A Flashcards
1
Q
Local group
A
A small cluster of galaxies that includes the Milky Way, Andromeda, the Large and Small Magellanic Clouds, and other dwarf galaxies, all bound by gravity.
2
Q
Virgo Supercluster
A
A massive collection of galaxy clusters, including the Local Group, that spans over 100 million light-years.
3
Q
SMC (Small Magellanic Cloud)
A
Another satellite galaxy of the Milky Way, smaller than the LMC.MC (Small Magellanic Cloud)
3
Q
Large Magellan cloud (LMC)
A
A satellite galaxy of the Milky Way and one of the closest galaxies to us. a smaller companion galaxy that orbits a larger host galaxy, also known as the primary galaxy
4
Q
Billion
A
A numerical value equal to 10 ^ 9 (1,000,000,000).
5
Q
Mega
A
A prefix meaning one million (10^6)
6
Q
Giga
A
A prefix meaning one billion (10^9)
7
Q
Celestial Sphere
A
An imaginary sphere surrounding Earth onto which all celestial objects appear to be projected.
7
Q
Constellation
A
A recognized pattern of stars in the sky, often named after mythological figures or objects.
7
Q
Light Year
A
The distance that light travels in one year, approximately 10 trillion kilometers or 9.5x10^12 km . It is a unit of distance.
8
Q
North and South Celestial Pole
A
The points where Earth’s axis intersects the celestial sphere.
9
Q
Celestial Equator
A
The projection of Earth’s equator onto the celestial sphere.
10
Q
Solar and Sidereal Day
A
A solar day is based on the Sun’s position (24 hours), while a sidereal day is based on the distant stars’ positions (~23 hours, 56 minutes).
11
Q
Ecliptic
A
The apparent path of the Sun across the sky over a year.
12
Q
Zodiac
A
The 12 constellations that the Sun appears to move through along the ecliptic.
13
Q
Summer and Winter Solstice
A
The points in Earth’s orbit where the Sun is at its highest (summer) and lowest (winter) in the sky.
14
Q
Vernal and Autumnal Equinox
A
The points where day and night are equal, occurring in spring and autumn.
15
Q
Celestial Coordinates
A
A system for locating objects in the sky, similar to latitude and longitude on Earth.
16
Q
Altitude
A
The angle of an object above the horizon.
17
Q
Azimuth
A
The direction of an object around the horizon, measured in degrees from north.
18
Q
Declination
A
The celestial equivalent of latitude, measuring an object’s position north or south of the celestial equator.
19
Q
Right Ascension
A
The celestial equivalent of longitude, measuring an object’s position eastward along the celestial equator.
20
Q
Precession
A
The slow wobble of Earth’s axis over a 26,000-year cycle.
21
Q
Triangulation
A
A method for measuring distances by forming triangles and using angles.
22
Parallax
The apparent shift in an object’s position due to the observer’s movement, used to measure distances to stars.
23
Angular Size
The apparent size of an object in the sky, measured in degrees, minutes, and seconds.
24
Angular Distance
The apparent separation between two celestial objects, also measured in degrees.
25
Phases of the Moon
The changing appearance of the Moon as it orbits Earth, including new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent.
26
Sidereal Month
The time it takes for the Moon to complete one orbit around Earth relative to the stars (about 27.3 days).
27
Synodic Month
The time between two consecutive new moons (about 29.5 days), which accounts for Earth's motion around the Sun.
28
Lunar Eclipse
Occurs when Earth blocks sunlight from reaching the Moon, causing it to darken. This happens only during a full moon.
29
Solar Eclipse
Occurs when the Moon blocks sunlight from reaching Earth, casting a shadow on the surface. This happens only during a new moon.
30
Total Eclipse
When the Moon completely covers the Sun (solar) or enters Earth's umbra (lunar).
31
Partial Eclipse
When only part of the Sun or Moon is obscured.
