Urania

A blog named for the muse of Astronomy containing musings by an astronomer

Archive for the ‘Science Education’


Another Update to Clear Sky Clock (Now Supporting Accented Characters) 0

Posted on October 03, 2011 by Juan

A Quebec-er informed me that certain sites in Quebec were not showing up in my Clear Sky Clock widget.  An investigation revealed that JavaScript doesn’t understand Unicode characters in its regular expressions.  A bit of thinking revealed a much simply regular expression that would match the site names from Attilla Danko’s Clear Sky Chart website.  So I have fixed the widget to support all accented characters, and for that matter, any name that the Clear Sky Chart presents.  The accented characters may appear as ‘diamonds’ in the menu, but selecting the sites will work now.

You can download this MacOS X widget from here.

If you have the old version installed, you can simply quit the widget, then replace the installed widget with this one.  You may have to log out and log back in for the new version of the Clear Sky Clock to be loaded after installing the new version.

Ripley’s Believe it or Not Understatement 0

Posted on March 30, 2011 by Juan

Astronomically Offensive Panel from March 30, 2011 Ripley's Believe It or Not comicToday’s Ripley’s Believe It or Not comic contained an understatement of extraordinary proportions.  I include a copy of the panel of particular interest to me.  It states the “unbelievable” fact that

By driving at 100 miles per hour in a car, if it were possible, it would take more than 28 years to reach the nearest star – Proxima Centauri.

This implies that you would get there in a little more than 28 years.  Unfortunately, this is horrifically off the mark!

Let’s see, at 100 miles per hour, you go 876,600 miles per year (assuming 365.25 days per year and 24 hours per day).  In 28 years you have gone about 24.5 million miles.  That doesn’t even get you to Venus, the closest planet, which at closest approach is about 25.5 million miles away!

This is a problem a lot of my incoming students have, they don’t realize just how “astronomical” astronomical distances tend to be.  Let’s use a few examples with this 100 mile per hour space car.

  • Driving to the Moon: The closest heavenly body is the moon, at an average distance of about 240,000 miles.  At 100 miles per hour, it will take this space car 2400 hours or approximately 100 days to reach the Moon. The Apollo astronauts took just over 3 days to get there!   I guess the Saturn V rocket moved them a bit faster than 100 miles per hour!
  • Driving to the Sun: The distance to the nearest star, the Sun, (yeah, Ripley’s got this one wrong too!) is approximately 93 million miles.  This distance is so huge, astronomers often replace miles with “astronomical units” where one “AU” is the average distance to the Sun.  It would take this space car 930,000 hours or just over 106 years to travel 1 AU to reach the Sun. So remember that, about 106 years to drive 1 AU (NOTE: Actually, that is the time to reach the center of the Sun, shave off half a year if you just want to reach the surface of the Sun.  Yes, the Sun is that big! It’s a star baby!)
  • Driving to the Neptune: The minimum distance to Neptune, the furthest planet out is approximately 28.8 AU.  So you are looking at a travel time in this space car of about 3050 years.
  • Driving to the Edge of the Solar System: The farthest large object in the solar system that I am aware of is Eris, the dwarf planet.  It’s average distance from us is about 67.7 AU or a drive time of about 7175 years.
  • Driving to Proxima Centauri: But all these distances pale in comparison to the distance to nearest star other than the Sun, Proxima Centauri.  Proxima Centrauri is 4.2 light years away.  1 Light year is the distance light travels in one year and light is the fastest thing in the universe.  Light travels about 186, 282 miles per second or 5,878,625,372,000 miles per year.  This works out to about  63240 AU per light year, so the distance to Proxima Centauri is about 265,600 AU!  This is enormous!  It would take Ripley’s space car traveling 100 miles per hour over 28 million years to get to Proxima Centauri.  “More than 28 years” indeed!

In all honestly, I suspect a typo on behalf of Ripley’s Believe It or Not (after all, that word “millions” is hard to fit in the space provided, might as well drop it), but this is illuminating to say the least!!!

