[The astronomical phenomenon has long known]
It is about to enter September, the weather is starting to cool, the rain is decreasing, and the sunny days are increasing. It is a good time to watch the stars and the moon.
The following will introduce some special astronomical phenomena and important astronomical time nodes that will occur in September.
September 10 Mid-Autumn Full Moon
The Mid-Autumn Festival falls on the fifteenth day of the eighth lunar month. This festival usually occurs between September 7 and October 6 in the Gregorian calendar. This year, the Mid-Autumn Festival falls on September 10, which coincides with Teachers' Day.
The Mid-Autumn Festival, also known as the Moon Festival, the Moon Worship Festival, the Moon Festival, the Moon Festival, the Reunion Festival, etc., together with the Spring Festival, the Qingming Festival and the Dragon Boat Festival, are also known as the four traditional Chinese festivals.
Since ancient times, folk customs such as viewing the moon, offering sacrifices to the moon, and eating moon cakes have been passed down to this day.
As the saying goes, "the moon on the fifteenth is sixteen rounds", which means that there are mostly full moons on the sixteenth of the lunar calendar.
However, the moon on the Mid-Autumn Festival on August 15 this year is fifteen round, and the specific full moon time is 17:59 on September 10.
The moon rise time in Beijing area that day is about 18:50.
We know that the months of the lunar calendar are completely based on the changes of the moon phases.
The phases of the moon are the parts of the moon that are illuminated by the sun as seen from Earth.
The moon moves around the earth and does not emit light by itself. In January, the relative positions of the sun, the earth and the moon are changing regularly, and the phases of the moon are also changing constantly.
This cycle of gain and loss of the moon is called the synodic cycle, and the average time is 29.53 days.
When the moon moves between the sun and the earth, the moon looks in the direction of the sun from the earth, and its dark side faces the earth. The phase of the moon at this time is called the new moon or the new moon. One must be on the day of the new moon. Since the moon phase cycle is 29.53 days, in order to meet this requirement, the lunar month is divided into large and small months, 30 days for the big month, and 29 days for the small month to ensure that the moon phase is the new moon on the first day of the new year. .
The time from the new moon to the full moon takes about fourteen or five days, but the length of time is not completely fixed. This is because the moon orbits the earth in an elliptical orbit, sometimes closer to the earth, sometimes farther, and closer to the earth The speed is faster when it is far away from the earth, and the speed is slower when it is far away from the earth.
Therefore, the shortest time from the new moon to the full moon is less than 14 days, and the longest is more than 15 days. From the statistical data, the full moon mostly appears on the fifteenth and sixteenth of the lunar calendar, and sometimes it can appear on the seventeenth or even the fourteenth. Among them, the full moon that appears on the 16th is the most, accounting for nearly 60% of the total, followed by the full moon that appears on the 15th, accounting for about 40%.
Therefore, there is a saying that "the fifteenth moon is sixteen rounds".
Jupiter conjunct September 11
On the night of September 11, there will be a celestial phenomenon of Jupiter conjunct the moon. The moon that has just passed the full moon and Jupiter that is close to the opposite sun will be in close conjunction. The angular distance between the two is only more than 2 degrees at the nearest time. The time of the conjunct is the same day. 23:17.
Jupiter's brightness is very bright, with a magnitude of -2.9. As soon as it gets dark, it rises from the ground in the due east, and then a bright moon will rise, with Jupiter on the left side of the moon.
With the passage of time, the altitude of the two gradually increased.
After midnight, the moon and Jupiter move to the high sky due to the south. At this time, Jupiter is above the moon, and the angular distance to the moon is the closest.
September 23 Autumn Equinox
There is an astronomically important time node in this month, that is, the autumnal equinox, which generally occurs from September 22 to 24 every year in the Gregorian calendar. The specific time of this year's autumnal equinox is September 23 at 9:04.
The autumnal equinox, like the spring equinox, summer solstice and winter solstice, is not only an important node in astronomy, but also one of the twenty-four solar terms in my country.
The twenty-four solar terms basically reflect the changing time of the four seasons in a year and the law of phenological changes in nature.
