Our Place in the Universe (HKU Common Core Courses)

The cycles of four seasons over a year has been well known to all humans since the beginning of civilization. By tracing the path of the Sun (the ecliptic) among the stars over the course of a year, the Greeks realized that the plane of the ecliptic is inclined relative to the celestial equator (as determined by the daily rotation of the stars). They realized that this inclination is the cause of the seasons. So the origin of the seasons was known over 2500 years ago.

If you have not yet seen the Venus-Jupiter conjunction, go out and look west to see the two planets together after sunset.

Today (February 4) is 立春 (beginning of Spring), the first of the 24 seasonal markers in the Chinese calendar. After the calendar reform of 1670 (時憲曆), 立春 is defined as the date when the Sun is at 315 degrees ecliptic longitude and is almost always on the same date in the Gregorian calendar. For details, see p. 119 of Our Place in the Universe.

Why do leap months 閏月 mostly occur in the summer?

A leap month occurs when there is no zhongqi 中氣 (12 of the 24 seasonal markers) in the lunar month. After the calendar reform of 1670, the time intervals between the seasonal markers are not longer fixed, but are dependent on the actual movement of the Sun. Since the Sun moves faster in the winter, the time intervals between seasonal markers are shorter, so there is a good chance that a lunar month has one 中氣 zhongqi. In summer, the Sun moves slower, and the chance of leap month 閏月 is higher. Most leap months occur between the 5th and 8th month of the Chinese calendar. This year is unusual as there will be a leap second month beginning on March 22nd 2023.

Winter solstice 2022 is on December 22 (Hong Kong time). The next new moon is on December 23. The second next new moon is Jan 22. Since the new moon happened so soon after winter solstice, the Chinese New Year is very early this year.

For determination of the Chinese New Year, see Chapter 9 of Our Place in the Universe.

Venus is a bright object in the sky and often surprises city-dwellers who are not accustomed to looking at the sky. In March 1945, the battleship U.S.S. New York was in the south Pacific when the crew noticed a bright object in the sky. Suspecting that it was a secret Japanese weapon, Captain K.C. Christian ordered the battleship’s anti-aircraft guns to fire at the object. After half an hour with no apparent effect, the firing stopped. The ship’s navigator then figured out that they had been firing at the planet Venus.

In fact, many UFO sightings reported by the public can be attributed to Venus. In one of the most publicized cases, police
officers in 11 counties in the state of Georgia, U.S.A. chased and followed the planet Venus for several days in 1967, believing that it was an UFO.

(Chapter 10, Our Place in the Universe)

Jupiter is at its brightest in 59 years. Jupiter is in opposition (directly opposite to the Sun as viewed from Earth). This couples with the fact that the Earth and Jupiter are closest to each other in their respective elliptical orbits, makes it appear the brightest.

Because it is in opposition, Jupiter is visible in the night sky from sunset to sunrise, and will be at its highest point in the sky after midnight. It is the brightest object in the sky and you can't miss it.

(On the history of our understanding of planetary motion, see Chapter 10 of Our Place in the Universe).

The first direct experimental proof of the rotation of the Earth was by Ferdinand Reich in 1831. He detected an eastward deflection of 2.8 cm from a drop of 160 m in a mine, confirming the effect of the Coriolis force. This was 288 years after the publication of the heliocentric theory by Copernicus in 1543.

For details, see Chapter 2 in Our Place in the Universe II: the scientific approach to discovery.

For 2000 years, we have followed the teaching of Aristotle that heaven is different from earth and celestial objects are physically distinct from the Earth. The work of Kirchoff and Bunsen represented the first challenge of the worldview of Aristotle (Chapter 9, Our Place in the Universe II: the scientific approach to discovery).

One of the questions on the final exam a few years ago;

3. The philosopher Karl Popper calls Anaximander’s idea that the Earth is a free floating object in space “one of the boldest, most revolutionary, and most portentous ideas in the whole history of human thinking”. What are the observational facts that led Anaximander to propose this hypothesis? (10%)

I did not talk at length about this in class so the question requires some extrapolation on the part of students. I am glad the some students did perfectly on this one.

There was a total lunar eclipse last night. In 1504, Christopher Columbus was running out of food in Jamaica. So he told the natives that there would be a lunar eclipse on February 29, 1504 and demanded that they provided him with food supplies. The natives were greatly impressed by his successful prediction and gave him what he asked.

Review exercise 44 in "Our Place in the Universe" (vol. I), p. 245: What was the phase of the Moon on that day?

Most science students have the perception that Copernicus' heliocentric theory is obviously correct, but in fact his theory took more than 100 years before acceptance. Skeptics of the theory cited the absence of observational evidence the orbital motion of the Sun and the self rotation of the Earth. The non-detection of stellar parallax implies that stars must be very far away if the heliocentric model is correct. But stars appeared to have finite apparent sizes. They also cited theoretical objections that if the Earth is moving at high speed, how come we don't feel it? As for Copernicus' theory itself, it is not more accurate than Ptolemy's in predicting future planetary positions but he needs more epicycles than Ptolemy.

