Everything Earth! Flashcards
What is the mean diameter of the Earth?
13,000km
Is the Earth’s crust made up of solid, plastic or liquid?
Solid
Is the Earth’s mantle made up of solid, plastic or liquid?
Liquid
Is the Earth’s outer core made up of solid, plastic or liquid?
Plastic
Is the Earth’s inner core made up of solid, plastic or liquid?
Solid
Is latitude vertical or horizontal?
Horizontal
Is longitude vertical or horizontal?
Vertical
What is the range of latitude?
90°N to 90°S
Due to the Earth’s rotation on its axis
What is the range of longitudes?
180°W to 180°E
What are the 2 possible longitudes of the International Date Line?
180°W or 180°E
What is the longitude of Greenwich (Prime Meridian)?
0°
What is the latitude of the North pole, and what is its astronomical significance?
90°N, it’s the axis of Earth’s rotation
What is the latitude of the South pole, and what is its astronomical significance?
90°S, it’s the axis of the Earth’s rotation
At the equator, and what 2 days is the Sun at zenith at noon?
Spring and Autumn equinox
What is the latitude of the Tropic of Cancer?
23.5°N
What is the latitude of the Tropic of Capricorn?
23.5°S
At the Tropic of Cancer, what day is the sun at zenith at noon?
Summer solstice
What is the zenith?
The point in the sky directly above the observer
At the Tropic of Capricorn, what day is the sun at zenith at noon?
Winter solstice
What is the latitude of the Arctic Circle?
66.5°N
What is the latitude of the Antarctic Circle?
66.5°S
Describe what happens to the Sun on Summer Solstice in the Arctic Circle?
The Sun does not set
Describe what happens to the Sun on Winter Solstice in the Arctic Circle?
The Sun does not rise
Describe what happens to the Sun on Summer Solstice in the Antarctic Circle?
The Sun does not set
Describe what happens to the Sun on Winter Solstice in the Antarctic Circle?
The Sun does not rise
What is the angle of the Earth axial tilt?
23.5°
What is the percentage composition of the Earth’s atmosphere?
78% Nitrogen 21% Oxygen 1% Water Vapour 1% Argon 0.04% Carbon Dioxide
What are the 5 benefits of the Earth’s atmosphere?
- Respiration
- Absorbs UV/Ozone
- Absorbs X-ray and γ-ray (gamma rays)
- Regulates and moderates temperatures
- Partly protects us from small meteoroids
What are the 3 drawbacks of the Earth’s atmosphere?
- Refraction
- Absorption
- Selective (Raleigh) scattering
Describe why refraction is a drawback of the Earth’s atmosphere
It changes the position of objects in the sky, making it difficult to measure angles
Describe why absorption is a drawback of the Earth’s atmosphere
It stops nearly all light from EM spectrum
Why is the sky blue?
Because of Raleigh scattering, where white light is scattered in the atmosphere. Blue light is scattered more causing sky to appear blue
For Raleigh Scattering, is blue light or red light scattered more and why?
Blue light because it has a short wavelength
When does a solar eclipse occur?
Occurs at a New Moon
In a total eclipse, what is the first contact?
When the Moon crosses the circumference of the Sun for the first time
In a total eclipse, what is the second contact?
At the beginning of totality (when the moon starts to block most of the light from the sun)
In a total, eclipse, what is the partial phase?
Halfway between first contact and second contact, then again halfway between third contact and fourth contact
What is the umbra for an eclipse?
The dark shadow where no light falls
When viewing an eclipse at the penumbra, would you see a total or partial eclipse?
Partial eclipse
Where is the only place you’ll see totality of an eclipse?
The umbra
What is the penumbra for an eclipse?
The partial shadow where some light gets through
What is the angular diameter of the sun?
0.5°
In a total eclipse, what is the third contact?
At the end of totality
In a total eclipse, what is the fourth contact?
When the Moon crosses the circumference of the Sun for the last time
What is the solar corona?
The outermost part of the Sun’s atmosphere
What type of eclipse can you see the solar corona?
Total eclipse
Where is the observer situated if viewing a partial eclipse?
In the penumbra
What is the difference between annular and total eclipse?
An annular eclipse is similar to a total eclipse, but the moon is further away from the Earth so not all of the surface of the sun is covered
When does a lunar eclipse occur?
At a full Moon
What colour is the moon during a lunar eclipse?
Copper
Why is the moon a copper colour during a lunar eclipse?
Direct sunlight is blocked by the Earth’s shadow. Some light does reach the moon, refracted through the shadow. Blue wavelengths are scattered away, leaving primarily those at the red end of the spectrum
Where is a lunar eclipse visible from?
