NATS 1745- Chapter 2
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. What would you like to do?
What motivated the imperial astronomers of
Ancient China to monitor the skies? Why were they more interested in comets and
supernovae than in the planets?
- For the ancient Chinese, the
- sky was the mirror of the Earth. By keeping a close eye on the heavens, the
- Emperor could check what was happening in China. Astrology was the whole reason
- for watching the sky. They believed that
- the sky was intimately related to events on Earth. It was a type of Astrology. The Ancient
- Chinese believed that when they saw chaos in sky, chaos was going to happen on
- earth -> specifically government.
- The planets, they understood
- that planets are normal. They have predictable order/ cycle whereas comets and
- supernovae don't. They are chaotic. When something unusual happened, like comet
- and supernovea, there was a sign that something chaotic was going to happen.
What produced the Crab Nubula and Crab
Pulsar? How do we know that the Crab Pulsar is just over 950 years old?
- The Crab Nebula is the debris
- from a supernova that the Chinese saw explode in AD 1054. At the heat of the
- twisted remains of the old supernova lies a rapidly spinning relic of the
- explosion, the Crab Pulsar. For today’s astrophysicists trying to understand
- the nature of pulsars, the Chinese records provide one vital clue that they
- can;t find out any other way: the age of the Crab Pulsar.
- It formed when the core of the
- supernova collapsed, so the Chinese skywatchers reveal that the pulsar is just
- over 950 years old - a mere youngster on the cosmic stage. In the center, is
- this star that is flashing, how do we know it’s 950? because pulsar occured
- when supernovea was born, and we know that the number of years ago of the
- supernovea marks the date of the pulsar.
- Know Date of Supernovea know date of it’s pulsar.
In what 2 ways does the construction of the
Mayan Pyramid of Kukulkan suggest a connection to the sky?
- The Mayan Pyramid of Kukulkan
- had 365 steps, which shows that the Mayans were aware of the Sun’s annual
- cycle. Also, there was a annual serpent
- - pattern of light and shades tracked the time of year ( for ex, on the
- equinoxes, a full serpent’s end appeared at Kukulkan’s head). The pyramid was
- used as a calendar, because the northern staircase is divided by a short wall,
- and at the bottom of the wall there is Kukulkan’s snake head. Throughout the
- year, there was a pattern of light and shadow which moved across the pyramid -
- created by steps.
What do the remaining openings in the Mayan
El Caracol suggest that this building was used for?
- The opening in the observatory
- dome was aligned to the North most and South most setting positions of the
- planet Venus ( which allowed the Maya to measure the duration of Venus’ full
- path in the sky)
two celestial cycles are tracked in the Dresden codex?
- The Dresden Codex describes in
- detail how the planet Venus moves in the sky; and it includes predictions for
- its future motion that are accurate to one day in 500 years.
did many ancient civilization believe that eclipses are bad omens as well as
- Eclipses were believed by many
- civilizations to be herald of bad times, due to the “damaged” appearance of the
- sun or moon. If you rely on sun, and
- suddenly it stars to darken, going to think that it’s bad. Why is it unpredictable?
- Because eclipses have a long complex cycle.
- Not a regular cycle.
causes the Moon's phases? What is a lunation?
- As the moon orbits earth once a
- month, earth sees different portions of its sunlit side, causing the moon’s
- appearance to cycle from completely dark ( NEW) to completely illuminated (
- A lunation is one complete
- cycle of moon phases.
are the configurations of the Earth, Moon and Sun during New moon, 1st quarter
moon, Full moon and 3rd quarter moon? What does a "waxing moon" mean?
How about a "waning moon"? Why are crescent moons seen primarily
during the day? Why are gibbous and full moons seen primarily at night? What
does a "waxing moon" mean? How about a "waning moon"?
- When dealing with a full moon
- that the earth is between the moon and the sun
- First quarters and third
- quarters dealing with a right angle
- Waxing moon means that we are
- seeing increasing amounts of the sun lit sides
- Waning moon means that we are
- seeing less and less of the sun lit sides
- Crescent moons are primarily
- seen during the day because it is on the same side of the sun
- When it is gibbous or full we
- generally see it at night because it’s on the other side of the sky from the
- sun and when the sun down
What is the Moon's phase during a solar
eclipse, and what is causing the Sun to darken?
The moon is blocking the sun
an observer sees a total solar eclipse, where is this observer standing?
- The observer is standing in the
- umbra the total shadow
an observer standing if he/she sees a partial solar eclipse?
