Fresnel Lenses | How They Work

In a recent post about Maine lighthouses, I included two photos of the Fresnel lenses used to project the bright light beam across the water. One of the readers is a man I’ve enjoyed working with before in the blog world. He suggested I add a post with some description of how the Fresnel lens works. Here it is.

Basics of Converging Lenses

The converging, or convex lens, is able to bring parallel rays of light toward a focal point. As a child, I played with a magnifying glass lens to burn leaves, grass, and other things.

ConvergeLens1

 

The lens can also be used in a different way to project light rays parallel to each other in a beam. Simple projectors work on this basic principle. A lighthouse is designed to do this.

ConvergeLens2

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Saturn | Geysers of Enceladus

Saturn is one of the most beautiful objects in the night sky. Anyone who has viewed it through a telescope probably remembers the moment. I have shown it to many people through my telescope. It is fun to hear them exclaim about it. Young and old alike are moved by that experience.

NASA/JPL-Caltech/Space Science Institute | G. Ugarkovic

NASA/JPL-Caltech/Space Science Institute | G. Ugarkovic

The feature people enjoy the most is the ring structure. They were first observed by Galileo July 30, 1610. Although, he did not describe them as rings. Instead, they appeared to him as two separate and nearby bodies on either side of Saturn in this arrangement oOo.

The spacecraft Voyager 1 and 2 in 1981 and 1980 passed near the rings and gave us the most astounding views up to that time. The detail was amazing. The views captivated our imaginations and prompted scientists to plan space missions to investigate further. This image below shows the main features of the ring structure.

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Dawn | Global Map Shows Features

The NASA Dawn spacecraft entered orbit around the large asteroid-dwarf planet Ceres on March 6, 2015. Mission scientists gathered the Dawn images and built this composite as it neared Ceres. More details about this image can be found in this press release.

Higher resolution images will be gathered at an altitude of 8,400 miles (13,500 kilometers) when the spacecraft begins an intensive science phase April 23, 2015. There is much more to come in the months ahead.

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA | Click to embiggen

Visible and infrared images from the approach phase of Dawn to Ceres were used to create the simulated rotation below. Analysis of those images created the various colors above. The colors indicate some keys to composition and history of the regions. The very bright spots are of particular interest.

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA | Feb. 19, 2015

During 2011 and 2012, Dawn investigated Vesta, the second largest asteroid after Ceres. Much was learned about it which contributed to our knowledge of the formation of the solar system bodies. Ceres is thought to consist of 25% water, much different from rocky dry Vesta. It will also give us insights into our planetary histories.

Previous update posts about the Dawn mission can be found here and here and here.

Lighthouses | Mid-Coastal Maine

The links to the images were broken in this previously published post. If you visited before, thank you. If this is your first time, enjoy.



The lighthouse at Marshall Point gives a flavor of the Maine coast experience. It was a beautiful day with sunshine and cool temps when this picture was taken. Two days later, the weather changed and dropped 5″ of rain. Down the coast in Portland they had 7 or 8″. This day was ideal.

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Spicy Food | Why Is It Hot?

This post was originally published August 2013. The images became unlinked which prompted me to republish. If you saw it before, thanks for your visit. If this is your first time, I hope you enjoy it.



Do you like hot and spicy foods? I do. What is the ingredient that makes a food HOT? During the last years of teaching high school physics, I was fortunate to have a colleague who taught some of the sections. He was a lot of fun. We always enjoyed making physics relevant and enjoyable for the kids regardless of the topic. After our unit on heat and calorimetry, we decided to add a lesson on spicy hot foods. He had friends in Indiana who grew peppers on their farm. In the summer, he would go help them harvest and come home with some amazing peppers and hot sauces. He put together a presentation to share with the kids in our classes. The graphics here are from that lesson. Thanks to my colleague, Matt, for permission to use them.


A spicy shout-out to fellow blogger Frank for his post On Hot Sauces at his blog A Frank Angle. His post prompted me to write this. Thanks, Frank.


OK…I’ll have a taste. Let’s go.

Drought 2015 | Several Things To Know

The Sierra Nevada mountains provide California with about 30% of its water supply. On April 1st 2015, the Department of Water Resources did its annual analysis of the snowpack. It was declared ‘virtually gone‘…lowest since 1950. It was only about 6% of normal.

snowpack

California Data Exchange Center (CDEC) | http://bit.ly/1FwfmjQ

  • The recent 2014-2015 winter was not the driest on record, but close.
  • Temperatures this winter for California and the western states have been the warmest on record.

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Lunar Eclipse | Tetrad Part 3 | 1 Image

The weather forecast was for clear skies before dawn and cold temperatures. The alarm went off at 5 am. Moonlight was shining in the bedroom window. I looked out to a bright full moon.

I dressed for 27˚, gathered my equipment, and a cup of coffee. The spot I had chosen was very dark. After I parked the car, I set the camera on the tripod and snapped the first photo at 5:30. The plan was to get an image every 15 minutes and paste them together into one composite. It looked like things were off to a good start.

I admired the constellation Scorpio to the south while waiting for the next photo op. As 5:45 came around, I got out of the warm car and set the camera on the tripod again. Got it. Back in the car to stay warm.

The sun was brightening the sky. I noticed a low bank of darker color below the moon in the west. Were those clouds? I waited a few more minutes. They approached and covered the moon. That was the end of my eclipse experience. I went home to see how the two images looked.

The first one was badly out of focus. The second shown below was only of so-so quality. Some clouds had already degraded the seeing.

5:45 am CDT | f/5.6 | 1/250 s | 160 ISO

5:45 am CDT | f/5.6 | 1/250 s | 160 ISO

Next chance is in late September to complete part 4 of the Tetrad. Maybe everything will go better then. I had a good time and was glad to see it.