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Astronomy > Midterm 1 > Flashcards

Midterm 1 Flashcards

1
Q

Zenith

A

The point directly overhead (based on a persons location standing on the earth)

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2
Q

Altitude

A

The height of a star above the horizon

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3
Q

Solstice

A

The date in the Northern hemisphere when the Sun is as high in the sky as it gets (Summer solstice - June 21)
-also highest point above celestial equator

-lowest in winter sky is the winter solstice (Dec. 21)

Caused bc of the tip of the earth

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4
Q

Ecliptic

A

The path of the Sun through the sky over the course of a year

  • moon and planets remain near this line
  • bc of the 23 degree tip of the Earth’s axis, the Sun doesn’t follow the celestial equator
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5
Q

Meridian

A

A line form due north, through Zenith, to due South

-based on your location on earth (diff. depending where you are - whereas equator and poles are always the same)

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6
Q

Equinox

A

The point where the ecliptic crosses the celestial equator

  • Vernal Equinox (Mar. 21)
  • Autumnal Equinox (Sept. 21)
  • represent beginning of spring and fall
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7
Q

Celestial Equator

A

The extension of the Earth’s equator onto the celestial sphere

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8
Q

Azimuth

A

An angle measured from due north (Around to the east) to a point along the horizon under a celestial objecy

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9
Q

Declination

A

An angular measure of the distance of a star north or south of the celestial equator

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10
Q

Diurnal motion

A

-the rotation of the Earth
-Causes the nightly motion of the stars
(rise in the East and set in the West)

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11
Q

Right ascension

A

A measurement of a stars position measured along the celestial equator starting at the Vernal Equinox. Measured in a unit of time

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12
Q

On a given night we see different stars at different times of the night. 6 months later we see a different set of stars during the night - why?

A
  • Stars change on a given night due to the rotation of the earth on its axis
  • after 6 months the stars change due to the orbit of the earth
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13
Q

The Old Testament talks about the north star..is it referring to Polaris?

A

This would not be reference to Polaris bc the earth wobbles in precession, causing the position of the stars to change in the night sky. (Changes slowly over 26,000 years) The position of the North Celestial Pole has changed over time and pointed to other stars besides Polaris.

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14
Q

Celestial sphere

A

N and S Celestial poles and Equator are extensions of Earth’s poles and Equator

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15
Q

Constellations

A

Latin ‘group of stars’

  • used to define regions of the sky and to tell the seasons
  • 88 constellations
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16
Q

Astronomy as navigation (2 systems)

A

Many observatories established to monitor the positions of stars so they could be used for navigation

  • also used to establish local time and local start to the longitude system
  • height of N star s important to navigation

2 systems to give positions of the stars

  • Altitude/Azimuth
  • Right ascension/declination
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17
Q

Altitude and Azimuth

A

Altitude - the height above the horizon
Azimuth - an angle measured from N around to the E
-in this system: measure to right below the star in azimuth and then measure up to get the altitude
(PROBLEM bc stars position changes as earth rotates)

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18
Q

Right ascension and declination

A

(Uses poles and equator)
Right Ascension
-longitude like measure
-measured about the Celestial Equator (in units of hour, min, sec
-0 point is at the vernal equinox - then measure around the equator to the east

Declination

  • latitude like measure
  • measure angle above or below the Celestial Equator
  • measured in degrees, min, sec
  • Celestial Poles are at 90 degrees N or S (+ or -)
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19
Q

“Precession of the Equinox”

A

Earth wobbles over time

  • changes the direction of the pole and therefore the position of the equinox and the N star
  • causes the celestial poles and equator to slowly change positions
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20
Q

Where is Universal Time for astronomy

A

Greenwich, England

-also the location of the Prime Meridian, or starting point of the system

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21
Q

Before time zones how was 12:00 pm defined in a given city?

A

The time when the Sun was due south (on the meridian)

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22
Q

How long does it take for the Earth to make one complete rotation on its axis

A

23 h 56 m of SOLAR time

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23
Q

For western world, what calendar do we use?

A

The Gregorian calendar

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24
Q

Took a trip to Anchorage, Alaska where latitude is 61.2 degrees N. Where would we expect to find Polaris in the sky?

