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Partial Solar Eclipse at New Jersey

August 24, 2017

My first experience with a solar eclipse was on July 20, 1963, when the path of an eclipse passed through Canada and Maine, resulting in a significant occultation at my childhood home near 43.12298 North Latitude, 75.20335 West Longitude. I've never experienced a total solar eclipse. For the recent eclipse of August 21, 2017, I was determined to make some scientific measurements at my far-from-ideal location at 40.8768 North Latitude, 74.6566 West Longitude, near New York City, where a 77% occultation was predicted.

I don't own a telescope, and I knew that many detailed photographs of the eclipse would be available on the Internet. Instead of photography, I decided to make photometric and temperature observations at my cloudy location. To that end, I designed and built a computer interfaced sensor module that incorporated a photometer and thermometer. The thermometer used the LM335 integrated circuit, as shown in the figure.

LM335 temperature sensor circuit

LM335 temperature sensor circuit.

(Created using Inkscape.)

The photometer used a silicon photodiode in a conventional transimpedance amplifier circuit, as shown in the figure. As could be expected, there was plenty of light available, so the needed gain was modest.

Transimpedance amplifier for a silicon photodiode.

transimpedance amplifier circuit for a silicon photodiode.

Jumpers are used to select the gain, with the 100 k-ohm resistor providing the highest gain. For the eclipse measurements, the 10 k-ohm resistor was selected.

(Created using Inkscape.)

It would be somewhat hard to track the Sun (I would use a servomechanism), and not that worthwhile, because of the expected cloudy day. Instead, I built a cowl for the photodiode that selected a small solid angle of the sky at zenith for measurement (see figure). The solid angle was large enough to sample blue sky through occasional clouds, but not large enough to capture any direct sunlight.

Photodiode cowl

The cowl used for the photodiode.

This was fabricated from a black plastic 35 mm film cannister, which is an uncommon item, today, but ideal for this task.

(Created using Inkscape.)

To avoid early morning and late afternoon shadows from surrounding trees, I placed the sensor module at the edge of my roof, as shown in the photograph. Data collection was through an analog-to-digital converter that connected to a USB port on my laptop computer, conveniently located in a room underneath the sensor module. The connecting cables were passed through an exterior door. I wrote the data collection software using Gambas, a programming environment for Linux not unlike Visual Basic. Data points were taken at 10 second intervals.

Eclipse sensor module

Eclipse sensor module in place at the edge of my roof.

The cables were routed through a sliding door beneath the sensor module location.

As expected, it was a cloudy day in New Jersey, with the Sun appearing just occasionally through the clouds. Passage of clouds through the zenith was detected by the photometer, both on the day of the eclipse, and the previous day, which was used as an equipment check and an opportunity of log some reference data. The reference data showed how the daytime light peaked at mid-day. Sunrise wass at 6:15 AM EDT, and sunset was at 7:45 PM EDT, so mid-day was about 1:00 PM.

Clouds at eclipse maximum occultation

Not ideal eclipse weather.

This a view of the sky looking NNE at eclipse maximum occultation.

The clouds notwithstanding, there was a noticeable darkening at maximum occultation. As the data show, the lightness of the sky was equivalent to what's experienced early morning or late afternoon.

Since the transient cloud cover added a lot chatter to the data, the data were post-processed using a ten minute moving average to give the graphs shown below. The dip in light intensity is easily seen when compared with the previous day's data. Also noted was a 3 °C cooling of the air temperature. Partial eclipse 8/21/2017, light curve.

Light intensity throughout the day, Monday, August 21, 2017.

The partial eclipse is evident, with minimum light at the predicted time of maximum occultation.

(Graphed using Gnumeric. Click for larger image.)

Partial eclipse 8/21/2017, light curve with reference data.

Light intensity throughout the day, Monday, August 21, 2017, including reference data from the day before.

The percentage drop in light intensity from the partial eclipse is what was expected, with allowance for error arising from cloud cover.

(Graphed using Gnumeric. Click for larger image.)

Partial eclipse 8/21/2017, temperature curve.

Cooling from the partial eclipse.

The solar irradiance in New Jersey can be as high as nearly a kilowatt per square meter.[1] Loss of all that energy results in significant cooling.

(Graphed using Gnumeric. Click for larger image.)

We should include at least one eclipse photo (below), and there are many others available on the Internet. Also on the Internet is a YouTube video of a satellite observation of the eclipse as it passed from the West Coast to the East Coast of the United States.[2]

Figure caption

A composite image of the partial solar eclipse over Ross Lake, North Cascades National Park, Washington State, August 21, 2017. (NASA image by Bill Ingalls. For more images, see this NASA Website.[3])


  1. NJ Statewide Solar Radiation (Daily Max), New Jersey Weather and Climate Network.
  2. Watch the Moon's Shadow Move from Coast to Coast, YouTube video of NOAA Satellite observations from 12:27 PM EDT through at 2:52 PM EDT, August 21, 2017.
  3. Total Solar Ecipse, August 21, 2017, NASA website.

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