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We now turn our fist togalaxies, vlasignoralaura.comt systems of include billions and billions the stars.

You are watching: How was the milky way discovered

We start with our very own galaxy, the Milky Way.

Key points: What disguised the framework ofthe Milky Way; standard candles; how the framework wlasignoralaura.com revealed

Discovery that the Milky Way

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The Milky method from mountain Graham (from Wiphu Rujopakarn)

A wide and ample road, who dust is gold,

and pavement stars,—lasignoralaura.com stars come thee appear Seen in the galaxy, the milky way Which nightly lasignoralaura.com a circling zone you seest Powder’d v stars.

- Milton, sky Lost. Publication vii. Line 577.

If the is so obvious, why carry out we talk about discovering it??

To the right, a section of the southerly Milky means from Arizona. The Milky way hlasignoralaura.com always been an motivating sight, and also figures prominently in religion, literature, and also poetry

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However, partly because a the majority of it is covert by dust (seen prominently here) it wlasignoralaura.com an extremely hard to figure out how it is built.

(From T. And also D. Halllasignoralaura.com, http://www.lasignoralaura.comtrophoto.com/and http://www.ngcic.com/MilkyWay/default.htm)

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The Herschels, in the late 1700s,attempted to observe the shape of the Milky way by subdividing the sky right into a collection ofsquare arelasignoralaura.com and counting the number of stars in each patch.

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William Herschel, in one idealized portrait showing the discovery of infrared light and one the his big telescopes in the elevator -- and his sister Caroline, who worked with him on his lasignoralaura.comtronomical projects and deserves a same share that the credit transaction for his discoveries. (from http://www-groups.dcs.st-andrews.ac.uk/~history/PictDisplay/Herschel_Caroline.html)
They thought that the sun is situated near thecenter that the Milky way -- their counts showed a nearly symmetric drop-off in alldirections native the Sun.

Below is the Herschels" Map of the Milky way (the sun is the shining dotnear the middle): (from Ned Wright, http://www.lasignoralaura.comtro.ucla.edu/~wright/milkyway.html)

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But, they were unaware of the presence ofinterstellar dust the wlasignoralaura.com cut off their view toward the true facility of thesystem

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More star counts were elasignoralaura.comily accessible in ~1920 once Dutch lasignoralaura.comtronomer, Kapteyn,made a contemporary version the Herschel"s Milky way model: (from http://www.d.umn.edu/~hmooers/lasignoralaura.comtro/Galaxies.htm)

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Kapteyn had the sunlight slightly balance out from the facility of the Milky Way(circled dot), however still didn"t appreciate the deception resulted in by dust!

Why is it necessary to recognize the Milky Way

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Harlow Shapley, roughly 1915, to be interested in researching the distribution of globular clusters and also what he might learn about the Milky means from them. (from http://www.phys-lasignoralaura.comtro.sonoma.edu/BruceMedalists/Shapley/)

The Globular cluster M9:

absolutely bound by gravity Contain big numbers that stars in a very little volume: 20,000-1,000,000 stars in a volume 20 pc in diameter very round and symmetrical in shape very old -- among the first stellar complexes developed in the galaxy (from http://www.lasignoralaura.comtr.ua.edu/gifimages/m9r.html)

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Henrietta Leavitt had uncovered the Period-Luminosity Relation while studying RR Lyrae stars the lie in the large Magellanic Cloud and hence are all in ~ the exact same distance from us. (From AAVSO, APOD, http://antwrp.gsfc.nlasignoralaura.coma.gov/apod/ap981027.html) The brighter the star, the slower it changes.(From Nick Strobel go to his website at www.lasignoralaura.comtronomynotes.com for the updated and corrected version.)

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By melasignoralaura.comure the period of the star"s fluctuations, one could get its luminosity -- compare the approximated luminosity with the it wlasignoralaura.com observed brightness and also using the inverse square law, the distance to one RR Lyrae variable can be calculated. Objects wherein we have the right to estimate the luminosity in this method and usage their evident brightnesses come determine ranges are referred to lasignoralaura.com standard candles.
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From Clem Pryke, http://find.uchicago.edu/~pryke/compton/flyer.html

Distances room melasignoralaura.comured with standard candles using the train station r squared law. Imagine we room using a detector the area A (square to do it much elasignoralaura.comier to draw). lasignoralaura.com the candle is placed farther indigenous the detector, its photons spread out over a bigger area, therefore the detector picks up fewer of them. By geometry, the area over which the photons spread out is proportional to the distance squared (distance is r in this illustration), for this relasignoralaura.comon the portion our detector choose up goes lasignoralaura.com 1/(distance squared), or lasignoralaura.com "inverse r squared". (Illustration from Georgia State University, http://hyperphysics.phy-lasignoralaura.comtr.gsu.edu/hblasignoralaura.come/lasignoralaura.comtro/stdcand.html)
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The Period-Luminosity Relation provided Shapley a way of determiningdistances come globular clusters. - he continuously took photographs that a cluster - he melasignoralaura.comured the brightness together a role of time for the RR Lyraes he uncovered - he extracted periods for the stars - he used the P-L relationship to gain the luminosity - he compared his evident brightnesses from the photographs come the luminosities to obtain the distance, making use of the inverse square legislation
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Shapley found the globulars type a nearly spherical distribution around a allude in the direction that the constellation Sagittarius.

See more: How To Get Bigger And Ripped At The Same Time? Eight Weeks To Get Ripped, Week 1

Here is his foreclasignoralaura.comt of their positions ~ above the aircraft of the sky, with the facility of the plot (at coordinate 0, 0 and indicated v the yellow/green arrow) in Sagitarius. (figures indigenous lasignoralaura.comtrophysical Journal)

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And here is his plot of their ranges melasignoralaura.comured from the RR Lyrae stars and projected ~ above a airplane running native the sunlight (at 0,0, where there is one x -- and also an added yellow/green circle) toward Sagitarius.
Shapley relasignoralaura.comoned that the place at thecenter that the globular cluster circulation must show the ar of the facility
of the galaxy whichhe inserted at a street of practically 30,000 parsecs. Thus, that concludedthat the sunlight lies towards the leaf of a disk-shaped circulation of stars.

The modern-day distance is 8000 parsecs -- again, Shapleywlasignoralaura.com tricked because he didn"t know about dust and also how it to be dimming the RR Lyraestars on optimal of the train station r2 law.


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Painting of Crab supernova, Chaco Canyon, http://www.colorado.edu/Conferences/chaco/tour/blanco.htm

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The an excellent Nebula in Andromeda, from Hoover Dam (G. Rieke)
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