A

Lower in the sky than in provo (40 degrees N)

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25
Q

How long does it take the earth to make one full orbit of the Sun

A

365.2564 days

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26
Q

A given star rises above the horizon at 12 midnight on a given day. When will that same star rise 10 days later?

A

40 min earlier (11:20 pm)

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27
Q

T/F the hottest day of the year occurs when the sun reaches its highest pt in the sky

A

FALSE

  • In provo the sun reaches highest pt on June 21
  • hottest temp are in July and August
  • other factors that just directness of sun light
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28
Q

Another planet almost exactly like earth in another solar system. It is orbiting at the same distance from its star as the earth from the sun. - however it rotates on its axis twice as fast as earth. How would this effect solar and sidereal days for this planet?

A
  • Sidereal days would be half as long
  • length of true days is harder bc it wouldn’t move as far in its orbit before it went back to lining up with the Sun. In the end the solar day might be a little under 2 min different than the sidereal day
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29
Q

What are the major factors that contribute to temperature in a given season?

A

-the input of Solar energy to the system (peaks near end of June) & heat capacity system (something hot takes time to cool off)
how direct the sunlight hits the earth and the amount of time the sun is above the horizon. In the summer months, the sun rises higher in the sky, meaning the sun is more direct in the sunlight it projects to a specific area. Whereas in the winter months, the sun is lower in the sky and projects heat at an angle, spread out across the land. Also in the summer months, the sun remains above the horizon for a longer period of time which makes the days longer and warmer. However, the earth stores energy, so although the sun is highest in the sky on June 21st, it is not the hottest day of the year

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30
Q

Use constellations to orient ourselves in the sky

A

Provo’s latitude is 40 degrees north

  • Polaris is currently near N celestial pole
  • therefore Polaris is 40 degrees above the horizon
  • can always know your latitude in N hemisphere by knowing where Polaris is

Altitude of Polaris?

  • altitude of NCP = the latitude
  • latitude of NCP is 90 degrees so the altitude is 90 degrees
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31
Q

In Provo (latitude approximately 40 degrees North) if i look due south, what is the altitude of the celestial equator?

A
  • celestial equator is 90 degrees from NCP
  • there are 180 degrees from N to S
  • the celestial equator is 50 degrees above due south
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32
Q

Constellations also tell you…

A

The time of year by looking to the east around the time of sunset

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33
Q

Why seasons?

A

(2: directness of the sunlight and the time the sun is above the horizon)
Due to the earth’s tip
-in the summer the sun is higher in the sky and the light is more direct (also up longer)
-in the winter the sun is lower in the sky and the light is more spread out

Seasons ARE different in N and S hemispheres
-NOT CAUSED by the distance of the sun

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34
Q

Solar time

A

Time we read off our watches - partially based off the Sun
-12pm is when the sun is due south each day (this is local time)
-in SOLAR TIME one day - 24 hrs
(BUT earth actually rotates once on its axis in 23 h 56 m of solar time)

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35
Q

Time zones

A

Time problems really seen in the development of railroad (up to 1875)

  • railroads ran on the time of their home city
  • Time Zones (we are Mountain time)
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36
Q

Sidereal time (Star time)

A

-bc earth is also moving on its orbit around the sun
The time it takes the stars to go from due south to due south is 23 h 56m of Solar time
-we define one full rotation of the earth as 24h of what we call Sidereal Time (Star time)

Local Sidereal time - the right ascension of the stars which are on the meridian

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37
Q

If one night a sidereal and solar clock match exactly - how much off one night later?

A

one night
-4 min (each day is 4 min off)

One month (30 days)
-120 min (2 hours)

6 months
-720 min (12 hours)

1 year
-24 hours off (but actually match again)

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38
Q

Sidereal Year

A
  1. 2564 days

- best way to calc a year but not used bc not convenient

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39
Q

Tropical Year

A

Julius Caesar wanted spring to always be Mar. 21, but bc of precession the equinox slowly moves and changes beginning of spring (CAUSED TO MOVE AWAY FROM LUNAR CALENDARS)
-tropical year (365.2422 days) used to keep spring on same date

