Sundial at Christ Church, Alexandria, VA USA

A horizontal sundial is located on the grounds of historic Christ Church in Old Town Alexandria, Virginia USA. The North American Sundial Society Dial Registry listing says, the “dial appears to have been designed for 32 degrees N.” In order to determine whether the sundial is in fact aligned properly, I examined a couple of photos that were geotagged by my Apple iPhone 4. (See “Tech Tips” for details, below.)

Similar to setting the correct time on an analog clock or wristwatch (by moving the hands of the timepiece into proper position), properly orienting a horizontal sundial will move the shadow of the gnomon (or style) into position so that the dial face displays the correct time.

1. The dial plate should be horizontal.
2. The shadow-casting edge of the gnomon should be parallel to the Earth’s axis, inclined at an angle equal to the latitude of the sundial.
3. The tip of the gnomon should point toward the North Celestial Pole (i.e., Polaris, the North Star). More simply, the dial face should be aligned so that 12 noon points toward geographic north and the 12 noon hour line is aligned with your local meridian.

Photos 1-2 of 8 (shown below) verify that the dial plate is horizontal. Photos 3-4 show the gnomon is inclined at an angle of 31.86 degrees (~32 degrees); Photos 5-6 show the latitude of the sundial is 38 degrees 48 minutes 22.2 seconds. Photos 7-8 show the image direction is 218.4602 degrees, meaning the tip of the gnomon is pointing southwest rather than true geographic north (0, 360 degrees).

Bottom line: The Christ Church sundial appears to have been made for another location and is aligned improperly for its new location. In other words, the sundial is strictly ornamental and will not tell time correctly.

Tech Tips: The iPhone Camera app works seamlessly with two built-in devices to geotag photos: the GPS sensor measures position on Earth; the digital compass measures “image direction.” PixelStick, an application for Mac OS X, was used to measure angles in one of the photos (see Photos 1-4, above). Apple “Preview” was used to display GPS info for both photos (see Photos 5-8, above).

Photos © Copyright 2012 Walter Sanford. All rights reserved. www.wsanford.com

Fossil sea snail shell, revisited

Fossil marine gastropod mollusk shell (Ecphora tricostata), approximately three inches (3″) in length, collected at an undisclosed location along the Potomac River, Westmoreland County, Virginia USA. The word “costa” means “rib,” derived from the Latin word “costae.” Notice that the shell of Ecphora tricostata has three costae (ribs). Photo 1 of 4 was annotated to highlight the three costae; Photo 2 of 4 is the original photograph. Photo 3 of 4 shows the relative size of the specimen (a quarter is ~1″ in diameter). Compare and contrast Ecphora tricostata with Ecphora quadricostata, the subject of one of my recent Posterous posts.

Habitat: A relatively “shallow” sea that existed along the east coast of the United States an estimated 10- to 15 million years ago, during the Miocene Epoch.

The following gallery displays a few alternate image crops, featuring reduced white space around the specimens while preserving the aspect ratio of the original photos — which versions do you prefer?

Editor’s Note: Are you a keen observer with eagle eyes? Did you notice I used “Virginia” quarters to show the relative size of a fossil from Virginia? That’s a subtle detail you may have overlooked.

Tech Tips: The preceding photos were post-processed using Apple “Aperture,” a professional-grade tool for organizing and adjusting photos. Apple “Preview” was used to annotate Photo 1 of 4.

The sidewalk is my canvas.

The sidewalk is my canvas; leaf stains are my brushes and paints. The following abstract photos of leaf stains remind me of paintings by Jackson Pollock, an American artist who participated in the abstract expressionism movement.

The preceding gallery shows leaf stains on a concrete sidewalk. Many of the stains were made by Maple tree (Acer sp.) leaves, as indicated by the “helicopter” seeds on the sidewalk (annotated in Photo 2 of 2).

The preceding gallery shows pine needle “leaf” stains on a concrete sidewalk. Photo 1 of 3 was cropped to create a “painting” canvas; Photo 3 of 3 is the original photograph. Photo 2 of 3 was annotated to highlight pine needles on the sidewalk.

Tech Tips: The preceding photos were post-processed using Apple “Aperture,” a professional-grade tool for organizing and adjusting photos. Apple “Preview” was used to annotate some photos.

Red Maple tree leaf stain

Photos 1-2 (of 4) show a Red Maple tree (Acer rubrum) leaf stain on a concrete sidewalk; the stain was the result of chemical- and physical changes as the leaf decomposed on a wet sidewalk. Photo 1 was annotated to highlight the leaf stain; Photo 2 is the original photo. Photos 3-4 show a Red Maple tree leaf, identified in situ using Leafsnap app for Apple iOS mobile devices. The leaf sample was collected from a tree located beside the leaf-stained sidewalk.

