Celestial Sphere, Coordinates and Time-Keeping Flashcards
How was the year divided up in Mesopotamian astronomy?
Sumerian year; 12x30d months plus 5d/
What kind of number system did the Babylonians use and what does this mean?
- Sexagesimal number system
- 360 degrees in a circle (days in a year), 60 minutes per degree, 60 seconds per minute
What model did Aristarchus/Copernicus believe in? What model did Hipparchus believe in? What model did Ptolemy believe in?
- Aristarchus - heliocentric model (sun as centre)
- Hipparchus - empirical astronomy
- Ptolemy - geocentric model
Describe the celestial sphere.
- Earth in centre
- Celestial sphere around it with north and south celestial pole
- Ecliptic at 23.5 degrees from Earths equator
What are the points where the ecliptic and the equator meet called? What are the points where the ecliptic and the equator are furthest called?
- Autumn equinox and vernal equinox
- Summer and Winter Solstice
What is latitude/declination?
Angle from equator on earth/celestial sphere
What is longitude/right ascension?
Angle along equator on earth/celestial sphere
What is the length of a sidereal day?
23:56:04
What is the length of a solar day?
24:00:00
What is the equation for period of solar day/sidereal day/year?
1/P (solar) = 1/P (sidereal) - 1/P (year)
How much is the rotation of the Earth slowing by?
0.0017 s/century
What is the current length of the year (equinox to equinox)?
365.2422 SI days
What is the length of the year in the Julian calendar?
365.25 days - leap years every 4 years
What is right ascension expressed as?
Hour angles.
What is declination expressed as?
Angles
