A vacuum is not nothing. It is only a region of three-dimensional space that is entirely devoid of matter, entirely devoid of particles.
The best laboratory vacuum contains about 25 particles (molecules, atoms) per cubic centimeter (cm3).
The atmosphere on the surface of the Moon (if you can call it that) contains a lot more particles than the best laboratory vacuum: about 40,000 particles per cm3. This extremely tenuous lunar atmosphere is mostly made up of the “noble” gases argon, helium, and neon.
The vacuum of interplanetary space contains about 11 particles per cm3.
The vacuum of interstellar space contains about 1 particle per cm3.
The vacuum of intergalactic space contains about 10-6 particles per cm3. That’s just 10 particles per cubic meter of space.
But what if we could remove all of the particles in a parcel of space? And somehow shield that empty parcel of space from any external electromagnetic fields? What would we have then?
It appears that even completely empty space has some inherent energy associated with it. The vacuum is constantly “seething” with electromagnetic waves of all possible wavelengths, popping into and out of existence on unimaginably short time scales—allowed by Heisenberg’s energy-time uncertainly principle. These “quantum flourishes” may be a intrinsic property of space—as is dark energy. Dark matter, on the other hand, is some weird form of matter that exists within space, exerting gravitational influence but not interacting with normal matter or electromagnetic waves in any other way.
Is there any evidence of this vacuum energy, or is it all theoretical? There are at least three phenomena that point to the intrinsic energy of empty space. (1) The Casimir effect; (2) Spontaneous emission; and (3) The Lamb shift.
The Casimir effect
Take two uncharged conductive plates and put them very close to each other, just a few nanometers apart. Only the shortest wavelengths will be able to exist between the plates, but all wavelengths will exist on the other side of the two plates. Under normal circumstances, this will cause a net force or pressure that pushes the two plates towards one another.
An example of spontaneous emission is an electron transitioning from an excited state to the ground state, emitting a photon. What causes this transition to occur when it does?
The Lamb shift
The Lamb shift is a tiny shift in the energy levels of electrons in hydrogen and other atoms that can’t be explained without considering the interaction of the atom with “empty” space.
Have you ever noticed how it is almost impossible to find documentaries made more than a few years ago? I was doing some reading on the Casimir effect this evening and came across the name of Julian Schwinger (1918-1994), the American theoretical physicist who shared the 1965 Nobel Prize in Physics with Richard Feynman (1918-1988) and Shin’ichirō Tomonaga (1906-1979). I remember, after all these years, that I had enjoyed watching a BBC documentary series that featured Schwinger (as well as George Abell) called Understanding Space and Time. It was broadcast in 1979 or 1980 and featured thirteen 28-minute episodes.
Ground control to Mr. Galileo
As Surely as Columbus Saw America
Pushed to the Limit
Conflict Brought to Light
E = mc2
An Isolated Fact
The Royal Road
At the Frontier
Shades of Black
Measuring Shadows: The Universe Today
A Note of Uncertainty: The Universe Tomorrow
Vanished Brilliance: The Universe Yesterday
Granted, some of this material is now dated, but much of it is still relevant and certainly of historical interest. Why is it (and a host of other documentaries) not available on DVD or for downloading?
We really need a company to fill a different niche alongside The Great Courses, Curiosity Stream, and Netflix. That niche would be to uncover and rerelease past documentaries of merit1, often hosted or presented by historically important individuals. Documentaries such as Understanding Space and Time would be nice to own and watch again.
1One must certainly include many PBS documentaries and older episodes of documentary series—NOVA, for example—that are no longer available.
In little more than six years, another total solar eclipse across the continental U.S. will pass as close as Southern Illinois and Indiana. Like our recent eclipse of August 21, 2017, the next total solar eclipse will also take place on a Monday and, remarkably, just a few minutes earlier in the day. Save the date: April 8, 2024. Actually, not long to wait. Think about what you were doing around December 7, 2011. Can you remember? No question about it, the next six years will go faster than the previous six did. Seems that as we age our sense of time changes, and time seems to go faster and faster.
The point of maximum length of totality for the 2017 eclipse was 12 miles NW of the center of Hopkinsville, Kentucky, where totality lasted 2m40s and the path of totality was 71 miles wide.
