은하수란 무엇일까요? What Is The Milky Way?

지구 관련 유명 웹사이트 ‘어스스카이’(earthsky.org)에서 2021년 2월16일자로 스페인 카탈루냐에 살고있는 천문학 분야의 30년 경력의 전문가  엔디 브릭스(Andy Briggs)가 기고한 은하수란 무엇일까요?(What Is The Milky Way?)를 게재하였다. 동 기사를 원문과 함께 구글번역기에 의해 소개합니다. 엔디 브릭스의 글을 통해 은하수를 보다 이해 하는데 도움이 되었으면 좋겠습니다.

What Is The Milky Way?

은하수 란 무엇일까요?

 

Posted by Andy Briggs

게시자: 앤디 브릭스

February 16, 2021

 

View at EarthSky Community Photos. | Michael Zuber caught the bright planets Jupiter and Saturn – above the building in this photo – near the starry band of the Milky Way, from Terlingua, Texas, on November 11, 2020. Thank you, Michael.

EarthSky 커뮤니티 사진에서 봅니다. Michael Zuber는 2020년 11월 11일 텍사스주 Terlingua에서 은하수의 별이 빛나는 밴드 근처에서 이 사진의 건물 위의 밝은 행성 목성과 토성을 포착했습니다. 감사합니다.  Michael.

 

Do you think of the Milky Way as a starry band across a dark night sky? Or do you think of it as a great spiral galaxy in space? Both are correct. Both refer to our home galaxy, our local island in the vast ocean of the universe, composed of hundreds of billions of stars, one of which is our sun.

은하수를 어두운 밤하늘을 가로지르는 별이 빛나는 띠라고 생각하십니까? 아니면 우주에 있는 거대한 나선 은하로 생각하십니까? 둘 다 맞습니다. 둘 다 수천억 개의 별으로 구성된 우주의 광대한 바다에 있는 우리 지역의 섬인 우리의 고향 은하를 가리키며 그 중 하나는 우리의 태양입니다.

 

Long ago, it was possible for everybody in the world to see a dark, star-strewn sky when they looked heavenward at night, rather than the obscuring glow of city lights. In those ancient times, humans looked to the starry sky and saw a ghostly band of light arcing across the heavens, from horizon to horizon. This graceful arc of light moved across the sky with the seasons. The most casual sky-watchers could notice that parts of the band are obscured by darkness, which we now know to be vast clouds of dust.

오래 전 세계의 모든 사람들은 밤에 하늘을 바라볼 때 도시의 불빛이 희미하게 빛나는 것이 아니라 별이 흩뿌려진 어두운 하늘을 볼 수 있었습니다. 그 고대 시대에 인간은 별이 빛나는 하늘을 바라보았고 지평선에서 지평선으로 하늘을 가로질러 호를 이루는 유령 같은 빛의 띠를 보았습니다. 이 우아한 빛의 호는 계절에 따라 하늘을 ​​가로질러 움직였습니다. 가장 평범한 하늘 관찰자들은 밴드의 일부가 이제 우리가 거대한 먼지 구름으로 알고 있는 어둠으로 가려져 있다는 것을 알아차릴 수 있습니다.

 

Myths and legends grew up in different cultures around this mysterious apparition in the heavens. Each culture explained this band of light in the sky according to its own beliefs. To the ancient Armenians, it was straw strewn across the sky by the god Vahagn. In eastern Asia, it was the Silvery River of Heaven. The Finns and Estonians saw it as the Pathway of the Birds. Meanwhile, because western culture had become dominated by the legends and myths of first the ancient Greeks and then the Romans, it was their interpretations which were passed down to a majority of languages. Both the Greeks and the Romans saw the starry band as a river of milk. The Greek myth said it was milk from the breast of the goddess Hera, divine wife of Zeus. The Romans saw the river of light as milk from their goddess Ops.

 

신화와 전설은 하늘에서 이 신비한 발현을 중심으로 다른 문화권에서 성장했습니다. 각 문화는 하늘에 있는 이 빛의 띠를 자신의 신념에 따라 설명했습니다. 고대 아르메니아인들에게 그것은 바하그 신이 하늘을 가로질러 흩뿌린 짚이었습니다. 동아시아에서는 천국의 은빛강이었다. 핀란드인과 에스토니아인은 이곳을 새들의 길이라고 생각했습니다. 한편 서구 문화는 처음에는 고대 그리스인, 그 다음에는 로마인의 전설과 신화가 지배하게 되었기 때문에 대부분의 언어에 그들의 해석이 전승되었습니다. 그리스인과 로마인 모두 별이 빛나는 띠를 우유의 강으로 보았습니다. 그리스 신화에 따르면 그것은 제우스의 신의 아내인 여신 헤라의 가슴에서 나온 우유였습니다. 로마인들은 빛의 강을 그들의 여신 Ops의 우유로 보았습니다.

 

Thus it was bequeathed the name by which, today, we know that ghostly arc stretching across the sky: the Milky Way.

