Happy New (Chinese) Year!

On Sunday, Feb. 14, while we were observing Valentine’s Day, a much bigger celebration got underway in the Far East.  That was the  Chinese New Year, the day when the Year of the Ox ended and the Year of the Tiger began.  And the celebration is still ongoing, as it lasts until the Lantern Festival on the 15th day of the month (this year, Feb. 28).

Lanterns
Creative Commons License photo credit: ken2754@Yokohama

Like most Americans, I learned the sky as imagined by westerners around the Mediterranean basin, with images from Babylon, ancient Egypt, ancient Greece and Rome, and star names preserved during the Middle Ages by Arabs. So I find it fascinating to think of an entirely different culture and how they imagined the night sky. The Chinese New Year celebration is a perfectly appropriate time to do this, especially since objects in the sky, in particular the moon and Jupiter, serve as the basis of the ancient Chinese calendar.

The date of Chinese New Year varies; it can occur as early as Jan. 21 or as late as Feb. 19. However, anyone familiar with the lunar cycle can easily predict the date for a given year. That’s because China’s New Year always begins with the second new moon after the winter solstice.

Our Gregorian calendar is a solar calendar, based on the apparent position of the sun (and thus, on the Earth’s orbit around the sun).  However, the apparent position of the sun compared to the stars is difficult to observe.  Much more readily observable are the phases of the moon.  Thus the Chinese, like many ancient cultures, adopted a lunar calendar, measuring months from new moon to new moon.  Unlike the Islamic or ancient Roman calendars, the Chinese calendar begins months with the dark of the moon–the day the moon is invisible, not the first slender crescent seen at dusk.

Full Moon
Creative Commons License photo credit: Andréia

It would be convenient if one year equaled an even number of phase cycles. In fact, however, the moon takes about 29.5 days to go through one phase cycle, so 12 such cycles is 354 days.  This is significantly less than the solar year of 365.25 days, so a purely lunar calendar quickly becomes disconnected from the seasons and useless as a guide for when to plant or harvest.   To keep their lunar months connected with the seasons, the Chinese added a rule: the second-to-last lunar month must contain the winter solstice.  If the old crescent moon of the eleventh lunar month is waning towards new and the winter solstice has not yet happened, that month is repeated.  Similar rules exist for the second lunar month (which must contain the spring equinox), the fifth lunar month (which must contain the summer solstice), and the eighth lunar month (which must contain the fall equinox).  Accordingly, the first new moon after the winter solstice always begins the last month in the Chinese year, and the second new moon after the solstice begins the next year.

Chinese astronomers noticed that every twelve years, Jupiter reappears next to the same stars.   (This is because Jupiter takes 11.86 years to orbit the Sun.)  There were twelve months in a typical Chinese year (although occasionally one was doubled, as explained above).  Also, the Chinese divided the day into twelve double-hours.  They used a system of twelve ‘Earthly Branches’ to designate the months of the year and the double-hours in a day.  Jupiter’s motion in the sky established a cycle of years analogous to the cycles of months and double-hours.  Thus Jupiter became the ‘Year Star’ (Suixing) and years, too, were designated with the Earthly Branches.

Lion Dance
Creative Commons License photo credit: geoftheref

Later, as a mnemonic device, the Chinese began to associate the Earthly branches with animals.  (Sources disagree as to exactly when.)  Legends tell that Buddha (or the Jade Emperor) summoned all of the animals to him; each of the first twelve to appear became associated with an Earthly Branch.  The twelve animals are:

1) Rat  2) Ox  3) Tiger  4) Rabbit  5)Dragon  6)Snake  7)Horse  8)Sheep  9)Monkey  10)Rooster  11)Dog  12)Pig

The signs of the Chinese zodiac, then, unlike those of the western zodiac, are not constellations in the sky.  The most well known of the Chinese constellations are the 28 ‘lunar mansions.’  These are small groups of stars very roughly arrayed along the ecliptic, which is the apparent path of the sun, moon and planets across the sky.  As you’ll see in the links below, the Chinese used some stars, such as those in Orion, that are too far from the ecliptic for the moon to pass through them.  The 28 mansions were subdivided into four groups of seven; each group of seven represented one of four Chinese animals associated with the directions and the seasons:

1) The Blue/Green Dragon (Qing Long) of the East, associated with spring.  Note that the ancient Chinese color word qing was quite broad in meaning.  Blue and green were considered different shades of this broadly defined color.

