我們不知道月亮有多亮，但我們需要知道

我們不知道月亮有多亮，但我們需要知道

Even though millions of us gaze at the moon every night, we don't know exactly how bright it is — which seems strange. I mean, we've already walked on it, tested moon rocks and NASA is planning a return to the lunar surface in 2024.

盡管我們數(shù)百萬人每天晚上都注視著月亮，但我們并不知道它到底有多亮——這似乎很奇怪。我的意思是，我們已經(jīng)在月球上行走，測(cè)試了月球巖石，美國(guó)宇航局計(jì)劃在2024年重返月球表面。

A crescent moon is an ideal time to think about the brightness of the lunar surface. Its appearance is created by the shadow of Earth and the light of the sun. (Photo: GreenSprocket/Shutterstock)

But there's a more practical reason: It's also incredibly important to know this detail with precision to keep our satellites running properly. That's because the way satellites work includes an important process of calibration.

但還有一個(gè)更實(shí)際的原因:精確地了解這些細(xì)節(jié)對(duì)保持我們的衛(wèi)星正常運(yùn)行也非常重要。這是因?yàn)樾l(wèi)星的工作方式包括一個(gè)重要的校準(zhǔn)過程。

To ensure they're getting the most accurate images, they regularly take photos at the same place and compare the brightness of the images to one other. The moon is a useful source as it's bright but not as harsh as the sun. If one of the images is off, the satellite will reset itself to make sure its sensitivity is correct. All of this is done automatically.

為了確保獲得最精確的圖像，他們經(jīng)常在同一地點(diǎn)拍照，并比較圖像的亮度。月亮是一個(gè)有用的來源，因?yàn)樗髁恋幌裉柲菢哟萄?。如果其中一幅圖像是關(guān)閉的，衛(wèi)星將自動(dòng)復(fù)位，以確保其靈敏度是正確的。所有這些都是自動(dòng)完成的。

This ensures that information from those satellites — which track weather, wildfires, floods, agricultural crops, and sometimes even wildlife (like mass migrations) — is accurate. To work properly, they need to have measurements of the moon that are 99 percent accurate, but we can't get that accuracy here on Earth.

這確保了來自那些衛(wèi)星的信息——跟蹤天氣、野火、洪水、農(nóng)作物，有時(shí)甚至野生動(dòng)物(如大規(guī)模遷徙)——是準(zhǔn)確的。為了正常工作，他們需要對(duì)月球進(jìn)行99%的精確測(cè)量，但我們?cè)诘厍蛏蠠o法做到這一點(diǎn)。

The best we can do from the planet's surface is about 95-97 percent accuracy due to atmospheric influences, from everything from clouds and weather to smoke, natural haze, and air pollution. Scientists at Hawaii's Moana Loa Observatory are taking the best Earth-based measurements they can and trying to calculate out the interference.

由于大氣的影響，從云層、天氣到煙霧、自然陰霾和空氣污染，我們對(duì)地球表面的最準(zhǔn)確估計(jì)大約是95%到97%。夏威夷莫阿納羅亞觀測(cè)站的科學(xué)家們正在進(jìn)行他們所能做的最好的基于地球的測(cè)量，并試圖計(jì)算出干擾。

But another team from the University of Guelph in Ontario, NASA, the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) have another plan to get hyper accurate moon-brightness measurements.

但是來自安大略省圭爾夫大學(xué)的另一個(gè)團(tuán)隊(duì)，美國(guó)國(guó)家航空航天局，美國(guó)地質(zhì)調(diào)查局(USGS)和國(guó)家標(biāo)準(zhǔn)與技術(shù)研究所(NIST)有另一個(gè)計(jì)劃來獲得超級(jí)精確的月球亮度測(cè)量。

The air-LUSI telescope during a calibration. The light on the other side of the room is an 'artificial moon,' a stable source of light that has already been well-characterized. (Photo: Ken Ulbrich/NASA)

Flying up into the stratosphere, above all visual interference, the air-LUSI (Airborne Lunar Spectral Irradiance Mission) is a NASA-sponsored mission that will take a set of measurements to determine lunar brightness from closer to the moon's surface. The 500-pound airborne telescope "uses optical and robotic equipment to autonomously capture radiometric measurements of the Moon from within the science pod of an ER-2 aircraft while flying at an altitude of 70,000 feet," according to a journal article that describes it in detail. Air-LUSI can provide 99 percent accurate measurements.

美國(guó)國(guó)家航空航天局發(fā)起的“空中月球光譜輻照度任務(wù)”(air-LUSI，即“空中月球光譜輻照度任務(wù)”)將飛行到平流層，首先是視覺干擾。這架500磅重的機(jī)載望遠(yuǎn)鏡“使用光學(xué)和機(jī)器人設(shè)備，從一架ER-2型飛機(jī)的科學(xué)艙內(nèi)自動(dòng)捕獲月球的輻射測(cè)量數(shù)據(jù)，而飛行高度為7萬英尺，”一篇詳細(xì)描述它的期刊文章稱。Air-LUSI可以提供99%的精確測(cè)量。

A number of flights are needed, since the moon's brightness has to be measured during the various phases of the moon. And these are detailed measurements — the camera captured light from 380 to 1,000 nanometers, which is across the visible spectrum and includes the near-infrared.

由于月球的亮度必須在月球的不同階段進(jìn)行測(cè)量，因此需要多次飛行。這些都是詳細(xì)的測(cè)量數(shù)據(jù)——相機(jī)捕捉了380到1000納米的光，這些光橫跨可見光譜，包括近紅外光譜。

The first flights began in November, and so far, so good. "The data we collected looks really nice," John Woodward, NIST physicist said in a NIST statement. "The whole team has done a great job getting this instrument to fly, and the ER-2 team at Armstrong has been a great partner in making this a success."

第一次飛行開始于11月，到目前為止，一切順利。NIST的物理學(xué)家約翰·伍德沃德在NIST的一份聲明中說:“我們收集的數(shù)據(jù)看起來真的很不錯(cuò)。”“整個(gè)團(tuán)隊(duì)在讓這個(gè)儀器飛起來方面做得很好，阿姆斯特朗的ER-2團(tuán)隊(duì)是讓它成功的一個(gè)很好的合作伙伴。”

The full survey will probably take three to vive years to get all the needed data.

完整的調(diào)查可能需要3到5年才能獲得所有需要的數(shù)據(jù)。

Then and only then will we really know how bright the moon truly is.

只有到那時(shí)，我們才能真正知道月亮到底有多亮。