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Foundations Unit: Part A

Foundations Unit: Part A. Charting the Heavens. Introduction. Astronomy The study of the Universe, which includes: Space Time Matter Energy Basically everything that has ever existed on the cosmic scale. Introduction. A shift in perspective scale, consider: An average galaxy

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Foundations Unit: Part A

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  1. Foundations Unit: Part A Charting the Heavens

  2. Introduction • Astronomy • The study of the Universe, which includes: • Space • Time • Matter • Energy • Basically everything that has ever existed on the cosmic scale.

  3. Introduction • A shift in perspective scale, consider: • An average galaxy • 100 Billion Stars (1011, or 100,000,000,000 stars) • More than all people who ever lived on earth. • To put it another way, try counting 1 number per second • To count to 1000- 16 minutes • To count to 1,000,000- Two Weeks* • To count to 1,000,000,000- 50 Years* • To count to 100,000,000,000- 4,756 years*

  4. Introduction • Lets look at how the distance scales. • A single galaxy can span 100,000 lightyears across • Lightyear = distance light travels in one year • The sun is about 8 light minutes away • Our nearest stellar neighbor Proxima Centauri, is about 4 ly away

  5. Introduction

  6. Introduction • Just imagine how large the universe is when we gradually scale back • Earth • Solar System • Milky Way Galaxy • Local Group • Local Supercluster • Universe

  7. Introduction

  8. The View from Earth • Early Astronomers • No understanding of the vastness of space • Associated stories, mythology with the objects visible in the sky “The sun is pulled across the sky by a chariot, drawn by winged horses…” • This is where the idea of constellations originated.

  9. The View from Earth • Constellations • Over 3000 points of light from sunrise to sunset. • Convenient to group regions of the sky.

  10. The View from Earth • Orion

  11. The View from Earth • “The Hunter”

  12. The View from Earth • What we see

  13. The View from Earth • Constellations are groups of stars whose light merely comes from the same general direction. • They’re positions remained fixed relative to each other. • They do seem to move across the sky.

  14. The View from Earth • Starry Night Simulation • Student Exercises • Earth, Moon, and Sun • Day and Night Cycle

  15. The View from Earth • The celestial sphere • One fixed canopy on which all stars rest • The apparent motion of the stars is east to west

  16. The View from Earth • In reality it is the earth’s eastward rotation that produces the stars apparent motion across the sky. • The north star (Polaris) appears (nearly) fixed in space as it lies on the axis of rotation of the earth.

  17. The View from Earth • Celestial Coordinates • We have a system for locating objects in the sky just like on earth • Earth = Latitude and Longitude • Celestial = Declination and Right Ascension • Just like Lat and Long, Dec and RA are measured in angle units

  18. The View from Earth

  19. Earth’s Orbital Motion • We measure our time with the 24 hour solar day. • The stars do NOT have the same position from one night to the next. • They are shifted slightly from where they were the night before.

  20. Earth’s Orbital Motion • The shift can be explained by the orbit of the earth around the sun. • If we track the earth’s rotation back to the same reference star we are measuring the sidereal day. • The earth has to rotate approximately one additional degree to face the sun.

  21. Earth’s Orbital Motion • That extra degree of rotation comes from the motion of earth along its orbit and makes the solar day ~4 min longer than the sidereal day.

  22. Earth’s Orbital Motion • Seasonal Changes • The Night side of the earth faces a different direction each night (1o) • For long periods the change is noticeable. • Different set of stars are visible as the seasons change.

  23. Earth’s Orbital Motion • Throughout the year, the sun appears to move relative to the background stars. • The path the sun travels is called the Ecliptic. • There are twelve constellations along the ecliptic, known as the zodiac.

  24. Earth’s Orbital Motion • Your “sign” is determined to be the constellation in which the sun sits for that particular month. • The use of the Zodiac for divination assumes that the alignment of the stars at your birth gives you certain personality traits.

  25. Earth’s Orbital Motion • Seasonal Changes Cont’d- • The earth’s axis does not sit perpendicular to its orbit. • The axis is inclined 23.5o from vertical

  26. Earth’s Orbital Motion • The direction the axis points changes very little throughout the course of the year. (remember: towards Polaris) • So the earth goes through phases where it tilts both towards and then away from the sun. • The change is gradual but there are 4 special days throughout the year to identify the new orientations.

  27. Earth’s Orbital Motion

  28. Earth’s Orbital Motion • The Four Special Days • Summer Solstice • June 21- The North Pole is closest to the sun. • Longest Daylight in N.H. • Autumnal Equinox • September 21- Neither North/South Pole is closer to the sun • Equal Length Day and Night

  29. Earth’s Orbital Motion • Winter Solstice • December 21- North Pole pointed furthest away from sun. • Shortest Daylight in N.H. • Vernal (Spring) Equinox • March 21- Neither North/South Pole is closer to the sun • Equal Length Day and Night • A Year (tropical) is defined as 365.242 days from the last Vernal Equinox.

  30. Earth’s Orbital Motion

  31. Earth’s Orbital Motion • Precession- • The direction of the axis rotates in a circle (Like a spinning top) • Polaris is not always the north star. • 26,000 Year Cycle • 5000 years ago, Thuban • 12,000 from now, Vega

  32. Earth’s Orbital Motion

  33. Measurement of Distance • Distance- How do we measure? • Triangulation • Sight the object from two locations, calculate the distance by measuring the baseline and the angle.

  34. Measurement of Distance • Triangulation works really well for close objects. • The further away the object is, the harder it is to accurately measure the angles at A and B. (Long narrow triangle) • For greater distances we need a longer baseline, but there are limits.

  35. Measurement of Distance • We can measure from opposite sides of earth’s orbit. • Baseline = Earth’s orbit Diameter • But now its easier to measure the third, distant angle. • This is known as Parallax • We measure the shift in celestial coordinates at one side, compared to the other. • Demo

  36. Measurement of Distance Stellar Parallax

  37. Measuring Distance • The angle of shift is known as the Parallax angle. • Closer objects have a larger parallax angle. • Further objects have a smaller parallax angle. • Similar techniques can also be used to determine the size of other objects like planets and moons.

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