What is time that is based on stars called?
What are the features of the celestial sphere?
The earth is at the centre
stars are imprinted on the inside of the sphere
the celestial equator and earth equator are on the same plane, and the poles are aligned
the sun orbits the earth as an ‘apparent sun’
What are the points where the path of the sun intersects the celestial equator called?
Points of equinox
What is the first point of Aries?
An equinox point that occurs on March 21st.
it is also the point at which the prime celestial meridian crosses.
What is hour angle?
essentially longitude for the celestial sphere.
What is declination?
Essentially latitude for the celestial sphere.
What are the 3 ways to measure hour angle?
From the Greenwich meridian - Greenwich hour angle
From the point of Aries - Sidereal hour angle
From a local point of observation - Local hour angle
What is Keplers first law?
The orbit of a planet describes an ellipse around the sun, with the sun at one of the foci of this ellipse
What is Keplers second law?
The radius vector of any planet sweeps out an equal area in equal time (law of equal areas)
What is Kepler third law?
The square of a planets sidereal period is equal to the cube of its orbital semi major axis (law of harmonies)
What date are seasons said to occur?
21st of each relevant month separated by 3 months
When does the greatest change in length of day occur?
At the equinoxes
What is the equation of time, what are the maximums and when do they occur?
The difference between mean solar time and apparent time
max equation of time:
16min in mid November, 14min in February
What is the difference in time across lines of longitude?
1 hour every 15deg
Considering a frozen point in time, which direction across the earth causes an increases in time of day?
How does Time change across the anti prime meridian?
The date goes down (easterly) or up (westerly)
What is the international date line?
a line which alters the anti prime meridian date line to allow for date manipulation for political or commercial reasons
How do you convert between standard time and UTC?
With the almanac
How do you convert from local mean time to UTC?
from the time at the local point, use the longitude difference to prime meridian with 15deg/hour to get a difference in time.
What is UTC?
The time at the prime meridian
What does a white box mean on the time almanac?
The sun is continuously above the horizon
What does a black box mean in the almanac?
The sun is continuously below the horizon
What do diagonal lines mean on the almanac?
Civil twilight exists all night (the sun is never more than 6deg below the horizon)