Transcript 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)
North
b)
Diurnal Circles
 Each
celestial
object
circles the
observer
each day
 Observer
sees part
of each
circle
Observer sees full
diurnal circle
Observer sees
half of the
diurnal circle
Observer sees none of
the diurnal circle
View of
Observer
Stars visible
for 12
hours/day
Stars
ALWAYS
visible
In the
observer’s
frame of
reference
Stars
NEVER
visible
Altitude & Azimuth
 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
North
Azimuth
Altitude
South
Time of Day
 Position of Sun with respect to Observer
 Noon = Sun on observer’s meridian
Wow! It’s
solar
noon!
East
North
South
West
Time
of Day
Wow! It’s
solar
Midnight!
East
North
South
West
 Position of Sun with respect to Observer
 Midnight = Sun opposite observer’s meridian
Time of day
 Earth Rotates Once Each Day
 360° with
respect to
Earth-Sun line
 All Earthlings
ride along
To Sol
Sunrise, Sunset …
 Everything in the sky (sun, moon, stars, etc.)
 Rises in the east
each day
 Sets in the west
Measuring Circles:
360° = 24 hr
15° = 1 hr
00°hr 15°
1hr
30°
2hr
45°
3hr
60°
4hr
75°
5hr
270°
18hr
hr
6
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
Observer’s View of the Day
 Sun rises in east,
moves 15°/hour from East to West
transits at noon
sets in west
Standard Clock Time
 Every Longitude at
It’s 9 pm.
It’s
midnight.
It’s 3 am.
It’s 6 am (sunrise).
It’s 6 pm
(sunset).different
slightly
time
It’s 3 pm.
It’s
noon.
It’s 9 am.
Clock Time = Position of Sol
 Observers move through times
It’s 9 pm.
It’s
midnight.
It’s 3 am.
It’s 6 am (sunrise).
It’s 6 pm
(sunset).
It’s 3 pm.
It’s
noon.
It’s 9 am.
Daylight Saving Time
 Shifts times one
It’s 10 pm.
It’s 1 am.
It’s 4 am.
It’s 7 am (sunrise).
It’s 7 pm
(sunset).
hour
later (USNO Explanation)
It’s 4 pm.
It’s 1
pm.
It’s 10 am.
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
Time Zones
 Politics complicates things …
Prime Meridian
Time Zone
Center at 0° E
Time Zone
~15° wide
North America Time Zones
120° W
Pacific
Time Zone
90° W
Central
Time Zone
105° W
Mountain
Time Zone
75° W
Eastern
Time Zone
Coordinated Universal Time
 UTC (UT or Zulu)
 Time at Greenwich
 no Daylight saving
 Conversion
UTC =
Standard Time
on
Prime Meridian
 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
Solar Time vs. Clock Time
 Solar time varies across time zones
Time Zone’s Solar Noon
Sun’s path seen from
time zone center
Clock Noon FOR ALL
Eastern Observer’s
Solar Noon
Rising
East
side
Western Observer’s
Solar Noon
Time
Zone
West
side
Setting
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
Rising
East
side
Time
Zone
West
side
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
East
side
Time
Zone
West
side
Solar Time vs. Clock Time
 Solar time varies across time zones
Time Zone’s Solar Noon
Clock Noon FOR ALL
Solar noon is
Solar noon is
(Degrees)(4 minutes/degree) (Degrees)(4 minutes/degree)
earlier than clock noon
Later than clock noon
Degrees
East of TZ
center
Eastern
Observer’s
Solar Noon
Rising
East
side
Degrees
West of
TZ center
Time
Zone
Western
Observer’s
Solar Noon
West
side
Setting
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
Eastern
Observer’s
Solar Noon
East
side
Degrees
West of
TZ center
Time
Zone
Western
Observer’s
Solar Noon
West
side
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
Star Transit Time
Gives position of star with respect to the sun
eg. Find transit time of
Aldebaran on December 15
6 pm 5 pm
4 pm
3 pm
9 pm
Standard
Time
2 pm
1 pm
11 pm
Aldebaran’s
Position on
12/15 12 am
nearly
opposite
Sol!
12 pm
3 am
9 am
6 am
Star Transit Time
Gives position of star with respect to the sun
eg. Find transit time of Vega on
July 15 (Daylight time)
7 pm 5
6
6 pm
5 pm
4
4 pm
3
10
9 pm
pm
Standard
Daylight
Time
3 pm
2
2
1 pm
12 pm
Vega’s
Position on
1 am
am
7/15 12
nearly
opposite
Sol!
12
1 pm
pm
4 am
3
10
9 am
am
7 am
6
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.
Longitude difference from
clock’s time zone center =
(Time difference)(15°/hour)
Degrees East
of TZ center
Celestial Navigation
 Example: Transit of Deneb on August 1
Observer sees Deneb
transit at 11 pm EDT
Looks up transit time in FG
On 8/1 Deneb transits at 1 am
At 1 am Deneb
will transit TZ
center at 75° W
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
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
(date may change!)
 UTC – 4 hours = EDT
 For cities listed, determine clock time of solar noon
4 min = 1° = 60’
1 min = 15’
10’ = 2/3 of 15’
10’ = 40 sec
10’
W
12:00:40
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
(date may change!)
 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!!!