2) The Red Bird (Zhu Que) of the South, associated with summer.   This mythical bird, with red and orange plumage, is distinct from the feng huang, also called the Chinese phoenix.

3) The White Tiger (Bai Hu) of the West, associated with autumn.

4) The Black Tortoise (literally Dark Warrior, Xuan Wu) of the North, associated with winter.  Xuan Wu was always shown as a tortoise with a snake wrapped around it, reflecting the folkloric belief that all tortoises were female and needed to copulate with snakes to reproduce.

Of the stars in tonight’s evening sky, those in Orion and Taurus form part of the White Tiger, while Gemini and the dimmer stars south and east of it belong to the Red Bird.

Along with the four large animals, Chinese astronomers defined three large constellations known as the three enclosures.  The largest of these is the ‘Purple Forbidden Enclosure‘ (Zi Wei Yuan) which includes all those stars near the North Pole of the sky which never set as seen from mid-northern latitudes.  The enclosure is ‘forbidden’ because it includes the North Star, which was the Emperor of Heaven because it always remains in one spot while other stars seem to go in circles around it, as if paying court.

The ‘Supreme Palace Enclosure‘ (Tai Wei Yuan) actually rises in the late evening in February.  Look east about 9 tonight for a set of stars in the shape of a backwards question mark.  We see this as the head of Leo, the Lion.  Rising under the backwards question mark is a right triangle of similar brightness.  For us, this is Leo’s hindquarters, but in China, it’s the northwest corner of the Supreme Palace enclosure.  The other side of this enclosure is a semi-circle of stars westerners recognize as part of Virgo, the Virgin.

The final enclosure, the ‘Heavenly Market Enclosure‘ (Tian Shi Yuan), won’t rise until very early in the morning in February, and isn’t in the evening sky until late May.  It centers on our constellations Ophiuchus and Serpens (Caput and Cauda), just north of the bright summer constellations Scorpius and Sagittarius.

So, I wish everyone a happy Year of the Tiger.  I’ll celebrate it by looking at the stars in a way I ‘m not accustomed to seeing them.

Go Stargazing! July edition

Jupiter becomes a late evening object by the end of the month.  It rises in the southeast just after 11 p.m. on July 1, although you may need to wait awhile for it to clear trees or buildings in that direction.  By month’s end, Jupiter rises at 9 p.m. — in late twilight.  Early risers can still see Jupiter in the southwest before dawn.  Next month, Jupiter is in the sky literally all night long.  Remember, Jupiter outshines everything in the sky except the Sun, the Moon, and Venus, so if you’re looking in the right direction, you can’t miss it.

Venus is a dazzling morning star this month.  Look east right as day begins to break for the brightest thing unless the Moon is nearby.  Venus remains the ‘morning star’ for the rest of 2009.  Mars is a little higher in the east at dawn than it has been.  Still, it remains fairly dim.  Look for Mars above Venus and to its right.  This is quite a mismatched pair; Venus is about 100 times brighter than Mars.

Saturn portrait
Creative Commons License photo credit: Elsie esq.

Saturn remains well placed in the evening sky this month.  Look for it in the west at dusk.  If you have seen Saturn through a telescope this year, you may have noticed how much thinner the rings appear now than in years past.  This is because Earth is beginning to align with Saturn’s ring plane, making the rings appear edge-on from our perspective.  On September 4, the Earth is exactly in Saturn’s ring plane, and the rings actually vanish from view!  It turns out, though, that Saturn is too close to the Sun in our sky on that date; the Earth will be about to pass on the far side of the Sun from Saturn.  No one can get a good look at Saturn this September.  However, we can still watch through our telescopes as Saturn’s rings appear thinner and thinner throughout July and August.