따라서 오늘날 우리는 하늘을 가로질러 뻗어 있는 그 유령 같은 호인 은하수라는 이름을 물려받았습니다.

 

View at EarthSky Community Photos. | William Mathe captured this image on August 15, 2020, and wrote: “Hiked up to the top of Rocky Mountain National Park in Colorado …just below 12,000 feet. Was greeted with a raging forest fire about 10 miles to the west … hung around long enough to get a couple of snaps of the Milky Way. You can see the brown clouds of smoke hanging in the valley below the rock outcrop on which I was perched.” Thank you, William.

William Mathe는 2020년 8월 15일 이 이미지를 캡처하고 다음과 같이 썼습니다. 서쪽으로 약 10마일 떨어진 곳에서 맹렬한 산불과 함께 인사를 받았습니다. 은하수를 몇 번 찍을 수 있을 만큼 길었습니다. 내가 앉은 바위 노두 아래 계곡에 드리워진 갈색 연기 구름이 보입니다.” 고마워요, 윌리엄.

 

When you are standing under a completely dark, starry sky, away from light pollution, the Milky Way appears like a cloud across the cosmos. But that cloud betrays no clue as to what it actually is. Until the invention of the telescope, no human could have known the nature of the Milky Way.

빛 공해를 피해 완전히 어둡고 별이 빛나는 하늘 아래 서 있을 때 은하수가 우주를 가로질러 구름처럼 보입니다. 그러나 그 구름은 그것이 실제로 무엇인지에 대한 단서가 없습니다. 망원경이 발명되기 전까지는 아무도 우리 은하의 본질을 알 수 없었습니다.

 

Just point even a small telescope anywhere along its length and you will be rewarded with a beautiful sight. What appears as a cloud to the unaided eye resolves into countless millions of stars, whose distance and close relative proximity to each other do not permit us to pick them out individually with just our eyes. In the same way, a raincloud looks solid in the sky but is made up of countless water droplets. The stars of the Milky Way merge together into a single band of light. But through a telescope, we see the Milky Way for what it truly is: a spiral arm of our galaxy.

작은 망원경이라도 그 길이를 따라 아무 곳이나 가리키기만 하면 아름다운 광경을 보게 될 것입니다. 맨눈으로 보기에는 구름처럼 보이는 것이 무수히 많은 수백만 개의 별들로 분해되는데, 그 별들의 거리와 상대적인 근접성으로 인해 우리의 눈으로는 개별적으로 구별할 수 없습니다. 마찬가지로 비구름은 하늘에서 단단해 보이지만 무수히 많은 물방울로 이루어져 있습니다. 은하수의 별들은 하나의 빛 띠로 합쳐집니다. 그러나 망원경을 통해 우리는 우리 은하의 진정한 모습인 나선팔을 볼 수 있습니다.

 

We can’t get outside the Milky Way, so we have to rely on artist’s concepts, like this one, to show us how it might look. The larger orange/yellow blob in the lower part of the image is a massively glorified representation of our sun, showing its approximate location with respect to the center. Image via ESA.

우리는 은하수 밖에는 나갈 수 없으니 이런 모습을 보여주기 위해서는 작가의 컨셉에 의존해야 한다. 이미지 아래 부분에 있는 더 큰 주황색/노란색 얼룩은 중심에 대한 대략적인 위치를 보여주는 우리 태양의 거대한 미화 표현입니다. ESA를 통한 이미지.

 

Thus we arrive at the second answer to the question of what the Milky Way is. To astronomers, it is the name given to the entire galaxy we live in, not just the part of it we see in the sky above us as that river of light. If this seems confusing, we must acknowledge the need for our galaxy to have a name. Many other galaxies are designated by catalogue numbers rather than names, for example the New General Catalogue, first published in 1888, which merely assigns a sequential number to each. More recent catalog numbers contain information of far more use to astronomers, for example the galaxy’s location on the sky and during which survey it was discovered. Moreover, a galaxy may appear in more than one catalog and thus possess more than one designation. For example, the galaxy NGC 2470 is also known as 2MFGC 6271.

따라서 우리는 은하수가 무엇인지에 대한 두 번째 대답에 도달합니다. 천문학자들에게 그것은 우리가 살고 있는 전체 은하계에 주어진 이름이지, 우리 위의 하늘에서 빛의 강으로 보이는 부분만이 아닙니다. 이것이 혼란스러워 보인다면 우리 은하에 이름이 있어야 할 필요성을 인정해야 합니다. 다른 많은 은하는 이름보다는 목록 번호로 지정됩니다. 예를 들어 1888년에 처음 발행된 New General Catalogue는 각각에 일련 번호만 부여합니다. 더 최근의 카탈로그 번호에는 천문학자들이 훨씬 더 많이 사용하는 정보가 포함되어 있습니다. 예를 들어 하늘에서 은하의 위치와 이 은하가 발견된 조사 기간 등입니다. 더욱이 은하는 하나 이상의 목록에 나타날 수 있으므로 하나 이상의 명칭을 가질 수 있습니다. 예를 들어, 은하 NGC 2470은 2MFGC 6271로도 알려져 있습니다.