Caesar assumed 365.25 days
-off by 11m14s tropical
-off by 9m13s sidereal
-by 16th century it was off by 10 days (Spring started Mar. 11)
Bad for Roman Catholic church bc Easter kept coming earlier

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40
Q

Pope Gregory XIII

A

Roman Catholic problem with Caesar’s calendar bc spring kept coming earlier and therefore easter

  • Pope Gregory XIII reformed the calendar in 1582 A.D.
  • started by dropping 10 days out of 1582 (Oct. 4 was followed by Oct. 15)

Papal Decree

  • leap year modified to be every 4 years
  • except the end of a century which must be divisible by 400 (1900 wasn’t, but 2000 was)
  • this is our current system called the GREGORIAN CALENDAR
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41
Q

Astronomy calendars

A

elimate the year (time is expressed in terms of days)
-Julian Date (JD) - the # of days since a fixed date in the past, plus a fraction of a day
-Julian Date is based on the # of days that have elapsed since Jan. 1 4713 BC at noon in Greenwich
(Based on Universal Time - but starting at noon)

JD right now = 2456905.208

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42
Q

What time of day should you expect to easily see a waxing crescent moon?

A

During sunset

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43
Q

During the waning gibbous phase, how much of the entire Moon’s surface is illuminated by the sun?

A

1/2

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44
Q

During a total lunar eclipse what would be the phase of the moon

A

full moon

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45
Q

How long does it take the moon to orbit the Earth?

A

27.3 days

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46
Q

T/F We can see the entire surface of the moon from the earth

A

FALSE

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47
Q

Why does the moon go through phases?

A

Half the moon is always lit by the sun. Because the moon orbits the Earth, those on the earth will see a different portion of the lit side of the moon

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48
Q

Why is the area of the earth that can see a lunar eclipse much larger than the area that can see a solar eclipse

A

Lunar eclipse = when earth casts a shadow on the moon
Solar eclipse = when moon casts a shadow on the earth

-bc earth is bigger and casts a larger shadow than the moon does

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49
Q

Suppose moon was on its current orbit and all characteristics are same, except the moon was only 3/4 of its current radius.
-what would be the impact on its phases and on eclipses

A
  • No change in phases or the orbit of the moon.
  • The moon wouldn’t be large enough to block the entire disk of the sun so no total solar eclipse, only annular
  • lunar eclipses would be longer
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50
Q

Moon phases (Lunar phases)

A

-we see moon bc of reflected sunlight - the moon is illuminated by the sun just like earth (half the moon is in shadow and half in light)

  • New moon (when moon is btwn the earth and the sun, the dark half is facing earth)
  • Full moon (earth is in middle we only see lit half)
btwn new and full
-waxing crescent
-1st quarter
-waxing gibbous
btwn full and new
-waning gibbous
-3rd quarter
-waning crescent

*biblical new moon is actually a very thin waxing crescent moon - the first moon that can be seen in the night sky at sunset

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51
Q

Faces if the moon

A

The same features are always facing us on earth
-therefore the rotation of the moon occurs at the same rate as the revolution of the moon and earth

Earthshine - the part of the moon that isn’t illuminated by the sun (looks like a shadow)
-not a shadow but reflected light - light being reflected off the earth that is being reflected by the moon

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52
Q

Two types of months in astronomy

A

Sidereal month

  • the time it takes the moon to be in the same position with respect to the background stars
  • one true orbit (27.3 days)

Synodic (lunar) month

  • period from new moon to new moon
  • also the length of a day on the moon (29.53)
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53
Q

Eclipses

A

When sun, moon, and earth are in a straight line

  • Lunar: if moon passes through shadow of the earth
  • Solar: if shadow of the moon moves across the earth’s surface
54
Q

Lunar eclipse

A

only happens in FULL MOON
(sun, earth, moon)
-moon appears reddish
-umbra smaller and penumbra surrounds it

Total eclipse
-moon passes entirely through the umbra of earth’s shadow
(COMING UP APRIL, 2015)
Partial lunar eclipse
-moon passes partially through the umbra but is partly in the penumbra
Penumbral eclipse
-moon passes through the penumbra only

55
Q

Solar eclipse

A
  • NEW MOON (sun, moon, earth)
  • moon casts small shadow on earth
Total solar eclipse
-moon fully blocks the sun
Partial solar eclipse
-only part of the sun blocked - must be in the penumbra
Annular eclipse
-moon at apogee (furthest point from the earth!)
-moon leaves a ring
-one seen in utah 2012
56
Q

Why don’t we see eclipse every month?