32
Annular Eclipse
A solar eclipse where the Moon appears slightly smaller than the Sun, leaving a bright ring (annulus) visible around the edges.
33
Umbra
The darkest, central part of a shadow where the light source is completely blocked
34
Penumbra
The outer, lighter part of a shadow where only part of the light source is blocked.
35
Synchronous Rotation
The Moon's rotation period matches its orbital period around Earth, causing the same side to always face Earth.
36
Geocentric Model
An ancient model where Earth was believed to be at the center of the universe, with celestial bodies orbiting it.
37
Heliocentric Model
The correct model of the solar system, where the Sun is at the center, and planets orbit around it.
38
Retrograde Motion
The apparent backward movement of a planet in the sky due to Earth’s motion relative to the planet.
39
Opposition
When a planet is directly opposite the Sun in the sky as seen from Earth, making it appear brightest.
40
Stellar Parallax
The apparent shift in a star’s position due to Earth's movement around the Sun, used to measure distances to stars.
41
Ellipse
Ellipse – The shape of planetary orbits, which is an elongated circle with two foci.
42
Semi-Major Axis
Semi-Major Axis – Half the longest diameter of an ellipse, representing the average distance from the Sun in an orbit.
43
Semi-Minor Axis
Semi-Minor Axis – Half the shortest diameter of an ellipse, perpendicular to the semi-major axis.
44
Eccentricity
A measure of how elongated an ellipse is, ranging from 0 (a perfect circle) to close to 1 (a highly stretched ellipse).
45
Aphelion
The point in a planet's orbit where it is farthest from the Sun.
46
Perihelion
The point in a planet's orbit where it is farthest from the Sun.
47
Apogee
The point in the Moon’s orbit where it is farthest from Earth.
48
Perigee
The point in the Moon’s orbit where it is closest to Earth.
49
Astronomical Unit (AU)
The average distance between Earth and the Sun, approximately 150 million kilometers (93 million miles).
50
Geosynchronous/Geostationary Satellite
A satellite that orbits Earth at the same rotational speed as the planet, appearing fixed in the sky (geostationary) if it orbits above the equator.
51
What is the big bang theory?
the theory of cosmic evolution. How every atom, star and galaxy came to exist. How the universe evolved and changed.
52
Why "big bang" name is not 'appropriate' or misleading?
There was no bang because there was no air and it wasn't big because it started from a singularity point.
53
What's the aftermath of the big bang?
Everything we see hear,taste, smell and touch. It is the evolving and expanding universe.
54
How old is the solar system?
4.5 Billion years
55
How is our sola system not stationary? At what speed is it moving?
It is spinning and flying through space at 134 miles/s
56
How the universe would be when we go back in time to the beginning?
It would be smaller than a galaxy, smaller than our solar system, smaller than a stadium, coffee cup, 13 billion years ago the universe was unbelievably small.
57
When did the big bang occur? How old is the universe?
13.7 Billion years ago everything expanded due to a hot densed universe.
58
What was the purpose behind building the ancient structures, like stonehenge & Gozeck?
Primitive people needed to understand their world to survive, and they relied on simple structures like Stonehenge in England or Chichin in Mexico to help them understand the skies and connect with the heavens, which they perceived as the home of the gods
59
How the sky acts like a clock and would help the ancients?
Tells them when to plant and harvest according to the seasons.
60
What is the difference between astronomy & astrology?
Astronomy predicted the motion of the starts and astrology how the stars affect us.
61
What are the two types of stars that the ancient Greeks recognized? And how did their movement differ?
Fixed, small and moved together. Large and move haphazardly, planets.
62
How many planets were recognized by Greeks? Name them and what is the origin of these names?
Mercury, Venus, Saturn, Jupiter. Named after their gods but are presently recognized as their roman designation.
63
Describe Aristotle model of the universe?
Ancient astronomy assumed a concept of the universe proposed by Aristotle, who imagined the Earth at the center of the universe with the Sun, Moon, stars, and planets revolving around it in perfect crystalline spheres
64
Describe the work of Ptolemy? Why was it complex?