 

These galaxy designations are certainly unromantic, belying the dazzling beauty of the objects they are attached to. But other galaxies, particularly those brighter, closer galaxies which appear as more than just fuzzy smudges of light in a telescope, were given names by astronomers of the 17th and 18th centuries according to their appearance: the Pinwheel, the Sombrero, the Sunflower, the Cartwheel, the cigar and so forth. These names were attached to galaxies long before there were any systematic sky surveys that made it necessary to use numerical labeling systems, due to the sheer number of galaxies the surveys discovered. In time, the galaxies bearing these descriptive labels were incorporated into various catalogs, but many are still known by their names. Our own galaxy does not appear in any index of galaxies. There was, however, a need for a name to refer to it by. Thus we call it “The Milky Way” instead of “the galaxy” or “our galaxy”. So that name refers to both that river of light across the sky, which is part of our galaxy, and the galaxy as a whole. When not using the name, astronomers refer to it with a capital G (the Galaxy), and all other galaxies with a lowercase g.

이 은하계 명칭은 그들이 부착된 물체의 눈부신 아름다움을 잊게 하는 확실히 낭만적이지 않습니다. 그러나 다른 은하는 특히 망원경에서 흐릿한 빛의 얼룩 이상으로 보이는 더 밝고 가까운 은하는 17세기와 18세기의 천문학자들이 그 모양에 따라 이름을 붙였습니다. 바람개비, 솜브레로, 해바라기, 수레바퀴, 시가 등등. 이 이름은 은하계에 붙은 이름으로, 그 조사에서 발견한 은하의 수 때문에 숫자 표기 시스템을 사용해야 하는 체계적인 하늘 조사가 있기 훨씬 이전에 붙여졌습니다. 시간이 지나면서 이러한 설명 레이블이 붙은 은하는 다양한 목록에 통합되었지만 많은 은하가 여전히 이름으로 알려져 있습니다. 우리 은하는 은하계의 어떤 색인에도 나타나지 않습니다. 그러나 그것을 지칭하는 이름이 필요했습니다. 따라서 우리는 그것을 "은하" 또는 "우리 은하" 대신에 "은하수"라고 부릅니다. 그래서 그 이름은 우리 은하계의 일부인 하늘을 가로지르는 빛의 강과 은하계 전체를 모두 나타냅니다. 이름을 사용하지 않을 때 천문학자들은 대문자 G(은하)로, 다른 모든 은하는 소문자 g로 표시합니다.

 

In this artist’s conception of the Milky Way, the sun’s location is shown below the central bar, at the inward side of the Orion Arm (called by its slightly dated name, the Orion Spur). The Orion Arm lies between the Sagittarius Arm and the Perseus Arm. Image via NASA/ JPL/ ESO/ R. Hurt/ Wikimedia Commons.

이 예술가의 은하수 개념에서 태양의 위치는 중앙 막대 아래, Orion Arm(약간 오래된 이름인 Orion Spur로 불림)의 안쪽에 표시됩니다. 오리온 팔은 궁수자리 팔과 페르세우스 팔 사이에 있습니다. NASA/ JPL/ ESO/ R. Hurt/ Wikimedia Commons를 통한 이미지.

 

Our solar system is located about 2/3 of the way out from the Galactic Center toward the edge of the galaxy. We are, in fact, 26,000 light years from the center, or 153,000 trillion miles (246,000 trillion km). Under the stars we can look toward the middle of the galaxy or we can look in the other direction, out toward the edge. When we look to the edge, we see a spiral arm of the Milky Way known as the Orion-Cygnus Arm (or the Orion spur): a river of light across the sky that gave rise to so many ancient myths.  The solar system is just on the inner edge of this spiral arm. If we look in the other direction, one would naturally expect to be able to see the center of the galaxy, which is located in the constellation of Sagittarius. But unfortunately, we cannot see it. The Galactic Center is hidden from us behind vast clouds of dark gas that telescopes operating in visible light cannot see through. It is only in recent decades that astronomers have been able to pierce that dusty fog with infrared telescopes to reveal what, throughout human history, has been concealed. With these new additions to astronomers’ arsenal of instruments, the study of around 100 stars at the galactic center revealed that those giant clouds of dark dust were hiding a monster: a black hole, designated Sagittarius A*, with a mass four million times the mass of our sun.

