Radio Quiet Zones

If you thought light pollution is bad (and it is!), radio pollution for radio astronomers is much worse.  Even years ago, terrestrial pollution of the radio spectrum tended to swamp faint celestial sources at many frequencies, and in 1958 the FCC established a 13,000 square mile rectangular region of West Virginia, Virginia, and Maryland as the National Radio Quiet Zone.  Two facilities within this protected region—whose natural topography helps to screen out many terrestrial radio emissions—are the Sugar Grove Station and the Green Bank Observatory near Green Bank, West Virginia.  The world’s largest fully-steerable radio telescope dish was built at Green Bank in 1956.  Though the original 300-ft. dish collapsed in 1988 due to a structural failure, it was rebuilt in 2000 as the Robert C. Byrd Green Bank Telescope, a leading facility for radio astronomy.

National Radio Quiet Zone

Counties wholly within the NRQZ, where many radio-emitting sources are regulated or banned outright, are Alleghany, Augusta, Bath, Highland, Nelson, and Rockbridge in Virginia, and Hardy, Pendleton, Pocahontas, Randolph, and Upshur in West Virginia.

The NRQZ isn’t the only radio quiet zone.  Here are some others:

  • Arecibo Observatory, Puerto Rico
  • Astronomy Geographic Advantage Act (AGAA), South Africa
  • Atacama Large Millimeter Array (ALMA), Chile
  • Australian Radio Quiet Zone WA (ARQZWA), Murchison Radio-astronomy Observatory (MRO)
  • Dominion Radio Astrophysical Observatory (DRAO), Canada
  • Five hundred meter Aperture Spherical Telescope (FAST), China
  • Institute for Radio Astronomy in the Millimeter Range (IRAM), Spain
  • Itapetinga Radio Observatory (IRO), Brazil
  • Large Millimeter Telescope (LMT), Mexico
  • Pushchino Radio Astronomy Observatory, Russia

The best place in the world to do radio astronomy is not on our world at all but instead on the far side of the Moon.  Radio telescopes deployed on the lunar farside could “listen” to the universe with absolutely no interference from Earth.  The solid body of the Moon (and its lack of an atmosphere) would completely block all radio signals and noise emanating from the Earth and Earth orbit.  And some radio telescopes could be quickly and easily deployed (think long-wire antennas rather than radio dishes).  Of course, the Moon itself will need to be designated as a radio quiet zone so that any lunar colonies, rovers, or satellites operate at frequencies and times that will not interfere with scientific work.  Maybe infrared or optical lasers would be a better way to communicate?

How would data from a lunar farside radio observatory be transmitted back to Earth?  One way would be to have a dedicated lunar satellite that receives data from the radio observatory while it is traveling over the lunar farside.  It would then re-transmit that data to Earth while it is traveling over the Earth-facing nearside.

Another (probably more expensive) approach would be to have a series of radio relay towers spaced at intervals from the radio observatory around to the lunar nearside where a transmitter could send the data back to Earth.

A third choice would be to locate the radio observatory in a libration zone along the border between the lunar nearside and farside.  At a libration zone radio observatory, data would be collected and stored until each time libration allows a direct line-of-sight to Earth.

The crater Daedalus, near the center of the lunar farside, has been suggested as the best location for a radio astronomy facility on the Moon (Pagana et al. 2006).

There is also a region above the farside lunar surface where radio emissions from Earth and Earth-orbiting satellites, would be blocked by the Moon, called the “Quiet Cone”, as illustrated in the diagram below.

The Earth-Moon L2 Lagrange point (EML2) is probably going to be within the lunar quiet cone.  Because L2 is an unstable Lagrange point, a radio telescope in the quiet cone would need to be in a halo orbit about EML2, and a tight one at that to avoid “seeing” any radio emissions from the highest Earth-orbiting satellites.

https://2.bp.blogspot.com/-ZQVqI6ob6jA/VVJbJS_DYDI/AAAAAAAABCM/jLNBE_lRVxU/s640/EarthMoon5LPoints.jpg

References
Antonietti, N.; Pagana, G.; Pluchino, S.; Maccone, C.
A proposed space mission around the Moon to measure the Moon Radio-Quiet Zone, 36th COSPAR Scientific Assembly. Held 16 – 23 July 2006, in Beijing, China.

Like Sun, Like Moon

The Earth orbits the Sun once every 365.256363 (mean solar) days relative to the distant stars.  The Earth’s orbital speed ranges from 18.2 miles per second at aphelion, around July 4th, to 18.8 miles per second at perihelion, around January 3rd.  In units we’re perhaps more familiar with, that’s 65,518 mph at aphelion and 67,741 mph at perihelion. That’s a difference of 2,223 miles per hour!

