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Astronomy > Chapter 1 - Naked Eye Astronomy > Flashcards

Chapter 1 - Naked Eye Astronomy Flashcards

1
Q

What is the mean diameter of earth?

A

13,000 km

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2
Q

Earth is the largest of what type of planets?

A

Earth is the largest terrestrial plant because of its mean diameter of 13,000 km

The others are mercury, Venus and Mars

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3
Q

How much smaller is earths polar diameter to its equatorial diameter ?

What does that do to the earths shape?

A

It is only slightly smaller by 42km

It makes the earths shape and oblate spheroid ( like the shape of a squashed beach ball when someone is sitting on it )

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4
Q

How much of the earths surface is converted by water?

A

70% of the earths surface is covered by water

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5
Q

Name the layers of the earth.

A

Atmosphere -> Crust -> Mantle -> Outer core -> Inner core

most of the crust is covered by saltwater oceans

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6
Q

How deep is the earths crust relatively speaking?

A

The earths crust is very thin with a thickness of 0-70 km

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7
Q

Why type of rock does oceanic crust consist of?

A

It consists of a darker, denser rock such as basalt.

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8
Q

What does the older continental crust consist of ?

A

It consists of low-density rocks such as Grannite and younger, thinner crust that is up to 10 km thick

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9
Q

What makes up 80% of the earths volume?

A

The silicate mantle which extends half way into the earths centre

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10
Q

What is the crust split up into?

A

A number of continental sized tectonic plates that literally float on top of the silicate mantle

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11
Q

What is the temp of the outer core?

A

~5,000k

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12
Q

What is the outer core made of?

A

It is made up of liquid iron with some nickel

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13
Q

What is responsible for the earths magnetic field?

A

It is these currents of charred particles that flow in the outer core

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14
Q

What is the temp of the inner core?

A

~5,500k ( that is about the same temp of the suns photosphere which is one of the outer layers of the sun )

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15
Q

What is it made of?

A

It is made up of nickel and iron but because of the high pressure from gravity, it prevents them from melting

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16
Q

What do the network lines that criss-cross an ordnance map that is a page in an atlas and a 3 dimensional globe help us find?

A

They help us locate an area such as a 4 figure grid reference or pinpoint a particular location in terms of its LATITUDE and LONGITUDE

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17
Q

Although latitude and longitude are drawn on maps as lines, what are they in real life?

A

They are actually angles subtended at the centre of the earth by imagery curved lines (arcs) on the earths circumference

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18
Q

Where is latitude measured from?

A

Latitude is measured North and South from the Earths equator

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19
Q

Where is longitude measured from?

A

Longitude is measured East and West from the Prime Meridian

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20
Q

In what year did seafarers stop using different meridians to define the zero of longitude?

A

They did it up to 1884 when they had a international meridian conference held in Washington D.C.

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21
Q

How much is the earths polar axis tilted by?

A

It is tilted by 23.5 degrees to the ‘vertical’

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22
Q

What are the consequences of acknowledging the earths correct tilt ?

A

It’s that observers at different latitudes in earlier years would of seen the sun at different altitudes in the sky

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23
Q

What is significant about the dates close to or on March 21st and September 23rd?

A

These are the dates when the sun lies dir fly over the equator.

These dates also correspond to the spring and autumnal equinoxes

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24
Q

What happened midway through the 21st of June and the 21st of December ?

A

The sun lies directly over the tropics of cancer (latitude 23.5 degrees) and Capricorn (23.5 degrees S)

These dates also correspond to the northern hemisphere’s summer and winter solstices

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25
Q

What do the Arctic and Antarctic Circles represent?

A

They represent the most northern (66.5 degrees N) and Southern (66.5 degrees N) latitudes from which the sun can be seen to rise and set ( if weather permits) every day of the year

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26
Q

What does our atmosphere provide us?

A

Oxygen to breathe, absorbs harmful solar UV and X-radiation, regulates our planets temperature to a mean 15C and protects us from most meteor strikes

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27
Q

What are some problems with our atmosphere for astronomers?

A
  • The Sky is blue and so observations can only occur at night. This is because light is scattered by oxygen and nitrogen molecules which occurs and the shortest wave length (blue)
  • Air in the atmosphere is continuously in turbulent motion -this is because air density’s rise and fall causing light to refract and so theses conditions could make it look like a star is twinkling
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28
Q

What is another word for glow and glare which is the problem astronomers have?