Saturn’s moons orbit in the same plane as its rings.  Since we ordinarily have a perspective looking over one of Saturn’s poles, moons such as Titan and Rhea can usually appear above or below Saturn as well as to its right or left in a telescopic image.  These moons are not normally blocked by Saturn.  That changes, however, when Earth aligns with Saturn’s ring plane.  Now that we’re seeing the entire system edgewise, we’re beginning to see Saturn’s moons pass in front of and behind Saturn’s disk.  The passage of a moon in front of a planet’s disk is a transit, while an occultation occurs when a planet’s disk blocks a moon.  When a moon transits, we can often see its shadow on the planet’s disk.  Here are some upcoming events for Saturn and Titan as seen from Houston:

7/9        Titan is partly occulted (blocked) by Saturn until 9:30 pm.

7/17      Titan is already in transit as night falls; it leaves the Sun’s disk between 9:45 and 10:20. (Titan appears as a disk and not a point, so it takes some time to move all of the way off Saturn’s disk.  Saturn sets by 11:15.

7/25      Titan is occulted by Saturn.

8/2        Titan is in transit from dusk until Saturn sets.  Titan’s shadow appears on Saturn’s disk at 9:30.

8/10      Titan occulted by Saturn

8/18      Titan transits Saturn.

By August 18, however, Saturn is so close to the Sun in our sky that it is only about five degrees high during late twilight and sets before night completely falls.

M42 Orion
Creative Commons License photo credit: makelessnoise

Look high in the west at dusk for stars in the shape of a backwards question mark, with a right triangle to the left of that.  These stars are in Leo, the Lion.  Saturn is under the ‘right angle’ in that right triangle.  The Big Dipper is high in the northwest on summer evenings.  From the Big Dipper’s handle, you can ‘arc to Arcturus.’  Arcturus, in the west at dusk, is the fourth brightest star we ever see at night and will be the brightest star in our night skies during all of July. Continuing the curve of the Big Dipper’s handle past Arcturus, you can ‘speed on to Spica,’ a star lower in the southwest at dusk.  Spica is a stalk of wheat held by Virgo, the Virgin, who represents the harvest goddess.

In the south as night falls is Antares in Scorpius, the Scorpion.  This is a red super giant star about 700 times as wide across as our Sun.  To the Scorpion’s left, look for eight stars in the shape of a teapot.  These stars are the bow and arrow of Sagittarius, the Archer.  In the east, the Summer Triangle dominates the evening sky.  The Triangle is up all night long until mid-August.  Vega is the brightest of the triangle’s three stars, followed by Altair in Aquila and Deneb in Cygnus.

Moon Phases in July 2009:

Full                                   July 7, 4:21 am
Last Quarter                     July 15, 4:53 am
New                                  July 21, 9:34 pm
1st Quarter                       July 28, 4:59 pm

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

The New Moon of July 21 lines up well enough with the Earth and Sun to cast its shadow on the Earth.  This causes a total solar eclipse.  The Moon’s shadow first encounters the Earth just north of Mumbai in India, so that’s where the path of totality begins.  From there, the shadow moves across Bhutan and then southern China, including Shanghai.  The shadow then ends up over the Pacific Ocean and leaves Earth before ever again reaching land.  The only part of the US anywhere close to this path is Hawaii, which experiences a partial eclipse.  This is mostly an event for Asia, where the date will be July 22.

The next total solar eclipse visible in the USA will occur August 21, 2017.

The Full Moon of July 7 almost enters the Earth’s shadow.  It does skirt the edge of the penumbra, in which the Earth partially blocks the Sun.  The resulting penumbral eclipse is scarcely noticeable at all, however.

At 3 a.m. on Friday, July 3, Earth is as far as possible from the Sun (i.e., at aphelion).  Planetary orbits are not perfect circles but ellipses.  Thus, Earth does not remain at the same distance from the Sun throughout its orbit, but gets slightly closer in January and slightly farther in July.  The difference is only about 3.4%, however—not enough to affect our seasons.  The change in seasons is due to the Earth’s tilt on its axis, not the distance from the sun.