Friends who like to take pictures know that even for the same scene, changing the angle of the shot can still get different results. Whether it’s a portrait photographer wandering around a model at an auto show, repeatedly squatting down, or a landscape photographer who’s been involved in a skyscraper construction site to record the city’s panorama and skyline, i believe it’s a matter of being personal. For heliophysical and space physicists, their desire is to see the sun up and down, inside and outside, so as to thoroughly understand the star that gives us light and heat.
However, since ancient times, the perspective of human observation of the sun has been limited to the plane in which the Earth’s orbit is located, and has never been able to make detailed observations of the north and south poles of the sun. What is more moving scientists is that what happens at the north and south poles of the sun is of great significance to how the sun affects the flight of spacecraft and the environment in which we live.
Solar Orbiter detector (Photo: ESA)
At 10:30 p.m. EST on February 9, or 11:30 a.m. EST on February 10, a new solar photographer will be online, and her name is Solar Orbiter. She will embark on a road that her predecessors did not walk, not only can clearly see the north and south poles of the sun, but also use the hands of eighteen-like weapons, nuanced lying every face of the sun.
The solar pole is important, but we can’t see it clearly.
Europe is the origin of human scientific understanding of the sun. When Galileo first applied the telescope to astronomical observations in the 17th century, sunspots were an important object of observation for telescopes. In 1844, records of the number of sunspots accumulated for 18 years inspired German astronomer Schwarbeto to discover the pattern of changes in the number of sunspots: during the 11-year cycle, the number of sunspots increased first, then gradually decreased, and eventually returned to the level at the beginning of the 11-year cycle.
Astronomer Wolf’s retrospective of historical data is more definitive evidence of Schwarber’s conclusion.
Sunspots appear in a chart of latitude changes over time, also known as a “butterfly map” (picture source Wikipedia)
Through the accumulation of observations and research, people have a deeper understanding of the appearance and change of sunspots. Blacks generally appear in pairs on the sun’s surface, like a U-shaped magnet protruding from the sun’s surface, and the two sunspots in the pair have different magnetic field polarity. Under the action of the sun’s surface flow, the sunspot magnetic field that appears in the mid-latitudes (or more precisely the flux, in order to avoid getting the reader lost in the complicated terminology, the following is not distinguished) is transported to the equator and the poles at the same time. Near the equator, the magnetic field, which is transported from both north and south, has the opposite polarity, and is at the same end here. The magnetic field that is transported to the polar region, on the other hand, is able to establish a single magnetic field polar base here after removing the residual forces of the magnetic field in the previous solar perimeter region.
Sunspots always appear in pairs, as if a U-shaped magnet were placed inside the sun (picturesourced from https://www.Windows2.org/)
After the magnetic line starts from the “base” of the polar region, it has to extend to interplanetary space away from the sun as it can’t find a place nearby, becoming part of the interplanetary magnetic field. The open interplanetary magnetic field provides an unobstructed highway for the solar wind to flow out of the sun’s surface, so the base of the polarity of a single magnetic field is also the birthplace of the high-speed solar wind. In observations in the ultra-ultraviolet, soft X-ray and other bands, the magnetic field of the polar region “based on the ground” shows a dark color, such as a large hole in the lower corona near the sun’s surface, so scientists call it the polar coronal hole.
A composite image of polar ultraviolet and white-light coronal observations. The yellow image at the center is a polar ultraviolet observation of the sun, and the black region of the north and south poles is the coronal hole. Outward white-light coronal observations show the trajectory of the open magnetic field here (Photo: NASA)
Coronal holes are not only polar, but also appear at low latitudes. But as the number of new sunspots continues to decline and the sun enters a period of extreme and low-fall during the 11-year activity week, the polar coronary hole is the main source of interplanetary magnetic fields and high-speed solar winds. In other times, the disappearance and re-emergence of polar coronal holes is also an important process that determines the overall structure of the sun’s magnetic field. Unlike the Earth’s dipole magnetic field, which takes a very long time to turn its head, the solar dipole magnetic field, which is based on the coronary holes of the sun’s poles, flips every 11 years.