A

Light pollution

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29
Q

What is sky glow?

A

It is a rusty orange haze cast by the lights of near urban conurbations

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30
Q

What does local glare form sports grounds, street lights etc do to our eyes?

A

They ruin our eyes night vision or dark adaptation through light pollution

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31
Q

What is the sky split up into?

A

It is split up into 88 different areas called CONSTELLATIONS

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32
Q

What is significant about the stars constellations and their names

A

They bear no resemblance apart from a few exception like Orion’s Belt

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33
Q

What is an asterism ?

A

It is an unofficial, popular pattern of bright stars that do have a close likeness to their name

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34
Q

What might the stars in an asterism also belong to?

A

They could belong to the same or different constellations and include the plough (urea major), Orion’s Belt, the W (in Cassiopeia) and the summer and winter triangles

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35
Q

What is one of Orion’s neighbouring constellations ?

A

It is Taurus, the bull, which boasts one of the most beautiful open cluster of stars , the Pleiades
-Orion itself contains a faint, rather fuzzy pink patch of light just below the Orion’s Belt. This is a Stella nursery of young stars, gas and dust. The Orion Nebula

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36
Q

What might an astronomer see in the corner of his eye during an observation ?

A

A meteor or a shooting star

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37
Q

Why can you see meteors or shooting stars ?

A

This is because a bright stark of light is caused by a dust particle, probably from the tail of a comet, burning up in the atmosphere

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38
Q

What are comets themselves ?

A

They are rare visitors to the inner solar system but observers might be lucky to spot one as an extended fuzzy object, possibly showing 1 or 2 tails, moving slowly against the background stars night to night

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39
Q

What would be even more lucky to observe than a comet etc?

A

A supernova as on,y 3 have ever been observed by the naked eye in the last 100 years

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40
Q

What would a supernova look like ?

A

A supernova would suddenly appear as a bright star, be visible for a few weeks and then slowly fade

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41
Q

What do plants move through ?

A

They move eastwards through an imaginary strip called the Zodiacal Band

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42
Q

What are the northern and southern lights and where can they be seen?

A

They are a dazzling display of green, yellow and red curtains and whirlpools of light in the sky

Often know as the Aurora borealis and Aurora Australis and can be seen in polar regions but on rare occasions can be observed from the mid-UK latitudes

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43
Q

What do many asterisms contain?

A

They contain stars that act as POINTERS to specific objects in the sky

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44
Q

What constellation is a great place to start when observing the andromeda galaxy ?

A

The great square of Pegasus

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45
Q

What does the andromeda galaxy look like with the naked eye?

A

A visible very faint, fuzzy patch of light

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46
Q

What might keep observers see?

A

Artificial satellite

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47
Q

What might artificial satellites be mistaken for?

A

They might be confused with aircraft that are easily identified from green and red right of way navigation lights

The aircraft engines can also be heard usually

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48
Q

What do we use to map stars and other objects in the sky with a network of lines that isn’t the longitude and latitude system ?

A

The celestial sphere

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49
Q

What does the prime meridian mark?

A

The zero on latitude

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50
Q

What does the celestial sphere use at its prime meridian ?

A
  • The path taken by the sun on the celestial sphere during 1 year
  • the point where the ecliptic cuts the celestial equator on its journey from south to north (the first pint of Aries )
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51
Q

What system do most astronomers use?

A

They use the equatorial coordinate system

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52
Q

What is the equatorial coordinate system?

A

It is a system in which the celestial equivalents of our latitudes and longitudes are declination and right ascension

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53
Q

What is declination ?

A

It is simply the projection of latitude onto the celestial sphere; it is measured in degrees (+ and - = north and south )

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54
Q

What is right ascension ?

A

It is measured eastwards from the first point or Aries; it is measured in hours and minutes where 1h = 15 degrees and like in time intervals, there are 60mins in 1h (so 1 min = 0.25 degrees)

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55
Q

Which star is closest to the celestial pole?

A

Polaris

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56
Q

What is azimuth ?