I’ll close with an analogy I use in my intro astronomy classes.  If we shrunk the Sun to be the size of a tennis ball, the Earth would be a small dot (roughly the size of a printed ‘period’ at the end of a sentence) about 38 feet away.  The entire solar system lies within 2000 feet of the tennis ball.  Proxima Centauri would be 1185 miles away.  Its a long distance between star systems compared to the distances between planets.

[Edit: Fixed a stupid error because I used kilometers like a good scientist, but normal Americans use miles.]

Asymmetric Thick Disk Project Bears Fruit 0

Posted on March 15, 2011 by Juan

Today the collaboration I am in published the last two papers (here and here) in our series of papers on the Asymmetric Thick Disk Project, a project which consumed the last four years of my research life.  I have posted a web page including links to the papers and data products from this project on my website here, but here is a copy of the writeup, which I thought turned out quite nice.

History of the Asymmetric Thick Disk

In 1996, Jeff Larsen (then at U Minnesota) and Roberta Humphreys (U Minnesota) discovered “a large and significant asymmetry in the number of stars in the first quadrant I of the galaxy compared to complementary longitudes on the other side of the center-anticenter line.” This work, focusing on probable thick disk stars 30 degrees above the plane of the galaxy showed a 30% excess in stars in the first quadrant versus the corresponding field in the fourth quadrant covering 90 degrees of galactic longitude! (Larsen and Humphreys 1996)

Followup work by Jennifer Parker (then at U Minnesota), Roberta Humphreys, and Jeff Larsen showed that the asymmetry in star counts extended over an even larger part of the sky and “While the region of the asymmetric distribution is somewhat irregular in shape, it is also fairly uniform, stretching over several hundred square degrees on the sky. It is therefore a major substructure in the Galaxy due to more than small-scale clumpiness in the thick disk or inner halo” (Parker, Humphreys, and Larsen 2003). Furthermore, they obtained spectra for 741 stars scattered across these fields. Using the spectral analysis pipeline developed by their collaborator, Tim Beers, they were able to use the metallicity estimates from the spectra to show most of the stars in the sample were Thick Disk stars. Isolating the thick disk stars, they demonstrated that the ” VLSR velocities reveals a significant lag of approximately 80 to 90 km/s in the direction of Galactic rotation for the thick-disk stars in quadrant I, while in quadrant IV, the same population has only a approximately 20 km/s lag confirming the kinematic asymmetry between the two directions” (Parker, Humphreys, and Beers 2004).

So by 2004 it was clear there was a significant feature in the Thick Disk of the Milky Way that was causing an asymmetry in both the star counts and kinematics of the thick disk. At the end of Parker, Humphreys, and Beers (2004), three possibie explanations were proposed for the asymmetry:

  1. The asymmetry is due to a fossil remnant of a merger passng through Quadrant I.
  2. The thick disk and/or halo is triaxial with the major axis in Quadrant I, thus they asymmetry just reflects that the long axis of the triaxial distribution is nearer to us in Quadrant I than Quadrant IV.
  3. The asymmetry is due to a “gravitational wake” caused by the interaction of the thick-disk/inner halo stars with the bar in the disk, which is in Quadrant I, but lies a few kpc beyond the thick disk stars in the asymmetry.

The “Mapping the Asymmetric Thick Disk” Project

Figure 11
Figure 1 [Click Image for Full Size Version]:
The location of excess for faint “Blue” stars with (top) 500 pc < Z < 1500 pc, (middle) 1500 pc < Z < 2500 pc, and (bottom) 2500 pc < Z < 4000 pc shown overlaid on the density contours of the bar in the Disk as traced by IRAS AGB stars from Weinberg (1992). All figures are in galactocentric Cartesian coordinates. (Figure 11 from Larsen, Cabanela, and Humphreys 2011)

In 2006, Roberta Humphreys (U Minnesota), Jeff Larsen (US Naval Academy), and Juan Cabanela (then at St. Cloud State University, currently at Minnesota State University Moorhead) proposed to NSF for a collaborative project to determine the spatial extent of the asymmetry both in star counts and kinematics and to better constrain the origin of the spatial and kinematic asymmetry. This project focused on obtaining (1) multibandpass CCD observations of 63 roughly 1 degree square fields to extend the star counts to deeper magnitudes and (2) obtaining high resolution spectra of several thousands stars in these fields to allow a more extensive investigation of the kinematics of this feature.

