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Phys. 102: Introduction to Astronomy

Phys. 102: Introduction to Astronomy. Circles and Time. Clicker Question. Which observer(s) would see the star travel on the diurnal circle shown? a) b). North. Diurnal Circles. Observer sees full diurnal circle. Observer sees half of the diurnal circle.

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Phys. 102: Introduction to Astronomy

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  1. Phys. 102: Introduction to Astronomy Circles and Time

  2. Clicker Question Which observer(s) would see the star travel on the diurnal circle shown? a) b) North

  3. Diurnal Circles Observer sees full diurnal circle Observer sees half of the diurnal circle Observer sees none of the diurnal circle • Each celestial object circles the observer each day • Observer sees part of each circle Celestial Equator

  4. View of Observer Stars visible for 12 hours/day Stars ALWAYS visible Observer sees half of the diurnal circle Observer sees full diurnal circle Celestial Equator Observer sees none of the diurnal circle In the observer’s frame of reference Stars NEVER visible

  5. Altitude & Azimuth Meridian Antares North South • Position of an object in the sky • Azimuth = Angle from north through east • Altitude = Angle from horizon to object Antares is at azimuth 170º and altitude 30º Altitude Azimuth

  6. Time of Day Meridian Sun's Summer Diurnal Circle East North South West • Position of Sun with respect to Observer • Noon = Sun on observer’s meridian Wow! It’s solar noon!

  7. Time of Day East West Wow! It’s solar Midnight! • Position of Sun with respect to Observer • Midnight = Sun opposite observer’s meridian Meridian Summer Sun's Diurnal Circle North South

  8. Time of day • Earth Rotates Once Each Day • 360° with respect to Earth-Sun line • All Earthlings ride along To Sol

  9. Sunrise, Sunset … • Everything in the sky (sun, moon, stars, etc.) • Rises in the east • Sets in the west each day 0° 0hr 15° 1hr 30° 2hr Measuring Circles: 45° 3hr 60° 4hr 360° = 24 hr 75° 5hr 15° = 1 hr 270° 18hr 6hr 90° Each hour, the sun moves 15 degrees in the sky 1° = 4 min or 15’ = 1 min Every 4 minutes, the sun moves 1 degree = 60’ in the sky 180° 12hr

  10. Observer’s View of the Day • Sun rises in east, moves 15°/hour from East to West transits at noon sets in west

  11. Standard Clock Time It’s 6 pm (sunset). • Every Longitude at slightly different time It’s 3 pm. It’s 9 pm. It’s noon. It’s midnight. It’s 3 am. It’s 9 am. It’s 6 am (sunrise).

  12. Clock Time = Position of Sol It’s 6 pm (sunset). • Observers move through times It’s 3 pm. It’s 9 pm. It’s noon. It’s midnight. It’s 3 am. It’s 9 am. It’s 6 am (sunrise).

  13. Daylight Saving Time It’s 7 pm (sunset). • Shifts times one hour later (USNO Explanation) It’s 4 pm. It’s 10 pm. It’s 1 pm. It’s 1 am. It’s 4 am. It’s 10 am. It’s 7 am (sunrise).

  14. Clock Time Time Zones: 24, roughly 15° apart 6 pm 5 pm 4 pm 9 pm 3 pm 2 pm 1 pm 12 am 12 pm 9 am 3 am 6 am

  15. Time Zones • Politics complicates things … Prime Meridian Time Zone Center at 0° E Time Zone ~15° wide

  16. North America Time Zones 120° W Pacific Time Zone 90° W Central Time Zone 75° W 105° W Eastern Time Zone Mountain Time Zone

  17. Coordinated Universal Time • UTC (UT or Zulu) • Time at Greenwich • no Daylight saving • Conversion • EST (Eastern Standard Time) = UTC – 5hr • eg. 2pm (14:00) EST = 19:00 UT • EDT (Eastern Daylight Time) = UTC – 4hr • eg. 2pm (14:00) EDT = 18:00 UT UTC = Standard Time on Prime Meridian

  18. Solar Time vs. Clock Time • Solar time varies across time zones Time Zone’s Solar Noon Clock Noon FOR ALL Sun’s path seen from time zone center Eastern Observer’s Solar Noon Western Observer’s Solar Noon Time Zone East side West side Rising Setting