우리 태양계는 은하 중심에서 은하의 가장자리 방향으로 약 2/3 지점에 있습니다. 실제로 우리는 중심에서 26,000광년, 즉 153,000조 마일(246,000조 km) 떨어져 있습니다. 별 아래에서 우리는 은하의 중앙을 볼 수도 있고 다른 방향인 가장자리 쪽을 볼 수도 있습니다. 가장자리를 보면 Orion-Cygnus Arm(또는 Orion spur)으로 알려진 은하수의 나선형 팔이 보입니다. 하늘을 가로지르는 빛의 강으로 수많은 고대 신화를 일으켰습니다. 태양계는 이 나선팔의 안쪽 가장자리에 있습니다. 다른 방향을 보면 자연스럽게 궁수자리에 위치한 은하의 중심을 볼 수 있을 것이라고 예상할 수 있습니다. 그러나 불행히도 우리는 그것을 볼 수 없습니다. 은하 중심은 가시광선에서 작동하는 망원경이 볼 수 없는 광대한 암흑 가스 구름 뒤에 숨겨져 있습니다. 천문학자들이 적외선 망원경으로 먼지 투성이의 안개를 뚫고 인류 역사를 통틀어 감춰져 있던 것을 밝혀낸 것은 최근 수십 년에 불과합니다. 천문학자들의 장비에 이 새로운 장비가 추가되면서 은하 중심에 있는 약 100개의 별에 대한 연구에서 그 거대한 검은 먼지 구름이 괴물을 숨기고 있음이 밝혀졌습니다. 궁수자리 A*로 명명된 블랙홀은 우리 태양 질량의 400만 배입니다. 

 

The Milky Way as seen in different lights, that is, different wavelengths of light. The most familiar view is the one seen in optical light, which is the 3rd image from the bottom. Here, most of the galaxy is obscured by gas clouds (dark areas). But look in the same direction in infrared light, and you can see through the clouds (4th, 5th and 6th image from the bottom)! Read more about these images. Image via NASA.

다른 빛, 즉 다른 파장의 빛에서 보이는 은하수. 가장 친숙한 뷰는 아래에서 세 번째 이미지인 광학 조명에서 보이는 뷰입니다. 여기에서 대부분의 은하계는 가스 구름(어두운 부분)으로 가려져 있습니다. 하지만 적외선으로 같은 방향을 바라보면 구름 사이로 보입니다(아래에서 4, 5, 6번째 이미지)! 이 이미지에 대해 자세히 알아보세요. NASA를 통한 이미지.

 

Our Milky Way galaxy is one of billions in the universe. We do not know exactly how many galaxies exist: a modern estimate vastly increases previous counts to as many as 2 trillion. The Milky Way is approximately 100,000 light-years across, or 600,000 trillion miles (950,000 trillion km). We do not know its exact age, but we assume it came into being in the very early universe along with most other galaxies: within perhaps a billion years after the Big Bang. Estimates of how many stars live within the Milky Way vary quite considerably, but it seems to be somewhere between 100 billion and double that figure. Why is there so much variance? Simply because it is so difficult to count the number of stars in the galaxy from our vantage point here on Earth. Imagine being in a crowded room full of people and trying to count them without being able to move around the room. From where you are standing, all you can do is make an estimate because those people farther away from you are hidden by those closer. Neither can you even see what size and shape the room is; its walls are hidden from you by the mass of people. It’s exactly the same from our position in the galaxy.

우리 은하수 은하는 우주에 있는 수십억 개 중 하나입니다. 우리는 정확히 얼마나 많은 은하가 존재하는지 알지 못합니다. 현대의 추정치는 이전의 수를 2조로 크게 증가시킵니다. 우리 은하의 지름은 약 100,000광년 또는 600,000조 마일(950,000조 km)입니다. 정확한 나이는 알 수 없지만 대부분의 다른 은하와 함께 아주 초기 우주에서 빅뱅 이후 10억 년 이내에 생성되었다고 가정합니다. 은하수 안에 얼마나 많은 별이 살고 있는지에 대한 추정치는 상당히 다양하지만, 1000억에서 그 두 배 사이인 것 같습니다. 왜 이렇게 편차가 클까요? 단순히 여기 지구상의 유리한 지점에서 은하계의 별 수를 계산하는 것이 너무 어렵기 때문입니다. 사람들로 가득 찬 붐비는 방에 있고 방을 돌아다닐 수 없는 상태에서 숫자를 세고 있다고 상상해 보십시오. 당신이 서 있는 곳에서 당신이 할 수 있는 일은 추정하는 것뿐입니다. 당신에게서 멀리 있는 사람들은 가까운 사람들에 의해 가려지기 때문입니다. 방의 크기와 모양도 알 수 없습니다. 그 벽은 많은 사람들에 의해 당신에게서 숨겨져 있습니다. 은하계에서 우리의 위치와 정확히 동일합니다.

 

It is this inability to see the structure of the Milky Way from our location inside it that meant for most of human history we did not even recognise that we live inside a galaxy in the first place. Indeed, we did not even realise what a galaxy is: a vast city of stars, separated from others by even vaster distances. Without telescopes, most of the other galaxies in the sky were invisible. The unaided eye can only see three of them: from the Northern Hemisphere we can see only the Andromeda galaxy, also known as M31, which lies some two million light-years from us and which is in fact the farthest object we can see with our eyes alone, under dark skies. The skies in the Southern Hemisphere have the Small and Large Magellanic Clouds, two amorphous dwarf galaxies orbiting our own. They are far larger and brighter in the sky than M31 simply because they are much closer.