All these problems were not resolved until more than 200 years after the death of Copernicus. For details, see Chapters 2-3 of Our Place in the Universe II: the scientific approach to discovery

Here is a question I used in one of my mid-term exam:

What would a calendar on an alien planet be like? (hint: imagine how the movement of such a planet could be different from the Earth) (10%)

The purpose of the question is to suggest to students not to blindly accept how things are. They are used to our calendar and never thought that any other forms of calendar is possible. In most science fictions (such as Star Track and Star Wars), planets all have day and nights, approximate 24 hour days, and seasons. The day/night sequence of the Earth is due to rotation of the Earth, the year is due to the Earth's revolution around the Sun, and seasons are the result of the inclination of Earth rotation axis w.r.t. the orbital plane. The chance of an alien planet so similar to Earth is zero.

How old you think is the Chinese calendar currently in use? For answers see section 9.4 of Our Place in the Universe.

I wish everyone a happy Chinese New Year!

The Chinese calendar is a mixed solar-lunar calendar and the date of the Chinese new year is defined by both the Moon and the Sun. The first day of the new year is on the second new moon after the winter solstice. For this year, the first new moon after the 2021 winter solstice was on January 3, and the second new moon on February 3. For details, see Chapter 9 of Our Place in the Universe.

Most media refer to the Chinese New Year as the Lunar New Year, which is strictly not correct. The Islamic calendar is a lunar calendar but the Chinese calendar is a mixed solar/lunar calendar. Farmers rely on the Chinese calendar because it is solar based. The Moon is important to fishermen, but not so much to farmers.

The second volume of Our Place in the Universe is now published and is available on amazon.com.

Wish all students of CCST 9012 a Merry Christmas and Happy New Year! Both origins of Christmas and new year are discussed in the course.

Although our common sense tells us that all directions are equal and there should be no preferred directions, the movements of the Sun and the stars tell us that there is a special direction. The search for answers to what this special direction means motivated our ancestors to understand the structure of the Universe.
https://youtu.be/62J2brxWjlk

Are all directions equal? Although our common sense tells us that all directions are equal and there should be no preferred directions, the movement of the Sun and the stars tell us t...

A topic in our class discussion:

The length of the year was known to be 365.2467 days by Hipparchus during the 2nd century B.C., why did it take more than 1700 years for the calendar to be reformed? What are the respective scientific, social, religious, and political reasons for this delay?

Where do stars go after they set? The answer to this question by Greek philosopher Anaximander is one of the most important idea in the history of human thinking.

https://youtu.be/PQrBxvYQXKs

where stars go after they set Where do stars go after they set? Do they continue to move along circular paths after they disappear from view? The answer to this question by Greek philos...

Position of the Sun among the star constellations is the basis of the horoscope. Although one cannot see the Sun and stars at the same time, but we can infer the position of the Sun among stars by noting the stellar constellation on the ecliptic just before sunrise and after sunset. This is a picture before sunrise as viewed from Alexandria, Egypt on winter solstice, 1000 BC, just before sunrise. One can infer that the Sun was in the constellation of Capricorn, just below the horizon.

"Our Place in the Universe II: the scientific approach to discovery" is now published. It is available on amazon.com and springer. com ( https://springer.com/9783030802592) in both e-book and softcover formats.

Our Place in the Universe - II | SpringerLink Using the history of astronomy to illustrate the process of discovery this book serves as text for common-core-curriculum astronomy education.

Why did China not know the Earth is round?
https://youtu.be/NXWpDnv0_yA

Why China did not know the Earth is round Ancient Chinese had the observational data and mathematical techniques to know that the Earth is round. Why did they fail to do so?

Why is the motion of the Sun so complicated?

The Sun generally rise near the east, but the exact direction of sunrise is different each day
The time it rises is different every day, first it rises earlier and earlier, and then later and later
The Sun rises to a different altitude each day
The length of the day is different from day to day

If the purpose of the existence of the Sun is to separate day and night, why does it have to be so complicated?

Why doesn’t God just switch on and off daylight and make the length of everyday the same?

Venus can now be easily seen in the evening. Although it is well known that Venus can be seen either in the morning or in the evening, it is less well known that it has 5 different apparitions as a morning or evening object. Below is one of its 10 apparitions as seen 30 minutes after sunset from London, England.

The complicated patterns of movement of Venus represent a major puzzle for ancient astronomers. For details, see Chapter 10 of Our Place in the Universe.

Today (September 22) is Autumnal Equinox, one of two days in a year when the Sun rises exactly in the East.

In 2016, I watched Mars every day (weather permitting) for 6 months in order to see how easy it was for our ancestors 3000 years ago to figure out the paths of planets. Since Mars and Saturn were in the same part of the sky then, I could easily see that Mars is moving much faster than Saturn. With air and light pollution, I can see far fewer stars than farmers 3000 years ago, but using Antares and other bright stars as reference, I can see that Mars is moving through the constellations. I think a casual but interested observer could easily determine the path of Mars through the fixed stars, including its retrograde motion.

The reason why the relative positions of Venus and Moon change from day to day is because when both have a daily motion of moving east to west, they also have a west to east motion relative to the stars. The Moon's motion (about 13 degrees per day) is much faster than that of Venus (about 1 degree per day).

If you go out in the early evening and look west, you can easily see Venus close to the crescent moon. This picture was taken on Sept 9, 2021. On Sept 10, 7 pm HK time, Venus should be right below the Moon.