The point of maximum length of totality for the 2024 eclipse will be near Nazas, Mexico (in the state of Durango), where totality will last 4m28s and the path of totality will be 123 miles wide. Yes, this will be a longer eclipse!
Remarkably, there is a location in southern Illinois that is on the centerline of both the 2017 and 2024 eclipses! That location is 37°38’32” N, 89°15’55” W, SW of Carbondale, Illinois, near Cedar Lake and the Midland Hills Country Club.
When did a total solar eclipse last grace Dodgeville, Wisconsin? Nearly 639 years ago, on May 16, 1379. The duration of totality was 3m48s. Perhaps the Oneota people then living in this area witnessed the event.
The next total solar eclipse visible from Dodgeville won’t happen for another 654 years. There’ll be annular eclipses in 2048, 2213, 2410, 2421, and 2614. Then, finally, on June 17, 2672, the totally-eclipsed Sun will once again grace the skies of Dodgeville—weather permitting, of course. The duration of the eclipse at Dodgeville will be 2m47s. There will be another annular eclipse in 2678, followed by another total eclipse (duration 3m01s) on June 8, 2681. Then, just two years later there’ll be another total eclipse at Dodgeville: on November 10, 2683 (0m49s). That’s three total eclipses and one annular eclipse visible at Dodgeville in just 11 years!
It may be rare for terrestrial planets to be accompanied by satellites, especially large ones. It is far too early for us to draw any conclusions about terrestrial exoplanets (as no terrestrial exoplanet exomoons have yet been detectable), but in our own solar system, only two planets have no satellites, and they are both terrestrial planets: Mercury and Venus. Mars has two small satellites that are almost certainly captured asteroids from the adjacent asteroid belt rather than primordial moons, and that leaves only the Earth among the terrestrial planets to host a large satellite, though it, too, is almost certainly not primordial. Only the giant planets (Jupiter, Saturn, Uranus, and Neptune) have large systems of satellites, at least some of which may have formed while the planet itself was forming.
Though neither Mercury nor Venus has any natural satellites, Venus is known to have at least four transient quasi-satellites, more generally referred to as co-orbitals. They are:
322756 (2001 CK32)
Comes close to both Earth and Mercury in its eccentric orbit (e=0.38). WikiJPLOrrery
Comes close to both Earth and Mercury in its eccentric orbit (e=0.41). WikiJPLOrrery
Comes close to both Earth and Mercury in its eccentric orbit (e=0.43). WikiJPLOrrery
Comes close to both Earth and Mercury in its very eccentric orbit (e=0.61), and is the only known trojan of Venus, currently residing near its L4 Lagrangian point. WikiJPLOrrery
2015 WZ12 is a possible fifth Venus co-orbital candidate. Observations during the next favorable observing opportunity in November of this year will hopefully better determine its orbit and nature.
Possible Venus co-orbital.
There is concern that there may be many more Venus co-orbitals, as yet undiscovered (and challenging to discover) that pose risks as potentially hazardous asteroids (PHAs) to our planet.
There are no known Mercury co-orbitals. If any do exist, they will be exceedingly difficult to detect since they will always be in the glare of the Sun as seen from Earth.
Asteroids orbiting interior to Mercury’s orbit (a < 0.387 AU) would be called vulcanoids. I say “would be” because none have been discovered yet, though in all fairness, they will be extremely difficult to detect.
A spacecraft orbiting interior to Mercury’s orbit looking outward would be an ideal platform for detecting, inventorying, and characterizing all potentially hazardous asteroids (PHAs) that exist in the inner solar system. A surveillance telescope in a circular orbit 0.30 AU from the Sun would orbit the Sun every 60 days.