우리가 은하수 내부에 있는 우리 위치에서 은하수의 구조를 볼 수 없다는 것은 인류 역사의 대부분에서 우리가 처음에는 우리가 은하계 내부에 살고 있다는 사실조차 인식하지 못했다는 것을 의미합니다. 사실, 우리는 은하가 무엇인지조차 깨닫지 못했습니다. 다른 것들과 훨씬 더 멀리 떨어져 있는 거대한 별들의 도시입니다. 망원경이 없으면 하늘에 있는 다른 대부분의 은하들은 보이지 않습니다. 맨눈으로는 그 중 3개만 볼 수 있습니다. 북반구에서는 M31이라고도 하는 안드로메다 은하만 볼 수 있습니다. 이 은하는 우리로부터 약 200만 광년 떨어져 있으며 실제로 우리가 볼 수 있는 가장 먼 천체입니다. 어두운 하늘 아래 홀로 두 눈. 남반구의 하늘에는 소마젤란운과 대마젤란운이 있습니다. 두 개의 무정형 왜소은하가 우리 은하를 공전합니다. 그것들은 훨씬 더 가깝기 때문에 M31보다 하늘에서 훨씬 더 크고 더 밝습니다.

 

The Andromeda Galaxy (M31) is the closest large galaxy to our Milky Way. It’s seen here with two satellite galaxies: M32 is the compact fuzzy object located to the right of the Andromeda Galaxy’s center, and M110 is the more extended nebulous object at the top left of the central galaxy’s nucleus. Image via Zolt Levay/ Flickr.

안드로메다 은하(M31)는 우리 은하에서 가장 가까운 거대 은하입니다. 이것은 두 개의 위성 은하와 함께 여기에서 볼 수 있습니다. M32는 안드로메다 은하 중심의 오른쪽에 위치한 콤팩트한 퍼지 천체이고, M110은 중앙 은하의 핵 왼쪽 상단에 더 확장된 성운 천체입니다. Zolt Levay/Flickr를 통한 이미지.

 

The Large and Small Magellanic Clouds over Paranal in Chile. These are satellite galaxies of the Milky Way and are only visible from the Southern Hemisphere. Image via the European Southern Observatory.

칠레 파라날 상공의 크고 작은 마젤란 구름. 이들은 우리 은하의 위성 은하이며 남반구에서만 볼 수 있습니다. 유럽 ​​남부 천문대를 통한 이미지.

 

Until the 1910s, the existence of other galaxies had not been observationally confirmed. Those fuzzy patches of light astronomers saw through their telescopes were long believed to be nebulae, vast clouds of gas and dust close to us, and not other galaxies. But the concept of other galaxies was born earlier, in the early and mid-18th century, by Swedish philosopher and scientist Emanuel Swedenborg and English astronomer Thomas Wright, who apparently conceived the idea independently of each other. Building upon the work of Wright, German philosopher Immanuel Kant referred to galaxies as “island universes.” The first observational evidence came in 1912 by American astronomer Vesto Slipher, who found that the spectra of the “nebulae” he measured were redshifted and thus much further away than previously thought.

1910년대까지 다른 은하의 존재는 관측으로 확인되지 않았습니다. 망원경을 통해 본 희미한 빛의 천문학자들은 오랫동안 다른 은하가 아니라 우리 가까이에 있는 거대한 가스와 먼지 구름인 성운으로 여겨졌습니다. 그러나 다른 은하계의 개념은 18세기 초반과 중반에 스웨덴 철학자이자 과학자인 Emanuel  Swedenborg와 영국 천문학자 Thomas Wright에 의해 탄생했습니다. Wright의 연구를 바탕으로 독일 철학자 Immanuel Kant는 은하를 "섬 우주"라고 불렀습니다. 최초의 관측 증거는 1912년 미국 천문학자 Vesto Slipher가 측정한 "성운"의 스펙트럼이 적색 편이되어 이전에 생각했던 것보다 훨씬 더 멀리 있다는 것을 발견한 데 있습니다.

 

And then, Edwin Hubble, through years of painstaking work at the Mount Wilson Observatory in California, confirmed in the 1920s that we do not live in a unique location: our galaxy is just one of perhaps trillions. Hubble came to this realization by studying a type of star known as a Cepheid variable, which pulsates with a regular periodicity. The intrinsic brightness of a Cepheid variable is directly related to its pulsation period: by measuring how long it takes for the star to brighten, fade and brighten again you can calculate how bright it is, that is to say, how much light it emits. Consequently, by observing how bright it appears from the Earth you can calculate its distance, in the same way that seeing distant car headlights at night can tell you how far away the car is from how bright its lights appear to you. You can judge the distance of the car because you know all car headlights have about the same brightness.