A

Moon doesn’t orbit in earth-sun plan
-moon’s orbit is tipped 5 degrees

Intersection is called LINE OF NODES

Eclipses happen when line of nodes is lined with earth-sun

57
Q

Geocentric model

A

A model of the solar system with the Earth at the center

58
Q

Epicycle

A

From Ptolemy’s model of the solar system. A small circle riding on the larger circle to explain the motion of the planets

59
Q

Retrograde motion

A

The apparent motion of a planet from east to west across the background stars

(Normally the planets move west to east)

60
Q

Inferior planet

A

A planet that orbits closer to the Sun than the earth (venus, mercury)

Superior planets - those that orbit further from the sun than the earth

61
Q

Parallax

A

The apparent shifting of a star because of the orbital motion of the earth

62
Q

Opposition

A

when a planet is directly opposite the sun

63
Q

Elongation

A

When a planet interior to the Earth’s orbit is as far away from the sun as possible

64
Q

Cosmology and cosmogony

A

Cosmology - models of the universe

Cosmogony - the study of the earth’s place in the universe

65
Q

Aristotle

A

Believed Universe is governed by physical laws

  • believed in geocentric model
  • noted the earth cast a spherical shadow during a lunar eclipse
  • no math in science
  • considered the final voice on science after Galileo
66
Q

Aristarchus (300 B.C.)

A
  • broke with tradition of his day
  • GAVE FIRST heliocentric model
  • earth was 3rd planet from sun, but moon orbits earth
  • also proposed method to determine distance of sun and moon
  • (Much like our CURRENT SYSTEM)
  • allowed to work but criticized
  • people didn’t believe him bc of parallax - didn’t think earth was moving bc the stars didn’t appear to shift

-didn’t measure a parallax until 1839

most knowledge was stored in library at Alexandria - it burned down

67
Q

Early astronomy

A

Celts (Druids) - had an observatory to watch position of sun, moon, and planets (2700 B.C.)

Egyptians
-calendars and time keeping - cosmologies

Mesopotamia - Babylonian (5000 B.C.)
-time keeping - possible heliocentric model

68
Q

Egyptian and Mesopotamian astronomy leads to…

A

Modern Western Astronomy - with GREEK PHILOSOPHERS (7th century B.C.)

Thales of Miletus (546 B.C.)
-founded school where natural phenomena explained by math

69
Q

Kepler’s second law says, “a line joining the planet and Sun weeps out equal areas in equal time intervals” - if we had a stretched out eccentric orbit, what would best describe the motion of the orbiting planet

A

It would move fastest when it is nearest to the sun

70
Q

Retrograde and prograde motion (motion of planets through the background of the stars)
-how fast does a retrograde loop take?

A

Takes place over a few MONTHS

71
Q

Eratosthenes

A

measured the circumference of the earth

72
Q

Hipparchus

A

The beginnings of a system to describe the brightness of stars.

  • OUR MODERN MAGNITUDE SYSTEM is based on his model
  • Btwn bright and faint stars)
  • examined precise positions of the stars (believed in observation)
73
Q

Eudoxus
Pythagoras
Anaxagoras

A

Eudoxus
-majority of northern sky constellations

Pythagoras
-proposed that the objects of solar system (sun, earth, moon, planets) where spherical

Anaxagoras
-first accurate model of eclipses

74
Q

Ptolemy (150 A.D.)

A

Model of solar system with DEFERENT and EPICYCLES
-last word on western astronomy until Copernicus

Major problem facing early astronomers in geocentric model was retrograde motion - geocentric model didn’t explain it
-Ptolemy brought math into geocentric models (perfect heavens)

Explained retrograde motion bc each planet had two perfect circles

  • deferent (orbit)
  • epicycle

PROBLEMS

  • treated each planet independent of others
  • held for 1000 yrs until scientists wanted a more simple system
  • RULE: simplest solution is most likely the correct solution
  • his model was hard to accept bc so complex
75
Q

Btwn Ptolemy and Copernicus

A

Dark Ages

  • Chine (sunspots)
  • Islam (observation to confirm theory - many star names are Arabic)

Renaissance and reformation affect Copernicus

76
Q

Nicolaus Copernicus

A

Poland (1473-1543 A.D.)