By 2008, it was clear the stellar asymmetry had been confirmed by Juric et al (2008) using the Sloan Digital Sky Survey (SDSS). However, their interpretation of the excess in the star counts as a ringlike structure is not supported by critical complementary data in the fourth quadrant, which is not covered by the SDSS. Therefore, we published a short letter (Larsen, Humphreys, and Cabanela 2008) to present stellar density maps from the Minnesota Automated Plate Scanner Catalog of the POSS I showing that the over density does not extend into the fourth quadrant and therefore the over density is most probably not a ring. The asymmetry feature was named the Hercules Thick-Disk Cloud.

Our initial analysis of the star count data focused on searching for a clear signature of triaxiality, an asymmetry in the star counts that extended to higher and higher Galactic longitude. However we found no evidence for an excess of faint blue stars at l≥55° including the faintest magnitude interval. This demonstrated the asymmetry’s spatial limits and ruled out a triaxial thick disk as a likely explanation of the excess of Thick Disk stars in Quadrant I (Larsen et al. 2010).

By 2010, we had obtained multi-color UBVR photometry for 1.2 million stars in 63 fields approximately 1 square degree each. This extensive star count dataset allowed us to determine the spatial extent of the over density across and along the line of sight, and estimate the size and mass of the Hercules Thick Disk Cloud. Using photometric parallaxes we determined the stars responsible for the excess are between 1 and 6 kiloparsecs from the Sun, 0.5 – 4 kpc above the Galactic plane, and extend approximately 3-4 kiloparsecs across our line of sight (See Figure 1). This is a major substructure in the Galaxy. The distribution of the excess along our sight lines corresponds with the density contours of the bar in the Disk, and its most distant stars are directly over the bar. We also see through the Cloud to its far side. Over the entire 500 square degrees of sky containing the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses of material. If the over density is associated with the bar, it would exceed 1.4 billion stars and more than than 50 million solar masses. (Larsen, Cabanela, and Humphreys 2011)

Figure 10
Figure 2 [Click Image for Full Size Version]: Mean VLSR velocity as a function of distance from the Sun for the thick disk stars in the first quadrant. Note the turnover or shift to less negative velocities at distances greater than 4 kpc. (Figure 10 from Humphreys, Beers, Cabanela, Grammer, Davidson, Lee, and Larsen 2011)

By the end of this project we had also obtained radial velocities and derived metallicity parameters for over 4000 Thick Disk-candidate stars in Quadrant I (hereafter Q1), above and below the plane and in Quadrant IV (hereafter Q4) above the plane. Using these spectroscopic observations, we have confirmed the corresponding kinematic asymmetry first reported by Parker et al. (2004), extended to greater distances and with more spatial coverage. The metallicity parameters allowed us to separate the stars by population type: Halo, Thick Disk, Metal-Weak Thick Disk, and (Thin) Disk stars. The Thick Disk stars in Q1 have a rotational lag of 60 – 70 km/s relative to circular rotation, and the Metal-Weak Thick Disk stars have an even greater lag of 100 km/s. Both lag their corresponding populations in Q4 by about 30 km/s. Interestingly, the Disk stars in Q1 also appear to participate in the rotational lag by about 30 km/s. The enhanced rotational lag for the Thick Disk in Q1 extends to 4 kpc or more from the Sun. At 3 to 4 kpc, our sight lines extend above the density contours on the near side of the bar, and as our lines of sight pass directly over the bar the rotational lag appears to decrease (See Figure 2).This is consistent with a “gravitational wake” induced by the rotating bar in the Disk which would trap and pile up stars behind it. (Humphreys, Beers, Cabanela, Grammer, Davidson, Lee, and Larsen 2011)

Summary of Our Conclusions:

When we started this project in 2004, there were three proposed explanations for the asymmetry in the star counts and kinematics of the Thick Disk stars: (1) a fossil remnant, (2) a triaxial Thick Disk or Halo, or (3) a dynamical interaction of the Thick Disk stars with the stellar bar. Our new deeper star counts across 63 fields extending to higher Galactic latitude and longitude than previous plate based work, eliminated a Triaxial Thick Disk as an explanation of the observed star count asymmetry. Our spectroscopic observations of over 4000 Thick Disk-candidate stars showed the kinematics of these stars in the asymmetry were strongly tied to their position relative to the stellar bar of the Galaxy in a way that is consistent with a “gravitational wake” induced by the stellar bar in the Disk. Based on our observational evidence, we conclude the best explanation of the Hercules Thick Disk Cloud is that it is the result of the dynamical interaction of the Thick Disk with the stellar bar.

Cool Physics demos site 0

Posted on March 02, 2011 by Juan

I am always on the look out for inspiration for physics demos for my classes.

One my my students, Ben, just walked into my office to tell me to check out Fizik.si.  This is the English version of a Slovakian website which has a bunch of information on Physics demos.  The cool part is the science videos page which presents a few videos of physics demos (no audio in the videos).  Don’t forget to check out the links on the right hand side of the page for demos in other areas.

Ben specifically pointed me to this video:

This video demonstrates total internal reflection of a laser beam being bent by a column of water leaking out of a pop bottle, just like a fiber optic cable.  Cool ideas abound on this website.

How a scientist sees the world… 0

Posted on June 12, 2010 by Juan

When I first started teaching at Saint Cloud State over a decade ago, I worked with a fellow named Ted Bunn. He is a theorist, which of course means as a observational astronomer that I have to joke about how all he had to do to get a Ph.D. was “invent a particle.” The truth is however that theorists sometimes amaze me. It has taken me a decade a teaching to feel like I really understand undergraduate physics. These guys get there quicker.

Anyway, Ted now keeps a blog which often has what I find to be insightful little posts one what it is like to be a scientist. Today (June 12, 2010) Ted posted a short post about an Abstruse Goose comic about how scientists view the world:

Abstruse Goose 275

Ted then quotes Richard Feynman on something that I think is very true about scientists:

I have a friend who’s an artist, and he sometimes takes a view which I don’t agree with. He’ll hold up a flower and say, ‘Look how beautiful it is,’ and I’ll agree. But then he’ll say, ‘I, as an artist, can see how beautiful a flower is. But you, as a scientist, take it all apart and it becomes dull.’ I think he’s kind of nutty …. There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower. It only adds. I don’t understand how it subtracts. (From What Do You Care What Other People Think?)

I’ll admit, I don’t quite see the world as equations as implied by the figure, but I am constantly fascinated by trying to understand “how things work.”  Earlier this week, I was mowing the grass and I started wondering “what are the minimal conditions necessary for a planet to form on which grass could grow?”  I started thinking about the need for the planet to be composed of the right materials, that is rock.  For a planet to be rocky, there needs to be  heavier elements like silicon and iron in the early solar nebula.  The universe started with no silicon or iron, these elements are forged at the centers of high mass starts and then expelled into the interstellar medium when these high-mass stars explode in supernova.  This means grass can only grow in a universe that has been around long enough for a few generations of high-mass stars to have lived there lives so that the fraction of heavier elements is high enough for rocky worlds to form…  This thought process  happened in a span of maybe 15 seconds… and I didn’t even get started on considering all the other factors which actually affect the ability for a rocky world to harbor life.  Scientists really do get to awe at the universe around them in a way other people don’t.

STS-131 Re-Entry over Minnesota !?! 0

Posted on April 19, 2010 by admin

[Addendum: NASA TV reports showers within 30 miles of Kennedy Space Center means landing on Orbit 237 has been cancelled. 🙁 – Updated at 5:57 am CDT, April 20. The landing on Orbit 238 looks more likely. Unfortunately for us, that takes the Shuttle far to the west of us during its landing.]

