Author Archives: mathscinotes

Percentage of Atmosphere Beneath Observatories

Posted on 3-March-2016 by mathscinotes

I often see popular descriptions of observatories that say things like the observatory "is above 40% of the Earth's atmosphere". I had not thought much about this kind of statement until I saw the Wikipedia's list of the world's highest-altitude observatories, which surprised me as to the height and remoteness of the largest telescopes. I cannot imagine trying to build on these locations (Figure 1 is an extreme example). In some respects, the construction challenges remind me of what builders must have gone through on some lighthouses. Continue reading →

Posted in Astronomy | 1 Comment

How to Read a Book

Posted on 2-March-2016 by mathscinotes

Last week, I was having a conversation with my youngest son about how I read the books that I own – he sees that I vigorously engage with these books, and he was wondering why I read this way. I shared the following story with him, and it may be of interest to some of you. Continue reading →

Posted in Personal | 3 Comments

Roche Limit Examples

Posted on 1-March-2016 by mathscinotes

While listening to the audio book The Search for Exoplanets: What Astronomers Know, I heard the lecturer (Professor Joshua Winn) mention the Roche limit and gave a simple approximate formula for evaluating it. The Roche limit provides a lower boundary on how close a satellite may revolve around a planet or star. It is based on the idea that the gravitational and centrifugal forces of the planet work to pull a satellite apart, while the self-gravity of the satellite tends to hold it together. The Roche limit is where these forces are in balance – any closer and the satellite's gravity will be weaker than the centrifugal force plus the planet or star's gravity. Within the Roche limit, the satellite is subject to forces that tend to break it apart. Satellites moving inside the Roche limit are thought to be one way that planetary rings are formed. Continue reading →

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Book Review: A Passion for Leadership

Posted on 26-February-2016 by mathscinotes

I just finished reading Bob Gate's A Passion for Leadership, and I am a bit torn. I regularly read books on management and most of them do not contribute anything to improving management– that is not true for A Passion for Leadership. The book is a well-written memoir in which Gates shows how he applied standard management lessons in difficult circumstances. These standard management lessons are worth repeating. My feelings about the book are torn because there is nothing new here. I understand that one could argue that the principles of good management are timeless, but I tend to like authors who give me a new way to look at things. Continue reading →

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A Quick Power Over Ethernet Review

Posted on 24-February-2016 by mathscinotes

I have been asked to write some requirements for an optical product that is powered using Power Over Ethernet (PoE). It has been a few years since I have worked on a PoE-based design, I thought it would be useful to review the standard and ensure that I still understand it. This is a good exercise in basic electrical design and will also illustrate how to design circuits using Mathcad utility functions that I have written over the years. Continue reading →

Posted in Electronics | 1 Comment

45-Star US Flag Heirloom

Posted on 23-February-2016 by mathscinotes

A friend showed me a family photo of a 45-star US flag that was purchased in 1898, which was the year their grandfather was born. Figure 1 shows an example of the flag in their photo. The flag, which is quite large, is often used as a backdrop for a family photos. The flag is carefully stored and only taken out for special events, like reunions. I think this is a great use for an old flag. Continue reading →

Posted in History Through Spreadsheets, Personal | Comments Off on 45-Star US Flag Heirloom

Moving Lake Ice in Northern Minnesota

Posted on 22-February-2016 by mathscinotes

I just came back from a weekend visiting friends in Northern Minnesota. The snow is beginning to melt, and this makes everyone excited about the arrival of spring. During my weekend, I spent some time walking the streets around Gull Lake, which is near the city of Nisswa. I often see things that strike my fancy while walking. For example, I am always looking for good ideas to apply to my cabin, which is in the Grand Rapids area. Figure 1 shows a unique street light consisting of a wooden carving of a bear holding an old-style hurricane lamp. Bears and moose are common themes in northern Minnesota lore. Continue reading →

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Challenge of Viewing an Earth-Sized Planet

Posted on 18-February-2016 by mathscinotes

I listen to audio books during my nightly walks around a local lake. My current selection, Searching for Exoplanets, is one of the best audiobooks I have listened to. The book consists of a series lectures on the state of the search for exoplanets by MIT Professor Joshua Winn. The lectures provide an excellent summary of how astronomers are using remarkably sensitive methods for indirectly detecting the presence of exoplanets circling remote stars. Continue reading →

Posted in Astronomy | 1 Comment

WW2 Submarine Endurance on Batteries

Posted on 16-February-2016 by mathscinotes

I have been reading the book The Bravest Man, a biography of the WW2 exploits of US Navy submarine commander Dick O'Kane. I have not formed an opinion on the book since I just started reading it, but the book does highlight the submerged maneuvering limitations imposed on a ww2 submarine because of its lead-acid battery-based power plant. The book's discussion made me curious about the operational characteristics of a Gato-class submarine when operating submerged on batteries. In this post, I will be examining the Gato-class submarine's run time versus speed plot (Figure 1). Continue reading →

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Floating Habitat on Venus

Posted on 13-February-2016 by mathscinotes

I have been keeping a close eye on the discussions occurring about sending people to Mars on both one-way and two-way trips. You do not hear similar discussions about Venus because its surface temperature (467 °C) and pressure (93 bar) are too extreme to imagine people surviving there. Continue reading →

Posted in Astronomy | 6 Comments