A

Is is a simple bearing ( in degrees ) from due north (that’s geographical and not magnetic) moving round Eastwood to the point on the observers horizon directly under the star; it ranges from 0 to 360 degrees

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57
Q

How is altitude found from azimuth ?

A

Altitude is found by the angle from the observers horizon upwards to the star or other celestial object and ranges from 0 to 90 degrees (the observers zenith)

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58
Q

When is azimuth and altitude used together ?

A

They are used together for a more observer friendly horizontal coordinate system that involves azimuth and altitude

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59
Q

Like the sun, which way to the stars rise?

A

In the east

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60
Q

Wha5 is the name of the highest point that the stars reach ?

A

The culminate

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61
Q

Where do the stars reach when they are due south?

A

The cross the observers meridian and later set in the west

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62
Q

What is the apparent motion of the stars called and why does it happen?

A

It is called diurnal motion and is simply the result of the earth rotating on its polar axis from west to east

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63
Q

How much does the earth rotate in a sidereal day and how long does it take?

A

The earth rotates 360 degrees and it takes 23h and 56mins

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64
Q

During a sidereal day, how much has the earth moved around the sun?

A

It rotates 1 degree around the sun and so needs to rotate a further 4 min to align a given point on its surface with the sun once again

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65
Q

How many hours is 1 solar day?

A

1 solar day = 24h

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66
Q

Most astronomers observe what instead on the sun?

A

Stars

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67
Q

What do astronomers use rather than a clock for observing stars?

A

They use clocks based on local sidereal time (LST)

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68
Q

What is the local sidereal time of an observer?

A

It is the right ascension that lies on the observers meridian at a given moment in time

This means that if a star with RA=14h 45min lies on observers meridian, the LST is 14:45

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69
Q

What is a stars hour angle?

A

It is the time (in hours and mins) since the object was last crossing the observers meridian:

-It follows that - HOUR ANGLE = LOCAL SIDEREAL TIME - RIGHT ASCENSION

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70
Q

What does it tell an astronomer if the hour angle is negative?

A

It tells an astronomer how much time must elapse before the star or other celestial object will be crossing his or her meridian (the best time to observe it) - it is like waiting for a bus

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71
Q

What does altitude on NCP ( or SCP ) equal?

A

altitude of NCP (or SCP) = observers latitude

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72
Q

Since Polaris is only 0.5 degrees from the NCP, then to a good approximation :

A

Altitude of Polaris = observers latitude

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73
Q

What is a polar distance sometimes called?

A

Co-declination

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74
Q

What is a useful angular measure for astronomers ?

A

A stars polar distance

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75
Q

What is a stars polar distance ?

A

It is the angular distance of a star from the NCP

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76
Q

Since the declination of the NCP is +90 degrees, it follows that:

A

Polar distance = 90 degrees - declination

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77
Q

Each small circle that a star traces during one sidereal day has a radius which is equal to ?

A

Radius = polar distance

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78
Q

What are the points called when a star crosses the local meridian?

A

The upper and lower TRANSIT

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79
Q

What does the altitude at the upper and lower transits allow people to do?

A

Allows us to link it equatorial and horizontal coordinates

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80
Q

State the equation that shows us that the altitude of a star at the upper and lower transit allows us to link equatorial and horizontal coordinates?

A

Altitude ( upper and lower transits )= latitude + or - ( which means do both and get two answers ) polar distance

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81
Q

At what point does a star culminate?

A

At the upper transit

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82
Q

What are circumpolar stars?

A

Stars who polar distance is so small that that they do not set it remain visible all the time

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83
Q

What is required for a star to be circumpolar?

A

It’s polar distance must be less than the altitude of the NCP (which is equal to the latitude of the observer)

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84
Q

Since polar distance = 90 degrees - declination then :

A

90 degrees - declination < latitude of observer

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85
Q

What are some perfect ‘targets’ of a naked eye observer?

A

Large constellations, full span of Milky Way, earth orbiting artificial satellites and spectacular meteor showers

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86
Q

What is the best time to observe celestial objects?

A

When they are close to culmination ( which is when they are the highest in the sky and the brightest )

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87
Q

What does culmination allow for stars?

A

It allows the clouds of some stars to be detected and more detail to be resolved in ‘extended’ objects such as nebulae and star clusters

88
Q

What should the information of rising and setting times enable observers to estimate?