Aristotle's universe was finite, resembling an onion with many concentric spheres, and first-century astronomer Ptolemy improved on this by accurately tracing the paths of the planets using complex circular motions called epicycles.
65
What was the main idea behind heliocentric model?
The sun was at the center of the universe.
66
Why Heliocentrism ‘horrified’ the church clergy?
During the 15th century AD, the idea of heliocentrism claimed the Sun, not the Earth, was at the center of the universe, which horrified Christian clergy who felt it contradicted the word of God
67
What was ‘magical’ and seemed elegant about Copernican theory regarding the planets?
Copernicus discovered that when he put the planets going around the Sun, Mercury automatically fell closest to the Sun, and Saturn fell at the outside edge, creating a harmonious connection between the size of the orbit and its period
68
In Copernican model the daily motion of stars around Earth is an illusion? Explain.
Copernicus also insisted that the Earth was rotating, spinning completely around on an axis every 24 hours, and that the heavens didn't move, but rather the rotating Earth created the illusion of stars chasing across the sky.
69
Why Copernicus didn’t publish his work and kept it for himself until he was about to die?
Afraid of church reprisals, Copernicus withheld publishing his theory until he was on his deathbed in 1543, but his book paved the way for Johannes Kepler, the champion of observational science.
70
How did Kepler improve on Copernican system?
Kepler's data revealed that planets speed up as they approach the Sun and slow down as they move further away, which supported the Sun-centered universe model and provided better predictions than the Earth-centered model.
71
What was the ‘strange phenomenon’ that Kepler struggled with?
Shortly before his death in 1642, Galileo inadvertently stumbled upon a clue to Kepler's puzzle about the sun's strange influence on planetary motion, which would help future generations toward a theory of the Big Bang
72
Describe the discoveries Galileo made first with his telescope, regarding the stars, Moon, Jupiter, Saturn & Venus.
Through his telescope, Galileo saw thousands more stars, a moon with craters, satellites circling Jupiter, and Saturn's giant ears, providing clear evidence that Venus orbits the Sun and proving the Sun-centered solar system theory
73
Which observation of Galileo proved conclusively that planets rotate around the Sun?
Venus has phases like the moon.
74
Why the church was upset about Galileo work?
Galileo quoted St. Augustine, who suggested reconsidering an interpretation of scripture if it seemed to be contradicted by well-established knowledge, but the church was concerned with perceived threats to its power and could not concede biblical interpretation
30:10.
75
Galileo was called by the church to stand for trial, for what? What did the church force him to do? What was the punishment?
In 1633, Galileo was summoned to stand trial for heresy after publishing a book championing the Sun-centered system, and he was forced to give up his Copernican ideas, although he quietly held fast to his beliefs throughout his final years under house arrest
76
Why Galileo is considered the first modern scientist?
Galileo is considered the first modern scientist, as he actively engaged in observations with the telescope, proposed theories consistent with the telescope, and dared to challenge the orthodoxy of the moment
77
According to Newton, what is common among: falling apple, orbiting planet, tides, projectiles….?
Newton realized that the things that make projectiles move and fall on Earth are the same things that make the planets go around the Sun, and that the planets are falling toward the Sun, just as Galileo's falling bodies fell towards the Earth. Gravity.
78
According to Newton, how does gravity work and act among objects?
The crux of it all is gravity, the strange action at a distance that holds everything together, which Newton drew up as a provable equation, showing that gravity was the energy that kept matter objects from flying headlong into interstellar space
79
What was not clear about definition of gravity or “Bizarre”?
Although Newton formulated the laws that govern gravity, he never explained or understood why it works, and instead focused on the fact that the laws work. How did the earth know the position of the sun.
80
What did Einstien prefer to have: a static universe (no beginning or end) or -a universe with a beginning? Why?