- They must be standing in the
- penumbra for a partial solar eclipse looks like a chunk taken out of the sun
What does a partial solar eclipse look
like? What will the Sun look like if you are standing outside the umbra and
- outside of the penumbra they are seeing a perfectly normal sun
. What is the Moon’s phase during a lunar
eclipse, and what is causing the Moon to darken?
- Full moon for a lunar eclipse
- and it is dark b/c it passing through the Earth’s shadow
total lunar eclipse is seen, what is the Moon passing through?
- The moon in its entirety is in
- the umbra the shadow
about a partial lunar eclipse?
- Partially in the umbra and the
How about a penumbral eclipse?
- n the penumbra and not in the
If an observer on the night side of Earth
witnesses a total lunar eclipse, will all observers on the night side of Earth
see a total lunar eclipse at the same time?
- Yes the eclipses moon appears
- the same for all observers that is not the case for the sun it is location
Why do eclipses not occur every lunation?
What do we call the time period when eclipses can occur? On average, how many
lunations are there between these time periods? Why are there always at least 1
(or 2) solar eclipses and 1 (or 2) lunar eclipses during these time periods?
- Its because that the moon has a
- 5 degree tilt
- Occur approximately twice a
- It is because an eclipse season
- is longer and lasts 31-38 days
are lunar eclipses seen more frequently than solar eclipses?
- It’s simply because Lunar
- Eclipses are easier to see. Lunar Eclipses and Solar eclipses occur at same
- frequency, but to see lunar eclipse you
- have to be on night side of the earth. To see solar eclipse you have to be in
- shadow. More regions of the Earth see lunar than solar.
In the Dresden codex, what does the
repeated occurrence of the numbers '177' and '154' tell us that the Maya
understood? What is the significance of the length of the table?
- 177 and 154 are the six or five
- lunations and that tells us they when they occurred
- Covers the full cycle of
- eclipses therefore predicts eclipses for eternity (significance)
2 characteristics of the planet Venus caused the Mayans to identify it as a
special kind of star? Why did they worship this planet?
- The Mayans believed that Venus
- was their god Kukulkan. This hero, Kukulkan, disappeared in the mountains one
- day, and then the planet Venus appeared where he disappeared. So the Mayans
- believed that Venus was the spirit of Kukulkan.
- Brightness and wandering motion
- across the sky
is a "heliacal rise" of Venus? What is it about Venus' appearance at
this time that made it a day of worship for the Maya?
- 1st appearance is brightest and
- at sunrise ( heliacal rise)
- Helical rise of Venus means it
- rises with the sun. Venus' appearance is unusually bright because its closest
- to the earth at that phase. that was the day the Maya believed Kukuhlcans
- spirit was embodied in the planet itself because it appeared this bright right
- after he disappeared in the mountains
When is Venus seen (morning or evening)
during the 236 days after its bright heliacal rise?
it reappears as a morning star
is it getting brighter or dimmer?
Dimmer, b/c its further from the sun
does venus disappear after the period?
venus dark side faces earth
when venus reappears, is it a morning star?
No, evening star
In the next 250 days, is venus getting brighter or dimmer
why does it disappear after the next heliacak rise
venus is hidden by sun's glare
In the Dresden codex, what do the pages
containing the rows of 4 Tzolk'in dates represent? What is the significance of
the total number of rows in the table?
- Each row gives the 4 Mayan
- dates of the appearances and disappearances in each 584 - day Venus cycle
- They represent Venus'
- appearances and disappearances. Significance is that they are able to predict
- it for eternity
was the primary motivation for studying the sky in Ancient Egypt?
- In Ancient Egypt, survival
- depended on the annual floorings of the Nile river. The sky was therefore
- studied for time keeping. The development of astronomy was their need to know
- their sky in order to track time. Nile river -> flooding -> had to know
- when it flooded
Why do we see different stars and
constellations at different times of the year?
due to earths annual orbits
Why were the Ancient Egyptians able to use
the heliacal rise of Sirius to determine when the Nile river would flood? What
was their mythical explanation for the cause of the flood?
- When the Egyptian skywatchers
- saw the brightest star rise in the morning sky just before the Sun, they knew
- that the Nile was about to flood. This annual inundation covered the land with
- fresh soil, enabling them to grow another year’s crops.
- Sirius, the most brilliant star in the sky,
- governed the Egyptians’ year. They called the star Sothis, and personified it
- as the goddess Sopdet. When Egyptians first saw Sothis rising just before the
- Sun, each July, they knew that the Nile was about swell into its annual life -
- giving flood - cause, they believed, by Sopdet weeping
Why did the Ancient Egyptians divide the
day into 24 hours?
