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Chapter 2: The Sky

Chapter 2: The Sky. Ms. Meijer. Astronomical Units. The Astronomical Unit (AU) is the distance between the Earth and the Sun 1 AU = 1.5 x 10 11 meters The light year (lyr) is the distance light can travel in one year 1 light year = 9.4605284 × 10 15 meters

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Chapter 2: The Sky

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  1. Chapter 2: The Sky Ms. Meijer

  2. Astronomical Units • The Astronomical Unit (AU) is the distance between the Earth and the Sun • 1 AU = 1.5 x 1011 meters • The light year (lyr) is the distance light can travel in one year • 1 light year = 9.4605284 × 1015 meters • 1 light year =5.87849981 × 1012 miles • The Parsec is an astronomical unit we use to measure distances to stars • 1 pc = 3.26 lyr or 1pc =206,265 AU

  3. Apparent Visual Magnitude (mv) • The apparent visual magnitude is the brightness of a star as seen from Earth • Only includes light that can be seen with the human eye • The subscript v reminds you that it is visual magnitude, only what can be seen with the human eye • Originally catalogued stars into 6 classes where 1st class were the brightest and 6th the dimmest • Not enough range to include all the new stars we have found with telescopes • Does not take into account how far away the star is located

  4. Apparent Magnitude Today • We have extended the range to include negative numbers for really bright stars and larger numbers for very dim stars • Sirus, the brightest star in the sky has a magnitude of -1.42 • The sun has a magnitude of -26.5

  5. Absolute Visual Magnitude (Mv) • If all stars were the same distance away then we could compare them to see which is emitting more light • The absolute visual magnitude is the visual magnitude the star would have if it were 10 parsecs away • The absolute visual magnitude scale also ranges from positive to negative where negative numbers mean a brighter star

  6. Comparing Apparent and Absolute Magnitudes • If a star has a large apparent magnitude of -2, but a small a absolute magnitude of 4, what do you know? • If a star has a small apparent magnitude of 13, but a large absolute magnitude of 3, what do you know? • If the apparent and absolute magnitude of a star are the same, what do you know?

  7. HOW THE EARTH MOVES

  8. Revolution • The earth revolves around the sun once per year

  9. Rotation The Earth rotates on it’s axis once per day

  10. The Motion of the Sun Because the Earth moves around the sun it appears that the Sun moves across the sky in relation to the celestial sphere The path it takes across the sky is called the ecliptic

  11. The Zodiac

  12. Precession • Like a top because of its rotation the Earth also precesses • The Earth is inclined by 23.5 Degrees • It takes the Earth 26,000 years to precess all the way around once

  13. Seasons!

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