Einstein initially preferred a static, infinite universe, but his new understanding of forces like gravity ultimately suggested that the universe was not eternal, contradicting his philosophical beliefs
81
Watching the demo, how does the massive object affect the fabric of space-time and how does it attract a ball according to relativity theory?
It works like a blanket with a weight on top. When you send a second ball, it is attracted by the heavy one because of the dent in the fabric. The larger the mass, the larger the distortion and fabric.
82
In general relativity, why gravity is not a ‘force’ as we know it, like push or pull?
According to general relativity, gravity is not a force but rather the curvature of SpaceTime caused by the presence of matter, and the larger the mass of an object, the greater its distortion of the SpaceTime fabric
83
Describe the first experiment that was done to prove the general relativity? Was it success? When?
Einstein's theory predicted that not even light can escape the effects of gravity, and this was proven in 1919 during a solar eclipse when Arthur Edington observed the bending of starlight around the Sun
The success of general relativity made Einstein a superstar, and he received the Nobel Prize in physics in 1921.
84
Describe the consequences of Einstein relativity on the universe?
However, general relativity also opened a Pandora's Box, as it implied that the Universe must be either expanding or contracting, and Einstein's static Universe was unstable due to the attractive force of gravity.
85
Why Einstein had to introduce his cosmological constant?
To counter this, Einstein postulated a cosmological constant, a force equal to and opposite gravity, to achieve a static Universe
86
How is gravity described and explained by Newton? Compare that to Einstein’s view of gravity. Show how each of these scientists has a completely different view of gravity and how it works.
Newton saw gravity as a force between masses, working through empty space, while Einstein viewed gravity as the bending of spacetime itself caused by mass and energy.
Newton’s theory worked perfectly for most everyday situations and the orbits of planets. However, Einstein’s theory is needed to describe extreme scenarios like black holes, the bending of light near massive objects, and the behavior of time near strong gravitational fields (like those near a neutron star or black hole).
While Newton’s gravity was a “force,” Einstein’s is a geometrical effect of spacetime curvature.
87
Earth distance from:
Moon
Sun
Pluto
Moon - 1.3 light second
Sun - 8.3 light minute
Pluto (farthest planet in the solar system) - 5.5 light hour
88
Voyager
Spacecraft voyaging outside the solar system in hopes of reaching alpha-centauri.
89
Oort Cloud
Oort Cloud lies
beyond Pluto and
marks the edge of
our solar system.
Beyond Oort Cloud
you start travelling
in galactic space.
90
Distance to nearest star?
a) Alpha centauri
b) Barnard's star
c) Lalande
d) Sirius
Alpha centauri, 4.3 light year away, Barnard’s star = 6 ly, Lalande around 8 ly, Sirius around 9 ly
91
The solar system is made up of:
Ordinary small star with 8 planets and few dwarf planets is
called: solar system.
92
How many stars in the galaxy?
The blue dot is
exaggerated in
size. Our sun will
look like a dust size
among other 200
billion stars in the
galaxy.
93
Where is the solar system located in the milky way?
Half-way
94
State Kepler’s three laws.
The first law states that the orbit of a planet is an ellipse with the Sun at one of the two foci.
The second law asserts that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time, meaning that a planet moves faster when it is closer to the Sun (perihelion) and slower when it is farther away (aphelion). The third law, also known as the law of harmonies, states that the square of a planet's orbital period is proportional to the cube of the length of the semi-major axis of its orbit
95
How many dimensions (coordinates) are required to map the sky, as seen from Earth?
Two. We treat the sky as if it were mapped onto the inside of a two-dimensional surface we call the celestial sphere. We
know that space is three dimensional, that is, there is a distance to the stars, but we do not need to know the distance to a star in
order to point our telescopes at it.
96
33) Describe the position and orientation of the celestial sphere relative to the Earth.
The celestial sphere is positioned concentric with the Earth and oriented such that they share a common axis of rotation
(and thus have aligned poles and equators).
96
What are the three basic units of measure for angles, and how are they related to each other?