The entire night side of the Earth
Why don’t lunar eclipses occur every month?
The alignment isn’t right, as the moon doesn’t lie on the ecliptic plane during full or new Moon
What is tidal bulge?
Causes tides to form an elliptical shape around the Earth due to the gravitational effects of the moon and sun
Describe the position relative to the moon of the 2 tidal bulges?
One is opposite the moon (other side of Earth to where Moon is) and the other is towards Moon
What is the time between consecutive high tides?
12 hours
What causes the time between high tides?
The Earths rotation
Why so high tides occur 50 mins earlier everyday?
Due to the Moon’s orbit around Earth
How many minutes is every high tide earlier each day?
50 mins
When do spring tides occur?
At full or new Moon
When do neap tides occur?
When Sun is at right angle to position of Moon (First Quarter or Last Quarter)
How far apart approximately are spring and neap tides?
1 week apart
What is the difference between a spring tide and a normal tide?
High tide seems a bit higher and low tide a bit lower than usual
What are neap tides the result of?
The tidal bulge of the ocean caused by the sun partially cancels out the tidal bulge of the ocean caused by the moon
What is precession?
Where as Earth rotates, it wobbles slightly upon its axis
What is the period of precession?
26,000 years
What is precession caused by?
The gravitational pull of the Sun and the Moon on the Earth
In 13,000 years time, what direction will the Earth’s axis be pointing?
In the opposite direction (rather than being at 23.5° to the left of the normal, it will be 23.5° to the right)
What is the angular diameter of the Moon?
0.5°
Why does the Sun and Moon have approximately the same angular diameter (same size in the sky)?
Because the Moon is a lot closer than the Sun, so appears the same size even though it’s smaller
Who made the first accurate calculation of the Earth’s circumference (and thus diameter) and when did they do it?
Eratosthenes in 3rd Century BC
How did Eratosthenes measure the circumference of the Earth?
He read in a book that the Sun was at zenith on the noon of Summer Solstice at a place called Syene. Syene was 790km south of Alexandra, where he was situated. He measured the angle of the Sun from where he was at noon of Summer solstice and found that it was 7° (1/50th of circle). Therefore the Earth’s circumference must be 50 times the distance between him and Syene.
What is the Earth’s circumference?
40100km
What value, and what percentage error, was Eratosthenes value of the Earth’s circumference?
39,500km so a 5% error
Having obtained a value for the size of the Earth, what did Aristarchus subsequently measure?
He used the size of the Earth to measure the size of the Moon
How did Aristarchus measure the size of the Moon?
By watching a lunar eclipse, he realised that the Moon must be smaller than the Earth because it takes several hours for the Moon to pass through the central ‘umbra’ part of the Earth’s shadow. Therefore, he measured the amount of time taken for the Moon to move into the Earth’s shadow, and then measured the time taken for the Moon to cross the Earth’s shadow. He then divided these values and multiplied by the diameter of the Earth to get the diameter of the Moon
What is the equation for the diameter of the moon?
Diameter of the Moon = Diameter of the Earth x Time taken from umbral to begin of totality / Time taken from umbral to end of totality
What is the equation for the distance of the Moon from Earth?
Distance to Moon = Diameter of Moon x tan(θ)
θ= Angle subtended by Moon’s diameter
How did Aristarchus measure the distance to the Sun?
When the Moon is at Last of First Quarter, it must be at right angle to the sun forming a right-angle triangle. He measured the angle between the Sun and the Moon to be 87°. He then used trigonometry to work out that the Earth-Sun distance was 19 times the Earth-Moon distance (we now know that it’s actually more like 400 times)
How did Aristarchus measure the diameter of the Sun?
He measured the angle subtended by the Suns diameter, then used trigonometry to work out the diameter
What is 1 AU (astronomical unit)?
The mean distance between the Earth and the Sun
Why is AU a mean distance from the Sun to Earth?
Because the Earth’s orbit is elliptical
What is 1 AU equal to?
1.5x10^8 km
How did the scientist Edmond Halley measure the astronomical unit accurately?
He observed the transit of Mercury from 2 widely spaced latitudes on Earth to calculate what 1 AU is. 2 observers standing at 2 different locations will see Mercury cross the sun’s disc at slightly different places. The size of the parallax between the 2 results is linked to the distance between the Earth and the Sun
What is the Ecliptic?
The plane of Earth’s orbit around the Sun
When viewing planets, why do all planets seem to move in a narrow band either side of the ecliptic?
Because they lie on approximately the same plane as the Earth’s orbit of the Sun (the Ecliptic)
What is the Zodiac?
The 12 constellations
What is the Zodiacal Band?