The fine structure of sunspots and their nearby light spheres (Photo: ESA)
The high-speed solar wind that gushed out of the polar coronal hole itself has an impact on the weather conditions in space near the Earth. For example, when high-speed solar winds hit Earth more frequently, spacecraft such as the International Space Station and tiangong space station, which have been working in low-Earth orbit for a long time, will experience orbital decay more quickly, requiring more fuel for orbital maintenance to keep them from falling. And when a typhoon in space, coronal mass ejection, erupts from the sun, the interplanetary magnetic field and the overall structure of the solar wind determined by the polar coronahole are important factors in determining whether it can hit the Earth. The most serious coronal mass ejection will not only cause the satellite spacecraft to suffer, but also more likely to paralyze the high-voltage power grid on a large scale, forcing humans to live a primitive life without electricity – no lights, no water, no modern life.
During the solar period, the polar coronal holes disappear and the coronal holes appear more at low latitudes, sometimes in special shapes, such as the “bird holes” in this image (Photo: NASA)
In short, to study and understand what is happening in the sun, accurate forecastof solar activity for the space weather effects of flying spacecraft and life on earth and prepared, need to see the sun’s poles.
Unfortunately, we haven’t been able to see it clearly.
Get off that plane.
Why can’t you see? Let’s start with the example of satellite observation of the earth.
The following image is a daytime image of earth taken by the Working Geostationary Orbit 4-A satellite on February 4 this year, from which we can clearly see the region, including our son, but for the North and South, only the approximate outline of a part of the region can be seen. To make clear observations of the North and South Poles, satellites cannot operate in geostationary orbits above the equator and must enter orbits with higher inclinations.
Fengyun 4A satellite visible light imaging (Photo Source: National Satellite Meteorological Centre website)
Images of the Earth’s South Pole, observed by the Terra satellite, which are not available at this angle by satellites above the equator (Picture: NASA)
When we extend our perspective from nearearth to the entire solar system, we will see that all planets, including Earth, are concentrated in a plane near the sun’s equator. Limitations of space technology, spacecraft launched from Earth, even if free of gravity, most of them can only operate near the Earth’s orbit. Therefore, SDO, SOHO and other solar detectors already working in space, can only provide the Earth’s rotation near the observation already, can not be particularly accurate to see the situation of the solar pole. This is especially true for solar telescopes that are located on the ground.
The SOHO satellite is located at the point of The Earth L1, which is the orbit ingress of the Earth’s rotation. Like satellites above the Earth’s equator, SOHO cannot see the sun’s poles (Photo: ESA)
Images of the sun observed from different bands can bring different information about the sun. This image was taken by the SDO satellite near Earth. Due to location constraints, she has difficulty seeing the sun’s poles (Picture: NADA)
The Ulysses spacecraft, which was co-operated with Europe and the United States, once completed a flight beyond the orbit of Earth. During this flight, the Ulysses spacecraft found that solar winds from the sun’s poles had a fairly stable structure during the very small and falling periods of solar activity, and that ulysses could hardly feel a change in speed and density as it traveled through it. And when solar activity enters a period of greatness, solar winds at different speeds alternate as they do near the Earth’s rotation almost as soon as they occur. These three-dimensional structural perceptions of the solar wind are impossible without flying out of the plane where the Earth’s orbit is located.
Solar wind observations from the Ulyssse spacecraft. The image of the sun was not obtained by Ulysses itself, but by other solar observation satellites at the same time (Photo: ESA)
Unfortunately, Ulysses was only equipped with instruments for local exploration, could only feel the solar wind near her, but could not see images of the sun’s surface using telescopes observed by remote sensing imagery. In fact, even with remote sensing equipment, It’s hard for Ulysses to see how clear the sun looks: Ulysses’ distance from the sun is about 2AU-4AU (AU is astronomical, indicating the average distance between the Earth and the sun), that is, 2-4 times the distance between the Earth and the sun, the farther away, The more unsightly it is, the more clear it is.