The three basic units are degrees, minutes and seconds. There are 360 degrees in a circle, 60 minutes in a degree and 60
seconds in a minute. These relations originated in ancient Babylon
97
35) What is the meaning of negative altitude?
When the altitude is negative, the object of interest is below the observer’s horizon
98
36) Where (at what altitude) is the zenith? Describe its location relative to the observer.
The zenith is at altitude +90◦, straight above the observer’s head. A plumb-line would extend from the zenith to the
nadir (ignoring the effects of the Earth’s rotation)
99
37) What is the range of possible values for altitude?
Altitude may range from −90◦ at the nadir, to 0◦ at the horizon, to +90◦ at the zenith.
38) What is the possible range of values for azimuth? Along what line is it measured?
100
38) What is the possible range of values for azimuth, Az? Along what line is it measured?
Azimuth ranges from 0◦ (due north) to 360◦ (returned to due north) increasing eastward, along the observer’s horizon.
Although in some situations it may be more convenient to use due south as the origin of the system.
101
39) What are the azimuth angles, Az, for the eight major compass points?
When using due north as the origin, north = 0◦, north-east = 45◦, east = 90◦, south-east = 135◦, south = 180◦, south-west
= 225◦, west = 270◦, north-west = 315◦. When using due south as the origin, south = 0◦, south-west = 45◦, west = 90◦, north-west
= 135◦, north = 180◦, north-east = 225◦, east = 270◦, south-east = 315◦.
102
40) Why do the altitude (Alt) and azimuth (Az) of a star depend on the date, time and location of the observer?
They depend on time because the Earth is rotating, causing the sky to appear to move from east to west on a minute to
minute basis. They depend on date because the Earth is orbiting the Sun, causing the positions of all objects to migrate from east
to west on a daily basis. They depend on (Earthly) location because the horizon determines the object’s azimuth and altitude, and
the horizon is unique to each observer (because the horizon is defined by the zenith, which is unique to each observer).
41) Describe an observer’s local meridian. Why is every observer’s local meridian unique?
103
41) Describe an observer’s local meridian. Why is every observer’s local meridian unique?
The local meridian is a line drawn from due north on the horizon, through the observer’s zenith, to due south on the
horizon. Every observer’s local meridian is unique because every observer’s zenith is unique.
104
What are the names of the coordinates of the equatorial coordinate system or the Celestial Coordinates and how are they
measured?
Right ascension is measured in units of time (hours, minutes and seconds) along the celestial equator. Declination is
measured in degrees, minutes and seconds along a celestial sphere meridian (passing through the object).
105
43) How is, the altitude of a celestial pole (north or south) related to an observer’s latitude? (Discuss both hemispheres.)
In the northern hemisphere, the altitude of the north celestial pole is equal to the observer’s latitude and the altitude of
the south celestial pole is equal to the negative of the observer’s latitude. In the southern hemisphere, the altitude of the south
celestial pole is equal to the observer’s latitude and the altitude of the north celestial pole is equal to the negative of the observer’s
latitude.
106
44) How is, the altitude of the celestial equator (on the local meridian) related to an observer’s latitude?
the altitude of the CE is equal to 90o – latitude. Check diagrams given above.
107
45) In what region of the Earth would an observer be if the altitude of Polaris is negative?
In the southern hemisphere
108
46) What are the equatorial system’s or Celestial coordinates advantages over the horizon system?
Celestial coordinates (RA, DEC) are nearly independent of time or date of the observation and of the observer’s location
(latitude and longitude). However, It is not completely independent because of the Earth’s precession motion and because of the
stars’ proper motion.
109
47) What is the meaning of “Epoch 2000.0” on a star chart?
It means that the Celestial or Equatorial coordinates of the objects shown on the chart have been updated to 1 January of
the year 2000. Celestial coordinates change due to precession of Earth axis.
110
48) What is the original intent of constellations? How does modern Astronomy use constellations?
