How do astronomers celebrate Chinese Valentine's Day? Popular online strategies
2024-08-10
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The seventh day of the seventh month is indeed a good day for getting married, traveling, praying, and seeking children. It is translated as Chinese Valentine's Day! Cats like us who focus on scientific research are only aware of this kind of love after the fact.Don’t look around. It’s you who are reading this post. You wouldn’t have forgotten it too, right?Fortunately, the big cat is an elite, a creature that can always find a window of time between Valentine's Day and Chinese Valentine's Day when it comes to love!Don’t worry if you forget about Qixi Festival, after all it’s not my holiday, hehehe.Not a cat anymore, temporarily a monkey!
Qixi Festival Guide 1: Watch the Altair and Vega Stars
We have been reciting poems since we were young: "The thin clouds are playing tricks, the flying stars are conveying hatred, the Milky Way is far away in the dark. When the golden wind and jade dew meet, it is better than countless things in the world.", "The tiny moon is dim in the smoky sky, and the Milky Way is the same in autumn forever.", "The distant Altair and the bright Vega." Every word and sentence outlines the scene where the Cowherd and the Weaver Girl look at each other on both sides of the Milky Way but cannot meet, and sings praises to their loyal love.I remember that every summer vacation when we watched our Monkey King Sun Wukong accompanying Tang Monk to the West to obtain Buddhist scriptures, he mentioned, "One day in heaven is one year on earth." So every year on the Chinese Valentine's Day, the Cowherd and the Weaver Girl meet on the Magpie Bridge, so they see each other once a day!If you want to watch the couple's date from the front row, you need some skills! Fortunately, Altair and Vega are both bright stars visible from Earth. They are both members of the Summer Triangle and are very easy to locate.Note: Altair's apparent magnitude is 0.76, and Vega's apparent magnitude is 0.02, both very close to 0. Therefore, Vega is often chosen as a standard star for telescope photometry during astronomical observations.The Summer Triangle is one of the first choices for beginners of visual stargazing. It consists of Vega in Lyra (α Lyrae, HIP 91262); Altair in Aquila (Aquilaα, HIP 97649); Deneb in Cygnus (swanAlpha Centauri, HIP 102098), their approximate positions in the sky look like this:▲ © Vito Technology, Inc.Altair is also known as Altair II. The stars on both sides of Altair are Altair I (a binary star) and Altair III (a VAR variable star).▲ © Vito Technology, Inc.
Qixi Festival Strategy 2: Give You a Rose Nebula
Since the light pollution in the city eliminates the interference of other low-brightness stars around, it is very easy for stargazers to find the Summer Triangle, because you can only see the most obvious triangle and a few other bright stars scattered around the sky (such as Arcturus). If you have a well-equipped astronomical telescope, there are some other highlights in the same sky area, such as the M27 Dumbbell Nebula, the Cr399 Hanger Cluster, and the M57 Ring Nebula.Of course you have to bring flowers to the holidays. The Rosette Nebula NGC2237 and the Iris Nebula NGC7023 are both suitable objects for observation.
Qixi Festival Guide 3: Watch the Meteor Shower Together
In addition, around the Chinese Valentine's Day every year, the Earth gradually passes through the dustiest area on the dusty orbit of Comet Swift-Tuttle, and the Perseid meteor shower, one of the three major meteor showers in the Northern Hemisphere, enters its active period. Making wishes to shooting stars from the late night of tonight to early tomorrow morning can also be added to your Chinese Valentine's Day list.▲ © Sky & Telescope Magazine▲ Perseid meteor shower©Vito Technology, Inc.So far, spending the Chinese Valentine's Day by watching the stars can be a perfect ending, but considering the target audience of Mozi Salon, let's go a little deeper.
Qixi Festival Strategy 4: How do astronomers celebrate Qixi Festival?
