When Did We Learn About Other Galaxies

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Introduction to Astronomy       Introduction to Astronomy Syllabus     ane.0 - Introduction
    two.0 - How Science is Washed
    3.0 - The Big Bang

  4.0 Discovery of the Galaxy
· 4.one - Hist. Overview - Discovery of Galaxies    v.0 - Age and Origin of the Solar System
    6.0 - Methods of Observational Astronomy
    vii.0 - The Life-Giving Sun
    8.0 - Planets of the Solar Arrangement
    9.0 - The Earth in Space
    x.0 - The Search for Extrasolar Planets
    11.0 - Mod Views of Mars
    12.0 - Universe Endgame

Life in the Universe Glossary: Climatic change
Glossary: Astronomy
Glossary: Life in Universe

Historical Overview of the Discovery of Galaxies

There are two privileged lines in the sky. One is the familiar ecliptic, the path traveled by the Sun. It is the image of our orbit around the central star, every bit seen from the Earth, against the stars. The Moon travels not far from this path and it even occasionally eclipses the Lord's day, and sometimes the Earth's shadow falls on the Moon. Likewise, the main planets stay fairly close to this line in the sky. We see that the orbits of the planets tend to lie in the same plane and this airplane is shut to that of Earth's orbit.

The other privileged line is the i centered on the Milky way. While the proper noun of the beginning line ("ecliptic") suggests a function (the line where eclipses occur), the name "Milky way" suggests nothing useful other than general milky appearance (the proper name is derived from a Greek fairy tale involving a goddess and her milk). Later telescopes became commonplace, following the efforts of Galileo, it was presently realized that the Milky Way is an unusually dumbo collection of stars, all lined upwardly. Where it is dark, it was found, dust clouds cake the lite of stars behind. In essence, we are looking at the main aeroplane of an enormous aggregation of stars, and nosotros are correct in the middle of information technology.

The realization that we live inside a milky way and that there are other galaxies besides ours came in stages. Information technology all started with the observation of fuzzy spiral objects which were grouped with other such "nebulae" and with star clusters as interesting curiosities in the heaven, not to be confused with really interesting things such every bit comets. In western tradition, toward the cease of the 18th century, the German philosopher Immanuel Kant (1724-1804), who had earlier proposed that the solar organization arose from a disk of rotating dust and gas, suggested that the Milky Way is one of many "island universes", that is, that some of the "nebulae" seen in telescopes may exist galaxies themselves.

His younger contemporary, the astronomer William Herschel (1738-1822) systematically measured the proper motion of stars in the sky. He found that stars were moving apart in one region and coming closer together in another, and concluded that the Sun was moving toward the region where stars are moving apart. Manifestly, the Lord's day is non the Heart of the Universe, but has its own proper motility. This opened the question nearly where the heart of the universe really is. Every bit telescopes improved, information technology emerged that sure nebulae have a screw shape. Thus, afterward the centre of the 19^th century the thought was floated, more than than in one case, that the Galaxy itself might be a spiral nebula. For this idea to be evaluated, i had to know the position of the Sunday and the dimensions of the habitation galaxy.

In 1918, the American astronomer Harlow Shapley (1885-1972) showed that the Sun is well off center of our dwelling milky way, past some thirty,000 low-cal years. He used a certain type of variable star (with known luminosity) to estimate distances from the differing brightness of these stars in various parts of the heavens. Shortly afterward, Edwin Powell Hubble (1889-1953) demonstrated that most "nebulae" are objects exterior our galaxy, using the 100-inch telescope at Mt. Wilson (in 1924). With this powerful instrument, he was able to apply the distance-from-variable-star method to the Andromeda nebula itself, observing stars within that neighboring galaxy. Thus, the enormous distance to this neighbor became clear: Hubble gave it almost a million lite years. Every bit it turned out, this was nevertheless quite a fleck short of the truth. The distance is greater than 1.5 one thousand thousand calorie-free years. With this greater distance, the information coming in from the Andromeda could be interpreted correctly, and information technology turned out to be a sister milky way, quite similar to our own.

The Andromeda Milky way, M31. With the Galaxy, the largest members of the Local Grouping of galaxies. Our ain galaxy is thought to exist a big screw similar in apperance to M31. (The 31^st object in the Messier itemize.) (Source: NASA)