To honor or represent people, deities, animals or things important to a culture. In modern Astronomy, constellations
designate regions of the sky (certain area with borders like map of countries), making it easier to label and find specific objects
such as stars, nebulae and galaxies in the sky
111
49) Is it possible that some stars do not belong to a constellation?
Is it possible that some stars do not belong to a constellation? How many stars do not belong to a constellation? Answer: Every
star belongs to a constellation. There are no stars that do not belong to a constellation, although there are a couple of stars that are
on the border and thus shared by two constellations.
112
50) What do we mean by a star’s proper name? Is it possible to give proper names for all stars? What issues that may cause?
This is the name given to a star by the ancient Greek or Arabic astronomers, such as, “Rigel” or “Betelgeuse.” However,
there is a limited number of proper names available making it impossible to name billion of stars. In addition, some stars were
given the same name or very
113
51) What is apparent magnitude, m?
Apparent magnitude (symbol, m) is a comparative measure of a star’s brightness as seen from Earth.
114
52) Why do the constellations not change their shape (stick figure) over a year’s time?
Any change in the shape of a constellation is due to the proper motion of the stars. This motion is so slow, that it
requires hundreds or thousands of years for any noticeable change (by naked-eye) in the constellations.
115
54) What is the apparent path of the Sun called? At what rate does the Sun’s position change along its apparent path?
The ecliptic line. Based in sidereal time, the Sun moves approximately one degree per day.
116
53) List and briefly describe the three major motions of the Earth.
The 3 major motions are: diurnal – the daily rotation of the Earth on its axis (24 hours); annual – the orbital motion of
the Earth around the Sun (1 year); precession – the “wobble motion” of the Earth caused mainly by the tidal forces of the Moon
(around 26000 years)
117
55) Describe the location (on the celestial sphere) of the vernal equinox. On which date, is the Sun found there?
The vernal
equinox is the point in the sky where the Sun crosses the celestial equator, from south (negative declination) to north (positive
declination), during its annual motion, on or about 21 March.
118
56) What are those constellations through which the ecliptic passes called?
The zodiac constellations
119
57) What is the difference between a zodiac sign and a zodiac constellation?
Each zodiac sign, as defined by astrologist, is a 30◦ segment measured from west to east along the ecliptic line, starting
from the vernal equinox. A zodiac constellation, as defined by astronomers, is a region of the sky, defined by its borders, which
happens to contain a segment of the ecliptic line.
120
58) Why do the dates of the Sun’s entry into the zodiac constellations not match with the dates of its entry into the zodiac
The Earth’s precession motion has caused them to become misaligned. Three thousand years ago, when the zodiac was
established by astrologist, the signs and constellations were relatively well aligned.
121
59) How precession is sometimes described? What is the period of the Earth’s precession motion?
Precession is sometimes described as a “wobble motion.” The period is 25 982 rounded to 26000 years.
122
60) Why hasn’t Polaris always been our North Star?
One of the results of the Earth’s precession motion is the movement of the position of the north celestial pole on the
celestial sphere. As the pole moves on the sphere it comes closer to and moves away from various stars. It just happens to be near
Polaris at the present.
123
61) List the effects of the motion of the vernal equinox.
The right ascension and declination of all objects must be periodically updated due to precession of Earth’s axis. The
calendar must be adjusted to keep the date of the vernal equinox from moving toward the beginning of March. The zodiac signs
and constellations no longer match.
124
62) Explain how the ecliptic plane is used to define “up” and “down” in the solar system.
If we are located above the ecliptic plane, then we can look “down” to see the Earth’s north pole. If we are below the
ecliptic plane, we can look “up” to see the Earth’s south pole. The line, perpendicular to the ecliptic plane defines the vertical (up
and down) of the solar system. This perpendicular line passes through the north and south ecliptic poles (NEP and SEP).
125
63) Describe possible climate zones of the Earth, if the Earth’s axis was not tilted.