As we are on a spinning globe, the direction towards which the Earth is orbiting is different at different times of the day.  When the Sun crosses the celestial meridian, due south, at its highest point in the sky around noon (1:00 p.m. daylight time), the Earth is orbiting towards your right (west) as you are facing south. Since the Earth is orbiting towards the west, the Sun appears to move towards the east, relative to the background stars—if we could see them during the day.  Since there are 360° in a circle and the Earth orbits the Sun in 365.256363 days (therefore the Sun appears to go around the Earth once every 365.256363 days relative to the background stars), the Sun’s average angular velocity eastward relative to the background stars is 360°/365.256363 days = 0.9856° per day.

The constellations through which the Sun moves are called the zodiacal constellations, and historically the zodiac contained 12 constellations, the same number as the number of months in a year.  But Belgian astronomer Eugène Delporte (1882-1955) drew up the 88 constellation boundaries we use today, approved by the IAU in 1930, so now the Sun spends a few days each year in the non-zodiacal constellation Ophiuchus, the Serpent Bearer. Furthermore, because the Earth’s axis is precessing, the calendar dates during which the Sun is in a particular zodiacal constellation is gradually getting later.

Astrologically, each zodiacal constellation has a width of 30° (360° / 12 constellations = 30° per constellation).  But, of course, the constellations are different sizes and shapes, so astronomically the number of days the Sun spends in each constellation varies. Here is the situation at present.

Constellation
Description
Sun Travel Dates
Capricornus
Sea Goat
Jan 19 through Feb 16
Aquarius
Water Bearer
Feb 16 through Mar 12
Pisces
The Fish
Mar 12 through Apr 18
Aries
The Ram
Apr 18 through May 14
Taurus
The Bull
May 14 through Jun 21
Gemini
The Twins
Jun 21 through Jul 20
Cancer
The Crab
Jul 20 through Aug 10
Leo
The Lion
Aug 10 through Sep 16
Virgo
The Virgin
Sep 16 through Oct 31
Libra
The Scales
Oct 31 through Nov 23
Scorpius
The Scorpion
Nov 23 through Nov 29
Ophiuchus
Serpent Bearer
Nov 29 through Dec 18
Sagittarius
The Archer
Dec 18 through Jan 19

 

The apparent path the Sun takes across the sky relative to the background stars through these 13 constellations is called the ecliptic.  A little contemplation, aided perhaps by a drawing, will convince you that the ecliptic is also the plane of the Earth’s orbit around the Sun.  The Moon never strays very far from the ecliptic in our sky, since its orbital plane around the Earth is inclined at a modest angle of 5.16° relative to the Earth’s orbital plane around the Sun.  But, relative to the Earth’s equatorial plane, the inclination of the Moon’s orbit varies between 18.28° and 28.60° over 18.6 years as the line of intersection between the Moon’s orbital plane and the ecliptic plane precesses westward along the ecliptic due to the gravitational tug of war the Earth and the Sun exert on the Moon as it moves through space.  This steep inclination to the equatorial plane is very unusual for such a large moon.  In fact, all four satellites in our solar system that are larger than our Moon (Ganymede, Titan, Callisto, and Io) and the one that is slightly smaller (Europa) all orbit in a plane that is inclined less than 1/2° from the equatorial plane of their host planet (Jupiter and Saturn).

Since the Moon is never farther than 5.16° from the ecliptic, its apparent motion through our sky as it orbits the Earth mimics that of the Sun, only the Moon’s angular speed is over 13 times faster, completing its circuit of the sky every 27.321662 days, relative to the distant stars.  Thus the Moon moves a little over 13° eastward every day, or about 1/2° per hour.  Since the angular diameter of the Moon is also about 1/2°, we can easily remember that the Moon moves its own diameter eastward relative to the stars every hour.  Of course, superimposed on this motion is the 27-times-faster-yet motion of the Moon and stars westward as the Earth rotates towards the east.

Now, take a look at the following table and see how the Moon’s motion mimics that of the Sun throughout the month, and throughout the year.

