“Landing” on a comet

Rosetta_at_Comet_Poster_landscape_node_full_image_2On Friday, September 30, 2016, the Rosetta space probe will crash land on a comet. It is not the first time a mission has landed on a small solar system body. In fact, 15 years ago, on February 12, 2001, NASA spacecraft NEAR*, touched down on the surface of asteroid EROS. It was not originally intended to land, but controllers decided to take it down to get closer and closer images of the surface, knowing that contact with the spacecraft would soon be lost anyway. It sent back photos from as close as a few meters from the surface, but contact was lost on touchdown.

Philae_close-up_node_full_image_2Then just two years ago in 2014, a small probe called Philae, a lander from the very same  Rosetta mission, scheduled to contact the the comet on Friday, “soft” landed on the surface of a comet for the first time. In this case, Philae was designed and intended to land, which it did, although with complications. Photos and other data were received, but contact was spotty and was lost permanently a few months later.

Now, this week, the Rosetta mothership itself also will touch down on comet (67P/Churyumov–Gerasimenko), although like the NEAR-Shoemaker probe, it was never designed nor intended to do so. It will take photos and readings on the way down, but all contact is expected to be lost with first contact with the surface of the comet. It may be more accurate to refer to the “landing” as a controlled impact.

67PChuryumovGerasimenkoToo far and faint to be seen in Earth-telescopes, the comet and spacecraft are passing through the area of sky between Spica and Gamma Virginis in the constellation Virgo. (For northern observers, this area of sky sets very shortly after sunset.) The comet and probe will be roughly 719 million kilometers (447 million miles) at the time of spacecraft impact.

The “collision manoeuvre” will begin at  20:50 GMT on Thursday, September 29. That’s 2:50 pm MDT or 4:50 pm EDT. The slow descent will take about 14 hours, with the expected cometary contact within 20 minutes of 10:40 GMT on Friday. This is 4:40 am MDT or 6:40 am EDT.  You can follow this online here: http://go.nasa.gov/2cLhy0q67PChuryumovGerasimenko_Ma'at_region

The cometary nucleus is approximately 4.3 by 4.1 km (2.7 by 2.5 mi) in size, and composed primarily of dust-covered ice. 67P/Churyumov–Gerasimenko is a short period comet, reaching its closest point to the Sun every 6.45 years, although never getting bright enough to be seen without a telescope. In fact, in its current orbit it never gets as close to the Sun as the Earth, and is essentially just a cometary nucleus without a visible coma or tail. Its orbit has been significantly altered by the gravity of Jupiter, but it likely originated much farther out in the Kuiper Belt.

(All images courtesy of the European Space Agency, ESA)

* Near Earth Asteroid Rendezvous, later rechristened NEAR-Shoemaker in honor of pioneering Earth-space science Eugene Shoemaker

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The Equinox: When day and night are not equal

Let’s try this again…. this was originally posted on September 20, 2012, but it is completely valid today with slight changes to the date and time.

A lot of people know that on the Equinox, every location on Earth is supposed to get 12 hours of daylight. In fact, the term “Equinox” means “equal night,” signifying that the period of night should equal the period of daytime, and since the day is 24 hours long, we should have 12 hours of each. This year, the September Equinox occurs at exactly at 8:21 a.m. MDT on Thursday, September 22 (2016). At that moment, Autumn or Fall begins for the Earth’s Northern Hemisphere. [Note that I avoid calling it the “Autumnal Equinox” simply because that is true only for half of the Earth. In the other half, the Southern Hemisphere, the same event marks the transition from Winter to Spring.]

MWSnap150 2012-09-20, 09_47_30So it might be expected that September 22 would have exactly (or almost) 12 hours of possible sunshine and 12 hours of night. But it doesn’t. A simple check of sunrise and sunset times will show that there are more than exactly 12 hours on that date. In Denver, the Sun rises at 6:48 a.m. and sets at 6:56 p.m., with each time rounded to the nearest minute. This yields 12 hours and 8 minutes.

In reality, no day has exactly 12 hours of sunshine. In Denver, the day that most closely matches this is September 25 this year. (It changes a bit from year to year, due mostly to the Leap Year cycle). Rounded to the nearest minute, the Sun rises at 6:51 a.m. and sets at 6:51 p.m. on September 25th in Denver. Much the same is true for other cities. (See link below.)

So are astronomers, who normally are very accurate, wrong on this one? Is the Equinox really on the 25th this year?

No, the astronomers are correct. The Equinox occurs at  8:21 a.m. MDT on Thursday, September 22 (2016).  Astronomy is an observational science, but in this case, observations can be misleading. The times of sunrise and sunset are given for the apparent rise and set times. In other words, given clear skies and an unobstructed horizon, the times given are those that the Sun would be seen to rise and set. The key word here is “apparent.”