What’s going on with this page? The Space Shuttle Discovery was not able to land on the morning of Monday, April 19 due to bad weather atthe Kennedy Space Center. This however means we in Minnesota now have a good chance to see and maybe even hear the Space Shuttle Discovery re-enter the atmosphere in the early morning of Tuesday, April 20 in the half-hour before sunrise!

How will we know if the re-entry of the Space Shuttle will be over Minnesota? You can check the STS-131 Landing Blog. By 5:31 am CDT the Space ShuttleDiscovery will have to start its deorbit burn, so we should know by then if the landing will be over Minnesota. [Addendum: NASA TV reports showers within 30 miles of Kennedy Space Center means landing on Orbit 237 has been cancelled. 🙁 – Updated at 5:57 am CDT, April 20. The landing on Orbit 238 looks more likely.]

What is the Path the Space Shuttle will follow During Re-Entry? The first landing opportunity for the Space Shuttle Discovery comes during Orbit 237 and would follow the path shown below (From NASA’s STS-131 Ground Tracks page)

What do you mean “hear” the space shuttle? If the Space Shuttle passes over Minnesota, it will have slowed down a bit already, but it will still be traveling about 13,600 miles per hour or a bit over Mach 18!  As such, even if we don’t see the Space Shuttle, we may in fact hear the twin sonic booms about half a second apart of the re-entry a few minutes after it flies overhead since the shuttle will be only about 45 miles overhead!  There are two sonic booms, one generated by compression of air near the nose of the Shuttle, and another by compression near the tail.  Its not just me, AccuWeather is claiming we might well hear the sonic boom! Furthermore, Space.com has this article on the (now aborted) entry that was going to be over the Dakotas on Monday morning, and it says the first effects of Earth’s atmosphere on the Space Shuttle are at an altitude of about 75 miles. Since it would be only about 44 miles over Minnesota, I suspect we might well hear it. I figure if the Space Shuttle is at 44 miles and sound takes about 5 seconds per mile, we should hear any sonic boom about 2 to 3 minutes to get to the ground (WARNING: I am not taking into account variations in the speed of sound due to varying air density/temperature. I could be off by up to a minute).

What do the twin sonic booms sound like? Here is a YouTube recording of the Shuttle’s twin sonic boom. From what I have read, the twin sonic booms can be heard about 40 miles to either side of the flight path in the right situations.

When will the Space Shuttle Pass over Minnesota if it does Re-Enter over Minnesota? If the Space Shuttle Discovery re-enters the Earth’s atmosphere during Orbit 237, the NASA Human Space Flight Realtime data page tells us the following:

 

Details for the Fargo-Moorhead Area:

The Space Shuttle will come over the horizon in the northwest at 6:12:58 am CDT in the northwest. However, it will not clear the Earth’s shadow until about 30 seconds later at 06:13:29 am CDT. It will appear to speed up as it rises in the sky over the next 2 minutes until it is almost overhead. The closest approach will be at 6:15:16 am CDT when the Shuttle is only 43 miles away when it 71 degrees above the horizon (almost overhead) a little bit to the northwest moving toward the southeast! The Shuttle will remain over the horizon until 6:17:50 am CDT. Fortunately for Fargo-Moorhead, sunrise is at 6:30 am CDT, so we have the best shot in Minnesota for seeing the Shuttle in dark skies. It may still be difficult to spot given the dawn sky. if you don’t see it, be sure to stick around long enough listen for the sonic boom a few minutes later (about 6:17 to 6:19 am it should reach the ground)! Details on the passage are listed below (azimuth is angle east of north, elevation is angle above the horizon).