 
——— Moon’s Phase and Path ———
Date
Sun’s Path
New
FQ
Full
LQ
Mar 20
EQ
EQ
High
EQ
Low
Jun 21
High
High
EQ
Low
EQ
Sep 22
EQ
EQ
Low
EQ
High
Dec 21
Low
Low
EQ
High
EQ

 

New = New Moon
near the Sun
FQ = First Quarter
90° east of the Sun
Full = Full Moon
180°, opposite the Sun
LQ = Last Quarter
90° west of the Sun

 

EQ
= crosses the celestial equator heading north
High
= rides high (north) across the sky
EQ
= crosses the celestial equator heading south
Low
= rides low (south) across the sky

 

So, if you aren’t already doing so, take note of how the Moon moves across the sky at different phases and times of the year.  For example, notice how the full moon (nearest the summer solstice) on June 27/28 rides low in the south across the sky.  You’ll note the entry for the “Jun 21” row and “Full” column is “Low”.  And, the Sun entry for that date is “High”.  See, it works!

What is a Vacuum?

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.

Spontaneous emission
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.

References
Reucroft, S. and Swain, J., “What is the Casimir effect?”, Scientific American, https://www.scientificamerican.com/article/what-is-the-casimir-effec/.  Accessed 20 Feb 2018.

Koks,D. and Gibbs, P., “What is the Casimir effect?”, http://math.ucr.edu/home/baez/physics/Quantum/casimir.html.  Accessed 20 Feb 2018.

 

Saturn V

Today we celebrate the 50th anniversary of the inaugural flight of Wernher von Braun’s magnum opus, the giant Saturn V moon rocket.  This first flight was an unmanned mission, Apollo 4, and took place less than 10 months after the tragic launch pad fire that killed astronauts Gus Grissom, 40, Ed White, 36, and Roger Chaffee, 31.

Apollo 4 launch, November 9, 1967
Apollo 4 image of Earth at an altitude of 7,300 miles

The unmanned Apollo 4 mission was a complete success, paving the way for astronauts to go to the Moon.  After another successful unmanned test flight (Apollo 6), the Saturn V rocket carried the first astronauts into space on the Apollo 8 mission in December 1968.  On that mission, astronauts Frank Borman, Jim Lovell, and Bill Anders orbited the Moon for 20 hours and then returned safely to Earth.

Bill Anders took this iconic photo of Earth from Apollo 8 while in orbit around the Moon

“As of 2017, the Saturn V remains the tallest, heaviest, and most powerful (highest total impulse) rocket ever brought to operational status, and holds records for the heaviest payload launched and largest payload capacity to low Earth orbit (LEO) of 140,000 kg (310,000 lb), which included the third stage and unburned propellant needed to send the Apollo Command/Service Module and Lunar Module to the Moon.  To date, the Saturn V remains the only launch vehicle to launch missions to carry humans beyond low Earth orbit.”

Reference (for quoted material above)
Wikipedia contributors, “Saturn V,” Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Saturn_V&oldid=808028027 (accessed November 9, 2017).

Changing Solar Distance

Between January 2 and 5 each year, the Earth reaches orbital perihelion, its closest distance to the Sun (0.983 AU).  Between July 3 and 6 each year, the Earth reaches orbital aphelion, its farthest distance from the Sun (1.017 AU).  These dates of perihelion and aphelion slowly shift across the calendar (always a half year apart) with a period between 22,000 and 26,000 years.

These distances can be easily derived knowing the semi-major axis (a) and orbital eccentricity (e) of the Earth’s orbit around the Sun, which are 1.000 and 0.017, respectively.

perihelion
q = a (1-e) = 1.000 (1-0.017) = 0.983 AU

aphelion
Q = a (1+e) = 1.000 (1+0.017) = 1.017 AU

So, the Earth is 0.034 AU closer to the Sun in early January than it is in early July.  This is about 5 million km or 3.1 million miles.

How great a distance is this, really?  The Moon in its orbit around the Earth is closer to the Sun around New Moon than it is around Full Moon.  Currently, this difference in distance ranges between 130,592 miles (April 2018) and 923,177 miles (October 2018).  Using the latter value, we see that the Moon’s maximum monthly range in distance from the Sun is 30% of the Earth’s range in distance from the Sun between perihelion and aphelion.

How about in terms of the diameter of the Sun?  The Sun’s diameter is 864,526 miles.  The Earth is just 3.6 Sun diameters closer to the Sun at perihelion than it is at aphelion.  Not much!  On average, the Earth is about 108 solar diameters distant from the Sun.

How about in terms of angular size?  When the Earth is at perihelion, the Sun exhibits an angular size of 29.7 arcminutes.  At aphelion, that angle is 28.7 arcminutes.

Can you see the difference?

In the Shadow of the Moon

Every once in a while a really great documentary comes along.  In the Shadow of the Moon is one of them. This 2007 British film, which like most documentaries (unfortunately), had a very limited theater engagement, is now widely available for rental or purchase.

