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Flashcards in Time (12-06-18) Deck (23)
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1

What is time that is based on stars called?

Sidereal time

2

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’

3

What are the points where the path of the sun intersects the celestial equator called?

Points of equinox

 

4

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.

5

What is hour angle?

essentially longitude for the celestial sphere.

6

What is declination?

Essentially latitude for the celestial sphere.

7

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

8

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 

(foci)

9

What is Keplers second law?

The radius vector of any planet sweeps out an equal area in equal time (law of equal areas)

(area)

10

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)

(distances)

11

What date are seasons said to occur?

21st of each relevant month separated by 3 months

12

When does the greatest change in length of day occur?

At the equinoxes

13

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 

14

What is the difference in time across lines of longitude?

1 hour every 15deg

15

Considering a frozen point in time, which direction across the earth causes an increases in time of day?

Easterly

16

How does Time change across the anti prime meridian?

The date goes down (easterly) or up (westerly)

17

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

18

How do you convert between standard time and UTC?

With the almanac

19

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.

20

What is UTC?

The time at the prime meridian

21

What does a white box mean on the time almanac?

The sun is continuously above the horizon

22

What does a black box mean in the almanac?

The sun is continuously below the horizon

23

What do diagonal lines mean on the almanac?

Civil twilight exists all night (the sun is never more than 6deg below the horizon)