Solar Obiter : Let shimating at once
This time, SO will meet all the scientists’ wishes: to get close to the sun, to fly out of earth’s orbit, and to see through the solar polar regions with remote sensing instruments in various bands.
Solar Orbitor track schematic (Photo: ESA)
To accomplish this, of course, there must be a special track. With the gravitational pull of Venus and Earth, SO will have an orbital resonance with Venus during the flight after launch, meeting regularly. Each encounter, it is possible to draw closer to the sun with the help of the gravitational pull, while gradually straying from the earth’s orbit. During the first four years of the basic mission phase, the orbital inclination relative to the equatorial surface of the sun can reach 17 degrees, and the solar polar region sits more clearly than earth. In the subsequent expansion mission stage, the orbital plane can reach 33 degrees in cladding relative to the sun’s equator, and the observation almost significant mass of the solar polar region will be further improved.
Solar Orbiter’s 18th class of weapons, the observation instrument she is equipped with (Picture: ESA)
When we break down the radiation signals from the sun, we get information about different aspects of the sun. In order to obtain the widest possible observation, up to six remote sensing observation instruments are on so. Among them, EUI instruments observed in the extreme ultraviolet band can obtain the conditions of color balls, transition zones and lower coronas. Although the instrument was mostly carried on previously launched solar-detecting satellites, the location and structure of the coronal hole were mainly based on the instrument slotted in this band. However, thanks to so’s unique observational position, it is believed that new information can be provided to the fine structure of the corona and important physical processes of coronal heating and solar wind acceleration. The observation of the magnetic field itself is carried out by X instrument with the Seman effect of visible light as the basic principle. By analyzing the polarization state of sunlight, the polarity and intensity of the magnetic field of the sun’s light sphere can be obtained.
Because it is too close to the sun, the SO is equipped with a high-performance thermal shield for the sun’s side, which can withstand temperatures of up to 500 degrees. Remote sensing observation instruments, which open a small hole on their protective shields, are also protected from the desired signals without being baked by the sun. Pictured is the SO undergoing a vacuum heat test (Photo: ESA)
The SO is in an elliptical orbit with a distance of about 0.28AU closest to the sun and the furthest around 1AU, which is equivalent to moving back and forth inside the Earth’s orbit. In addition to remote sensing observation instruments similar to telescopes that can see the sun directly, SO is equipped with four geo-exploration instruments to “feel” the magnetic field and plasma parameters of its location. As they approach and move away from the sun from time to time, SO can record how these parameters change as they move away from the sun, allowing scientists to understand what has changed during the solar wind and coronal mass ejection sproks from the sun to Earth — which is equally important for accurate space weather forecasts.
Images of the corona used X-rays and ultra-ultraviolet bands to observe composited images (Picture: NASA)
Launched in August 2018, the Parker Solar Probe (PSP) is a pair of so-going: although the REMOTE sensing observation instrument is not SO-rich and its orbit is basically within the Earth’s rotation, its minimum distance from the sun is smaller than SO, and it can detect the most primitive process of coronal heating and solar wind acceleration. So rich remote sensing observation data and different day-to-day distance of local detection data, can provide a wealth of clues to uncover the secrets behind PSP data. In short, PSP and SO double sword, will certainly be able to laugh proud of the day-to-day layer of the river and lake.
PsP and SO’s double sword combination (Photo: ESA)
Science can not only satisfy human curiosity, provide the theoretical source for new technologies, but also give human freedom from fear. At that time, when the scientific understanding of the sun is almost zero, but the natural solar eclipse will also cause panic, and when modern people are accustomed to electricity, satellite positioning, satellite communications, transoceanic flights brought about by the convenience, the storm from the sun is a real threat to modern life and space activities. If one day in the future, disaster does come, whether we can calmly predict its occurrence, prepare for it, rely on our scientific understanding of the sun and space weather. It can be expected that the unprecedented observation already location slots of PSP and SO will enable us to understand the sun better, our parent star.
Solar storm schematics (Photo: AGU)