It is the remarkable story of the Apollo missions to the Moon, told eloquently by many of the astronauts who journeyed there: Buzz Aldrin, Michael Collins (Apollo 11), Alan Bean (Apollo 12), Jim Lovell (Apollo 8 & 13), Edgar Mitchell (Apollo 14), David Scott (Apollo 9 & 15), John Young (Apollo 10 & 16), Charles Duke (Apollo 16), Eugene Cernan (Apollo 10 & 17), and Harrison Schmitt (Apollo 17).  You certainly get the impression that not only are these guys personable and intelligent, but that they have aged well and still have much insight and wisdom to offer us about the past, present, and future.

The historical importance of this documentary cannot be overstated.  There is nothing, and I mean nothing, like hearing about the first (and still only) human missions to the Moon firsthand from the astronauts who journeyed there.  And, sadly, these pioneering astronauts are not going to be with us much longer. Most have already left us.  In the eleven years since this documentary was released, Edgar Mitchell, the last surviving member of the Apollo 14 crew, passed away in 2016, Gene Cernan, the last man to walk on the Moon, passed away in 2017, John Young, the longest-serving astronaut in NASA history, and Alan Bean, the last surviving member of the Apollo 12 crew, left us in 2018.  The six surviving Apollo astronauts who shared their stories with us in this film are all octogenarians and nonagenarians: Buzz Aldrin is 88, Michael Collins is 87, Jim Lovell is 90, David Scott is 85, Charles Duke is 82, and Harrison Schmitt is 82.

This is a story that needed to be told by those who can tell it best.  There is no narrator, nor is there any need for one.  Kudos to directors David Sington & Christopher Riley, producers Duncan Copp, Christopher Riley, Sarah Kinsella, John Battsek, & Julie Goldman, and  composer Philip Sheppard for making this a film of lasting cultural significance, a film that will be admired and appreciated a hundred-plus years from now.

Bringing Home Pieces of the Moon

The astronauts on Apollo 11, 12, 14, 15, 16, and 17 between 1969 and 1972 brought back a total of 840 lbs of moon rocks and soil.  Each successive Apollo mission brought back a larger amount of lunar material.

The Soviets brought back a total of 0.7 lbs of lunar soil through their robotic sample return missions Luna 16 (1970), Luna 20 (1972), and Luna 24 (1976).

So, excluding lunar meteorites that have befallen the Earth, a total of 840.7 lbs of lunar material has been delivered to research laboratories here on Earth.

It has been over 40 years since we have brought anything back from the lunar surface.  There are many interesting areas yet to be explored.  Why not send a series of robotic geologists to the Moon in advance of human missions? The success of the Spirit, Opportunity, and Curiosity rovers on Mars show us the exciting work that can be done at a fraction of the cost of human missions.  One enhancement would be the ability of the lunar robotic rovers to collect moon rocks and soil and return them to the mother ship for delivery to Earth.

But our 40+ year wait for additional lunar material may soon be over!

China plans to launch the Chang’e 5 lunar lander in November of this year.  It is expected to land in the Oceanus Procellarum (“Ocean of Storms”) region of the Moon, scoop up at least 4.4 lbs of lunar soil and rock—including some at least six feet below the surface!  The lunar haul will be launched into lunar orbit, where it will rendezvous with the sample return module that will bring it back to Earth.  After a high-speed entry into Earth’s atmosphere, the sample return module will rapidly decelerate, then gently parachute down to the Earth’s surface, presumably somewhere in China.

Chang’e 5 promises to be one of the most exciting and important space missions this year.  Stay tuned!

Below the Lunar Surface

Between 1969 and 1972, a dozen human beings walked upon the surface of the Moon, amounting to a total lunar exploration time of 3d 8h 32m 26s.  Gene Cernan returned to the Lunar Module at 11:40:56 p.m. CST on December 13, 1972.  In the over 44 years since, no one has followed in his footsteps.  Sadly, Gene Cernan, who died in 2017, never lived to see another human walk on the Moon.  Ever since his Apollo 17 mission, he has held the dubious distinction of being the “last man to walk on the Moon”.

Only four of the twelve Apollo astronauts who walked on the Moon are still living.  Will humans return to the Moon before the last of them dies?