A

It allows then to estimate the ‘half-way’ time at which injects culminate

89
Q

What must happen before any serious naked eye observing can take place?

A

Your eyes must become fully - dark adapted -

90
Q

How long does it take for eyes to become dark adapted ?

A

It take roughly 20 - 30 minutes

91
Q

The retina of the eye contains two contains 2 types of photoreceptive cells which are called?

A
  • Rod (which are not colour sensitive)

- Cones (which are colour sensitive)

92
Q

What are the rods cells in your eyes sensitive to and what are they ideal for?

A
  • They are sensitive to changes to changes in light intensity and are over-sensitive in daylight
  • They are ideal for night vision, but require time to ‘adapt’ to low light levels
93
Q

If a star or nebula is insufficiently bright to stimulate the cones then what will happen?

A

It will not be seen if looked at directly and this is because the cones are not activated in dim light

94
Q

Where are the rods in the eyes located?

A

They are located on the outside of the optical axis

95
Q

What is averted vision?

A

It is looking slightly to the side of a the object

96
Q

What does averted vision allow the cones to do?

A

It allows its light to fall onto the rods and the object to be ‘seen’

97
Q

What are factors that can affect the visibility of the night sky?

A

The land scape (trees, buildings, etc…), the presence of cloud, amount of light pollution, the transparency of the atmosphere ( recent rain can remove dust particles ) and the seeing conditions ( relating to the steadiness of the atmosphere, which can be quantified using the I - V (ANTONIADI SCALE))

98
Q

What is the most spherical shape out of the Earth, Moon and Sun?

A

It is the sun

99
Q

What is the mean diameter of the moon?

A

3500km

100
Q

How much smaller is the moons polar diameter than its equatorial diameter ?

A

It’s is smaller by 4km

101
Q

How much smaller is the suns polar diameter than its equatorial diameter ?

A

10km

102
Q

What is the suns mean diameter ?

A

1.4 million km

103
Q

What does the full disc of the moon subtend an angle of at the human eye?

A

Only 0.5 degrees at the human eye

104
Q

What happened early in the moons history that formed it land scapes to what it is today ?

A

It was bombarded heavily with left over debris ( meteors and asteroids ) from the formation of the solar system

105
Q

How long ago did the storm of debris adapt and Motown lava was able to sleep through the relatively thin near side crust?

A

4000 million years ago

106
Q

What did the lava that seeped through the relatively thin crust of the moon do ?

A

It solidified and formed the lunar marina; mountain ranges upwards near the edges of the marina, creating deep valleys in between mountains.

107
Q

How where lunar craters formed?

A

Lunar craters where formed by meteoroids striking the lunar surface and each impact caused a shockwave that compressed the surface material to leave a large cavity

108
Q

What is the subsequent ‘rebound’ splattered material from impacts on the moon called?

A

Ejecta

109
Q

What do we know ejecta as?

A

It went in all directions, creating the bright streaks we see as rays

110
Q

How long does it take for the moon to revolve around the earth once?

A

27.3 days

111
Q

How many days does it take for the moon to rotate 360 degrees on its axis ?

A

27.3 days

112
Q

What is it called when it takes the same amount of time for main moon to rotate around its planet as it does to rotate 360 degree on its axis?

A

Synchronous rotation

113
Q

Why does synchronous rotation occur ?

A

It arises from the internal tidal gravitational forces lowing down the moons period of rotation until these become tidally locked (equal) to their orbital periods

114
Q

What is the moons orbital period of 27.3 days also know as?

A

A sidereal month

115
Q

What allows us to see 59% of the moon over time over than the normal 50%

A

Lunar liberation

116
Q

How is it possible to see under and over the moons polar regions?

A

From low and high altitudes from the earth

117
Q

Does the moon wobble a little?

A

Yes

118
Q

When are observers able to peek around edges of the moon’s Easter and western limbs ?

A

When seen from different view points at moon rise and moon set

119
Q

What is liberation usually due to?

A

The whereabouts about where the moon is placed in its orbit

120
Q

How much is the moons equator inclined to the plane of its orbit around the earth?

A

It’s by 1.5 degrees

121
Q

How much is the plane of the moons orbit inclined at?

A

5.1 degrees to the epileptic

122
Q

What does liberation from longitude arise from?