The Parker Solar Probe, scheduled to launch later this year, will orbit the Sun between 0.73 AU and an extraordinarily close 0.04 AU, though it will be looking towards the Sun, not away from it. The Near-Earth Object Camera (NEOCam) is a proposed mission to look specifically for PHAs using an infrared telescope from a vantage point at the Sun-Earth L1Lagrangian point.
de la Fuente Marcos, C., & de la Fuente Marcos, R. 2014, MNRAS, 439, 2970
de la Fuente Marcos, C., & de la Fuente Marcos, R. 2017, RNAAS, 1, 3
Sheppard, S., & Trujillo, C. 2009, Icarus, 202, 12
The Mars Exploration Rovers Spirit and Opportunity landed on Mars on January 4, 2004 and January 25, 2004, respectively. Spirit continued operating until contact was lost on March 22, 2010, a total of 2,269 Earth days, which is 2,208 days on Mars (sols)1. Spirit operated on the Martian surface 24.5 times as long as its design life of 90 sols.
Even more amazing: Opportunity has been operating on the Martian surface (as of this publication date) for 5,108 Earth days, which is 4,971 sols. That’s 55.2 times its design life of 90 sols!
Spirit and Opportunity faced their greatest challenge up to that point during the global Martian dust storm of July 2007. Here is what I wrote about it back then.
Spirit and Opportunity‘s Greatest Challenge (7-26-07)
The intrepid Mars Exploration Rovers Spirit and Opportunity—which have been operating on the surface of Mars over 14 times longer than planned—each carry two 8 amp-hour lithium batteries, and these batteries are charged by solar panels. Before dust storms began significantly reducing the amount of sunlight reaching the rovers’ solar panels, they were generating about 700 watt-hours of electricity each day—enough to power a 100-watt light bulb for seven hours. Not much, it may seem, but plenty enough to operate each rover’s internal heaters, motors, scientific instruments, and communication equipment.
In recent weeks, both rovers have seriously been affected by the dust storms, particularly Opportunity which last week was able to generate only 128 watt-hours of electricity on the worst day. With precious little energy to replenish the internal batteries, controllers have hunkered down the rovers to conserve energy for the most critical need—internal heaters to keep the core electronics warm enough to operate. Remember, the average surface temperature on Mars is -85° F!
At press time, weather conditions appear to be improving for both rovers, but there are still worries that the rovers could have been damaged by all that dust blowing at them for days on end.
As it turns out, after the global dust storm of 2007 subsided, the rovers benefited from subsequent “cleaning events” where the winds of Mars blew most of the dust off of the solar panels.
There have been no global dust storms on Mars since 2007; however, another one is anticipated later this year. Hopefully, our intrepid Opportunity will weather the storm and continue to generate enough life-giving power from its precious solar panels .
1A Martian day is called a sol and is slightly longer than an Earth day. A mean solar day on Earth is 24h00m00s, by definition, but a mean solar day on Mars is 24h39m35.244s Earth time. To convert Earth days to Martian sols, divide the number of Earth days by 1.0275.
We live in a society where science is little more than a “spectator sport” for most of us who have an interest in it. Data collection and original research often require substantial investments of time and money, as well as a long-term commitment. Those of us who are already working full time and, in spite of that, have little discretionary income, often find “participatory science” out of reach, no matter how great our enthusiasm or aptitude.
As today’s scientific instruments increasingly generate enormous quantities of data, the people who “do science” for a living are too few in number to analyze all that data. Fortunately, this is one area where “citizen scientists” can help.
There are a number of interesting scientific projects that lend themselves well to “crowd sourcing”, and Zooniverse is a portal to many of them.
Here are the currently active Zooniverse projects in the disciplines of astronomy and physics.
Backyard Worlds: Planet 9
Discover new brown dwarfs and possibly a new solar system planet by scrutinizing images from the Wide-field Infrared Survey Telescope (WISE).
Discover new comets previously misidentified as asteroids by analyzing deep images taken by the Subaru 8.2-meter telescope in Hawaii.
Disk Detective Help search for stars with undiscovered disks of dust around them. These stars show us where to look for planetary systems and how they form.
Galaxy ZooGalaxy Zoo: 3D
Classify galaxies, many of which have never been studied before, and look for unusual features.
Identify and characterize “glitches” in LIGO data to make it easier to identify gravitational wave events.
Help search for unknown exotic particles in data from the Large Hadron Collider (LHC), the world’s largest and most powerful particle collider.
Milky Way Project
Classify images from two infrared space telescopes: the Spitzer Space Telescope (SST) and the Wide-field Infrared Survey Telescope (WISE).