The path taken by planets through the Zodiac
What does prograde motion mean in terms of a planets movement?
An object that spins in the same direction as its orbit
What is retrograde motion in terms of a planets movement?
An object that spins in the opposite direction of its orbit
Does Earth have prograde motion or retrograde motion?
Prograde motion
Which direction do planets appear to move in the sky, due to the rotation of Earth?
They move from East to West across the sky
Why do some outer planets occasionally display retrograde motion?
They appear to reverse their movement when viewed from Earth, travelling relative to the stars, which is caused by the Earth passing the outer planets in their orbits
What are inferior planets?
Planets inside the Earths orbit
What are superior planets?
Planets outside the Earths orbit
What is elongation in astronomy?
An angle between the Sun and a planets when viewed from Earth
What does a greater angle of elongation mean for viewing planets from Earth?
The greater the angle of elongation the better the observation of the planets will be
Why does a greater angle of elongation mean that the observation of the planets will be better?
Because there is a greater angular distance from the sun and the planets can be observed for longer in the night sky before sunrise
What is the greatest elongation?
The maximum angle between the Sun and planet when viewed from Earth
At what angle is it the best time to observe a planet from Earth?
When at the greatest elongation angle
What is the angle of elongation for all superior planets?
180°
Where is a superior planet relative to Earth if it is at opposition?
When it is on the opposite side of the Earth from the Sun
What is the angle of elongation when a superior planet is at opposition?
180°
What is the angle of elongation of Venus?
47°
What is the angle of elongation of Mercury?
28°
What is inferior conjunction?
An inferior conjunction occurs when a Solar System body lies along a straight line between the Earth and the Sun
What is a superior conjunction?
A superior conjunction occurs when a Solar System body, such as a planet, lies along a straight line joining the Earth and the Sun, but is on the opposite side of the Sun from the Earth
What is the angle of elongation for superior conjunction
0°
What is occultation?
An event that occurs when one object is hidden by another object that passes between it and the observer
What is transit?
The passage of a relatively small body across the disk of a larger body, usually a star or a planet, occulting (hiding) only a very small area
Why is inferior conjunction not possible for superior planets?
They can never pass between us and the sun
Give an example of a transit
Venus transit the Sun - used to measure the Astronomical Unit
Give 2 examples of an occulation
Moon occludes a star
Uranus occludes a star
What is a geocentric model of the Solar System?
Earth-centred model
What is a heliocentric-model of the Solar System?
Sun-centred model
Which Solar System model did Hipparcus and Ptolemy argue for?
Geocentric model
Why did Ptolemy suggest epicycles?
Because of the observed retrograde motion of the superior planets
What are epicycles?
An orbit revolving around a point on the deferent (the circle that planets were believed to orbit the Earth around)
How did Copernicus improve the understanding of the heliocentric model?
He was able to explain the retrograde motion of Mars
What was Copernicus explanation of the retrograde motion of Mars?
The Earth catches up and then passes the orbit of Mars
Name 2 of the discoveries that Galileo made?
The phases of Venus
Moons of Jupiter
What is Kepler’s 1st Law?
Planets move in elliptical orbits with the sun at the focus
Where is the Perihelion?
The point where a planet in an elliptical orbit is closest to the sun
Where is the Aphelion?
The point where a planet in an elliptical orbit is furthest away from the sun
Where is the Perigee?
The point where an object (e.g. a satellite) in an elliptical orbit is closest to the Earth
Where is the Apogee?
The point where an object (e.g. a satellite) in an elliptical orbit is furthest away from the Earth
What is Kepler’s 2nd Law?
The Sun-planet line sweeps out equal areas in equal times
What is Kepler’s 3rd Law?
The orbital period of a planet squared is proportional to its mean distance from the sun cubed
What is the equation for Kepler’s 3rd Law?
T^2/R^3 = constant
What 2 things are needed to derive Kepler’s 3rd Law?
Law of Gravitation F=Gm1m2/r^2
Circular Motion F=m2rω^2
How do you derive Kepler’s 3rd Law?
Make the centripetal force equal the force of gravity
Gm1m2/r^2 = m2rω^2 then simplify to get T^2 = R^3 multiplied by a constant
ω^2 = (2π/t)^2 = 4π^2/t^2
In Kepler’s 3rd Law what do t and r have to be measured in for the constant to equal 1?
t (orbital period) measured in years
r (mean radius of orbit) measured in AU
What force is responsible for maintaining planets in orbit?
Gravity
What type of law is Gravitation?
An inverse square law
What 2 things is the force of gravity proportional to?
F is proportional to mass
F is proportional to 1/r^2 r = mean radius of orbit
What direction does the Sun rise and then set in?