그리고 나서 에드윈 허블은 캘리포니아의 윌슨 산 천문대에서 수년간의 고된 작업을 통해 1920년대에 우리가 독특한 위치에 살고 있지 않다는 것을 확인했습니다. 우리 은하는 아마도 수조 개 중 하나일 뿐입니다. 허블은 규칙적인 주기로 맥동하는 세페이드 변광성으로 알려진 유형의 별을 연구하여 이 사실을 깨달았습니다. 세페이드 변광성의 고유 밝기는 맥동 주기와 직접적인 관련이 있습니다. 별이 밝아지고 희미해지고 다시 밝아지는 데 걸리는 시간을 측정하여 별이 얼마나 밝은지, 즉 얼마나 많은 빛을 방출하는지 계산할 수 있습니다. 결과적으로, 지구에서 얼마나 밝게 보이는지 관찰함으로써 거리를 계산할 수 있습니다. 마치 밤에 멀리 있는 자동차 헤드라이트를 보는 것과 같은 방식으로 자동차가 얼마나 밝게 보이는지와 자동차가 얼마나 멀리 떨어져 있는지 알 수 있습니다. 모든 자동차 헤드라이트의 밝기가 거의 동일하다는 것을 알고 있기 때문에 자동차의 거리를 판단할 수 있습니다.

 

An example of a Cepheid Variable star is RS Puppis. It varies in brightness by almost a factor of 5 every 40 days. Image via NASA/ ESA/ Wikimedia Commons.

세페이드 변광성의 예는 RS Puppis입니다. 40일마다 거의 5배 정도 밝기가 달라집니다. NASA/ESA/Wikimedia Commons를 통한 이미지.

 

One of Edwin Hubble’s great achievements was finding Cepheid variables in M31, the Andromeda galaxy. Hunched under the eyepiece of the huge Hooker Telescope in the cold night air, Hubble repeatedly photographed it, eventually finding what he was seeking in that distant spiral: stars which changed in brightness over a regular period. Performing the calculations, Hubble realised that M31 is not astronomically close to us at all. It is 2 million light years away. It is a galaxy like our own, long thought to be a third as big again as the Milky Way but which is now believed to be about the same size.

에드윈 허블의 위대한 업적 중 하나는 안드로메다 은하인 M31에서 세페이드 변광성을 찾은 것입니다. 차가운 밤 공기 속에서 거대한 후커 망원경의 접안렌즈 아래에 웅크리고 있는 허블은 그것을 반복해서 촬영했고, 결국 그 먼 나선에서 그가 찾고 있던 것, 즉 일정한 기간에 걸쳐 밝기가 변하는 별들을 발견했습니다. 계산을 수행하면서 허블은 M31이 천문학적으로 우리와 전혀 가깝지 않다는 것을 깨달았습니다. 2백만 광년 떨어져 있습니다. 그것은 우리 은하와 같은 은하로, 다시 우리 은하의 3분의 1만큼 크다고 오랫동안 생각되었지만 지금은 거의 같은 크기로 믿어지고 있습니다.

 

Hubble, for whom this discovery must have been a monumental shock, surmised that our galaxy was no different from M31 and the others he observed, thus relegating us to a position of lesser importance in the universe. This was as big a revelation and diminution of our position in the universe as when humans came to understand that the Earth is not the center of the universe: that we, along with the other planets we see, orbit the sun. We do not live in a special or privileged location. The universe does not have any vantage points which are superior to others. Wherever you are in the universe and you look up at the stars, you will see the same thing. Your constellations may be different, but no matter in which direction you look, you see galaxies rushing away from you in all directions as the universe expands, carrying the galaxies along with it.

이 발견이 기념비적인 충격이었음에 틀림없는 허블은 우리 은하가 M31 및 그가 관찰한 다른 은하들과 다르지 않다고 추측하여 우리를 우주에서 덜 중요한 위치로 격하시켰습니다. 이것은 인간이 지구가 우주의 중심이 아니라는 사실, 즉 우리가 보는 다른 행성과 함께 태양을 공전한다는 사실을 이해하게 되었을 때와 마찬가지로 우주에서 우리의 위치에 대한 큰 계시이자 축소였습니다. 우리는 특별하거나 특권적인 위치에 살고 있지 않습니다. 우주에는 다른 것보다 우월한 유리한 점이 없습니다. 우주 어디에 있든지 별을 올려다보면 똑같은 것을 보게 될 것입니다. 별자리는 다를 수 있지만 어느 방향으로 보든 우주가 팽창함에 따라 은하가 함께 은하를 운반하면서 모든 방향으로 당신에게서 멀어지는 은하를 볼 수 있습니다.

 

Until the work by Slipher and Hubble (and others), we did not know the universe was expanding and it took a surprisingly long time for this fact to be accepted by the astronomical community. Even Albert Einstein did not believe it, introducing an arbitrary correction into his Relativity calculations which would result in a static, non-expanding universe. However, Einstein later called this correction the greatest error in his career when he finally accepted that the universe is expanding.

Slipher와 Hubble (그리고 다른 사람들)의 작업이 있기 전까지 우리는 우주가 팽창하고 있다는 것을 몰랐고 이 사실이 천문학계에서 받아들여지기까지 놀랍도록 오랜 시간이 걸렸습니다. 알버트 아인슈타인조차도 그것을 믿지 않았고, 상대성 이론에 임의의 수정을 도입하여 정적이고 팽창하지 않는 우주를 만들었습니다. 그러나 아인슈타인은 나중에 우주가 팽창하고 있다는 것을 마침내 받아들였을 때 이 수정을 그의 경력에서 가장 큰 오류라고 불렀습니다.

