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just this morning (mid-autumn festival), chinese scientists used thethe fengxingtian space x-ray telescope (fxt) on board the einstein probe (ep) satellite, a complete x-ray full moon image was sent back from space. this is a chinese scientistthe first x-ray photo of the complete moon obtained using a space telescope developed by the company。

the fengxingtian space x-ray telescope was developed by chen yong's team from the institute of high energy physics of the chinese academy of sciences in collaboration with the technical institute of physics and chemistry of the chinese academy of sciences. the european space agency (esa) and the max planck institute for extraterrestrial physics (mpe) of germany also participated.

▲x-ray images of the moon taken by the fengxingtian x-ray telescope during the mid-autumn festival

01

the veil of mystery is hard to “tear”

it is very difficult to take pictures of the moon in the x-ray energy range.

the x-rays emitted by the sun can stimulate the elements on the lunar surface to produce x-ray fluorescence radiation. since the characteristic energy of x-rays of different elements is different,by studying x-ray images of the lunar surface at different energies, the distribution of various elements on the lunar surface can be revealed.。

however, x-ray radiation cannot penetrate the earth's atmosphere and therefore cannot be detected on the ground. on the other hand, x-rays are difficult to focus and can only be focused using grazing incidence, which results in a very small field of view for x-ray telescopes, usually only about 20 arc minutes, which cannot cover the entire moon.

to this end, scientists usually use x-ray satellites to conduct observations outside the atmosphere, but so far no complete x-ray image of the full moon has been successfully captured. the moon seems to be shrouded in a mysterious veil.

02

when the time comes, everything is ready

we are currently in the peak year of solar activity, with frequent solar flares. when a solar flare occurs, the sun's x-ray flux will increase sharply, the energy spectrum will become harder, and the x-ray radiation on the lunar surface will also increase. this provides favorable conditions for taking x-ray photos of the lunar surface.

what is valuable is thatthis year's mid-autumn festival coincides with the moon being near the perigee of the earth-moon orbit., the closest point to the earth is only 357,400 kilometers. at this time, the moon is about 14% larger than the normal full moon, with an apparent diameter of 33.4 arc minutes, and is brighter, so it is calledsupermoonthis is a great time to take clear x-ray pictures of the moon.

however, to take a complete x-ray photo of the "supermoon", the following conditions need to be met:

● satellites need to have the ability to track the moon, that is, adjust the direction of the telescope at any time according to the lunar ephemeris so that the moon is always in the center of the field of view.

● the telescope should have a large enough field of view(the field of view diameter must be at least larger than 33.4 arc minutes) so that it is possible to take a complete photo of the moon.

● the telescope should have a high angular resolution, which is an important prerequisite for taking clear pictures.

● the visible light radiation of the “supermoon” is very strong.a thicker light-shielding film is required in front of the detectorblock visible light while being able to transmit x-rays。

● the detector energy resolution should be good, so as to obtain x-ray fluorescence images of different elements and then study the distribution of each element on the lunar surface.

▲"einstein probe" satellite

03

"feng xingtian" captured the "super moon"

"fengxingtian" meets all requirements for photographing the "supermoon" and is the best choice to unveil the mystery of the moon.

it uses multi-layer nested wolter-1 metal focusing mirrors, and the focal plane detector uses a parallel readout imaging detector.

fengxingtian's imaging field of view is square, with a side length of about twice the diameter of the moon, so that the "supermoon" can be seen at a glance. fengxingtian has a high angular resolution of about 20 arc seconds, corresponding to a circular area on the moon with a diameter of about 37 kilometers. fengxingtian is also equipped with a filter wheel with a variety of shading films available for selection, among which the "middle film" has a strong ability to block visible light. when observing the "supermoon", the middle film can be selected.

compared with other x-ray satellites in orbit around the world, the fengxingtian satellite carried by the einstein probe isit also has good x-ray energy resolution and high effective area., which can reveal the distribution of elements such as oxygen, iron, magnesium, aluminum and silicon on the lunar surface。

"tonight the moon is bright and everyone is looking at it, but i wonder whose house the autumn thoughts fall on". fengxingtian conducted x-ray observations of the moon during the mid-autumn festival and successfully transmitted clear x-ray photos of the complete lunar surface, sharing the fun of moon-watching with everyone from another perspective. the ep satellite science team is currently analyzing and processing data, and looks forward to producing fruitful results in lunar-related scientific research.

▲"fengxingtian" space x-ray telescope