Download Astronomy = Timekeeping

Astronomy =
Timekeeping
•  Day, month, year
•  Important for seasons - hunter
gatherer– Annual migrations
•  Seasons important for farmers –
Heliacal rising of Sirius
•  Important for navigation –
Longitude & GPS
•  Important for modern society–
Time stamps on files
In a year the Sun appears
to move 360° along the
Ecliptic ~ the Zodiac
Ecliptic and Zodiac
•  Mercator projection map of celestial sphere in ecliptic & equatorial
•  Shows position of Sun at Summer Solstice 21Jun, Autumnal
Equinox 21Sep, Winter Solstice 21Dec, Vernal Equinox 21Mar
21Mar
21Dec
21Sep
21Jun
21Mar
Seasons
•  Earth’s axis tilted 23°
•  Sun appears higher in
sky in summer
•  Longer days
•  Sun shines down more
directly
Precession
•  Earth rotates like a gyroscope
•  Pulled by Sun and Moon
•  Earth precesses so the axis of
rotation points to different
stars – circles in 26,000 years
•  North star was Thuban
3000BC when pyramids were
built
•  Sun in Gemini on 21Jun not
Cancer – Tropic of Cancer?
Julius Caesar (July)
Reformed Calendar 46BC
•  Sidereal Year is 1 orbit around sun
•  Tropical Year (Calendar Year) is from
Vernal Equinox to Vernal Equinox
•  But Equinox precesses with Earth’s pole
•  Year is 365.24219 days
•  Abolished extra month
•  Set months to present number of days
•  Add 1 day every 4 years to February
•  Quintilius renamed July (ius)
•  Sextilis renamed August (us)
•  Sept should have been 7
Gregorian Calendar
•  Julian calendar worked until
5-14 Oct 1582 when Pope
Gregory dropped 10 days
•  England & colonies
reformed, 3-13 Sept 1752
•  Russia in 1917
•  Skip leap year when year
ends with 00
•  Keep leap year when year
evenly divisible by 400
The seasons change during
the year because:
a.  Because we have Daylight Savings time, the
days are longer in the summer and its hotter
b.  Of precession of Earth’s axis of rotation
c.  Tilt of the Earth’s axis of rotation to the ecliptic
causes sun to shine more directly in summer
d.  The winter solstice is in December and the
summer solstice is in June
e.  We are closer to the sun in the summer so it’s
hotter
Sidereal and Solar Day
•  Earth rotates once with respect
to the stars in one Sidereal Day
•  But Earth orbits the sun
(revolves around)
•  So it must rotate a little extra to
point to the sun again for one
Solar Day
•  4 minutes or 1 degree each day
Names of the Days of the Week
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
• 
Latin
Old English English
German
French Italian
Spanish
Dies Solis
Sun's Day
Sunday
Sonntag
dimanche Domenica domingo
Dies Lunae Moon's Day Monday
Montag
lundi
Lunedì
lunes
Dies Martis Tiw's Day
Tuesday
Dienstag mardi
martedì martes
Dies Mercurii Woden's Day Wednesday Mittwoch mercredi mercoledì miércoles
Dies Jovis Thor's Day
Thursday Donnerstag jeudi
giovedì
jueves
Dies Veneris Frigg's Day
Friday
Freitag
vendredi venerdì
viernes
Dies Saturni Seterne's Day Saturday Samstag
samedi sabato
sábado
Named after the seven “planets” = wanderers
Not in the right order???
4 – 7 day weeks almost = a month
Self Consistent
Horoscopes?
Eugenia Last in Van. Sun
•  Aries: A partnership can help
you expand your interests and
take on tasks you have not done
in the past. Uncertainty
regarding a job or career choice
can be dealt with if you take
control and make the necessary
changes before someone makes
a decision for you.
Sally Brompton in TC Tues.
•  Aries: Your current situation
may look chaotic but if you
stand back and look at it from
a distance you should be able
to see a pattern beginning to
emerge. The same applies to
your life in general: it does
have a meaning.
Astrology the Pseudoscience
•  Astrology makes predictions (sort of) so test
•  American Marines who re-enlist show no
correlation with birth date
•  Any reasonable/logical connections– Signs
and planets on far side of Earth have effect
but only after birth – not conception.
•  Tides of the Doctor larger than moon
1.  Aries March 21-April 19
2.  Taurus April 20- may 20
3.  Gemini May21-Jun20
4.  Cancer Jun21-July22
5.  Leo July23-Aug22
6.  Virgo Aug 23-Sept22
7.  Libra Sept23-Oct22
8.  Scorpio Oct23-Nov21
9.  Sagittarius Nov22-Dec21
10. Capricorn Dec22-Jan19
11. Aquarius Jan20-Feb18
12. Pisces Feb19-Mar20
Month
•  From new moon-new moon=one month=29.53 days
•  12 months=354.37 days
•  Islamic calendar = lunar calendar: slips relative to
seasons
•  Chinese, Hindu, Hebrew add extra month to some
years
Mean Solar Day
•  Because the Earth does not orbit the sun at a
constant distance or speed, Sun appears fast or slow
•  Ecliptic at angle to Equator so sun’s motion is
parallel to Equator at Solstice & at angle at Equinox
•  Mean Sun travels at average rate