It plays an important role in guiding agricultural production.
Farmers sow and cultivate according to the solar terms in order to have a good harvest.
Autumn is a good time to harvest. Since 2018, the State Council has designated the autumn equinox as the "Chinese Farmers Harvest Festival".
The twenty-four solar terms are invented and created by the working people and astronomers in ancient my country in the production practice, and are unique to the traditional Chinese calendar.
As early as before the Spring and Autumn Period and the Warring States Period, our country has been able to measure the length of the shadow of the noon sun with a standard watch or a pole erected on the ground, and determine the four solar terms of winter solstice, summer solstice, spring equinox and autumn equinox.
In the Qin and Han Dynasties, there was a complete set of twenty-four solar terms, which has been used to this day.
The earth revolves around the sun, but from the earth, it appears as if the sun is moving slowly.
The sun walks a circle in the sky in a year. Astronomy calls the route the sun travels in the sky the ecliptic. The ecliptic is a large circle of 360 degrees. The circle is divided into 24 sections, each section is 15 degrees, and the sun faces from the west. Every 15 degrees in the east passes a solar term.
The ecliptic crosses the celestial equator twice a year, once on the vernal equinox and once on the autumnal equinox.
Astronomy stipulates that the ecliptic longitude of the vernal equinox is 0 degrees, and the ecliptic longitude of the autumnal equinox is 180 degrees.
Many people mistakenly believe that since the twenty-four solar terms are a unique tradition in China, they should be formulated according to my country's unique lunar calendar, the lunar calendar.
In fact, the twenty-four solar terms should completely belong to the category of the Gregorian calendar, which is determined according to the position of the sun in the sky.
The ancients calculated the solar terms according to the apparent motion of the sun, and divided the year into twenty-four solar terms.
It should be noted that the year here is not the lunar year, but the return year of the solar calendar.
For the 24 solar terms, the date is basically fixed for the Gregorian calendar year that we generally use today, with a difference of one or two days before and after.
The autumnal equinox is the fourth solar term in autumn. On this day, the sun shines directly on the earth's equator, and day and night are equally divided around the world.
During the year, the position of the sun rises and sets regularly every day. In summer, the sun shines directly north of the equator, the sun rises from the north-east and sets in the north-west, and the sun is higher at noon.
In winter, the sun shines directly south of the equator, the sun rises in the south-east and sets in the south-west, and the sun is lower at noon.
During the spring and autumn equinoxes, the sun shines directly on the equator, the sun rises due east and sets due west.
If the influence of the atmosphere is not considered, it is almost equal to the equinox.
September 27 Jupiter Opposition
On September 27th we will have Jupiter opposition.
Jupiter is in the constellation Pisces at opposition and reaches magnitude -2.9.
Jupiter opposition refers to the time when the earth is exactly between Jupiter and the sun. At this time, Jupiter is in a straight line with the earth and the sun. From the earth, the difference between Jupiter and the sun in the sky is about 180 degrees, which is the largest angle. when.
Jupiter is the closest to the Earth when it is opposed to the sun, the brightness is the brightest, and the apparent diameter is the largest.
Jupiter rises from the eastern horizon as soon as it gets dark, and is at its highest altitude in the due south at midnight. Jupiter sets from the western horizon at sunrise in the morning and is in the sky all night, making it the best time to observe it.
Jupiter is the second brightest star in the sky. Its brightness is second only to Venus and brighter than other planets and stars. Only Mars will surpass Jupiter in brightness for a short period of time during the great opposition.
Not only does Jupiter radiate dazzling light, but it is also the largest planet in the solar system, twice and a half as massive as all the other planets combined.
Observing Jupiter with a small astronomical telescope, we can clearly see the 4 brighter moons around Jupiter.
More than 400 years ago, the Italian astronomer Galileo Galilei discovered them when he first observed Jupiter with a telescope, and determined that they are satellites orbiting Jupiter, so these four satellites are called Galilean satellites.
(The author is a senior engineer at Beijing Planetarium)
The pictures in this edition are provided by Vision China