Identify and measure features on the surface of Mars.
Discover transiting exoplanet candidates in data from the Kepler spacecraft.
Radio Galaxy Zoo
Search radio images of galaxies for evidence of jets caused by matter falling into supermassive black holes.
Radio Meteor Zoo
Identify meteors through the reflection of radio waves from their ionization trails.
Solar Stormwatch II
Characterize solar storms and their interaction with the solar wind through the analysis of images from NASA’s twin Solar Terrestrial Relations Observatory (STEREO) spacecraft.
Scrutinize the most recent images collected by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii in comparison to reference images to discover new supernovae that can then be immediately followed by ground-based and space-based telescopes.
All of these projects utilize “machine learning” computer algorithms such as neural networks and random forests (artificial intelligence, or AI) to some extent, and in fact citizen scientist participants help “train” these algorithms so they do a better job of finding or classifying or whatever. For a great introduction to this subject, see “Machines Learning Astronomy” by Sky & Telescope news editor Monica Young in the December 2017 issue, pp. 20-27.
As machine learning algorithms get better and better, they may no longer need citizen scientists to train them.
In the meantime, have fun and contribute to science!
In this year of 2018, the best dates and times for observing the zodiacal light are listed below. The sky must be very clear. The specific times listed are for Dodgeville, Wisconsin.
Fri. Feb. 2
Sat. Feb. 3
Sun. Feb. 4
Mon. Feb. 5
Tue. Feb. 6
Wed. Feb. 7
Thu. Feb. 8
Fri. Feb. 9
Sat. Feb. 10
Sun. Feb. 11
Mon. Feb. 12
Tue. Feb. 13
Wed. Feb. 14
Thu. Feb. 15
Fri. Feb. 16
Sat. Mar. 3
Sun. Mar. 4
Mon. Mar. 5
Tue. Mar. 6
Wed. Mar. 7
Thu. Mar. 8
Fri. Mar. 9
Sat. Mar. 10
Sun. Mar. 11
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Tue. Mar. 13
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Thu. Mar. 15
Fri. Mar. 16
Sat. Mar. 17
Sun. Mar. 18
Mon. Mar. 19
Mon. Apr. 2
Tue. Apr. 3
Wed. Apr. 4
Thu. Apr. 5
Fri. Apr. 6
Sat. Apr. 7
Sun. Apr. 8
Mon. Apr. 9
Tue. Apr. 10
Wed. Apr. 11
Thu. Apr. 12
Fri. Apr. 13
Sat. Apr. 14
Sun. Apr. 15
Mon. Apr. 16
Tue. Apr. 17
Thu. Aug. 9
Fri. Aug. 10
Sat. Aug. 11
Sun. Aug. 12
Mon. Aug. 13
Tue. Aug. 14
Wed. Aug. 15
Thu. Aug. 16
Fri. Aug. 17
Sat. Aug. 18
Sun. Aug. 19
Mon. Aug. 20
Tue. Aug. 21
Wed. Aug. 22
Thu. Aug. 23
Fri. Aug. 24
Sat. Sep. 8
Sun. Sep. 9
Mon. Sep. 10
Tue. Sep. 11
Wed. Sep. 12
Thu. Sep. 13
Fri. Sep. 14
Sat. Sep. 15
Sun. Sep. 16
Mon. Sep. 17
Tue. Sep. 18
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Thu. Sep. 20
Fri. Sep. 21
Sat. Sep. 22
Sun. Sep. 23
Sun. Oct. 7
Mon. Oct. 8
Tue. Oct. 9
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Thu. Oct. 11
Fri. Oct. 12
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Sun. Oct. 14
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Tue. Oct. 16
Wed. Oct. 17
Thu. Oct. 18
Fri. Oct. 19
Sat. Oct. 20
Sun. Oct. 21
Mon. Oct. 22
On the February, March, and April evenings listed above, you will see a broad, faint band of light extending upwards from the western horizon, sloping a little to the left, and reaching nearly halfway to the top of the sky.
On the August, September, and October mornings listed above, you will see a broad, faint band of light extending upwards from the eastern horizon, sloping a little to the right, and reaching nearly halfway to the top of the sky.