  • lawyer, physician, economist, church, artist)
  • heliocentric model with earth 3rd planet (explained inferior planets and retrograde motion)
  • influenced by the church he still had perfect circle orbits for perfection of heavens
77
Q

Conjunction and Elongation

A
  • Inferior conjunction: btwn earth and sun
  • superior conjunction - on other side of sun
  • greatest western elongation: as far west of sun as it can get
  • greatest eastern elongation: as far east of the sun as it can get

Superior planets

  • conjunction - directly behind the sun
  • opposition - opposite the sun in the sky
78
Q

Tycho Brahe

A

(1546-1601)

  • court astronomer for King of Denmark
  • interesting lifestyle
  • king built Uraniborg observatory for him
  • rejected both Ptolemy and Copernicus system
  • Tychonic system
  • –moon and sun orbited earth and everything else orbits sun

HIS CONTRIBUTION

  • extensive set of precise position measurements of planets
  • positions of comets and supernova
  • failed to measure parallax and said objects are far away
79
Q

Johannes Kepler

A

(1571-1630)

  • Tycho’s assistant
  • used Tycho’s data and math skills to refine Copernicus system
  • ELLIPTICAL ORBITS instead of perfect circles
80
Q

Kepler’s three laws of planetary motion

A
  1. planets move in ellipse with the sun at one focus
  2. a line joining planet and sun sweeps out equal areas in equal time intervals
  3. the size of the orbit and the period are related by the equation: a3/p2 = constant (1)
    - therefore a3 = p2
    - a (astronomical unit - distance from earth to sun)
    - p (period of the orbit in units of years)
81
Q

Galileo Galilei

A

Final blow to geocentric model

  • in trouble with Catholic Church (POPE PAUL V AND POPLE URBAN VIII)
  • first in trouble with stmt that objects fall at same rate
  • Galileo made his own version of Dutch telescope and saw:
  • –phases of Venus
  • –mountains on moon
  • –sunspots on sun
  • –moons of jupiter
  • –individual stars in milky way
  • –rings of saturn

Catholic Church couldn’t support his observe. with Bible or Aristotle writings - so he got in trouble - spent years in house arrest

82
Q

How did Ptolemy’s model explain retrograde motion?

A

Has the prograde motion of the deferent.
-The short epicycle moves prograde half the time and retrograde half the time
=retrograde motion

83
Q

Why was Tycho’s data so valuable in taking the Copernican model to the Keplerian model?

A

Ellipses in Kepler’s model was not that far off circles

-needed Tycho’s precise and accurate date to see the difference

84
Q

Observations to argue geocentric model

A
  • Can’t feel motion while on earth so would assume earth is still
  • no parallax of stars
  • no brightening of stars as we move toward them
85
Q

Holding a ball 3 ft. above ground and it is not moving. What kind of energy does it have?

A

Potential energy

86
Q

Newton’s law describes the physical attraction of 2 objects. What does not affect the amount of gravitational force say btwn the sun and earth?

A

The radius of the sun

87
Q

If the moon were the same radius but twice as much mass, what would happen to your weight on the moon’s surface?

A

It would increase

88
Q

Holding a ball 3 ft above the surface on the moon..what is the diff. btwn situation on earth and on moon?

A

It will take longer to reach the ground than on the earth

89
Q

T/F According to Newton’s Law of Gravity there will be a force on light (light has no mass)?

A

FALSE

90
Q

Ball of gas (sun). If it were to shrink to a smaller radius, but maintain its mass, what would happen to gravitational binding energy?

A

It would increase

91
Q

What did Galileo’s observations really change about our understanding of the solar system?

A

They destroyed the idea of the perfection of the heavens - mountains on the moon, phase of Venus, moons of Jupiter

92
Q

Take the example of the ball on a string and explain the direction of the forces, accelerations, and velocities

A

The ball on a string has a velocity moving at 90 degrees to the string. The acceleration is along the string toward the center, this is also the direction of the force on the ball.

