphelion: means that the object is farthest away from the sun
What time of year is Earth the closest to the sun, and the farthest from the sun?
Earth is closest to the Sun in Early January
Earth is the farthest from the Sun in early July
Why doesn’t Earth’s change in distance affect the seasons? What would be the scenario if distance did change things?
Because the sun would eventually shine onto the Earth because of the Earth’s axial tilt. If it was the case, North and South would have the same seasons at the same time, and Summer would be in January
What are Phases of the Moon?
What are Primary Phases and Intermediate Phases?
Primary Phases: Occur at a specific moment in time
Intermediate Phases: Only occurs between Primary Phases
What are the four Primary Phases?
- New Moon
- First Quarter
- Full Moon
- Third Quarter
What are the four Intermediate Phases?
- Waxing Crescent
- Waxing Gibbous
- Waning Gibbous
- Waning Crescent
What are all the Moon phases together?
- New Moon
- Waxing Crescent
- First Quarter
- Waxing Gibbous
- Full Moon
- Waning Gibbous
- Third Quarter
- Waning Crescent
What does Waning and Waxing mean?
Waning = Shrinking
Waxing = Growing
What is the Sidereal Period, and the Lunation Period? What’s the difference?
The Sidereal Period: Is the time for the Moon’s actual orbit around the Earth which is 27.3 days
What is the Lunation Period?: Is the time between successive reoccurrence of the same phase (new moon to next new moon) which takes 29.5 days
The difference is that the Sideral Period is how long the Moon takes the complete it’s orbit, and the Lunation Period is how long it takes for the Moon to go from the phases “New Moon to New Moon”
Why do we only see ONE side of the Moon? What can it also be called?
Because the Moon rotates on it’s North-South axis one full rotation in exactly the same time it takes to orbit the Earth.
In other words, the Moon rotates the same speed as it orbits the Earth
It can also be called a ‘synchronous rotation’ or ‘tidally locked’
Why is the Moon tidally locked?
Tidal forces aim to elongate the Moon in the direction of the Earth. As the Moon spins faster, the part of the Moon that faces the Earth starts to stretch, causing a mis-alignment because it takes time to shift that much rock.
Since the tidal bulge is always mis-aligned, the Earth would try to pull it back to alignment, causing it to slow down it’s rotation
How does location on Earth affect gravity?
Since the Moon’s gravity pulls on the Earth’s surface unevenly, the gravity is at it’s strongest closest to the Moon, and is weakest at the spot farthest from the Moon
What is a Tidal Force?
A Tidal Force is the difference between the gravitational attraction of the solid Earth towards the Moon, and the gravitational attraction at a specific point in the ocean
What are Spring Tides, and What are Neap Tides?
Spring Tides: Tides are higher than usual, and occur during full and new moons
Neap Tides: Only appears after a spring tide, which refers to a period of moderate tides when the sun and moon are at right angles of each other
What are the three different types of Solar Eclipses?
Partial: The Moon partially covers the sun
Annular: The Moon covers the sun however there is a sun outline around the moon
Total: The moon fully covers the Sun
When do Solar Eclipses happen?
Solar Eclipses happen during a New Moon
What happens during Solar Eclipses?
It happens when the New moon moves between the Earth and the Sun, resulting in the three celestial bodies to form a straight line, or almost a straight line
What happens on Lunar Eclipses?
Lunar Eclipses result when a full moon falls into the Earth’s shadow, resulting in the Moon having a reddish hue
What is the difference between a Solar Eclipse, and a Lunar Eclipse?
A Solar Eclipse involves the New moon going between the Sun and the Earth, essentially covering the sun
A Lunar Eclipse involves a full moon falling into the Earth’s shadow from the Sun
Why does the Moon turn red during Lunar Eclipses?
The Moon turns red because the only light that goes onto the Moon are sunlight that passes through the Earth’s atmosphere
What does Circumpolar mean?
Provide an example
Circumpolar means that the object is continuously visible above the horizon, no matter if its day or night
For example, stars within 38o of the North Pole never sets, and are always visible, therefore Circumpolar
How does the Ecliptic relate to the Zodiac?
The constellations are called the ‘zodiac’ and all lie on the Ecliptic path
How does Planet’s act in the sky, and what do they mean?
Planets tend to change their positions slowly from day to day
The word Planet means ‘wanderer’ in ancient Greek
What is the Arctic Circle?
As the Earth rotates on its axis, all places within 23o of the North Pole are continuously illuminated by the sun
In other words, that area is exposed to the sun for 24 hours
What is the Antarctic Circles
All places within 23o of the South Pole do not see the Sun at all for 24 hours
What makes Solstice and Equinox special?
Solstice’s: Are the longest and shortest days of the year
Equinoxes: Are times when the day and night are equally as long
How are Seasons affected by Latitude?
As we travel more North or South, the seasons become more pronounced (more hot/more cold)
Explain the Astronomical roots of the names for the days of the week?
Within Western culture, the seven days of the week were named after the seven wanderers that the ancients saw in the sky
The Sun, The Moon, and the five planets visible to the unaided eye (Mercury, Venus, Mars, Jupiter, and Saturn)
Why does the phrase ‘dark side of the Moon’ not make sense?