 

Although Hubble showed us that ours is just one galaxy among perhaps trillions, this did not tell astronomers what the Milky Way would look like it if you were to see it from outside. We knew it has spiral arms: that band of light across the sky was clear evidence of that. But as to how many spiral arms there are, or how big the galaxy is, or how many stars inhabit it, those were questions still unanswered in the 1920s. It took most of the 20th century after Hubble’s discoveries to piece together the answers to these questions, through a combination of painstaking work with both Earth- and space-based telescopes.

허블은 우리 은하가 아마도 수조 개의 은하 중 하나일 뿐이라는 것을 보여주었지만, 이것은 우리 은하가 외부에서 본다면 어떻게 보일 것인지를 천문학자들에게 알려주지 않았습니다. 우리는 그것이 나선형 팔을 가지고 있다는 것을 알고 있었습니다. 하늘을 가로지르는 그 빛의 띠가 그것을 증명하는 분명한 증거였습니다. 그러나 나선팔이 몇 개인지, 은하가 얼마나 큰지, 그 안에 얼마나 많은 별이 살고 있는지는 1920년대에도 여전히 풀리지 않은 질문이었습니다. 허블의 발견 이후 20세기 대부분이 지구 망원경과 우주 망원경으로 힘든 작업을 결합하여 이러한 질문에 대한 답을 모으는 데 걸렸습니다.

 

So if one could travel outside our galaxy, what would it look like? A standard analogy compares it to two fried eggs stuck together back-to-back. The yolk of the egg is known as the Galactic Bulge, a huge globe of stars at the center extending above and below the plane of the galaxy. The Milky Way is now thought to have four spiral arms winding out from its center like the arms of a Catherine wheel. But these arms do not actually meet at the center: a few years ago astronomers discovered that the Milky Way is in fact a barred spiral galaxy, having a “bar” of stars running across its center, from which the spiral arms extend at either end. Barred spiral galaxies are not uncommon in the universe, so our galaxy is certainly nothing out of the ordinary. We do not yet, however, understand how that central bar forms.

그래서 우리 은하계 외부로 여행할 수 있다면 어떤 모습일까요? 표준 유추는 두 개의 계란 프라이를 연속적으로 붙인 것과 비교합니다. 달걀의 노른자는 은하계 팽대부(Galactic Bulge)로 알려져 있으며, 은하계의 위아래로 뻗어 있는 중심에 있는 거대한 별 구입니다. 이제 은하수는 예카테리나 바퀴의 팔처럼 중심에서 4개의 나선 팔을 감고 있는 것으로 생각됩니다. 그러나 이 팔은 실제로 중심에서 만나지 않습니다. 몇 년 전에 천문학자들은 우리 은하가 실제로 막대 나선 은하이며 중심을 가로질러 달리는 별의 "막대"가 있고 나선 팔이 양쪽 끝에서 뻗어 있다는 것을 발견했습니다. . 막대 나선 은하는 우주에서 드문 일이 아니므로 우리 은하는 확실히 특별한 것이 아닙니다. 그러나 우리는 아직 중앙 막대가 어떻게 형성되는지 이해하지 못합니다.

 

This Hubble image shows galaxy NGC 7773, an example of a barred spiral galaxy thought to be similar to the Milky Way. Its bulge is stretched out into a bar-shaped structure, extending to the inner parts of the galaxy’s spiral arms. Astronomers believe a bar in the center of a galaxy is a sign of galaxy maturity. Younger spiral galaxies do not feature barred central structures as often as older spirals do. Image via ESA/Hubble, CC BY 4.0, Creative Commons.

이 허블 사진은 우리 은하와 유사하다고 생각되는 막대나선은하의 한 예인 NGC 7773 은하를 보여줍니다. 그 팽창은 막대 모양의 구조로 뻗어 있으며 은하의 나선 팔의 안쪽 부분까지 확장됩니다. 천문학자들은 은하 중심에 있는 막대가 은하가 성숙했다는 신호라고 믿습니다. 더 젊은 나선 은하는 오래된 나선 은하는 자주 막힌 중심 구조를 특징으로 하지 않습니다. ESA/Hubble, CC BY 4.0, Creative Commons를 통한 이미지.

 

Only two years ago, another major discovery was made: the Milky Way is not a flat disk of stars but has a “kink” running across it like an extended “S”. Something has warped the disk. At the moment the finger points at the gravitational influence of the astronomically-close Sagittarius dwarf galaxy, one of perhaps twenty small galaxies that orbit the Milky Way, like moths around a flame. As the Sagittarius galaxy slowly orbits around us, its gravity has pulled on our galaxy’s stars, eventually creating the warp.

