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SpaceX Falcon 9 Flyby

I glanced out a window last night and saw this brilliant spectacle unfurl as the second stage of a Falcon 9 traversed the sky west of Phoenix at an altitude of 90 miles and ground speed reaching more than 10,000mph:

Since this was shortly after sunset, the exhaust plume was high enough to be illuminated by the sun from over the horizon. (Here’s SpaceX’s video and mission summary.)

Venus with Crescent Moon

Now in the first week of February 2025, Venus is approaching its peak brightness. Here is a picture of it near the waxing crescent moon while at a brightness magnitude of -4.8.

This makes it 23 times as bright as Mars, which had a magnitude of -1.4 in the photos following its lunar eclipse three weeks ago:

Mars emerges from lunar occultation, photo by David Bookstaber 20250113

Venus has almost twice the diameter of Mars (which itself has twice the diameter of the moon), and presently it is also only 75% as far from Earth as is Mars.

Martian Eclipse (Lunar Occultation)

Last night (13 January 2025), North American observers could see the nearly full Moon pass in front of Mars, hiding it for as long as an hour. I got some photos of Mars emerging on the other side:

As noted last week, right now Mars is relatively close to Earth and in nearly full phase, just like the Moon in these pictures, so we are seeing the entire “day” side of Mars. Mars is twice the diameter of the Moon, but presently it is more than 200 times as far from Earth.

Bright Planets: Venus and Mars

Coming into 2025, have you noticed that Venus and Mars are growing quite bright? Looking at a map of planetary positions it’s easy to see why Mars is approaching a point of peak apparent brightness (which it will reach on January 16): it’s on the same side of the sun as we are, so it’s relatively close; and we are aligned to see the full reflection of the sun-lit “day” side.

Inner planet positions on 16 January 2025

With Venus it’s not as easy to figure out when its apparent brightness will be maximized. When Venus is closest to Earth we are looking at its night side, so there’s no reflected light to see. When we can see the full day side of Venus it’s at its furthest from Earth on the other side of the sun, so it’s reflecting the maximum amount of light in our direction, but being so much further away the amount of light that reaches us is lower. In fact Venus goes through “phases” just like our moon does based on its position relative to the Earth and Sun, as shown in this diagram:

Phases of Venus: How much of the “day” side of Venus we can see at different points in its orbit relative to Earth.

Next is another diagram that shows two significant points in the relative orbit of Venus: “Greatest Elongation” is when (from our perspective) the angular distance between Venus and the sun is largest. It turns out that the peak apparent brightness for Venus occurs when it is just inside its points of greatest elongation, with slightly less than half of its day side facing Earth.

Venus is at greatest eastern elongation on January 10, which puts it at its highest point in the evening sky. Its brightness will peak on February 14, at which point it will be more than 20 times brighter than the brightest star we can see (Sirius). This is so bright that it can be seen during broad daylight, if you know where to look.

Alcohol is more efficient than sugar

Centuries ago, when bulk transportation was expensive and raw foods were at risk of loss to spoilage or pests, distant farmers might prefer to convert sugar-bearing grain and fruit into ethanol, distill it to concentrate it, and transport that concentrate to distant markets. (This fact was a primary cause of the Whiskey Rebellion in response to the imposition of a tax on distilled alcohol.)

I was surprised at how much more efficient ethanol is as a source of energy, even though energy is lost through fermentation! The chemical equation for fermentation of sugar (glucose chosen here) is:

C₆H₁₂O₆ (glucose) → 2C₂H₅OH (ethanol) + 2CO₂ (carbon dioxide) + Energy

Considered by weight: For every kilo of glucose fermented, we get half a kilo of ethanol and 300 calories of heat (which is typically wasted). But ethanol is more energy dense than sugar: Humans extract 3700 calories per kilo of glucose but 7000 calories per kilo of ethanol! I.e., the metabolic energy available in a kilo of sugar is mostly preserved when converted to alcohol, but its weight is cut in half.

