Full Moon Trajectory

May 07, 2013  •  Leave a Comment

Capturing full moon with Seattle cityscape has been always fascinating me and I wanted to capture beautiful scene as much as I have opportunities. In my previous Photo Note titled "Full Moon 2013 April", I predicted the moon trajectory based on past photo image and TPE (The Photographer's Ephemeris) data but my calculation contain an error and the moon passed significantly above the observation deck of Space Needle on 24th of April (see the photo image in the bottomo of this page shown as taken from C1). I've adjusted my calculation and tried following day and the moon trajectory was as I expected (photo image shown as taken from C2).

Below photo was taken in early morning from Fairview Avenue East (47.6319, -122.3270) on May 6th, 2012.

This Photo Note describes the method to predict the moon trajectory. Moon trajectory is not only factor which determines successful full moon image but one of the most important elements. Other important elements includes exposure, background, foreground, focal length, composition, and so on.

 

[Method 1] by using TPE, 3rd party website, Google Maps.

Step #1: Find a full moon day (or crescent or whatever you want to capture). TPE has event feature which provides many celestial events including full moon. Full moon (100%) may take place any time in the day. It could be in during day time, or night time or in between. Therefore the moon maturity could be 98% at the night time when you shoot even on the [full moon day]. More than 95% of maturity appears like full moon. The day before and after [full moon day] could be good day to capture the [full moon]. Moon trajectory and moon rising time will be quite different on before or after [full moon day].

 

Step #2: Find a photo shooting spot. Following 4 spots are my favorite full moon shooting locations in Seattle. (1) Queen Anne, Kerry Park. (2) Alki, West Seattle, (3) Magnolia Bridge, (4) Dearborn Bridge. Each location has potentially excellent candidate for ideal composition. The best angle at each shooting locations varies as well as moon rising, passing angle relative to any target such as Space Needle. In general, Queen Ann is good between April through June. West Seattle is good for November and February, Magnolia is good for April and May, Dearborn Bridge (moon set) is quite open as composition can be flexible.

 

Step #3: Estimate the moon trajectory and calculate viewing angle from shooting location. Following steps are based on the method shared by our team member Phil Shen and some additions as my understanding.

  1. Used TPE to approximate the shooting spot
  2. Picked a spot (like Smith Cove Park)
  3. Used Google Maps to find the latitude & longitude coordinates of the spot (right click on spot, select "drop LatLong marker" in Google Chrome or "What's here" in MS Explore). Alternatively you can find the LatLong data from TPE.
  4. Used elevation tool to find the altitude of the spot
  5. Used Google Search to find the height of the Space Needle (observation deck & antenna)
  6. Used Google Maps to find the coordinates of the Space Needle. Alternatively you can find the LatLong data from TPE.
  7. Used distance tool to find the distance between shooting spot & Space Needle. Alternatively you can find the distance by using 2nd pin of TPE.
  8. Used elevation tool to find the altitude of the Space Needle. Alternatively you can find relative elevation height, height, and the distance from TPE.
  9. Used trig calculator tool to find the altitude angle (Accounting for the difference in their elevation above sea level)

 

Specific calculation example from above steps:

Magnolia Bridge (midway)

Coordinates: 47.63348, -122.38771

The elevation tool, like TPE, could not give the exact altitude of the bridge midway, so it is estimated to be 35 m (based on Ursula Judkins viewpoint of 45 m).

 

Space Needle

Coordinates: 47.62081, -122.34937

Antenna spire 184.41 m (605.0 ft)

Observation Deck 158.5 m (520 ft)

Calculated Altitude: 41 meters (134 feet) (from elevation tool)

 

Difference above sea level = 41 - 35 = 6 m Alternatively you can use 2nd pin function of TPE to find out the elevation difference.

 

Target height = 184.4m (Antenna height) + 6m - 10m* = 180.4m

Distance between 47.63348N 122.38771W and 47.62081N 122.34937W is

3.2035 km

 

Trig angle calculator:

a = height = 180.4m

b = distance = 3203.5m

Calculated angle = 3.22° = tan -1 (180.4/3203.5)

 

Going back to TPE, the moon will reach 3.2° at 21:02 (9:02pm).

 

 

[Method 2] by using TPE and Scientific Calculater (or MS Excell). Formula to calculate target viewing angle in the spreadsheet is =DEGREES(ATAN(E13/E10)) where E13 is the relative height of Observation Deck and E10 is the distance from shooting location as an example.

  Ursula Judkins viewpoint  Mid of Magnolia Bridge Space Needle
  C1 C1 C2 T
Lat 47.6326 47.6326 47.6326 47.6204
Lon -122.3897 -122.3897 -122.3897 -122.3491
         
Elevation [m] 48 48 15 47
Relative height to T [m] 1 1 -32  
Distance [m] 3300 3300 3200  
Relative Az angle [°] 113.6 113.6 119.3  
Relative Vert angle [°] -0.017 -0.017 0.57  
Relative height to O.D. [m] 157 157 190 158
Relative Vert angle [°] 2.72 2.72 3.40  
         
Moon Vert angle [°] 4.7 2.8 3.7  
Moon Az angle [°] 113.6 113.6 119.2  
  4/24/2013 4/15/2014 4/25/2013  
Time Moon rise 19:19 20:48 20:35  
Time Moon Passage 19:53 21:11 21:05  
Time Sun set 20:12 19:59 20:13  
         
         
Antenna Spire [m]       184.41
Observation Deck=O.D. [m]       158.5

 Photo taken from C1 (Ursla Judikins Viewpoint) on 4/24/13. Moon passing angle was 4.7 degrees and too high.

 

Photo taken from C2 (Mid span of Magnolia Bridge) on 4/25/13. Moon passing angle was 3.7 degrees and ideal trajetory.

 

The result is remarkable. The image taken by our team member Hai is featured Reader's Lens of Seattle Times.

http://seattletimes.com/html/outdoors/2020901862_readerslensmay05xml.html

The moon viewing angle at a specific time from nearby location does not vary since the distance from shooting location to the moon is almost infinity (comparing to several miles within the city). On the other hand, the viewing angle of nearby object such as Space Needle will vary as you can see in above calculation. Therefore, once we know the viewing elevation angle of the target (Observation Deck of Space Needle) from shooting location, we can move to left or right to adjust relative moon trajectory. In order to lower the relative trajectory, move to right or low. In order to heighten trajectory, move to left or high. TPE will be very useful and essential tool to predict the moon trajectory.

 

Based on above calculation, the full moon on April 15th, 2014 will pass the observation deck of Space Needle if we shoot the image from the parking lot of Magnolia Ursla Judikins Viewpoint. I am looking forward to shooting full moon in Next April.

Your comments are most welcome.

 


Comments

No comments posted.
Loading...

Archive
January (1) February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June July August September October November December
January February March (1) April (1) May (2) June (1) July August (1) September (1) October November December (3)
January (3) February March April May June (1) July (1) August September (1) October (1) November December (1)
January February March (1) April May (1) June July August September October November December
January (1) February March April May June July August September October November (1) December
January February March April May June July August September (1) October November December