Vega is the first star other than the Sun to be photographed by humans, and the first star to have its spectrum recorded. As early as July 17, 1840, George Phillips Bond and John Adams Whipple, scientists at the Harvard Observatory, used the daguerreotype method to photograph Vega.▲ The picture shows the wavelength of the spectral lines of the main Balmer system of VegaIn 1953, American astronomers Harold Lester Johnson and William Wilson Morgan used the McDonald Observatory's 33-cm and 2.08-m reflecting telescopes to select six stars of spectral type A0V (Vega was one of them) and took their average color index as zero. Johnson and Morgan used filters in three bands, U, B, and V (Ultraviolet 364nm, Blue 442nm, Visual 540nm), to measure the photometry of the stars. This is the UBV photometry system.In the UBV system, the average magnitude of Vega is defined as UB=BV=0. What do UB and BV mean? In use, the name of the filter can directly represent the apparent magnitude in a specific filter. If the apparent magnitude of a V-band star is mv=14.5, the magnitude difference between the two filters is called the color index. If the magnitude of a star in two filters is V14.5 and B=15, then BV=0.5 is the color index of the star. The same is true for UB.▲ Photo of the UBVRI filter. The U and I filters appear black because they transmit light far beyond the wavelength range that the eye can detect.Astronomers use filters to isolate parts of the spectrum and thus measure monochromatic flux.The amount of light spectrum a filter allows to pass is called the passband. Filters are generally classified as narrowband filters, which have a passband of 10 nanometers, typically isolating one spectral line, or broadband filters, which have a passband of 100 nanometers. The center wavelength of a filter's passband is called the effective wavelength. Most modern filters are made of different colored glass, often in conjunction with thin film coatings to help define the passband and minimize surface reflections. Photometry of a light source in a set of filters provides rough spectral information about the light source. A well-defined set of filters is called a photometric system. If there are too many filters in a photometric system, and each filter has a very narrow passband, it will be difficult to detect enough photons from the light source, and strong absorption/emission features in the spectrum may adversely affect certain passbands. Conversely, if there are too few filters in a photometric system, and each filter has a very wide passband, it will not provide enough spectral information.Based on the first standardized photometric system UBV, Johnson added R and I ("red" and "infrared") filters to the system in the mid-1960s, but these filters were replaced by R and I filters with shorter effective wavelengths introduced by Cousins in the mid-1970s. It has become the most widely used UBVRI system in astronomical observations, covering ultraviolet, blue, visible, red, and infrared light bands.▲ In the table above, the magnitude of Vega in each filter is 0. By definition, the magnitude of Vega is actually zero for all colors (such as BV). Magnitudes defined in this way are called the Vega magnitude system.▲ Filter profiles for the Johnson-Morgan-Cousins UBVRI system, the world's most widely used broadband photometry system. The transmittance of the atmosphere (dashed line) and the flux of a typical CCD (dashed line) are also plotted. Image credit: Vik DhillonThe only change to the UBVRI system since then has been the filter recipe, until the advent of CCDs, which had a completely different spectral sensitivity than the photomultiplier tubes used to define the original UBRVI system, prompted Michael S. Bessell to come up with a new recipe in 1990 to make UBVRI filters out of common colored glass that, when used with CCDs, more closely reproduced the original Johnson-Morgan-Cousins filter profile. Today, most observatories around the world use Bessell's UBVRI filters.So if astronomers use different telescopes in different regions and configure the same filters, will the photometry results of the same star be the same? As mentioned in the previous article, Vega is often used as a photometry standard star, and it is used here.▲ Altair spectrum (NASA JWST)The spectrum of Altair drawn from the photometric data of the James Webb Space Telescope. This type of spectral line is called an absorption spectrum. Hydrogen is specially marked in the figure. Through the photometry of celestial bodies, we can obtain a lot of information to infer the temperature, composition, movement and other characteristics of stars.▲ Spectra of common gases in the universe, from top to bottom: sodium, nitrogen, hydrogen, oxygen (NASA, JWST)Compared with the spectrum of Altair, the dark line of hydrogen appears in the same band position. Combined with other information, astronomers have determined that the core of Altair is composed of helium produced by hydrogen nuclear fusion reaction. We can also see hydrogen in the spectrum of Vega, but the energy source of its core is more complicated. It is a nuclear fusion process that uses carbon, nitrogen and oxygen nuclei as intermediaries to aggregate protons into helium. I didn't expect that the protagonists of the legendary Qixi Festival, the Cowherd and the Weaver Girl, could produce so many stargazing techniques and scientific research. I'm going to go stargazing now. You are also welcome to leave a message in the comment section to tell us how you spent Qixi Festival.
Mozi was a famous thinker and scientist in ancient my country. His thoughts and achievements embody the early scientific buds in my country. The establishment of the Mozi Salon aims to inherit and carry forward the scientific tradition, advocate and promote the scientific spirit, improve citizens' scientific literacy, and build a social atmosphere that respects science.
Mozi Salon is aimed at the general public who love science, have a spirit of exploration and curiosity. Through face-to-face public activities and various new media platforms, we hope to let everyone understand the world's most cutting-edge scientific progress and most advanced scientific ideas, explore the secrets of science, and feel the beauty of science.
The Mozi Salon is hosted by the Shanghai Research Institute of the University of Science and Technology of China and the Nanqi Quantum Technology Exchange Center of Pudong New Area, and is supported by the USTC New Alumni Foundation, the University of Science and Technology of China Education Foundation, the Pudong New Area Science and Technology Association, the China Association for Science and Technology, and the Pudong New Area Science and Technology and Economic Committee.