Rises in the East
Sets in the West
What is the period of the Sun rising and setting?
24 hours
On the Spring Equinox, where is the Sun located?
At the first point of Aries
On the Autumn Equinox, where is the sun located?
At the first point of Libra
What is the celestial sphere?
An imaginary sphere surrounding the Earth on which all celestial objects are placed
What is the Ecliptic?
The circular path which the sun is observed to take through the celestial sphere in one year
What is the angle of inclination of the ecliptic?
23.5°
Why is the ecliptic inclined at 23.5° with respect to the celestial equator?
Due to the axial tilt of the Earth
Where does the Sun and planets lie with respect to the ecliptic?
The Sun lies on the Ecliptic and planets are located near the Ecliptic
What is Declination?
A projection of latitude onto the celestial sphere
What is Declination measured in?
Degrees, Arc Minutes and Arc Seconds (° ′ ″)
What is the North Celestial Pole?
A projection of Earths North Pole onto the celestial sphere
What is the declination of the North Celestial Pole?
+90°
What is the declination of the celestial equator?
0°
What is the declination of the South Celestial Pole?
-90°
What is Right ascension?
The equivalent of longitude for the celestial sphere
Where is the prime meridian for right ascension?
The point at which the ecliptic crosses the celestial equator
How many major lines of right ascension are there from the First Point of Aries?
24
What is 1 hour of right ascension equal to in degrees?
15°
Where is right ascension measured from?
From the First Point of Aries when the Sun crosses the celestial equator from North to South
In star charts, which direction do you start from 0h and go to 24h of right ascension?
From right to left
What right ascension does the Sun have on the Summer Solstice?
6h
What right ascension does the Sun have on the Winter Solstice?
18h
What right ascension does the Sun have on the Spring Equinox?
0h
What right ascension does the Sun have on the Autumn Equinox?
12h
What is the angle of declination for the Autumn and Spring Equinox?
0°
What is the angle of declination for Winter Solstice?
-23.5°
What is the angle of declination for Summer Solstice?
23.5°
What is altitude?
Angle of the object measured upwards from the horizon of the observers view
What is the altitude of the observers zenith?
90°
What is Azimuth?
The bearing of an object taken from true north moving in a clockwise direction from the observers position
What is the meridian from the observers position?
A line that runs from due north on the horizon up to the zenith and then reaches due south at the horizon
What is Diurnal motion?
The apparent motion of an object due to the daily rotation of the Earth
Describe the motion of stars in the sky and what is the period of that motion?
They appear to rotate anti-clockwise around the north celestial pole with a period of 23h 56m (one sidereal day)
When is a star at culmination?
When it’s at its greatest altitude and therefore highest in the sky
What is Local Sidereal Time?
Time at which the First Point of Aries crosses the observers meridian
How long is a sidereal day?
23h 56m
How long is a solar day?
24h 00m
What is a circumpolar star?
A star, viewed from a given latitude on Earth, that never sets below the horizon
What is the hour angle of a star?
The time since the star last culminated across the meridian
What is hour angle measured in?
h m s
What is the equation for the hour angle (HA), local sidereal time (LST) and right ascension (RA)?
HA = LST - RA
What does a negative hour angle mean?
How long to wait before the star crosses the observers meridian
What does a positive hour angle mean?
The time since the star last culminated
How do you calculate when a star will culminate?
A star culminates when its right ascension = the observers local sidereal time
so RA = LST
What can be said about where the north celestial pole lies in respect to the observer
Always lie on the meridian and its altitude is roughly equal to the observers latitude
What is co-lattitude?
90° - lattitude
What equation is there to determine if a star is circumpolar?
Stars declination > 90° - observers latitude
What is the upper transit of a star?
When a star is culminating
How do you calculate the altitude of a star when culminating?
Observer’s latitude + (90° - declination)
What are 3 naked-eye viewing techniques that can be used to help view stars?
Dark-adapted eye
Relaxed eye
Averted vision
What is averted vision, and how does it help to view faint stars?
Looking at the object in your peripheral vision because the receptor cells are most sensitive to light
What are meteoroids?
Small rocky irregular lumps of debris in the solar system
What is the rough size range of a meteoroid?
Size ranges from several micrometers to several meters
What is a meteor?
Streak of light lasting a few seconds
What causes meteors to occur?
When a meteoroid enters the Earth’s atmosphere, the friction causes it, and the surrounding air, to heat up
What is a fireball?
A meteor with an apparent magnitude of more than -3
What is a meteorite?
If a meteoroid survives passing through the Earth’s atmosphere, it is found on the surface of the Earth as a meteorite
What is a Sporadic meteor?