The equatorial regions would remain as hot as they are now. The Polar Regions would be somewhat colder, because
they would never receive any solar radiation. The polar ice sheets would probably be larger. The temperate zones would not see
the changes in weather patterns associated with the seasons. They would probably have weather similar to that currently
associated with the spring or fall seasons – for any particular latitude, a mix of the typical weather seen on the equinox dates.
126
What are the names of the two coordinates used in the horizon coordinate system? Describe the measurement made by each
coordinate.
Azimuth is measured in degrees along the horizon starting with due north at 0◦. Altitude is measured along a zenith
meridian, in degrees from the horizon at 0◦ to the zenith at +90◦.
127
Why do stars appear fixed in the sky?
The appear fixed because they're very far away from us.
128
How were stars name and ranked in 1604?
stellation were ranked in order of
brightness, and labeled with Greek letters (Alpha Centauri,
Beta orion)= Bayer scheme
129
How were stars named in the 18th century?
In the early 18th century, stars were numbered from
west to east in a constellation (61 Cygni)= Flamsteed
catalog
130
Why was there a confusion between the names? What system do we use now?
However, there are confusion of naming and some overlap.
Like Betelguese is known as :
58 Ori (flamsteed), alpha Orion (Bayer), and also
HD39801 and SAO 113271.
Now, new stars are simply labeled by their celestial
coordinates
131
Why do we see different constellations during each season?
We see different constellation each season.
Seasonal changes to night sky are due to
Earth’s motion around Sun
132
What are the constellation are on the ecliptic.
12 constellations that Sun moves through during
the year are called the zodiac; path is ecliptic
133
Converting angular diameter and distance into size
0=D/d in radian where 0= angles, D, diameter, d distance.
134
Triangulation
measure baseline
and angles, can
calculate distance
135
why do we have day and night?
Earth experiences day and night due to its rotation on its axis, which is an imaginary line running through the planet from the North Pole to the South Pole.
136
Earth revolution
1 year or 365 days
137
Earth's rotation
24h
138
Why do we have seasons?
The Earth axis of rotation is not perpendicular to that plane.
The Earth axis is tilted by 23.5o
from the perpendicular line.
18
Ecliptic Plane:
The plane that holds Earth
orbit around the Sun is
called the ecliptic plane.
Due to this tilt of Earth axis, which remains steady over the
years, the Sun’s apparent path in the sky keep changing with
from one month to the next.
139
Why does the moon have different phases?
Phases are due to
different amounts of
sunlit portion being
visible from Earth.
The position of the
Moon with respect to
Earth & Sun gives it a
unique phase!
140
How far is andromeda from the milky way?
2.5 M L. y.
141
When each moon phase is visible in the sky?
Full Moon : 6 pm - 6pm
First quarter: Noon - midnight
Third quarter: Midnight - Noon
New moon - Near the sun
142
Name all the motions of Earth.
1st motion:
Earth rotation: spinning
around an axis
period = 24 hours
2nd motion:
Earth revolution: orbiting
the Sun
period= 1 year (365 days)
3rd motion:
Precession = wobbling of
Earth’s axis
period = 26,000 years
4th motion: Earth, with the Sun and the whole solar system orbit the center of the Milky Way = 225 million year
143
Solar cycle
* Daily cycle, noon to
noon, is diurnal
motion – solar day
144
sidereal day
Stars aren’t in quite
the same place 24
hours later, though,
due to Earth’s
rotation around Sun;
when they are, one
sidereal day has
passed
145
The burial chamber
of the Great
Pyramid
The burial chamber
of the Great
Pyramid has two
shafts that align
with the stars that
determine true
north
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Inertia
Mass is a measure of inertia.
Inertia is the tendency of object to resist change in its motion.
If an object is at rest, it tends to remain at rest.
If an object is moving, then it tends to remain moving at
constant speed in a straight line!
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Motion 1st law:
If an object is moving, it will continue moving with
constant velocity (same direction, same speed),
unless a force is applied on it.