The fact is that the Sun appears to rise a few minutes before it actually crosses the eastern horizon, and stays in the sky a few minutes after it has, in fact, disappeared below the western horizon.

The reason lies with the Earth’s atmosphere, which bends the sunlight around the horizon. It is somewhat like peering around the corner with a periscope. The atmosphere bends the Sun’s light around the horizon slightly, such that the Sun appears in the East a couple of minutes before it actually rises. In the evening the reverse happens – the Sun’s light is bent around the horizon to cause the Sun to remain visible for a few minutes after it has really dipped below the western horizon.

This is known as refraction, a fancy way of saying bending, due to the atmosphere. It is the same effect that causes a pencil stuck in a glass of water to appear offset slightly. Truth is, when you sight along the horizon, you are looking through much more atmosphere then when you look high in the sky. Because of this, the refractive effect is much greater near the horizon, even allowing objects that are technically just beyond the horizon to appear.

Thus on the day of the Equinox the theoretical period of sunlight is 12 hours, but because of this refraction or bending of sunlight around the horizon, the apparent day is longer.

However, at this time of year the days are getting shorter. So a few days later, when the theoretical period of sunshine should be significantly less than 12 hours, the lengthening due to refraction brings it up to 12 hours even (or almost).

So the Equinox occurs on the 22nd, but the day with 12 hours of sunshine comes 3 days later. (Again, this can vary a bit with geographic location…. for example, in Houston it is on the 26th). In the Spring, the opposite effect occurs. As days get longer, the observed equinox comes a few days before the official Equinox.

(If you are not lucky enough to live in Denver, you can compute the rise and set times for your location from this US Naval Observatory page: http://aa.usno.navy.mil/data/docs/RS_OneDay.php)

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Think that you are “bad” at math?

USDeptofEd

You are not bad at math

Are you one of those people who tell yourself that you are “bad” at math? Does just the thought of numbers cause you to seize up and maybe start foaming at the mouth?

Relax. You are not bad at math. You have just talked yourself into the belief. Teachers and others may have let you believe it, or may even have encouraged this self-defeating behavior. I do not know why. It’s kind of ridiculous. I’ve even had students seem almost proud of their self-proclaimed ignorance of math (and science). The truly sad thing is simply that anyone would want to think like that.

Apparently there are primary and secondary school teachers and even college instructors who undermine students’ confidence in their math abilities by claiming and displaying their own hatred and contempt for math. This is amazing and very disturbing. If you have ever had such a teacher, I am here to tell you that they were wrong. Math is not some horrible invention of the devil. Instead it is one of the greatest accomplishments of humankind.

Personally, I’m not “bad” at math. I am certainly not a “whiz” at it either, but basic math is simple, easy and oh, so useful. Every adult American — every adult anywhere — should be able to perform simple addition, subtraction, multiplication and division in their heads. I can, and so can you.

You are not “bad” at math. You have talked yourself into the belief. It is a self-fulfilling prophecy. Certainly you can do the math I require for my classes. I don’t require much, and I won’t require anything more than you can handle. But if you continually tell yourself that you can’t, then your mind will accept that assessment and make sure that you get the wrong answers or just give up in despair. That is too bad, because you are better than that. You are smarter than that.

I do not intend to turn this into a pep talk, but I do want to point out this fact and drive it home:

You are not bad at math

Want more? Check out this article from the Washington Post: “Stop telling kids you’re bad at math. You are spreading math anxiety ‘like a virus.’”

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What’s With Gravitational Waves?

Simulation of gravity wave productionThe first observation of “gravitational waves,” a prediction of Einstein’s General Theory of Relativity, was announced in February, 2016.

Although the significance may be unclear to many, the discovery of these immensely tiny ripples in the fabric of space were the last major part of the theory to be confirmed by actual observation. They amount to slight distortions in space. Some have likened them to a sound wave traveling through air or water. However, sound waves are moving compressional waves (alternating areas of compression and rarefaction) in a medium like water or air. Gravitational waves are really more like transverse sinusoidal waves similar to ripples on the surface of a pond, although considerably more complicated. And rather than propagating only along the surface of a plane as water ripples propagate across a pond, gravitational waves travel outward in three dimensional space.

While any interaction between gravitating bodies produce gravitational waves, only waves produced by the interaction of massive bodies (such as black holes or massive stars)  out in space are currently within our observational grasp; the ripples are through what we normally consider a vacuum rather than through water or air; and they are phenomenally weak .

Although the discovery is a major breakthrough for physics and astronomy, and may lead to completely new ways of looking at the Universe, the exotic nature of gravitational waves has spawned some misconceptions.

Shortly after the announcement, a student asked me whether or not these waves could be used to explain such things as the occasional loss of communications with satellites, the purported dangers for ships and planes in the so-called “Bermuda Triangle,” and even the turbulence experienced by passengers on commercial airlines.