불과 2년 전, 또 다른 중요한 발견이 이루어졌습니다. 우리은하는 별의 평평한 원반이 아니라 확장된 "S"처럼 가로질러 "꼬임"이 있습니다. 디스크가 휘었습니다. 그 순간 손가락은 천문학적으로 가까운 궁수자리 왜소은하의 중력 영향을 가리키고 있습니다. 이것은 불꽃 주위의 나방처럼 우리 은하를 도는 20개의 작은 은하 중 하나입니다. 궁수자리 은하는 우리 주위를 천천히 공전하면서 중력이 우리 은하의 별들을 끌어당겨 결국에는 뒤틀림을 만듭니다.

 

These dwarf galaxies are not the only astronomical objects bound to our own. The Milky Way is surrounded by a halo of globular clusters, concentrations of stars looking like fuzzy golf balls, containing perhaps a million or so extremely ancient stars.

이 왜소은하는 우리 은하에만 묶여 있는 것이 아닙니다. 은하수는 100만 개 정도의 아주 오래된 별을 포함하고 있는 흐릿한 골프공처럼 보이는 별들이 모여 있는 구상 성단의 후광으로 둘러싸여 있습니다.

 

It is highly probable that we will continue to make more landmark discoveries about the Milky Way. The study of its nature and origin is accelerating as new astronomical tools become available, such as the European Space Agency’s orbiting Gaia telescope, which is making a three-dimensional map of our galaxy’s stars with exquisite and quite unprecedented accuracy: it aims to map a billion of them. Gaia’s data allows astronomers to see where the stars are, in which direction they are moving and how fast. This incredible map is already revealing previously-unknown features of our galaxy: the discovery of the galaxy’s warp by Gaia is one such feature. It is an extremely exciting time for the study of our galaxy, and the discoveries being made are telling us so much about not just our own galaxy but other spiral galaxies as well.

우리은하에서 더 많은 획기적인 발견을 계속할 가능성이 매우 높습니다. 그 본질과 기원에 대한 연구는 유럽 우주국(European Space Agency)의 궤도를 도는 가이아 망원경(Gaia telescope)과 같은 새로운 천문학 도구가 사용 가능해짐에 따라 가속화되고 있습니다. 그 중 10억. 가이아의 데이터를 통해 천문학자들은 별의 위치, 별의 이동 방향 및 속도를 확인할 수 있습니다. 이 놀라운 지도는 이미 이전에 알려지지 않은 우리 은하의 특징을 드러내고 있습니다. Gaia가 은하의 뒤틀림을 발견한 것도 그러한 특징 중 하나입니다. 지금은 우리 은하에 대한 연구에 있어 매우 흥미로운 시기이며, 진행 중인 발견은 우리 은하뿐만 아니라 다른 나선 은하에 대해서도 많은 것을 알려줍니다.

 

A composite image of the orbiting telescope Gaia, mapping the stars of the Milky Way. Image via ESA.

우리은하의 별을 매핑한 궤도 망원경 가이아의 합성 이미지. ESA를 통한 이미지.

 

It is all a far cry from when, thousands of years ago, our ancestors ascribed fantastic beasts and gods to that mysterious band of light they saw as they stood in awe under the starry sky.

수천 년 전 우리 조상들이 별이 빛나는 하늘 아래 경외감에 빠져서 본 신비한 빛의 띠를 환상적인 짐승과 신들에게 돌리던 것과는 전혀 거리가 멉니다.

 

Bottom line: Our galaxy, the Milky Way, is a lot more than we can see from Earth without instruments. Here, we look into the origin of the name, the structure, and the fascinating history of how our knowledge of our own galaxy has developed over the centuries and continues to develop today.

결론: 우리 은하는 우리 은하는 도구 없이 지구에서 볼 수 있는 것보다 훨씬 더 많습니다. 여기에서 우리는 이름의 기원, 구조, 우리 은하에 대한 지식이 수세기 동안 어떻게 발전해 왔으며 오늘날에도 계속 발전해 왔는지에 대한 매혹적인 역사를 살펴봅니다.

 

출처; https://earthsky.org/astronomy-essentials/what-is-the-milky-way-galaxy/

What is the Milky Way?

 

기고자 Andy Briggs

Andy Briggs(사진 출처: astro radio earth)

기고자 Andy Briggs는 지난 30년 동안 천문학, 천체 물리학 및 정보 기술을 사람들에게 전달했습니다.

월요일마다 글로벌 인터넷 라디오 채널 AstroRadio(http://www.astroradio.earth)에서 그의 주간 천문학 및 우주 뉴스 업데이트를 들을 수 있으며, 다른 프로그램에도 기고하고 있습니다.

그는 영국의 많은 천문학 학회에서 활동했으며 Astronomy Ireland 잡지에 자주 기고하고 있습니다.

Andy는 중력파 및 블랙홀과 같은 천체 물리학 관련 주제에 대해서도 정기적으로 강의합니다.

그는 딸과 함께 스페인 카탈루냐에서 살고 있다.

2019년부터 최근까지 웹사이트 '어스스카이'에 올린 20편의 기사를 아래 주소를 클릭하면 찾을 수 있다.

https://earthsky.org/author/andybriggs/