Topic 4 Flashcards
What is a synodic day?
The time taken for the sun to arrive in the same position in the sky as the day before
How long is a synodic day?
24 hours
Why is the synodic day not true
NOT TRUE- the Earth rotates while orbiting the SUn
What is a sidereal day
The time taken for a relatively distant star to arrive at the same position in the sky
How long is a sidereal day
23 hours and 56 minutes
Why is there a 4 minute difference between the sidereal and synodic day?
THe four minute difference is caused by the Earth orbiting the SUn at the same time is rotates about its own axis
What is apparent solar time
time dictated by the position of the sun in the sky
What is mean solar time
time on our watches that humans invented to compensate for innacuracies of AST
Why can AST be inaccurate
-elliptical orbit of Earth around Sun
-axial tilt
Why does the equation of time vary
because Earth’s axial tilt and elliptical orbit of Earth around Sun
What is the equation of time
EOT = AST - MST
Produce a plan for the shadow stick experiment
-Use a thin stick like a dowel and lace perpendicular to floor somewhere sunny
-put card below
-every 5 minutes from 11:00-14:00 draw the shadow and label length and time shown on watch
-plot graph of length against time
-Use observations to find when the shortest shadow was cast
-This is our AST noon
-Use EOT to find longitude of observer
-4 min difference = 1 degree longittude
What doe a positive difference in the equation of time mean?
East of meridian
What does a negative difference in the equation of time mean?
West of meridian
What is a sundial used for
Used to tell time based off a shadow of the gnomon (large protrusion in the middle) created by the sun
True or false
Angle of gnomon should equal latitude of the sundial
True
What should the latitude of the sundial equal
Angle of gnomon
WHat are 2 disadvantages of using a sundial
-Doesn’t operate when there’s no sunlight
-Inaccurate to a certain degree due to the equation of time
What other planets show phases?`
Venus and Mercury
How long is the sidereal month
27.3 days
What is the sidereal month
TIme taken for the moon to fully orbit the Earth
What is the synodic month
Period between a full moon and the next
How long is a synodic month
29.5 days
WHat type of rotation does the Moon have
synchronous rotation
Why can we only see one side of the moon?
The moon has a synchronous rotation which means it keeps the same face towards Earth
What is summer solstice
The day with the most daylight.
THis is because the path of the sun in the sky is highest, so the Sun is over the horizon for the longest
When is summer solstice
21st June
What is winter solstice
Day with the least sunlight, the path of the Sun in the sky is lowest as the Sun is over the horizon for the shortest time
When is winter solstice
21st December
What is vernal equinox
day & night are equal length, the equinoxes get earlier every year due to precession
What is autumnal equinox
day & night are equal length, the equinoxes get earlier every year due to precession
Where is latitude measured from>
Equator
Where is longitude measured from
Prime meridian
Describe how to find longitude using the LUNAR method
-longitude can be found by calculating the distance between the moon & a distant star
-THe moon moves 13 degrees in the sky over 24 hours
this means that a person would find the altitude of a star and use an octant to find the angle between the moon & the star
-They would then use an almanac(Set of recorded data) to work out their longitude
Why is the lunar method of working out longitude inaccurate
-Outdated data
-Unclear skies
-Being at sea
Describe how to find longitude using the HOROLOGICAL method
Marine Chronometer
Who invented the Marine chronometer
John Harrison
Who was John Harrison
Clock maker in the 18th century who noticed the movement of a ship at sea affects a clock’s pendulum
-he invented the marine chronometer which allowed people to find their time & longitude at sea