It is essential that your view is not spoiled by nearby streetlights, parking lot lights, or dusk-to-damn insecurity lights, nor any city to the west (Feb-Apr) or east (Aug-Oct). Give your eyes a few minutes to adjust to the darkness. Slowly sweeping your eyes back and forth from southwest to northwest (Feb-Apr) or northeast to southeast (Aug-Oct) will help you spot the zodiacal light band. Once spotted, you should be able to see it without moving your head.
On the February, March, and April evenings listed above, the zodiacal light is best seen right at the end of evening twilight, and remains visible for an hour or so after that.
On the August, September, and October mornings listed above, the zodiacal light is best seen about an hour or so before the beginning of morning twilight, right up to the beginning of morning twilight.
While video recording the star Tycho 1311-1818-1 in Taurus on a very cold Thursday evening last week (-4° F) in the hope that asteroid 126561 (2002 CF105) would pass in front of it (it didn’t), I was surprised and delighted to serendipitously record a very slow moving Earth-orbiting satellite crossing the field. Now, in order to see a satellite, it must be illuminated by sunlight. But to see any satellite during the first week of January only 10 minutes before local midnight, it must be very far from the Earth indeed (more on that later).
Here’s a video of the event showing its complete traversal of the field of view:
I’m hoping that one of the good people that frequent the satellite observers’ forum SeeSat-L will be able to identify this unusual object. Requisite to that, of course, are two precise positions at two precise times and the observer’s location.
A very useful online tool provided by the Department of Physics at Virginia Tech allows one to input the right ascension, declination, and x-y coordinates of between 4 and 10 known objects, and it does an astrometric solution across the field so you can determine the right ascension and declination of an unknown object.
At 5 Jan 2018 5:42:58.122 UT, the satellite was located at:
5h45m48.14s +21°45’17.5″ (apparent coordinates, epoch of date).
At 5 Jan 2018 5:50:22.931 UT, the satellite was located at:
5h46m53.98s +21°48’06.3″ (apparent coordinates, epoch of date).
Observer Location: 42°57’36.9″N, 90°08’31.1″ W, 390 m.
Using the satellite coordinates above, and the angular separationcalculator kindly provided by the Indian Institute of Astrophysics, we find that the satellite traversed just 0.2590° in 0.1236 hours. That’s 2.095° per hour, or only about four moon diameters in an hour!
Surely, this satellite must be way out there. How far? To determine that, I did a couple of what we used to call during my college physics days “back-of-the-envelope” (BOTEC) calculations. These are rough approximations—using simplifying assumptions—that should get you to an answer that is at least the right order of magnitude.
If we can estimate the orbital angular velocity of the satellite, we can determine its orbital period, and if we could determine that, we can calculate it orbital distance. Now, we don’t know yet if this satellite is in a near-circular or highly-elliptical orbit. If the satellite is an a highly-elliptical orbit and we observe it near apogee, its angular velocity will be somewhat slower than the angular velocity of a circular orbit at that same distance. If we observe it near perigee, then its angular velocity will be somewhat faster that the angular velocity of a circular orbit at that same distance. First simplifying assumption: let’s assume a circular orbit.
The next simplifying assumptions are that (1) the satellite passes through the observer’s zenith, and (2) the distance to the satellite is large in comparison to the radius of the Earth. At the time of observation, the satellite was at an altitude between 65° and 66° above the horizon. Not quite the zenith, but maybe close enough.
First, we need to compensate for the fact that the observer’s location on the surface of the Earth is moving in the same direction (along right ascension) as the satellite is orbiting (eastward) as the Earth rotates. We need to add the Earth’s rotational velocity to the right ascension component of the satellite’s velocity to get its true angular velocity relative to the center of the Earth. This of course assumes that the radius of the Earth is small compared to the distance to the satellite.
During the 0.1236 hours we observed the satellite, it moved 0.2743° eastward in right ascension and 0.0469° northward in declination. We now need to add a portion of the Earth’s angular velocity to the right ascension component of the satellite’s angular velocity. If the satellite were at the north celestial pole, the amount we would add would be zero. If, on the other hand, the satellite were on the celestial equator, we would add the full amount. Since cos 90° is 0 and cos 0° is 1, let’s add the Earth’s rotational angular velocity times the cosine of the satellite’s declination to the right ascension component of the satellite’s angular velocity.