A

It arises from the caring speed in its elliptical orbits around the earth

123
Q

Where do all liberation effects take place on the moon?

A

They all take place close to the moons limbs and so are difficult to observe in detail

124
Q

What does the moon exert on the far and near sides of the earth?

A

Tidal forces

125
Q

What happens because of tidal forces from the moon?

A

As the earth spins, part of the coast experiences these bulges as the twice daily high and low tides

126
Q

What else’s gravitational pull contributes to tide other than the moon?

A

The suns gravitational pull

127
Q

What happens at full and new moon with the sun, moon and earth?

A

They are all aligned

128
Q

What happens to the tides at new and full moon ?

A

Particularly high and low spring tides occur

129
Q

How are neap tides made?

A

When the moon is half full, the sun and moons tidal forces act at a right angle to one another

130
Q

What are neap tides?

A

Tides whose variations are much lower and less dramatic

131
Q

What is the rate of the earths procession per century?

A

1.4 degrees

132
Q

What happens when the moon goes in front of the sun?

A

It obscures the light from the photosphere to produce a stunning total solar eclipse for observers in the dark shadow (umbra) on earth

133
Q

What happens during totality ( the eclipse ) ?

A

Some stars can be see , the sky darkens, the temp drops, suns corona can be seen

134
Q

What can happen just before and after the totality ( eclipse ) ?

A

Small bright spots of sunlight caused by the suns rays shining through valleys on the moon are visible ( theses are called Baileys beads and when one is visible, this is know as the diamond ring affect)

135
Q

How long do the solar eclipses last for?

A

A few minutes

136
Q

When do the solar eclipses usually take place ?

A

At a new moon if everything is lined up correctly

137
Q

Where is the observer located if the moon obscures just part of the sun?

A

Located in the penumbra

138
Q

What is the eclipse called if the sun only appears to have a small bright out of it?

A

A partial solar eclipse

139
Q

What is annular eclipse ?

A

A special type of partial solar eclipse in which the moons silhouetted disc is slightly smaller than at other times

140
Q

Why does an annular eclipse occur?

A

It is due to the moon being close to apogee in its elliptical orbit around the earth

141
Q

What happens up to the appearance of the sun in an annular eclipse ?

A

The sun appears as a ring of fire instead of being totally obscured

142
Q

When does a lunar eclipse occur ?

A

When the moon passes through the earths shadow

143
Q

How many years ago did the Greeks use their geometrical skills to determine the first scale and other things?

A

Over 2200 years ago

144
Q

Who where the first Greeks to establish the first rungs on the cosmic distance ladder?

A

Eratosthenes and Aristarchus of Samos

145
Q

What was Eratosthenes in charge of?

A

The great library of Alexandria in Egypt

146
Q

What did Aristarchus calculate ?

A

He was able to calculate the moons diameter was between 0.32 and 0.40 time that of the earth. ( it is actually 0.27 times)

147
Q

How many times does the earth rotate on its axis during 1 year?

A

365 and 1/4 times

148
Q

How long is one solar or synodic day?

A

24h

149
Q

What does the earths axis of rotation remains fixed with respect to and what dons’t it?

A

It does the stars

It doesn’t the sun

150
Q

The earths orbit around the sun and its fixed axis of rotation explain what?

A

The reason the sun rises and sets at different time on diffent dates during the year

Also the apparent motion of the sun on the celestial sphere and why the altitude of the sun at noon is different on different dates

151
Q

Close to the spring and summer equinoxes, what happens to the days and nights?

A

They become around the same length

Equinoctial in Roman means equal nights

152
Q

What happens to the days as spring advances?

A

They become longer with the times of the sunset and rise beginning gradually earlier and later in the day

153
Q

When does the sun usually rise in dates close to the summer solstice in June ?

A

The sun rises at its earliest and sets at its latest

154
Q

What times does the sun rise and set in the winter solstice around December?

A

It rises at the latest and sets at the earliest

155
Q

What is different about the summer and winter solstice in the Southern Hemisphere ?

A

The opposite applies than in the north

156
Q

How many days is the lunar phase cycle?

A

29.5 days

157
Q

Why are synodic months and lunar phases different lengths?