A random meteor which is not associated with a meteor shower
What is the radiant of a meteor shower?
The point at which all the light trails appear to originate from. This is actually due to perspective
How do you name meteor showers?
The name of the constellation that the radiant appears to be in
Describe a Nebulae
Diffuse ‘fuzzy’ clouds, irregular in shape, can be large but have a low surface brightness
Describe an Open Cluster
Region of newly formed, hot, young stars within the Milky Way. They’re irregular in shape and have 100’s of stars
Describe a Globular Cluster
Region of old, compact stars in a spherical shape. Can have 10^5 stars
Describe a Galaxy
Spiral, elliptical or irregular. Can have 100 thousand million stars
What is a constellation?
Groupings of stars that were imagined to form configurations of objects or creatures in the sky
How many constellations are there in the sky?
88
How do categorise stars in a constellation according to their brightness?
Given Greek letters, α to ε
α is brightest
What are Asterisms?
These are either part of a constellation or stars forming a pattern from several different constellations
What are Pointers?
2 stars which can be used to form a line and then point to objects of interest on the Celestial Sphere
Is ‘The Plough’ a Constellation or Asterism?
Asterism
What are the 2 Pointers of ‘The Plough’?
Points to Polaris (pole star) and Arcturus (4th brightest star)
Is ‘Cassiopeia’ a Constellation or Asterism?
Constellation
Is ‘Orion’ a Constellation or Asterism?
Constellation
Name 2 of the Pointers of ‘Orion’
Points of Sirius and Aldebaran
Is ‘Cygnus’ a Constellation or Asterism?
Constellation
Is the Summer Triangle a Constellation or Asterism?
Asterism
Is the ‘Square of Pegasus’ a Constellation or Asterism?
Asterism
What is a Pointer of the ‘Square of Pegasus’?
Points to the Andromeda Galaxy
Is the ‘Southern Cross’ a Constellation or Asterism?
Constellation
Why did early lists of Constellations not include the Constellations visible from the Southern Hemisphere?
They hadn’t visited the South Hemisphere yet so the stars were all undiscovered
What is Solar Time?
Measurement of time using the motion of the Sun
What is the Mean Solar Day, and how long is it?
Time it takes for the Mean Sun to cross the observers meridian consecutively. Mean Solar Day is 24 hours long
What is Sidereal Time?
Measurement of time using the motion of the stars
Is Solar time or Sidereal time the ‘true’ rotational period of the Earth?
Sidereal time
What is the time taken for a star to cross the observers meridian consecutively?
23h 56m 4s (length of a sidereal day)
How many minutes earlier each day will a star appear to rise and set?
4 mins earlier
How many hours earlier each month will a star appear to rise and set?
2 hours earlier
What is the equation to work out the sidereal time from a long exposure photo?
Sidereal time/Exposure time = 360° / Angle subtended by star trail
How long is a sidereal month?
27.3 days
What is the sidereal month?
The time for the Moon to complete one full revolution around the Earth
What is a synodic (solar) month?
The number of days it takes for the Moon to complete a Lunar Phase
How long is a solar month?
29.5 days
What causes the 2.2 day difference between the solar and sidereal month?
Because the Earth has moved around the Sun, so there are 2.2 days of extra rotation to align with the Sun
What is a Waxing Moon?
Each night you see more of the Moon
What is a Waning Moon?
Each night you see less of the Moon
What are the 5 waxing phases of the Moon?
New Moon Crescent First Quarter Gibbus Full Moon
What are the 5 waning phases of the Moon?
Full Moon Gibbus Last Quarter Crescent New Moon
What is the Apparent Solar Day?
Time it takes the Sun to cross the observers meridian consecutively. Approximately 24 hours
Why is apparent solar time (AST) not a uniform scale?
The Sun crosses the sky at slightly different rates at different times of the year
Why does the Sun not cross the observers meridian at the same time for the whole year?
Due to axial tilt of the Earth and its elliptical orbit
What is the Mean Solar Day?
Time it takes for the Mean Sun to cross the observers meridian consecutively. Exactly 24 hours
What is the Equation of Time?
Difference between Apparent Solar Time and Mean Solar Time (each day given a known value)
Is the time displayed on clocks Mean Solar Time or Apparent Solar Time?
Mean Solar Time
Is the time displayed on sundials Mean Solar Time or Apparent Solar Time?
Apparent Solar Time
How many degrees does the Earth spin in one hour?
15°
What is a gnomon?
Part of a sundial that casts a shadow
What is Universal Time?
Greenwich Mean Time but everywhere on Earth has the same time (no time zones)