The Earth turns through 360° in one mean sidereal day (23h 56m 04s = 86,164s). That’s 1.8591° during the 0.1236 hours we observed the satellite. Taking that times the average declination of the satellite during the observation time, we get 1.8591° cos 21.7783° =1.7264°. Adding this to the 0.2743° the satellite moved in right ascension, we get new components for the satellite’s angular displacement of 0.2743° + 1.7264° = 2.0007° in right ascension and 0.0469° in declination. This gives us the “true” angular displacement for the satellite of
This is a motion of about 16.19° per hour, giving us a rough orbital period of 22.235 hours or 80,045 seconds.
Using Newton’s form of Kepler’s Third Law to calculate the orbital semi-major axis, we get (as a very rough estimate):
where G is the gravitational constant, M is the mass of the Earth in kg, and P is the satellite’s orbital period in seconds.
Geosynchronous satellites have an orbital radius of 42,164 km, so our mystery satellite is almost as far out as the geosynchronous satellites. If it were further, the satellite would have been moving westward across our field of view, not eastward.
Admittedly, this is a lot of hand waving and is almost certainly wrong, but perhaps it gets us reasonably close to the right answer.
Now, let’s consider the shadow of the Earth to give us another estimate of the satellite’s distance.
At the time of observation, the Sun was located at 19h04m23s -22°36’40”. The anti-solar point, which is the center of the Earth’s shadow cone, was then located at 7h04m23s +22°36’40”. That is only 18.1° from the satellite. The Sun’s angular diameter at that time was 32.5 arcminutes. In order for the satellite to not be shadowed by the Earth, the angular diameter of the Earth as seen from the satellite must be less thanThe distance from the center of the Earth at which the Earth subtends an angle of 18.6° is given bySo, using this method, the satellite must be at an orbital radius of at least 38,905 km to be outside the Earth’s umbral shadow cone.
Now, on to something less speculative: the varying brightness of the satellite. I used Limovie to track the satellite across most of the field and got the following light curve.
At first blush, it appears the satellite is tumbling with a period of around 51.2s. But a closer inspection reveals that a larger amplitude is followed by a smaller amplitude is followed by a larger amplitude, and so on. So the tumbling period looks to me to be more like 102.4s. The mean (unfiltered) magnitude of the satellite looks to be around 11.8m, but ranging between 10.7m and 13.0m. Thus the amplitude is around 2.3 magnitudes. You will find the raw data here.
Update January 10, 2018
Alain Figer, French astronomer and satellite enthusiast, was kind enough to identify this object for me. Alain writes, “At first glance I noticed, using Calsky, that Falcon 9 rocket, 2017-025B, #42699, might be your satellite…From the MMT data (astroguard russian site) 2017-025B rotation period was measured at 89.55s on 13 OCT 2017. That figure seems to me in rather good agreement with yours at 102.4s, since the rotation period of this rocket might be quickly lengthening, a rather classical behaviour for such newly launched rockets.” Alain goes on to say, “For estimating the satellite altitude from your own observations you have to consider its highly eccentric elliptical orbit.” Thank you, Alain!
After I got home from work this evening, I began thinking, “Hmm, Guide is such an amazing program, maybe it can show me accurate satellite positions as well.” Turns out, it can! After downloading the current orbital elements for all satellites and turning on the satellite display, I was able to confirm Alain’s determination that this object is indeed Falcon 9 rocket body 2017-025B.
SpaceX launched the Inmarsat-5 F4 commercial communications satellite from historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida using a Falcon 9 rocket on May 15, 2017. Here are some pictures and a video of that launch.
The Falcon 9 rocket body currently orbits the Earth once every 23h21m19s in a highly-elliptical orbit (e=0.8358) that ranges from a perigee height of 432.4 km to an apogee height of 69,783 km. During the time of observation, its range (i.e. distance from me, the observer) went from 64,388 km to 64,028 km. The semi-major axis of its orbit is 41,481 km which is 3.3% higher than my (lucky) estimate above. The shadow criterion of > 38,905 km is met as well.