100 Free 4k UHD Background Photos

I went through my landscape photos and picked the best hundred, then spent time enhancing each one to make a good background image at 4k resolution (3840×2160 pixels). I have shared them through this Google Photos album under the CC BY-NC-SA license so you can save your favorites. If you simply save the images to an album in your own Google Photos then you can set that as your “Screensaver” for any Google-connected TV or device. Enjoy!

Today’s LLM Challenge: Create a diagram

Ask an LLM to create a technical diagram and they’ll use a diffusion generator, which produces funny but mostly nonsensical results. But they tend to be pretty good at writing code, so I thought I’d see how they can do with the following prompt:

Describe a diagram suitable for a textbook that illustrates the definition of “cross-sectional area”. Then create SVG code to render that.

The description is easy, so I’m only going to show the SVG images they produced.


ChatGPT 4o

Claude 3.5 Sonnet


Perplexity

Bing

Bing also volunteered four diffusion images, first of trees like this:

Then I asked it to try again using a simple cylinder and got these cool but not usable results:


The smaller models available through HuggingChat were worse, and Cohere didn’t even get the SVG namespace into the XML. Here’s what I got from the top three:

Privacy.com to thwart subscriptions

Businesses love the recurring revenue from subscriptions. And they love the fact that people tend to be so lazy and forgetful that customers don’t reliably cancel subscriptions that they wouldn’t otherwise keep. As a conscientious consumer, I dislike subscription services because businesses have a disincentive to make cancelling subscriptions easy. I disapprove of the roach motel business model. My favorite countermeasure: Privacy.com.

Privacy.com lets you create credit cards with all sorts of constraints, as shown in this screenshot:

Screenshot of Privacy.com credit card limits.

I particularly like the single-use card, which I create for subscription services. If I forget about the service they can’t keep sucking money from my bank. If I want to cancel the service, I don’t have to find and navigate their arbitrary cancellation processes … and keep records of cancellation attempts to dispute recurring charges from those businesses that are either incompetent or downright fraudulent when it comes to cancelling subscriptions. If I do want to continue subscribing, I have found that every business goes above and beyond to make that as easy as possible!

Inkscape vs Adobe Illustrator for Vector Graphics

I’m about to break 100 figures (that’s photos, diagrams, and combinations thereof) for my book, which in current draft is 150 pages. Whenever possible I create vector images because they scale perfectly. The alternative is a raster (pixel-based) image, which is defined for some number of pixels and becomes pixelated when enlarged. Here’s an extreme example: I drew a simple circle, rasterized a copy of it, and then zoomed in on the top section:

The vectorized version stays smooth at any scale, because the rendering engine is essentially told, “The drawing is a black circle, this size with this line thickness.” (The SVG code is actually <circle cx="50" cy="50" r="40" stroke="black" stroke-width="1" />.) The rasterized version is a fixed rendering of that circle using a specified number of pixels, and that’s as detailed as the image can get.

Raster images are natural for things like photos that begin life as pixel arrays. But computer drawings that are built up using primitive shapes and strokes almost always benefit by preserving that construction. A bonus is that vector files tend to be much smaller than legible raster versions – even in the human-readable Scalable Vector Graphics (SVG) format.

I have created vector images directly in Word (more on this later), Excel, and Python (using matplotlib and seaborn). For just $5 I got a Ukrainian freelancer on Fiverr to vectorize a diagram from an old military publication.

Until recently I used Adobe Illustrator to do more serious vector graphics. But my latest copy of that software is from 2007 and doesn’t always work well in Windows 10. (Yes, I got it back when you could buy and keep using an application instead of having to subscribe.) If I did this stuff all the time I would probably subscribe to Adobe Creative Cloud. But I don’t, so I took a look around and found a popular open-source alternative to Illustrator: Inkscape. It took a day to get comfortable with it, and now it’s great for my purposes. For example, I liked this drawing from a 2004 dissertation by Jorma Jussila, and he was kind enough to send me the vector image, which gave me a tremendous head start creating this diagram:

How Microsoft Let Me Down This Week

In college (1998) I wrote a graphics-heavy term paper in Word. I had invested days of work, saving frequently (as always). At some point Word corrupted the document, but I didn’t realize that because I had kept it open on my computer and the in-process version didn’t give a hint that anything was wrong. Until I tried sending it to a printer, at which point it crashed and I discovered that none of the files contained much that could be salvaged. It took a frantic day to reproduce the paper.