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Mass
Mass is an inherent property of an object
Mass is independent of the object’s surroundings
Mass is independent of the method used to
measure it
Mass is a scalar quantity
The SI unit of mass is kg
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Contact forces
Contact forces involve physical contact between two objects
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Field forces
act through empty space
No physical contact is required
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Newton’s Second Law
When viewed from an inertial reference frame, the
acceleration a of an object is directly proportional to
the net force Fnet acting on it and inversely
proportional to its mass m,
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Freely Falling Objects
A freely falling object is not restricted
to objects that are literally falling. Any
object moving freely under the influence
of gravity alone. This includes objects
falling down, or tossed up,
projectiles….etc
In Vacuum, we can easily see that
acceleration of a free falling object is
independent of its mass.
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Newton’s Third Law, Alternative
Statements:
Forces always occur in pairs
A single isolated force cannot exist
The action force is equal in magnitude to the reaction
force and opposite in direction
One of the forces is the action force, the other is the reaction
force
It doesn’t matter which is considered the action and which the
reaction
The action and reaction forces must act on different objects and
be of the same type
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Newton’s Law of Universal
Gravitation
Every particle in the Universe
attracts every other particle with
a force that is directly
proportional to the product of
their masses and inversely
proportional to the distance
between them
Fg=GMm/r^2
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16) Why do the planets always move around the celestial sphere in a narrow band centered on the ecliptic?
The planets move around the celestial sphere in a narrow band centered on the ecliptic because:
Formation of the Solar System: The Solar System formed from a rotating disk of gas and dust called the protoplanetary disk. As a result, the planets inherited the disk's nearly flat, planar structure.
Orbital Plane Alignment: The ecliptic is the plane of Earth's orbit around the Sun, and all other planets orbit the Sun in planes that are only slightly inclined relative to the ecliptic. This alignment is a consequence of the conservation of angular momentum during the formation of the Solar System.
Gravitational Influence: The Sun's gravity dominates the Solar System, and its gravitational pull keeps the planets' orbits close to the ecliptic plane.
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17) State Newton’s three laws of motion and the law of gravity.
Newton’s Three Laws of Motion:
First Law (Law of Inertia): An object remains at rest or in uniform motion in a straight line unless acted upon by an external force.
Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F=ma)
Third Law: For every action, there is an equal and opposite reaction.
Newton’s Law of Gravity:
F=GMm/r^2
is given by:
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18) Which are more fundamental, Newton’s laws or Kepler’s laws? Why?
Newton’s laws are more fundamental than Kepler’s laws because:
Universality: Newton’s laws apply universally to all objects and forces, not just planetary motion.
Explanation of Kepler’s Laws: Newton’s laws of motion and gravity explain why Kepler’s laws hold true. For example:
Kepler’s first law (elliptical orbits) is a consequence of the inverse-square law of gravity.
Kepler’s second law (equal areas in equal times) is a result of the conservation of angular momentum, which follows from Newton’s laws.
Kepler’s third law (relationship between orbital period and distance) can be derived from Newton’s law of gravity.
Broader Scope: Newton’s laws provide a framework for understanding motion and forces in all contexts, while Kepler’s laws are specific to planetary orbits.
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Moon position
The Moon's Phase Determines Its Rising and Setting Times:
A Full Moon rises at sunset (around 6 p.m.) and is highest in the sky at midnight.
A Third Quarter Moon rises at midnight and is highest in the sky at sunrise (around 6 a.m.).
The Moon is at its Highest Point at 6 a.m.:
If the Moon is highest in the sky at 6 a.m., it must have risen around midnight.
This behavior matches the Third Quarter Moon, which rises at midnight and is highest in the sky at sunrise.
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Distance in AU of planets in the solar system
Mercury: 0.40 AU
Venus: 0.70 AU
Earth: 1.00 AU
Mars:1.5 AU
Jupiter:5.2 AU
Saturn:9.5 AU
Uranus:19 AU
Neptune30 AU
