# Mr. Peterson, Science.  Helpful when working with small numbers…  Mass of an electron = 0.00000000000000000000000000000091 kg  Much easier to write.

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Mr. Peterson, Science

 Helpful when working with small numbers…  Mass of an electron = 0.00000000000000000000000000000091 kg  Much easier to write 9.1 x 10 -31 kg  Examples  0.017 =  0.000022 = 1.7 x 10 -2 2.2 x 10 -5

 Helpful when working with large numbers…  Mass of the Sun = 2,000,000,000,000,000,000,000,000,000,000 kg  Much easier to write 2 x 10 30 kg  Examples:  6,700,000 =  3270 =  475,000 = 6.7 x 10 6 3.27 x 10 3 4.75 x 10 5

 A galaxy is a large group of stars, gas, and dust held together by gravity.  A galaxy can contain millions to trillions of stars.  There are about a billion galaxies in the universe.

 Our solar system is in the Milky Way Galaxy.  Spiral Galaxy  Top view

 Milky Way Galaxy – Spiral Galaxy  Side view

 Elliptical Galaxies  Irregular Galaxies

Spiral GalaxyElliptical GalaxyIrregular Galaxy 20%60%20% Mass 10 11 – 10 12 SunMass 10 6 – 10 13 SunMass 10 9 Sun 5-50 kpc1-200 kpc1-10 kpc Young and old starsOld starsYoung and old stars Milky Way Galaxy (Spiral) mass = 10 12 Sun size = 30 kpc (30,000 pc or 97,000 light years)

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