The following was my response:

Gravitational waves have nothing to do with any of the things you mention. Really. Nothing at all. Gravitational waves are so incredibly weak and faint that they have nothing whatsoever to do with everyday life, and certainly nothing to do with any disappearances in any area such as the so-called “Bermuda Triangle” and such.

Go to some big lake when the water on the surface is completely flat. Now drop a single small grain of sand into the water at one edge. How easy do you think it would be for someone on the opposite side of the lake to detect the ripple? Now just consider that the gravitational waves recently detected are millions of times fainter and weaker than that. They have no measurable or observable effect on human activities. Einstein himself was convinced that we would never be able to observe them at all.

And again, gravitational waves have nothing whatsoever to do with any loss of communication with satellites (although solar radiation can) and certainly nothing to do with lost aircraft or ships. Many reports of such things are either exaggerated or due to weather conditions and such. We may not have discovered the causes in some cases, but gravitational waves have no effect and it is highly unlikely that they are due to any as yet undiscovered aspect of physics. We may not know all the answers yet, but that doesn’t mean that the answers are anything exotic or due to some unknown force.

Turbulence in airplanes is due to pockets air at different densities, usually caused by uneven heating in the atmosphere, coupled with winds and perhaps other meteorological factors. The causes are complicated, but knowable with our current understanding of ordinary physics.

It is not that we know everything at this point. But we know enough to rule certain things out. There are connections between events and forces that are so subtle and complex that we cannot decipher them easily or at all. In fact there is a mathematic concept known as the “Butterfly Effect” that considers very minor effects that yield large results over time. Even if we were to consider gravitational waves in this context, I don’t think that they would have any effect because they are so small they would be masked and damped out by quantum effects (which is beyond the scope of this class).

For more, see The Landmark Discovery of Gravitational Waves by Brian Greene.

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10 Easy Ways You Can Tell For Yourself That The Earth Is Round

Next time a flat-earth conspiracy theorist confronts you, here are 10 ways to prove that Earth is spherical.

Sourced through Scoop.it from: www.popsci.com

See on Scoop.itStarman’s Miscellania

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Does the Sun Look Bigger Today?

2000px-Seasons.svgIf it seems warmer than you expect for this time of year, it is not because we are closer to the Sun. Of course, you say, how could we be closer to the Sun in January? It’s Winter, so we must be farther from the Sun, right? Wrong.

Every year, the Earth makes its closest orbital "approach" to the Sun in early January. Yes, early January.

For the Northern Hemisphere, that means that the coldest weather of the year normally comes when we are significantly closer to the Sun than in Summer. This is because the Earth’s orbital path is not a perfect circle, but rather is very slightly oval. The average distance to the Sun is about 150 million km, or roughly 93 million miles. But typically it is slightly closer or slightly farther away, depending on where the planet is in the orbit.

Yesterday, January 2, Earth was a little more than 98% of that distance. In other words, we are nearly 2% closer than the yearly average. That’s about 3 million km or nearly 2 million miles closer in early January. In early July, however, we will be same amount, or about 2% farther away. The fact is, we are closer to the Sun in Winter, farther in Summer. It is not our distance from the Sun that determines our seasons.

The real reason for the seasons is the Earth’s tilt on its axis. In Winter, the Northern Hemisphere tilts back, away from the Sun. If I may be anthropomorphic for a moment, it’s almost like the planet (or more specifically, the Northern hemisphere) were repulsed in fear. This causes the Sun has a shorter path in the sky, rises to a lower altitude at noon, casts longer shadows with slightly less heat and light reaching the surface of the Earth. Barring other factors, such as global climate change and localized weather anomalies, this causes lower temperatures. In Summer, the opposite situation prevails, and the Northern hemisphere tilts sunward as if listening intently. In this arrangement, the Sun takes longer to reach a higher point in the sky, shadows are shorter, and sunlight is more intense due to less absorption in the atmosphere. The result of course is higher summer temperatures.

My point is simply that our yearly variations in distance to the Sun have very little affect on temperatures through the year. The real reason, first and foremost, is the planet’s tilt toward (Summer) and away from (Winter) the Sun. Other factors for variations in this pattern include changes in the atmosphere due to volcanic and geothermal processes, and modifications to the atmospheric content due to biologic activities including the burning of fossil fuels and increased methane due to livestock.

The odd weather some areas currently are having — whether unusually warm or unusually cold or unusually wet or unusually dry — is due to some factor other than our distance from the Sun. Whether climate change is the specific cause of all of these unexpected weather events and conditions is unknown. But it is clear that a change in climate regime — for example, from the relatively clement climate we have grown to consider normal to the warmer world envisaged by most atmospheric scientists — will entail decades or more of wild and unexpected weather events.

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The Difference between Science and Pseudoscience

Discerning science from pseudoscience

Sourced through Scoop.it from: www.scientificamerican.com

See on Scoop.itStarman’s Miscellania

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