Eclipse Data Captured
Exploring an Eclipse

PASCO Probeware Captured Data Associated with an Eclipse from Four Points Around the Globe

Roseville, Calif. -- On June 10, 2002, an annular eclipse occurred. While the shadow's path of greatest interest was primarily over the Pacific Ocean, viewers from all over the world were able to witness the event.

An eclipse is a great opportunity to utilize PASCO sensors for scientific investigation. For this eclipse, PASCO organized volunteers from several parts of the world, including Roseville, Calif.; Vancouver, Canada; San Diego, Calif., and Taipai, Taiwan to collect data using PASCO probeware. The task put before the participants was to investigate the effects a solar eclipse has on light and temperature.

A solar eclipse occurs when the moon in its new phase passes directly in front of the sun, causing the moon to cast a shadow on the Earth. Because of the moon's eccentric orbit, solar eclipses come in two flavors: total and annular, depending on the moon's position between the sun and Earth. If you are far from the penumbral shadow (the outer or penumbral shadow is a zone where the Earth blocks part but not all of the sun's rays from reaching the moon) you will view a partial solar eclipse. Those in the path of the umbra (the inner or umbral shadow is a region where the Earth blocks all direct sunlight from reaching the moon) will witness either a total or annular eclipse.

Even if the sun is 50 percent covered during an eclipse it may still look like a bright, sunny day to the naked eye. A PASCO Light Sensor, however, can detect what is really happening by quantifying the change in light intensity. Other effects, such as an associated temperature change, can be simultaneously investigated using a Temperature Sensor.

Prior to the eclipse, PASPORT Light Sensors were positioned to measure sunlight reflected off a white board at all four locations. This method allows the sunlight to be averaged out while minimizing the affect of the change in the sun's position during data collection. The Light Sensors were then connected to Xplorer dataloggers and the sampling rates were set for .5 Hz (one sample every two seconds). The sensitivity was set to the largest scale for sunlight conditions.

Next, a PASPORT Temperature Sensor was connected to another Xplorer datalogger and the sampling rate was set at 2 Hz.

Before the eclipse began, all participants were careful to protect their eyes. Because viewing even a partly-eclipsed sun without proper protection will result in a retinal burn and may cause permanent damage to vision, eye protection must always be worn when viewing an eclipse.

At the time the eclipse was measured in Roseville, Calif., the weather was clear. Both Xplorers were "time synched" to the same computer to ensure correct data merging in DataStudio, PASCO's data collection and analysis software. The Light Sensor was attached to a tripod and aimed at the reflective white board.

From the start of the partial eclipse to the maximum sun coverage of 61 percent at 17:15 PST, the light data shows a dramatic decrease in light intensity reflected from the white board. The Temperature Sensor shows an almost identical pattern.

During data collection, the sun's position in the sky changed by 25 degrees, which means an overall downward trend in gross reflected light intensity. However, the change in light intensity was accelerated during the eclipse.

The relationship can be seen directly by plotting Temp vs. Light Intensity. In this graph the first half cycle is plotted.

From the data, it is apparent that as the reflected light intensity dropped, so did the temperature. When the maximum point of the eclipse was reached, the temperature had dropped 6 degrees Celsius. The graph supports a general trend that, as the reflected light intensity dropped, so did the temperature.

In Taiwan, the eclipse occurred during sunrise. Unfortunately, cloud cover obscured the view and the data collected was therefore poor.

While predicting an eclipse is relatively easy today, obtaining good measurements of the associated data depends on the conditions present at the time. Cloud cover, wind and other elements can greatly affect the outcome. But when conditions are favorable, probeware can give new insight into an eclipse that is not detectable to the naked eye.