The Daily Parker

Politics, Weather, Photography, and the Dog

Falling into the sun is hard

In the geocentric model of how things work, it's really easy for you to fall directly toward Earth. This happens because you are already moving fast enough to have a very small delta vee with the surface at any particular moment. Not so falling into the sun, which is so hard, we only just launched the first probe that can do it on purpose:

The reason has to do with orbital mechanics, the study of how natural forces influence the motions of rockets, satellites, and other space-bound technology. Falling into the sun might seem effortless since the star’s gravity is always tugging at everything in the solar system, including Earth. But Earth—along with all the other planets and their moons—is also orbiting the sun at great speed, which prevents it from succumbing to the sun’s pull.

This arrangement is great if you’d like to avoid falling into the sun yourself, but it’s rather inconvenient if you want to launch something there.

“To get to Mars, you only need to increase slightly your orbital speed. If you need to get to the sun, you basically have to completely slow down your current momentum,” says Yanping Guo, the mission-design and navigation manager for the Parker Solar Probe. Based at the Johns Hopkins Applied Physics Laboratory, Guo has been working on the probe for about 17 years.

Probes bound for deep-space destinations like Mars can piggyback off Earth’s momentum to fly faster. For a spacecraft to launch toward the sun, on the other hand, it must accelerate to nearly match the Earth’s velocity—in the opposite direction. With the planet’s motion essentially canceled out, the spacecraft can surrender to the sun’s gravity and begin to fall toward it. But this is almost impossible with current rocket technology, so spacecraft have to get some help, in the form of slingshot maneuvers off other planets, called gravity assists.

Douglas Adams, therefore, was partially correct: generally speaking, if you throw yourself at the sun, you will miss (and wind up in a stable orbit). NASA has just started the process of hitting it.

Meant to post yesterday

Four articles I read late in the day and wanted to spike here:

And now, I will start working.

Evidence suggests people heard Earhart's distress calls

More data has emerged about Amelia Earhart's final days:

Across the world, a 15-year-old girl listening to the radio in St. Petersburg, Fla., transcribed some of the desperate phrases she heard: “waters high,” “water’s knee deep — let me out”  and “help us quick.”

A housewife in Toronto heard a shorter message, but it was no less dire: “We have taken in water . . . we can’t hold on much longer.”

That harrowing scene, the International Group for Historic Aircraft Recovery (TIGHAR) believes, was probably one of the final moments of Earhart’s life. The group put forth the theory in a paper that analyzes radio distress calls heard in the days after Earhart disappeared.

Some of Earhart’s final messages were heard by members of the military and others looking for Earhart, Gillespie said. Others caught the attention of people who just happened to be listening to their radios when they stumbled across random pleas for help.

Almost all of those messages were discounted by the U.S. Navy, which concluded that Earhart’s plane went down somewhere in the Pacific Ocean, then sank to the seabed.

[Research director Ric] Gillespie has been trying to debunk that finding for three decades. He believes that Earhart spent her final days on then-uninhabited Gardner Island. She may have been injured, Noonan was probably worse, but the crash wasn’t the end of them.

Gardner Island, now called Nikumaroro, fits the classic description of a desert island: it's a small atoll with trees and a very long swim to the next nearest land mass. Crashing there might have meant a slow death from dehydration instead of a quick one from impact. We'll never know for sure, but this new data, if accurate, adds some weight to the hypothesis that Earhart crashed on Nikumaroro in 1937.

That's not a moon, that's a--wait, no that's a moon

Astronomer Scott Sheppard has discovered 10 more moons orbiting Jupiter, bringing the gas giant's coterie up to 79:

Sheppard found them with the help of a ground-based telescope in Chile that had recently received an upgrade: a camera made for scanning the night sky for very faint objects. Sheppard was looking for Planet Nine, the planet some astronomers believe lurks somewhere at the edge of our solar system, jostling the orbits of other objects in strange ways. As the telescope gazed in the darkness way beyond Pluto, it ended up catching something much closer: a flurry of glinting, tiny objects near Jupiter, the smallest of which was about half a mile wide.

Sheppard couldn’t say whether these points of light were actually moons, at least not right away. To determine whether something is indeed a moon, astronomers must track the object for about a year to determine that, yes, its motions are governed by the gravitational tug of a planet. Sheppard says he couldn’t get excited about his findings in earnest until he observed the objects again a year later, this past spring, and his suspicions were confirmed.

If you came to this story expecting to find dazzling, close-up images of Jupiter’s newly discovered moons, we have some bad news: The era of discovering massive worlds around the gas planet ended more than 400 years ago, with Galileo. Like this latest batch, many of the moons astronomers have discovered around Jupiter in the past several decades have been smaller than cities. Their minuscule size has prompted some astronomers, including Sheppard and Williams, to wonder whether they should even bother giving them names. Williams says that discoverers of moons don’t have to name them if they don’t want to. Sheppard suggests perhaps it’s time to add another layer to our definition of a moon. “The definition of a moon is just anything that orbits a planet, so maybe once you start getting down to a kilometer or so in size, maybe we should start calling these things dwarf moons,” he says.

Now they just have to name all of them...

Multiple heat records set this week worldwide

Large areas of the planet are experiencing record heat this week, as predicted by the anthropogenic climate change hypothesis:

No single record, in isolation, can be attributed to global warming. But collectively, these heat records are consistent with the kind of extremes we expect to see increase in a warming world.