Photos 1-2 also show signs of human life (see “SNOZ” graffiti). I can tell “SNOZ” is a sign of human life because I know of no other creature that likes to write in fresh concrete — can you name one? What does “SNOZ” mean? It could be a nickname for someone with a big nose. What do you think “SNOZ” means?

Tech Tips: The preceding photos were post-processed using Apple “Aperture,” a professional-grade tool for organizing and adjusting photos. Apple “Preview” was used to annotate Photo 1 of 4.

White-tailed deer tracks

White-tailed deer (Odocoileus virginianus) tracks spotted along the banks of an intermittent stream running through the “Wildlife Sanctuary,” one of seven small parks owned and maintained by the Community Association of Hollin Hills, Fairfax County, Virginia USA.

Photo 1 of 3 was annotated to show the deer’s direction of travel toward the stream (red arrow, pointing forward); Photo 2 of 3 is the original photograph. Grooves in the moist soil (perpendicular to the stream), evident in all photos, may indicate that the deer slid down the stream banks as it crossed the creek. Note: The blue rectangle in Photo 1 highlights human tracks (the impression made by an athletic shoe), probably made before the deer tracks.

Related Resources:

• How to Identify Deer Tracks from Other Similar Footprints
• White-tailed deer overpopulation (one of my recent Posterous posts)
• “Fairfax County opens parks to bowhunters for deer culling,” Washington Post (newspaper)

Tech Tips: The preceding photos were post-processed using Apple “Aperture,” a professional-grade tool for organizing and adjusting photos. Apple “Preview” was used to annotate Photo 1 of 3.

Insect exuvia

Insect exuvia, most likely a type of Cicada, spotted during a photowalk through the “Wildlife Sanctuary,” one of seven small parks owned and maintained by the Community Association of Hollin Hills, Fairfax County, Virginia USA. Photo 1 of 3 is a copy of the original photograph, cropped to highlight the exuvia. Photo 2 of 3 was annotated to highlight the exuvia; Photo 3 of 3 is the original photograph.

Tech Tips: Photo 1 of 3 was cropped using Apple “Aperture,” a professional-grade tool for organizing and adjusting photos. Apple “Preview” was used to annotate Photo 2 of 3.

Holes in Blue Atlas Cedar tree trunk

Holes drilled by sapsucker birds (Sphyrapicus sp.) in the trunk of a Blue Atlas Cedar tree (Cedrus atlantica). Photo 1 of 3 was annotated to highlight one of several rows of drill holes; Photo 2 of 3 is the original photograph. Habitat: Landscape planting in a residential community, Fairfax County, Virginia USA.

Tech Tips: The geotagged photos in the preceding gallery were taken using an Apple iPhone 3GS; Apple “Preview” was used to annotate Photo 1 of 3. The photos in the following gallery were taken using a Kodak M1093-IS point-and-shoot digital camera; Apple “iPhoto” was used to geotag the photos.

Flying frog attacks dragonfly

The following short video clip shows a female Great Blue Skimmer dragonfly (Libellula vibrans) as she oviposits eggs in the wetlands at Huntley Meadows Park, Fairfax County, Virginia USA. A male Great Blue Skimmer dragonfly patrols the area to protect the female from other males.

Question is, did the dragonfly survive the attack by the frog? The following time series of 10 still photos provides the answer.

Watching the second video in real-time, it looks like a close call for the dragonfly — was she safe or out (game over)? Looking at the “instant replay” (i.e., the preceding time series of still photos), it’s clear the frog missed “tagging” the dragonfly by a wide margin. For those of you scoring at home, the box score for the game of life looks like this: Dragonflies 1; Frogs 0.

The following photo gallery features annotated versions of the same time series of 10 still photos: the frog is highlighted in green (when necessary); the dragonfly is highlighted in blue.

So what’s the life lesson learned from witnessing this extraordinary event? From an evolutionary viewpoint (i.e., survival of the fittest), it pays to have compound eyes that see in all directions as well as amazing aerobatic skills!

Tech Tips: Apple “Aperture” was used to save the preceding JPEG photos as still frames from the second video clip (GPS info copied from the video clip metadata to the JPEG photos). Apple “Preview” was used to annotate the second gallery featuring a time series of 10 still photos.

Comma butterfly

Small Cabbage White Butterfly on Cabbage Plants

On 10 June 2011, I photographed a cluster of 43 Small Cabbage White butterfly eggs on the underside of a cabbage plant leaf. (Yes, I counted them.) In the following gallery, Photo 1 of 2 is a copy of the original photograph, annotated to highlight the egg cluster; Photo 2 of 2 is the original photograph. Apple Preview was used to annotate the photo.