A

During the time it takes for the moon to do one orbit, the earth moon system has moved through an angle of 27 degrees in its orbit around the sun

158
Q

How do sundials and shadow stock tell the time?

A

They use an opaque object to cast a shadow of the sun

159
Q

What is the sundials normally made out of and how does it work?

A

It is traditionally a metallic triangular gnomon whose slanting edge points to the north celestial pole (NCP)

The shadow is cast onto a horizontal plate that contains the graduated scale from which the time can be read

160
Q

Since when have sundials been telling time ?

A

Since antiquity

161
Q

When sundials are correctly aligned they indicate what?

A

Apparent Solar Time (AST)

162
Q

What is different about how clocks tick to the sun?

A

Unlike clocks where they tick the same time every day, the sun can move slower some days and faster others

163
Q

What did people have to do to make the time on the sun dial more constant ?

A

Corrections had to be made to the apparent solar time as indicated on a sundial in order to obtain the Mean Solar Time (MST) for a particular location

this was based of a imaginary mean sun that did cross the sky in a constant matter

164
Q

What is the correction that had to be made to sundials know as?

A

This equation is know as the Equation Of Time (EOT) and it’s value ( that can be negative as well as positive ) differs for different dates of the year

165
Q

What is the equation for EOT?

A

Equation Of Time (EOT) = Apparent Solar Time (AST) - Mean Solar Time (MST)

166
Q

When the EOT is positive and negative, what do we say about the sun?

A

Positive - We say that the real sun is fast ( faster than the mean sun )

Negative - We say that the real sun is slow

167
Q

What can a shadow stick be used for ?

A

Determine the time at which the sun culminates ( at local noon ) and the observers longitude

168
Q

What dies a shadow stick form a sundial use?

A

It often uses a vertical, wooden, circular and reasonably thin stick such as 1cm diameter dowel

169
Q

Other than graphs and tables, what can the EOT also be read from?

A

An analemma

170
Q

What does the mean sun form the basis of?

A

Civil time keeping

171
Q

How does the mean sun move?

A

It moves more precisely at a fixed rate across the celestial equator every day

172
Q

How does the real sun move?

A

It moves up and down along the ecliptic at different rates and so the annual variation in the EOT is due to two factors

173
Q

What are the two factors the annual variation in the EOT is due to?

A

The earths elliptical orbit

The tilt of the earths axis or obliquity of the ecliptic

174
Q

How much does the earth rotate on its axis every min?

A

1 degree per min

175
Q

What stopped local mean time being used by all people?

A

It was the rail way and its times and popularity in the second quarter of the 19th century

176
Q

Why did they change the times for railways ?

A

This was because it was different times in different city’s because of LMT and so they agreed on one time all together

177
Q

What did the 19th century see a rapid expansion in?

A

Number of sea vessels, exploring or conquering new territories, waging war and trading gold, silk prices and other such communities with distant land

178
Q

What did King Charles ll founded in 1675?

A

The Royal Observatory in a Greenwich

179
Q

What was the Royal Observatory meant for?

A

It had the intention of solving the longitude problem with ships

180
Q

Who eventually solved the longitude problem with ships?

A

Astronomers and clockmakers

181
Q

When, who and how - the longitude problem solved

A

In 1761, after many trials and tribulations, horologist John Harrison solved the longitude problem with the invention of the marine chronometer that kept accurate home port time aboard ships sailing in the most extreme conditions of temperature, humidity and salinity

182
Q

Since the dawn of time, keen watches of the night have noticed the changing positions of five points of what in relation to the other what

A

Changing positions of five points of light in relation to other stars

183
Q

What did the Greek call these five points of lights that moved?

A

Wanderers which the work planet derived from

184
Q

The Greeks noticed that the motion of the planets was confined to a narrow ……. that was centred on the suns motion and passed through 12 constellations

A

Zodiacal Band

185
Q

The Greeks noticed that the motion of the planets was confined to a narrow Zodiacal Band that was centred on the suns motion and passed through 12 constellations. How can this be explained?

A

This can be explained by the fact that all the planets orbit the sun in roughly the same place

186
Q

From night to night the planets move where?

A

They move slowly eastwards

187
Q

What did ancient astronomers notice that planets occasionally do?

A

The appeared to travel backwards from east to west in either a loop-the-loop or zigzag motion.