  19. Solar Time vs. Clock Time • Solar time varies across time zones Time Zone’s Solar Noon Clock Noon FOR ALL Solar noon is (Degrees)(4 minutes/degree) earlier than clock noon Degrees East of TZ center Eastern Observer’s Solar Noon Time Zone East side West side Rising

  20. Clicker Question Sept-Îles, Quebec, 66.25° W is in the Eastern Time Zone (center: 75° W). Solar noon occurs at a) 11:25 am, b) 11:51:45 am, c) 12:08:45 pm, d) 12:35 pm Degrees East of TZ center Eastern Observer’s Solar Noon Time Zone East side West side

  21. Solar Time vs. Clock Time • Solar time varies across time zones Time Zone’s Solar Noon Clock Noon FOR ALL Clock Noon FOR ALL Solar noon is (Degrees)(4 minutes/degree) earlier than clock noon Solar noon is (Degrees)(4 minutes/degree) Later than clock noon Degrees East of TZ center Degrees West of TZ center Eastern Observer’s Solar Noon Western Observer’s Solar Noon Time Zone East side West side West side Rising Setting

  22. Clicker Question Yuma, AZ, 114.5° W is in the Mountain Time Zone (center: 105° W). Solar noon occurs at a) 11:22 am, b) 11:50:30 am, c) 12:09:30 pm, d) 12:38 pm Degrees East of TZ center Degrees West of TZ center Eastern Observer’s Solar Noon Western Observer’s Solar Noon Time Zone East side West side West side

  23. Celestial Navigation • Finding Latitude & Longitude from • Altitude of Polaris (NCP) • Transit time of star to observer’s zenith to celestial equator to north celestial pole N S Observer at 20° N

  24. Star Transit Time 6 pm 5 pm 4 pm 3 pm 9 pm 2 pm 1 pm 12 am 12 pm 3 am 9 am 6 am Gives position of star with respect to the sun Standard Time eg. Find transit time of Aldebaran on December 15 11 pm Aldebaran’s Position on 12/15 nearly opposite Sol!

  25. Star Transit Time 7 pm 6 pm 5 pm 4 pm 10 pm 3 pm 2 pm 1 am 1 pm 4 am 10 am 7 am 6 pm 5 pm 4 pm 3 pm 9 pm 2 pm 1 pm 12 am 12 pm 3 am 9 am 6 am Gives position of star with respect to the sun Standard Time Daylight Time eg. Find transit time of Vega on July 15 (Daylight time) 12 pm Vega’s Position on 7/15 nearly opposite Sol!

  26. Celestial Navigation • Difference between observed and expected transit times gives longitude Observer watches star transit. Star’s Transit Clock’s Time Zone Longitude Clock is set to some time zone. Observed transit time disagrees with ephemeris. Degrees East of TZ center Longitude difference from clock’s time zone center = (Time difference)(15°/hour)

  27. Celestial Navigation Colorado Day! • Example: Transit of Deneb on August 1 Observer sees Deneb transit at 11 pm EDT At 1 am Deneb will transit TZ center at 75° W Looks up transit time in FG On 8/1 Deneb transits at 1 am Early  East of TZ center Longitude difference from clock’s time zone center = (2 hours)(15°/hour) = 30° East Observer’s Longitude = TZ center – Latitude difference = 75° W - 30° = 45 ° W

  28. Today’s FUN! • Time Zones • For western time zones, determine center longitude (do the math … it’s easy!) • Convert times of events to UTC • UTC – 5 hours = EST • UTC – 4 hours = EDT • For cities listed, determine clock time of solar noon (date may change!) 4 min = 1° = 60’ 1 min = 15’ 10’ = 2/3 of 15’ 10’ = 40 sec 10’ W 12:00:40

  29. Today’s FUN! • Time Zones • For western time zones, determine center longitude (do the math … it’s easy!) • Convert times of events to UTC • UTC – 5 hours = EST • UTC – 4 hours = EDT • For cities listed, determine clock time of solar noon • Celestial Navigation • Find Latitude from altitude of NCP • Find Longitude from ephemeris & observation • USE an ATLAS to find out where you are!!! (date may change!)

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