Well, that summer I had a great internship at Microsoft, and – not one to hold a grudge – I have been drafting my current book in Word. (As of today the DOCX is 100MB!) But I have been frequently creating and checking PDFs along the way. In the course of these reviews I discovered that Word is unpredictable in creating and handling vector drawing objects. For example, adding a bevel to a circle causes Word to rasterize it, but you probably won’t notice unless you make a point of inspecting things at high zoom multiples.

Create a circle in Word and it’s a vector drawing (left). Add a bevel and Word silently rasterizes it (right).

I also discovered that Microsoft’s PDF printers and export engines rasterize everything, which is not only a loss of detail, but also a travesty given that vectors are a foundation of the Portable Document Format. Fortunately there are free PDF printers (I verified both doPDF or CutePDF) that preserve vectors.

Two Weird Tricks for Presbyopia

I used to have perfect vision: In my 20s I passed the rigorous Air Force optometry screening for pilot candidates. Now in my late 40s I have developed the inevitable presbyopia that comes with age: The lenses of my eyes have lost so much flexibility that I can’t focus on things as close as I used to. I can no longer read fine print that used to be easily legible. In dimly lit restaurants I struggle to read menus. Both of these can be solved with reading glasses, but I don’t routinely carry those. So I often rely on two tricks to compensate.

The first trick is to increase light. I can read almost anything in direct sunlight.. In a restaurant I pull out my phone and shine its illuminator on the menu. Why does adding light sharpen text that is otherwise blurry or out of focus? There are some interesting optics at work.

The following image contrasts two photos of the same human eye. The photo on the left was taken in a dimly lit room, which has encouraged the pupil to open to let in more light. The photo on the right was taken with daylight coming through a window: The extra light causes the pupil to close.

Photos of the same eye in dim (left) and bright (right) light.

The wider the aperture (which in an eye is the pupil), the greater the focal range of a lens. In sunlight our pupils are as small as they can get, which gives us the maximum focal range. With presbyopia, my lenses can’t accommodate (i.e., change shape to shift focus) as close as they used to, but they can still go far enough that the added focal range from a small pupil brings close objects into focus. The same physics applies to camera lenses, as I demonstrate in the following image:

Illustration: First row: A camera pointed at a pill bottle inside its lens’s minimum focal distance. Second row: The lens aperture shown open to f/2.8, and the photo produced with the aperture wide open (f/1.7). Third row: The lens aperture stopped closed to f/22 and the photo of the same scene

I put a pill bottle closer than the minimum focal distance of this camera lens. A photo taken with the lens aperture wide open (f/1.7) shows that the lens can’t bring the text into focus. Keeping the lens at the same distance and focus setting, but stopping the aperture down almost as small as it gets (f/22) increases the focal range and brings the text into focus. (The photo of the lens in the second row actually shows the diaphragm at f/2.8 because at f/1.7 it can’t be seen.)

Bright light causes our pupil to contract naturally. The second trick is to create an artificially small aperture. You can do this by putting a pinhole lens close to your eye. I do this by closing my fingers and looking through the tiny opening left between two of them at the joint:

David Bookstaber creating pinhole lens for one eye to bring closer objects into focus.

The aperture trick can only compensate so much: With too little light the subject may be in focus but the contrast might be too low to read it. In the camera example: The exposure with the wide aperture was made in 1/640 of a second, but it took 1/4 second to get an adequate exposure at the minimum aperture (holding all other settings constant).


I have a related post on my substack: Why I Dislike Dark Mode.