93
Q

If we had a roller coaster with a vertical loop, why does the first hill have to be higher then the highest point of the loop?

A

You need to have enough potential from the first hill to be converted into kinetic energy to get around the loop

  • if the loop was higher than you wouldn’t have enough energy to even get to the top of the loop
  • remember you want to have velocity at the top of the loop so you don’t stop at the top
94
Q

Two parts of physics with most impact on astronomy

A

Light and Gravity

-astronomy is heavily dependent on the law of physics

95
Q

Isaac Newton

A

(1642-1727)
-began the development of physics and calc

Laws of Motion

  1. A body will remain at rest or moving in a straight line at a constant speed unless acted upon by an outside force
  2. F = ma
  3. Whenever one body exerts a force on a 2nd body, the 2nd body exerts an equal and opposite force on the 1st body
96
Q

Acceleration due to gravity

A

F = ma (force = mass*acceleration)

F = (GMm)/r2
a=GM/r2
-surface gravity of an object

your weight on a given object is your mass*gravitational acceleration at the surface of the object u are standing

  • 200 lbs. on earth
  • 75.7 lbs. on mars
  • 33 lbs. on moon

WEIGHT is always with respect to something
MASS doesn’t change

97
Q

Potential and kinetic energy

A

coaster at top of hill
P.E. = mgh (h = hight)

Kinetic energy (motion)
K.E. = 1/2 mv2, P.E. = K.E.
v2 = 2gh
98
Q

If i drop a ball from twice as high it will

A

Hit the ground with a value btwn the original velocity and twice the velocity

99
Q

Newton’s law of gravitation and orbits

A

2 bodies attract each other with a force directly proportional to the mass of each body and inversely proportional to the square of distance btwn them

F = (GM1*GM2)/d2
-find hoe fast an object must be moving to orbit in a circular path (m = mass of object being orbited)

100
Q

Escape velocity

A

throw an object into the air to have it escape a planets gravity all tougher

ve = sq rt. (2GM/R)

101
Q

Kepler’s law of planetary motion

A

used to find masses of objects

-Jupiter’s moons - use period and orbital size of each moon to find mass of Jupiter

102
Q

Light and Gravity

A

Major difference in the 2 theories is the effect on light

-the path of light is bent by gravity

103
Q

Reflecting telescope

A

telescope that uses mirrors to focus the light

104
Q

Refracting telescope

A

telescope that uses lenses to focus the light

105
Q

Focal length

A

The distance from the center of the objective lens to the point where the light focuses

106
Q

Objective lense (or mirror)

A

Takes light from infinity and bring it to a focus

107
Q

eyepiece lense

A

Used to take light from the focal point and bring it out parallel to be viewed with the eye

108
Q

Rod Cells

A

The cels in the human eye that respond to low light levels

109
Q

Cone cells

A

Responsible for our seeing color, but reacquire a larger light input

110
Q

What is the nature of light?

A

It has properties of both particles and waves

111
Q

How fast does light travel in a vacuum?

A

Light travels at about 300,000 km/sec

112
Q

T/F Astronomers use red flashlight when working bc the rods of the human eye don’t respond as well to red light

A

TRUE
-rods have little response to red region on the spectrum - using re light means we can better see through telescopes to see faint objects

113
Q

Coolest stars in the sky are which color?

A

RED STARS

114
Q

T/F The peak wavelength of the sun (from the blackbody curve) matches roughly the peak response of the human eye

A

TRUE

-The human eye is designed to work with sunlight

115
Q

Have a telescope with an objective focal length of 4000 mm, I use a 40 mm eyepiece to look through this telescope.
-what is the magnification

A

4000/40 = 100x

116
Q

T/F of the visible light spectrum (that can be seen by the human eye) the red light has the lowest energy per photon

A

TRUE

117
Q

What are absorption lines and how can they determine compositon

A

Absorption lines are formed when light passes through a gas. If the energy of the light matches the diff. in energy states in the atom then the electron will jump by absorption the photon. In a spectra you will see some wavelengths are missing (dark lines)

118
Q

Doppler effect

A

As on object emitting light or sound moves toward you each wave is released a little closer. This causes the wavelength to become shorter and compressed (blueshift for light)
-as light/sound is emitted from an object moving away from you. The wavelength is stretched longer (Redshift for light)

