Partial Phase Phenomena Education
Solar Eclipse Timer Is The ONLY Eclipse App Available That Tells You When To Observe For These Phenomena. You Will Not Miss This Fascinating Aspect Of An Eclipse
Temperature Data From A Field In Beitbridge, Zimbabwe, Africa. December 4, 2002
Totality Duration 1m 22s
My Data (GMT)
Partial Phase Phenomena warnings occur between 1st Contact and 2nd Contact. These announcements are only relevant for total solar eclipse, or extremely deep annular eclipses. The audible voice warnings that are played are timed backward from the programmed 2nd Contact time. You only have to worry about programming the correct 2nd Contact time; the app will do the calculations for the Partial Phase Phenomena. The warnings remind you to observe ambient temperature, ambient lighting, animal behavior and shadow bands.
The audible voice warnings for the Partial Phase Phenomena are as follows:
“Forty Five Minutes Until Totality, Observe Changes In Ambient Temperature”
“Thirty Minutes Until Totality, Observe Changes In Ambient Temperature”
“Fifteen Minutes Until Totality, Observe Changes In Ambient Temperature”
“Ten Minutes Until Totality, Observe Changes In Ambient Lighting”
“Eight Minutes Until Totality, Observe Changes In Animal Behavior”
“Three Minutes Until Totality, Observe For Shadow Bands”
"Second Contact In 60 Seconds - Observe For Shadow Bands"
The audible voice warnings that were chosen for the Partial Phase Phenomena were given a great deal of thought. Not all veteran eclipse chasers would agree on when and what was chosen to warn about, so let me explain a little about my selections.
Although much is written about the decrease in ambient temperature during a total eclipse of the Sun, the emphasis is usually placed on the time of totality. But in reality the temperature is slowly and steadily dropping during the partial phases. Depending on your observing location, the season, the outdoor temperature, relative humidity and wind conditions, it is possible to perceive the change in ambient temperature well in advance of totality. In Africa, in June of 2001, I was amazed to clearly feel the drop in temperature at 30 minutes before totality. My perception was confirmed by temperature data collected during that eclipse. Therefore, for Solar Eclipse TimerTM, I chose to alert you to observe for your perception of ambient temperature changes at 45, 30 and 15 minutes before totality.
By 10 minutes before totality, there is a distinct difference in the ambient lighting and I chose to put an alert about this phenomena at this time. Much is written about this and the most basic observation is that is it getting darker. However, it is a very interesting and unusual decrease in light. The following are my perceptions of the change in lighting and it is difficult to describe. The overall brightness is decreasing even though the Sun is high in the sky. But the change in brightness is not the same as when, for instance, a thick cloud passes in front of the Sun on a regular day. There is a subtle color change, which to me appeared to be slightly gray, or silvery gray. Similar to wearing a pair of very lightly tinted sunglasses with gray lenses or looking through a lightly tinted neutral density camera filter. But because the effect is all around you and you are not wearing sunglasses the scene has an eerie feeling. The reason you do not start to perceive the change in brightness until this point is that the brightness has been slowly decreasing but you iris has slowly been enlarging to allow more light in. But then there is finally a point where your iris cannot open any larger and you start to see the ambient light looking dimmer. The color change is thought to be due to a combination of things. One is that the color of the light coming from the edges of the Sun (the crescents) might be a slightly different color than that from the full surface Sun. The second has to do with the light receptors in your eye, cones and rods. With bright light, the cones which allow you to see color are functioning properly. But within 3 to 7 minutes before totality the light is dimming and now the rods are starting to work. And since those are more sensitive, but don't see color the surroundings take on that gray look perhaps with less color saturation.
Another phenomena at approximately 10 minutes before totality is the change in the appearance of shadows cast to the ground. The shadows cast in certain directions tend to have a sharper edge to them. Very little is written about this and I cannot say that in Africa I perceived the changes. On a normal day, the lighting from a full Sun disk is not a point source, light comes from all across it's surface. produces shadows that have fuzzy indistinct edges. During the final 10 to 20 minutes before a total eclipse, when the Sun is a thin crescent, two types of shadows can be cast. Shadows that are in line with the crescent of the Sun, are sharper at the edges that are in the axis of the crescent, but fuzzy that the upper or lower end-points of the shadow, because these allow a broader point source of light.
At 8 minutes before totality, I chose to alert you to observe for changes in animal behavior. This close to totality, it is becoming dark enough that animals can be fooled into thinking it is becoming nighttime and they will behave as such. There have been reports of bats beginning to fly, birds going to their perches to rest or sleep, grazing animals ceasing to feed, insects like crickets beginning to make their nighttime sounds and bees may stop flying. In Africa in June of 2001, the increase in the number and volume of chirping crickets in the field surrounding us was clearly evident!
At 3 minutes before totality there is a warning to observe for shadowbands and what is meant is to “start” to look for shadowbands. They are faint “bands of shadows” or undulations of light that can be see on the ground. Some describe the appearance as similar to the way sunlight moves across the bottom of a swimming pool, except shadow bands don't flutter in the same spot, they have directional motion. We saw them in Africa in 2002 and I would describe them as complex continuous parallel serpentine shadows that move in a snake-like motion away from you and sideways. Shadowbands are caused by the sunlight rays from the thin crescent of the Sun being bent as the light passes through warmer and cooler cells of air in the atmosphere. The phenomena will probably occur closer to totality when the crescent is even thinner. However, I wanted to give ample warning to begin to look for them because every eclipse is unique and everyone’s observing location is different. There is another short warning to observe for them just following the "Second Contact in 60 Seconds" announcement.
At 30 seconds after 3rd contact there, is another announcement to look for shadow bands because this thin crescent after totlaity gives the second opportunity for this spectacular phenomenon to occur.
There is one other an important alert which is just after max eclipse, I remind you to "Observe the Horizon". This is an important observation to enjoy. You are standing in the middle of a large shadow that the Sun is still lighting the entire perimeter so you see the effect of a colored Sunset 360 degrees around you.