Buzz Aldrin (1930-)

Neil Armstrong (1930-2012)

Alan Bean (1932-2018)

Gene Cernan (1934-2017)

Pete Conrad (1930-1999)

Charlie Duke (1935-)

Jim Irwin (1930-1991)

Ed Mitchell (1930-2016)

Harrison Schmitt (1935-)

Dave Scott (1932-)

Alan Shepard (1923-1998)

John Young (1930-2018)

Fortunately, robotic explorers orbiting and landing on the Moon in recent years have made some discoveries that provide a new impetus for humans to return to the Moon.  One of those discoveries is evidence for sublunarean structures that could provide “roughed in” habitats for human settlement.

Mother Nature may have done us a great favor thanks to lunar volcanism.

Most volcanism on the Moon occurred between 3 and 4 billion years ago when the lunar maria formed.

Sinuous rilles provide evidence of past volcanic flows and may be the collapsed remains of lava tubes.  There is some evidence to support that both Vallis Schröteri and Rima Sharp extend below the lunar surface as uncollapsed lava tubes.  Vacant lava tubes beneath the lunar surface may be quite common.

Vallis Schröteri
Vallis Schröteri (Schroter’s Valley) – More Beneath the Surface?
Rima Sharp
Rima Sharp – More Beneath the Surface?

Volcanism on the Moon may have continued almost up to the present day.  Not only do numerous small volcanoes on the Moon suggest active volcanism within the past 50 to 100 million years, but the irregular mare patch Ina in Lacus Felicitatis (“Lake of Happiness”) may be a volcanic feature no more than 10 million years old.

Ina
An Irregular Mare Patch (IMP) named Ina, in Lacus Felicitatis – Evidence of Geologically Recent Volcanism?

Could there be vacant lava tubes beneath the lunar surface?  On Earth, underground lava tubes can be found in Hawaii, Iceland, and many other locations around the world.

Thurston Lava Tube at Hawaii Volcanoes National Park, Big Island, Hawaii

Further evidence that there may be caverns and vacant tubes underneath the lunar surface are the many deep pits that have been discovered—over 150 so far.  Some of these pits may be openings into lava tubes beneath the surface, known as skylights.

Marius Hills Hole (MHH) – Lava Tube Entrance
Images of the Marius Hills Hole as observed under different solar illumination conditions by the SELENE/Kaguya Terrain Camera and Multiband Imager [JAXA/SELENE]
Mare Ingenii Hole (MIH) – Lava Tube Entrance?
Mare Tranquillitatis Hole (MTH) -Lava Tube Entrance?

NASA’s Gravity Recovery and Interior Laboratory (GRAIL) lunar orbiters mapped the gravitational field of the Moon in unprecedented detail, uncovering evidence of voids beneath the lunar surface.  Ground-penetrating radar, gradiometric, and gravimetric measurements are now needed to confirm the nature of these voids and whether they would be suitable structures for human habitation, shielding lunar residents from radiation, temperature extremes, and micrometeorites.

The Marius Hills Hole (MHH), about 160 ft. wide and 160 ft. deep at 14.100˚N, 303.262˚E, has been identified as leading to an intact lava tube below the lunar surface (Kaku et al. 2017).  The discovery was made after analyzing data from the Lunar Radar Sounder (LRS) instrument aboard the SELENE spacecraft.  LRS was an 800-watt ground penetrating radar, sweeping between 4 and 6 MHz every 200 μsec.  Each time these radio waves hit subsurface boundaries between rock and void, they reflected back towards the spacecraft and the lag times were used to estimate the depth and size of the voids.

Additional lava tubes or cavernous voids are thought to exist in the Marius Hills region, 13.5-13.8˚ N, 302.5-302.8˚ E.

The Lunar Advanced Radar Orbiter for Subsurface Sounding (LAROSS) mission has been proposed (Sood et al. 2016), and Gedex Inc., a Toronto-based geophysics company, is developing  a rover-mounted gravimeter and gravity gradiometer (Urbancic et al. 2015).  A gradiometer will be used to study the near-surface environment, and a gravimeter will go deeper.

These are exciting times for lunar exploration!

References
Beatty, K. 2014, (Geologically) Recent Volcanoes on the Moon?, Sky &    Telescope blog, October 14, 2014
Blair, D. M., Chappaz, L., Sood, R. et al. 2017, Icarus, 282, 47:55
Kaku, T., Haruyama, J. et al. 2017, Geophysical Research Letters, 44
Sood, R., Melosh, H. J., Howell, K. 2016, 26th AAS/AIAA Space Flight    Mechanics Meeting, AAS 16-464
Sumner, T. 2017, Science News, 191, 1, 5 (January 21, 2017)
Urbancic, N., Stanley, S., Ghent, R., et al. 2015, 46th Lunar and Planetary    Science Conference #1616