119
Q

Fizeau and Foucault

A

First precise measurement of speed of light

  • 300,000 km/sec
    current: 299,792.458 km/sec

Tells us light travels (THIS IS ITS VELOCITY)
-light is the fastest thing in the universe

120
Q

What is light

A

Newton thought particle
-light is composed of a tiny packet of energy (photon)
-can’t divide a photon - all or nothing
Newton also saw a rainbow created by a prism
-some thought prism broke perfect white light, it had color bc damaged by this theory
NEWTON demonstrated that the colors were in the light and not created by the prism
-created idea that color was a fundamental part of light

121
Q

Light as a wave

A

Thomas Young looked at ocean waves and light waves - looked at light coming through two outlasts showing it as waves

What is waving?

  • electric and magnetic fields are waving
  • James Maxwell 1680
  • Light is now called
  • –electromagnetic waves
  • –electromagnetic radiation

wavelength = distance from one maximum to the next

122
Q

Wavelengths

A

Different colors of light in the rainbow were due to the different wavelengths
-to human eye: violet is shortest (high energy) and red is longest (low energy)

Short side = Gama rays, X-RAY, ultraviolet, violet

Long side = red, infrared, microwaves, radio waves

123
Q

solution to the question of speed of light was first resolved by

A

OLAUS ROMER 1676

  • times the eclipses of Jupiter’s 4 moons and got diff. times than expected
  • due to earth’s positing with respect to Jupiter
  • light takes 8 min. to get from the sun to the earth - it is delayed (the light left the sun 8 min. ago)
  • the nearest star to us besides the sun is 4 light years away (Takes 4 years to get to earth)
  • Andromeda 2 million light-years away (the light we see today left 2 million years ago)
124
Q

How do astronomers learn about the Universe?

A

study the light - piece together what light tells us

125
Q

Blackbody radiation

A

Hot: glows deep red
Hotter: glows reddish orange
Even hotter: glows yellowish-white

Cool star: emits more red light than blue light, so appears red
Warmer star: emits = amts. so appears yellow.white (sun)
Hot star: emits more blue than red, so appears blue

Stars color tells us how hot they are (hot = more energy)

126
Q

Everything with a temperature….

A

gives off light (just not always visible light)

infrared rays - to see people (makes them look red)

127
Q

Absorption and emission

A

Absorption line spectrum
-atoms in gas cloud absorb light of certain wavelengths producing dark lines in spectrum

Emission line spectrum
-atoms in gas cloud re-emit absorbed light energy at same wavelengths at which they absorbed it (lots of black in spectrum)

Continuous spectrum
-blackbody emits light at all wavelengths (all color)

128
Q

Two types of telescopes

A

Refracting

  • using lenses to focus the light
  • glass cut so light beams are brought to a focus known as FOCAL POINT
  • distance from lens to focal points is FOCAL LENGTH
  • Light coming from infinity means light rays are PARALLEL (parallel light is focus to the focal point)
  • almost every object in astronomy is at infinity

Reflecting
-using mirrors to focus the light (Newtonian)

129
Q

Refracting telescope

A

Made of two lenses

  • objective lens: brings image to a focus at the focal point
  • eyepiece: brings the image from the focal point to the eye

therefore we have 2 focal lengths
fo: the focal length of the objective
fe: focal length of the eyepiece
(length of telescope is sum of these 2 numbers)

130
Q

Magnification for both types of telescopes

A 
m = fo/fe
magnification = focal length for objective/ focal length for eyepiece

light gathering power is related tot he area of the primary mirror or objective lens
pi(r[sq]) of pi(d/2)sq

131
Q

I have 5 eyepieces for my telescope with 10mm, 12mm, 15, 25, and 40 focal lengths. - which will give greatest magnification?

A

m = fo/fe
-so want to use smallest focal length eyepiece to get the most magnification
10 mm will give highest magnitude

132
Q

large telescope as 36” or .9m diameter mirror

-how much more light doe it collect than one of the deck telescopes with a 10” or .28m diameter mirror?

A

(0.9m/0.28m)sq = 10.5x

Astronomy (5 decks)

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