Local Time Azimuth Elevation Range Height of Sun above Horizon (as seen by Shuttle) Angle between Sun and Shuttle
Deg E of N Deg Miles Deg Deg
Tue-Apr-20@06:12:58 297.2 0.3 566 -1.2 158.6
Tue-Apr-20@06:12:58 297.5 1.3 503 -0.5 158
Tue-Apr-20@06:13:29 297.8 2.5 440 0.1 157.5
Tue-Apr-20@06:13:44 298.1 3.8 378 0.7 156.9
Tue-Apr-20@06:13:59 298.4 5.5 317 1.3 156.3
Tue-Apr-20@06:14:15 298.7 7.7 256 1.9 155.8
Tue-Apr-20@06:14:30 299 11 197 2.5 155.2
Tue-Apr-20@06:14:45 299.3 16.6 138 3.1 154.6
Tue-Apr-20@06:15:01 299.6 29.2 84 3.7 154
Tue-Apr-20@06:15:16 299.7 71 43 4.3 153.4
Tue-Apr-20@06:15:31 120.5 42.9 60 4.8 152.8
Tue-Apr-20@06:15:47 120.7 21.3 109 5.3 152.2
Tue-Apr-20@06:16:02 121.1 13.3 163 5.9 151.5
Tue-Apr-20@06:16:17 121.4 9.1 217 6.4 150.9
Tue-Apr-20@06:16:33 121.8 6.5 271 6.9 150.3
Tue-Apr-20@06:16:48 122.2 4.7 325 7.3 149.7
Tue-Apr-20@06:17:04 122.6 3.2 378 7.8 149.1
Tue-Apr-20@06:17:19 123 2.1 430 8.2 148.5
Tue-Apr-20@06:17:34 123.4 1.1 481 8.7 147.9
Tue-Apr-20@06:17:50 123.8 0.3 532 9 147.3

 

Details for the Twin Cities Area:

The Space Shuttle will come over the horizon in the northwest at 6:14 am CDT in the northwest and it will appear to speed up as it rises over the next 2 minutes until it is almost overhead. The closest approach will be at 6:16:17 AM when the Shuttle is only 44 miles away when it 65 degrees above the northeastern horizon (about 2/3 of the way to the zenith from the horizon) moving toward the southeast! The Shuttle will remain over the horizon until almost 6:19 am CDT. Unfortunately sunrise is at 6:19 am CDT, so you will be fighting the intense dawn sky light to see the Shuttle. However, listen for the sonic boom a few minutes later! Details on the passage are listed below (azimuth is angle east of north, elevation is angle above the horizon).

Local Time Azimuth Elevation Range Height of Sun above Horizon (as seen by Shuttle) Angle between Sun and Shuttle
Deg E of N Deg Miles Deg Deg
Tue-Apr-20@06:13:59 304.1 0.8 528 1.3 155
Tue-Apr-20@06:13:59 304.7 1.9 467 1.9 154.5
Tue-Apr-20@06:14:30 305.4 3 407 2.5 153.9
Tue-Apr-20@06:14:45 306.2 4.4 348 3.1 153.4
Tue-Apr-20@06:15:01 307.2 6.2 289 3.7 152.8
Tue-Apr-20@06:15:16 308.5 8.7 231 4.3 152.2
Tue-Apr-20@06:15:31 310.5 12.4 175 4.8 151.7
Tue-Apr-20@06:15:47 314 19 120 5.3 151.1
Tue-Apr-20@06:16:02 323.5 34.4 71 5.9 150.5
Tue-Apr-20@06:16:17 36.9 65.1 44 6.4 150
Tue-Apr-20@06:16:33 107.2 33.9 70 6.9 149.4
Tue-Apr-20@06:16:48 116.5 18.8 118 7.3 148.8
Tue-Apr-20@06:17:04 120.1 12.3 168 7.8 148.3
Tue-Apr-20@06:17:19 122.1 8.7 219 8.2 147.7
Tue-Apr-20@06:17:34 123.5 6.3 270 8.7 147.1
Tue-Apr-20@06:17:50 124.6 4.6 319 9 146.6
Tue-Apr-20@06:18:05 125.5 3.2 368 9.4 146
Tue-Apr-20@06:18:20 126.4 2.1 416 9.8 145.5
Tue-Apr-20@06:18:36 127.1 1.2 463 10.1 145
Tue-Apr-20@06:18:51 127.9 0.4 509 10.4 144.5

 

Details for the Rochester Area:

The Space Shuttle will come over the horizon in the northwest at 6:14 am CDT in the northwest and it will appear to speed up as it rises over the next 2 minutes until it is almost overhead. The closest approach will be at 6:16:33 AM when the Shuttle is only 65 miles away when it 37 degrees above the northern horizon (about 1/3 of the way to the zenith from the horizon) moving toward the southeast! The Shuttle will remain over the horizon until almost 6:19 am CDT. Unfortunately sunrise is at 6:18 am CDT, so you may lose the Space Shuttle in the dawn glare. However, listen for the sonic boom a few minutes later! Details on the passage are listed below (azimuth is angle east of north, elevation is angle above the horizon).

Local Time Azimuth Elevation Range Height of Sun above Horizon (as seen by Shuttle) Angle between Sun and Shuttle
Deg E of N Deg Miles Deg Deg
Tue-Apr-20@06:14:15 308.7 0.6 538 1.9 154.2
Tue-Apr-20@06:14:15 309.7 1.6 479 2.5 153.7
Tue-Apr-20@06:14:45 310.9 2.7 420 3.1 153.1
Tue-Apr-20@06:15:01 312.4 4 361 3.7 152.6
Tue-Apr-20@06:15:16 314.3 5.6 304 4.3 152
Tue-Apr-20@06:15:31 316.9 7.8 248 4.8 151.5
Tue-Apr-20@06:15:47 320.7 10.8 193 5.3 150.9
Tue-Apr-20@06:16:02 327.3 15.7 141 5.9 150.4
Tue-Apr-20@06:16:17 341.2 24.4 95 6.4 149.8
Tue-Apr-20@06:16:33 18.6 37.2 65 6.9 149.3
Tue-Apr-20@06:16:48 74.6 32.1 73 7.3 148.7
Tue-Apr-20@06:17:04 99.2 20.1 110 7.8 148.2
Tue-Apr-20@06:17:19 109.1 13.4 156 8.2 147.7
Tue-Apr-20@06:17:34 114.4 9.5 203 8.6 147.1
Tue-Apr-20@06:17:50 117.7 6.9 252 9 146.6
Tue-Apr-20@06:18:05 120.1 5.1 299 9.4 146.1
Tue-Apr-20@06:18:20 121.9 3.7 346 9.8 145.6
Tue-Apr-20@06:18:36 123.4 2.6 392 10.1 145.1
Tue-Apr-20@06:18:51 124.7 1.6 437 10.4 144.6
Tue-Apr-20@06:19:06 125.9 0.8 481 10.7 144.1
Tue-Apr-20@06:19:22 127 0.1 524 11 143.6

Science of the Olympic Winter Games 0

Posted on February 17, 2010 by admin

This is one of the cooler websites I have seen recently. My kids and I have been watching some of the Olympics on TV. The National Science Founds is hosting a 16-part video series put together by NBC on the Science of the Olympic games, which describes all the physics and mathematics behind Olympic sports including how equipment can make a difference in performance. Cool stuff and a nice contribution by the NSF and NBC to educators.

June Storms 0

Posted on June 15, 2008 by Juan

We had a set of hard storms come through yesterday afternoon. I was doing SkyWarn spotting with the local hams. I think (but will leave it to experts to confirm) that the structure under the smooth part of the storm (“the shelf) is a wall cloud. For a sense of scale, this is 8 photos stitched together covering above a fifth of my horizon and the leading edge of this storm when it was about five miles away.. Shortly after I shot this picture, the sirens went off. Rotation was spotted, but luckily, no funnel cloud touched down. Thankfully, while the storm blew through at 60 miles per hour, we had no significant damage… Still, it looked mean…

June 14, 2008 Storm

Addendum: I sent the picture to Greg Gust, who runs some of the SkyWarn stuff for the National Weather Service in Grand Forks. He sent me these additional comments:

Most of the structure is a classic shelf cloud on the leading edge of a line of thunderstorms… this the widespread strong to severe winds as it came through. One the south end was the feature that we believe was a wall cloud… rotating updraft… and was what prompted us to issue the Tornado Warning across the southern part of Fargo and Moorhead.