- The Egyptians tracked time at
- night using a set of constellations which rise at approximately equal
- intervals.On average, 12 of these constellations rise each night, so the
- Egyptians divided night and day into 12 hours each.The Egyptians understood
- that if approximately 12 constellations are rising during the night, then 12
- constellations are rising in the day. So, the Egyptians defined the 24 hours in
- a day; 24 hour clock.
Why do we add a leap day every 4 years? Who
incorporated this rule into our calendar, and from what civilization did he
learn this rule from?
- While the Earth spins once a
- day, it’s gradually slowing down all the time. That’s why, every couple of
- years, we have to add a “leap second” to our clocks. The culprit is the gravity
- of the Moon, which acts as a brake on our freewheeling planet.
- Julius Caesar and he learnt it
- from the Egyptians
- We add a leap day every 4 years
- so that our calendar year remains synchronized with the earths seasonal year
. What is the difference between a year in
the Julian calendar and a year in the Gregorian calendar? Which calender year
is equal to the solar year? Which calendar do we use today?
- There is a 11 minute difference
- and Gregorian calendar is the correct calendar
- We use the Greogrian calendar
- That one is in sync with the
was the primary motivation for studying the sky in Ancient Babylon? According
to the textbook, why did this happen in Babylon but not in Egypt?
- In Babylon, where you had the
- Tigris and Euphrates as very capricious rivers, the whole business of omens and
- astrology developed. This creates a different kind of religion. The Babylonians
- turned to all kinds of divination to help them propitiate the gods in the right
- way. One of which, they turned to the sky. They hoped to take something from
- the regularity of the heavens in order to understand the irregularity of what
- was below.
. Describe (very generally) what we've
learned about the Earth's daily spin from the ancient Babylonian records of
- At the moment the Earth’s spin
- is slowing down
From what civilization did we inherit our
units of time and angle? (e.g. 60 minutes in 1 hour, 360 degrees in a circle.) Why
are there so many 60s in these units?
- Along with their meticulous
- observations of the sky, the Babylonians developed some pretty clever
- mathematics. Instead of being based on 10, though, their number system hinged
- around 60. That’s why - to this day, we have 60 minutes in an hour, and 360 ( 6
- x 60) degrees around a circle.
- babylonians, because they used
- a base-60 number system; also b/c 60 is an easily divisible number
Where are the zodiac constellations? Why
were they significant to the Babylonian astrologers? Why can we not see our astrological
constellation in the month we were born?
- Astrologers were interested
- which constellations the sun and moon and planets were in in a certain night
- Your zodiac sign is defined as
- the constellation that the sun is in front of in the month one is born. Thus,
- sun is blocking it.
- because your zodiac sign is the
- constellation that the sun is in front of in the month of your birth. So,
- during this month, you can't see this constellation, cuz the sky is too bright
- with the Sun up.
each of the 5 visible planets, what aspect of their appearance was used to
choose the Babylonian/Greek god to name them for?
- Mercury (speedy scribe/
- messenger god) : named for its fast motion across the sky
- Venus : ( goddess of love/
- beauty) : named for its brightness
- Mars: ( god of war/bloodshed)
- named for its red colour
- Jupiter: ( father of the gods)
- : named for its brightness and "majestic" motion
- Saturn: (god of old age) :
- named for its faintness and slow motion
What are 3 star-like phenomena that match
the description of the Star of Bethlehem? Briefly describe each one. Why is it
unlikely that the Star of Bethlehem was one of these phenomena?
- supernova: the explosive death
- of a massive star ( can appear as a temporary star: " nova stella" =
- Latin for "new star")
- nova: the re-ignition of a dead
- star which has yanked fresh gas ( star fuel) from a companion star ( can appear
- as a sudden, temporary star)
- comet : a rocky snowball in
- orbit around the Sun ( can appear as a temporary star)
- A supernova, nova or comet is
- unlikely, as no other civilization recorded a sighting of one around 0 BC.
What is the only plausible celestial event
to explain the Star of Bethlehem? Describe what this event looks like and why
it occurs. Why would such an event have been ignored by the court astronomers
in Ancient China?
- The only other scientific
- possibility is a planetary conjunction: when multiple planets line up in the
- same region of the sky ( not star - like, but a rare and predictable event with
- astrological importance). Looks like
- -> planets come together in the sky.
- Planets are out lapping each other. Reaching similar spots in their
- Assiduous Chinese astronomers
- would have recorded the appearance of such a brilliant new- sky sight. Instead,
- the ‘star’ may have been a close approach of Jupiter and Saturn, the
- astrologically important occultation of Jupiter by the Moon, an unfathomable
- miracle - or just a myth. The Ancient
- Chinese Astronomers were only interested in unpredictable events in the sky. A
- Planetary junction was not something unpredictable.
What would you like to do?
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