188
Q

What is it called when plants appear to travel backwards from east to west in either a loop-the-loop or zigzag motion.

A

It is know as Retrograde Motion

189
Q

Where is the best place to observe a plant?

A

In its orbit

190
Q

Where is the best place for an inferior planet to be observed from the earth?

A

At a 90 degree angle from the earth to the sun ( pic in photo gallery ) which is called the greatest elongation

191
Q

Where is a superior planet best observed ?

A

At the opposition which is when it is directly behind the earth and all 3 are in a line

192
Q

What is an inferior junction?

A

An inferior junction is when the inferior planet is directly in the middle of the sun and earth

193
Q

What can happen when a planet is at an inferior junction?

A

The inferior planet may undergo a transit of the suns disc

194
Q

What are transits?

A

They are extremely rare events due to the orbital inclinations taking the planet either above or below the sun in the sky

195
Q

What is occultation ?

A

It is an event in which a planet may temporarily obscure a distant star as it moves in front of the star for a few moments

196
Q

What is the suns apparent motion due to?

A

It is due entirely to the orbital motion of the earth and the constant 23.5 degree tilt of the earths equator to the ecliptic

197
Q

What was astronomy born out of?

A

The need for human survival - to be able to sow and harvest crops, pick fruits and nuts, and hunt for antelope and buffalo

198
Q

What where many monuments and temples aligned specially for?

A

They where aligned for positions of key stars or to the rising of the sun on key dates of the year ( e.g Summer Solstice )

199
Q

Why are many old monuments and temples useless for what they where meant to do for observation?

A

Because the earths axis of rotation is not fixed but traces out a circular path against the stars

200
Q

What is precession ?

A

It is the relatively slow gyroscope wobbling of the earths axis

201
Q

What dies procession arise from?

A

The gravitational pull of the moon and the sun on the earths equatorial bulge ( one complete rotation of the earths axis take ~ 26,000 years )

202
Q

What where early models of the universe based on?

A

They where based on a geocentric ( earth centred ) systems Of Ancient Greek philosophers such as Plato and Aristotle

203
Q

How long did it take for Ptolemy’s model of the solar system to gain general acceptance ?

A

1500 years until polish monk Nicholas Copernicus applies some mathematical modelling to the problem and advocated a Heliocentric universe

204
Q

What is a Heliocentric Universe?

A

A sun centred universe

205
Q

Who thought of a Heliocentric universe before Copernicus and why?

A

Aristarchus of Samos argued for it in 270 BCE because his calculations showed that the sun was bigger than the earth and could solve loads of problems and confusion

206
Q

What was Copernicus reluctant to shows his model?

A

Some say because he was a monk, he did not wish to get in conflict with the church and others say he was worried of being ridiculed

207
Q

When did Copernicus finally release his book?

A

On his death bead in 1543 called - on the revolutions of the heavenly spheres

208
Q

When did Copernicus’s book gain acceptance ?

A

In the late 16th century, but astronomers were keen to reduce the disagreement between the predicated positions and true positions of the planets

209
Q

What does kepler’s first law of planetary motion state?

A

It states that the planets move in elliptical orbits around the sun at one focus of each ellipse

210
Q

What are the points called in orbit when a planet is closets and furthest from the sun?

A

Closet - perihelion

Furthest - aphelion

211
Q

What does Kepler’s second law state ?

A

It states that an imaginary line from the Sun to a planet sweeps out equal areas in equal intervals of time

212
Q

What does Kepler’s third law state?

A

It states that the square of the orbit period ( T ) of a planet is proportional to the cube of its mean distance ( r ) from the sun

213
Q

How can Kepler’s third law be mathematically written?

A

T2 a r3

                  Or

T2/r3 = a constant. (All numbers are squares)

214
Q

What is the only thing that will change in Kepler’s law in other systems?

A

The constant

215
Q

Why are time periods and mean orbit radii related to the mass of a central body ?

A

Gravity

216
Q

How did Issac Newton discover gravity?

A

Something to to with an apple as no one really knows

217
Q

What does Newton’s law of universal gravitational state?

A

Newton’s law of universal gravitational states that everybody in the universe attracts every other body with a force that is directly proportionally to the product of their masses and inversely proportional to the square of their distance apart

Astronomy (1 decks)

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