  • Denver tied its all-time high-temperature record of 105 degrees on June 28.
  • Burlington, Vt., set its all-time warmest low temperature ever recorded of 80 degrees on July 2.
  • Montreal recorded its highest temperature in recorded history, dating back 147 years, of 97.9 degrees (36.6 Celsius) on July 2. The city also posted its most extreme midnight combination of heat and humidity.
  • Scotland provisionally set its hottest temperature on record. The U.K. Met Office reported Motherwell, about 12 miles southeast of Glasgow, hit 91.8 degrees (33.2 Celsius) on June 28, passing the previous record of (32.9 Celsius) set in August 2003 at Greycrook. Additionally, Glasgow had its hottest day on record, hitting 89.4 degrees (31.9 Celsius).

As we reportedQuriyat, Oman, posted the world’s hottest low temperature ever recorded on June 28: 109 degrees (42.6 Celsius).

That's right; in Oman overnight on June 28th, it never got below a potentially lethal temperature.

It's beginning to look a little like Christmas...on Venus.

Hey, there's my old flint arrowhead!

Amsterdam is building a new subway line directly beneath the Amstel River, so they drained it, as one does. Then they let a team of archaeologists go wild:

The excavations in the Amstel yielded a deluge of finds, some 700,000 in all: a vast array of objects, some broken, some whole, all jumbled together. Damrak and Rokin proved to be extremely rich sites on account of the waste that had been dumped in the river for centuries and the objects accidentally lost in the water. The enormous quantity, great variety and everyday nature of these material remains make them rare sources of urban history. The richly assorted collection covers a vast stretch of time, from long before the emergence of the city right up to the present day. The objects paint a multi-facetted picture of daily life in the city of Amsterdam.

The city has published an online catalog that you can view chronologically or alphabetically.

Busy weekend; lunchtime reading

This past weekend included the Chicago Gay Pride Parade and helping a friend prepare for hosing a brunch beforehand. Blogging fell a bit on the priority list.

Meanwhile, here are some of the things I'm reading today:

Back to debugging service bus queues...

Late afternoon reading

Meetings and testing all day have put these on my list for reading tomorrow:

And with that, it's the weekend.

O is for O(n) Notation

Blogging A to ZFor day 15 of the Blogging A-to-Z challenge I want to talk about something that computer scientists use but application developers typically don't.

Longtime readers of the Daily Parker know that I put a lot of stock in having a liberal arts education in general, and having one in my profession in specific. I have a disclosed bias against hiring people with computer science (CS) degrees unless they come from universities with rigorous liberal arts core requirements. Distilled down to the essence, I believe that CS majors at most schools spend too much time on how computers work and not enough time on how people work.

But CS majors do have a lexicon that more liberally-educated developers don't really have. For example, when discussing how well code performs, CS majors use "Big O" notation.

In Big O notation, the O stands for "order of growth," meaning how much time could the algorithm could grow to take up given worst-case inputs.

The simplest notation is O(1), where the code always takes the same amount of time to execute no matter what the inputs are:

int q = 1;
int r = 2;
var s = q + r;

Adding two integers in .NET always takes the same amount of time, no matter what the integers are.

The titular notation for this post, O(n), means that the execution time grows linearly based on the input. Each item you add to the input increases the time the algorithm takes by exactly one unit, as in a simple for loop:

public long LoopExample(int[] numbers)
	long sum;
	for(var x = 0; x < numbers.Length; x++)
		sum += numbers[x];
	return sum;

In that example, each item you add to the array numbers increases the time the loop takes by exactly one unit of time, whatever that unit may be. (On most computers today that would be measured in units of milliseconds, or even hundreds of nanoseconds.)

Other algorithms may be slower or faster than these examples, except that no algorithm can be faster than O(1). The parenthetical can be any expression of n. Some algorithms grow by the logarithm of n, some grow by the double of n, some grow by the square of n.

This notation enables people to communicate precisely about how well code performs. If you find that your code takes O(n2) time to run, you may want to find a fix that reduces it to O(log n). And you can communicate to people how you increased efficiency in just that way.

So as much as I want application developers to have broad liberal educations, it's worth remembering that computer science fits into a liberal education as well.

What really was the Cuban sonic weapon?

About a year ago, a number of American diplomats and their families in Cuba were injured by what our military speculated might be a sonic weapon. A sonic weapon directs sonic energy at a target to disable, but not necessarily permanently damage, the person. Over a few months, people reported "blaring, grinding noise," hearing loss, speech problems, nausea, disequilibrium...exactly what a sonic weapon could cause.

Via Bruce Schneier, a team at the University of Michigan working in association with the IEEE has published a paper speculating on the variety of weapon how it might have worked:

On the face of it, it seems impossible. For one thing, ultrasonic frequencies—20 kilohertz or higher—are inaudible to humans, and yet the sounds heard by the diplomats were obviously audible. What’s more, those frequencies don’t propagate well through air and aren’t known to cause direct harm to people except under rarefied conditions. Acoustic experts dismissed the idea that ultrasound could be at fault.

Then, about six months ago, an editor from The Conversation sent us a link to a video from the Associated Press, reportedly recorded in Cuba during one of the attacks.

To make the problem tractable, we began by assuming that the source of the audible sounds in Cuba was indeed ultrasonic. Reviewing the OSHA guidance, Fu theorized that the sound came from the audible subharmonics of inaudible ultrasound. In contrast to harmonics, which are produced at integer multiples of a sound’s fundamental frequency, subharmonics are produced at integer divisors (or submultiples) of the fundamental frequency, such as 1/2 or 1/3. For instance, the second subharmonic of an ultrasonic 20-kHz tone is a clearly audible 10 kHz. Subharmonics didn’t quite explain the AP video, though: In the video, the spectral plot indicates tones evenly spaced every 180 Hz, whereas subharmonics would have appeared at progressively smaller fractions of the original frequency. Such a plot would not have the constant 180-Hz spacing.

Of course, to this day, no one knows exactly why the attacks occurred, and even to say "attacks" makes a reasonable but not certain assumption.