Since the Moon rotates, the Sun rises and sets on all sides of the Moon, meaning that there is no dark side of the Moon
What is the Definition of Differential Forces? and Why does this happen?
Since the Earth is not fully rigid, the differences in the Moon’s attraction on different parts of the Earth can cause the Earth to distort slightly
This is because the side of Earth nearest to the Moon is more attracted to the Moon than the Moon’s attraction towards the middle of the Earth
How are tides formed on Earth?
Tide-raising forces produce motions in the water that create tidal bulges in the oceans. The water on the side of Earth facing the Moon will flow towards it. It will also do this on the opposite side
What are Eclipse Seasons?
Eclipse seasons is when the Moon crosses paths with the Ecliptic Plane, which allows Eclipses to happen
What is the Umbra? And what is the Penumbra?
Umbra: The cone where the shadow is darkest
Penumbra: The cone where the shadow is lighter and a more diffuse region
What is the Corona of the sun? And how can we see it?
The Sun’s corona is the Sun’s outer atmosphere that consists of sparse gasses that extend for millions of miles in all directions
It can be visible during a total eclipse, where the Moon will have a shiny light around the Moon
Why are Lunar Eclipses easier to see than a Solar Eclipse?
It is because the Lunar Eclipse can be visible to anyone who sees the moon. It is also because Lunar Eclipses can be seen entirely through the night
What are some of humanity’s connections to astronomy socially, philosophically, and practically?
There are 4
- Keeping Track of time and seasons (practical, social, agricultural, and religious)
- Keeping track of lunar cycles
(calendar, agricultural, and religious) - Keeping track of planetary cycles
(religious, and societal) - Aiding navigation
(practical)
How do we know that Ancient Humans had a good grasp at the patterns of astronomy?
Atleast two ancient groups
- Ancient people of central Africa were able to predict seasons based on the orientation of the crescent Moon
- Ancient Egyptians were able to track the sky for time keeping, so they could accurately predict when the river was going to flood
Who is Ra? and how was he worshipped?
Ra is the God of the Sun and the King of all Egyption Gods
Egyptian religion worshipped Ra at night, in order for Ra to rise again the next morning
How was ancient Egyptian astronomy interwoven into the daily and annual life of the people?
The Egyptians had their own system when it came to time keeping
How did Egyptian Time Keeping work?
Egyptians identified a list of constellations which makes their helical rise roughly every 10 days (their year was originally 36 weeks of 10 days long)
They found 36 constellations that could be used to determine how close they were to sunrise
Who were the other cultures that understood astronomical ideas?
Polynesians: Very skillful in the art of celestial navigation
France: Cave paintings from 18,000 BCE suggested their knowledge of lunar phases
China: Earliest known records of supernova explosions (1400 BCE)
What is Cosmology?
Is the basic structure and origin of something
How did ancient people know that the Earth was spherical?
Two reasons:
Ancient Greeks knew the Earth was round because
- The Earth’s shadow is curved
- If you were to travel south for a significant distance, new constellations are revealed which are only possible on a spherical Earth
What is the Heliocentric model? and how was this conclusion found?
Aristarchus correctly deduced that the Earth orbited the Sun
He found this answer based on his measurements of the sizes and distances of both Sun and the Moon
What was the Geocentric Model?
It was suggested that the Earth is at the center of the Universe and that objects move on perfect spheres/move in perfect circles
What did Plato and Aristotle believe?
Both believed in the universe being Geocentric, however the Geocentric model resonated with Aristotle more
What was the problem with the Geocentric model?
It wasn’t able to explain the apparent retrograde motion of planets
How were the motions of the Planet explained in Ptolemy’s geocentric model?
A planet would circle around a smaller circle, and that small circle would go around a bigger circle
How did the rise of the Islamic world contribute to our understanding of Astronomy?
The rise of Islam and the Muslim world preserved and enhanced the knowledge they received from the Greeks when Europe fell into the dark ages
What is the Al-Mamun’s House of Wisdom?
The world’s foremost learning Centre in Baghdad
What did Aristotle cite in his arguments that the Earth was spherical?
Two arguments
First argument: He argued that when the Moon enters or emerges from the Earth’s shadow during an Eclipse, the shape of the shadow on the Moon can be seen as round, as only round objects can create round shadows
Second argument: His also argued that travelers who were to go a significant direction towards the south are able to observe stars that cannot be visible in the far north. If the Earth were to be flat, we would all see the same stars overhead, which also indicates that Earth is round
Who was Aristarchus of Samos?
Aristarchus was an ancient Greek astronomer who pushed the idea that the Earth was moving around the Sun
What is Stellar Parallax?
Is the term used to describe the shift in the apparent direction of a star due to the Earth’s orbital motion
What was the experiment Eratosthenes did to measure the Earth?
Eratosthenes first observed the angle by how the Sun rays hit the planet’s surface. Because the Sun rays were parallel, he knew that a ray at Syene came straight down, whereas a ray at Alexandria made an angle of 7o. In effect, going from Alexandria to Syene, had caused the Earth’s surface to curve away by 7o, or 1/50 of a full circle. Which meant that the distance between both cities must be 1/50 the circumference of Earth itself