[Added August 9,2008] It appears at least two people saw this wall cloud and posted videos on YouTube. I have embedded them below.

This first video is from “bluemanhal” and contains some audio. Notice how far he has to pan the camera to see this. My photo was a panorama about 150 degrees, which loses its perspective in the image:

This second video is from “cpilotkid” and appears to have been shot from the West Acres Mall parking lot, but again notice how far he has to pan to get the entire wall cloud:

The Difference between “Cooking” Data and Purging Bad Data 0

Posted on March 06, 2008 by Juan

There is a great article online at Scientific American’s website investigating the claim that Arthur Eddington and Frank Dyson might have “cooked” the data from their solar eclipse observations in 1919 in a way that supported Einstein’s (then new) General Theory of Relativity:

On May 29, 1919, two British expeditions, positioned on opposite sides of the planet, aimed telescopes at the sun during a total eclipse. Their mission: to test a radical theory of gravity dreamed up by a former patent clerk, who predicted that passing starlight should bend toward the sun. Their results, announced that November, vaulted Albert Einstein into the public consciousness and confirmed one of the most spectacular experimental successes in the history of science.

In recent decades, however, some science historians have argued that astronomer Sir Arthur Eddington, the junior member of the 1919 expedition, believed so strongly in Einstein’s theory of general relativity that he discounted data that clashed with it. [From Fact or Fiction: Did Researchers Cook Data from the First Test of General Relativity?]

The nice thing is this article illustrates one of the less well-appreciated challenges facing the functional scientist: distinguishing between bad data and data that conflicts with your theoretical expectations. Bad data, like other things in life, just happens. And when it happens, it can be a pain to deal with. How do you know when the data is “bad” (that is, the result of a problem at the telescope or a glitch in your software) versus when the data simply conflicts with your theory? In one case, getting rid of the data makes sense. However, being over-eager to reject conflicting data may make you reject a completely compatible alternative interpretation to your observation. Furthermore, if your data seem to support a controversial theory, you should be fairly confident your results are not the result of “bad” data. As Carl Sagan said in Cosmos , “Extraordinary claims require extraordinary evidence.” You have to be pretty confident you haven’t made a mistake if your data strays far from what you expect. Knowing the difference between “bad” data and data that supports a different theory the human part of the science I try to teach my students about. It is also the reason peer-review is such an incredibly important part of the scientific process.

By the way, the verdict of the article’s author is that Eddington and Dyson did the right thing. It turns out it was actually Dyson, who was initially inclined against Einstein’s theory, who made the decision to toss the bad data out. The final results when published[1] supported Einstein’s General Theory of Relativity, which still stands as the most well-supported model for gravitation to this day.

Linknotes:

  1. A Determination of the Deflection of Light by the Sun’s Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919 – Dyson, F. W.; Eddington, A. S.; Davidson, C. 1920, Philosophical Transactions of the Royal Society of London. Series A, 220, 291

Sign this Petition to Encourage a Presidential Science Debate 0

Posted on February 15, 2008 by Juan
We live in a strange era where some presidential candidates brag about their complete absence of knowledge of science but yet admit science plays such a gigantic role in the possible improvement (or destruction) of society. Given this election climate, the Union of Concerned Scientists is asking the presidential candidates to participate in a debate focused solely on the role of science-related policy in their proposed administrations. And they want them to do it before the presidential primaries in Pennsylvania. The full text of the petition says:
Dear presidential candidate,
Given the many urgent scientific and technological challenges facing America and the rest of the world, the increasing need for accurate scientific information in political decision making, and the vital role scientific innovation plays in spurring economic growth and competitiveness, we call for a public debate in which the U.S. presidential candidates share their views on the issues of The Environment, Health and Medicine, and Science and Technology Policy. We would like to hear how, as president, you plan to defend science from political interference, and how you plan to use science to inform your policies. We call on you to participate in Science Debate 2008 in Philadelphia on April 18. If you want to sign it, it’s too late… address removed (May 25, 2012 edit).
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