April 2, 2020

Review: Falling to Earth by Al Worden and Francis French.

Out from Smithsonian Press!

We’re approaching 40 years since the last human set foot on the Moon, and we’ve yet to have the ability to point at a calendar and state unequivocally when such a feat may happen again. Thus, the era is dwindling when we can hear the stories of these early astronauts, in their own words. This week’s review entitled Falling to Earth tells the tale of NASA astronaut Al Worden, the Command Module pilot for Apollo 15. [Read more...]

Astro-Challenge: Exploring Reiner Gamma.

Finding Reiner Gamma…note that the shot through the Astroguyz 8″ SCT is flipped and inverted!

(Credit: Wide shot by Author, closeup from Lunar Orbiter 4 in 1967/NASA).

The waning gibbous Moon may provide a good cause to do some early AM astronomy this week. Amidst the familiar features such as craters, rays, and lunar mountains are more mysterious anomalies, one of which we’d like to bring to your observing attention this week. Reiner Gamma is a curious feature located at 7.5°N 59°W on the edge of the Oceanus Procellarum. [Read more...]

AstroEvent: Will Anyone Welcome the New Saros?

A Remote partial for the hardcore…(Credit: Eclipse Predictions by Fred Espenak, NASA/GSFC).

This week, we’d like to turn your attention to a unique event that no one but a few penguins may witness. July 1st kicks off the month with a partial eclipse of the Sun, the second solar in the past month and the third eclipse overall. The penumbra of the Moon will barely kiss the Earth from 07:53 to 9:22UT and greatest eclipse is a paltry 9.7% around 8:39UT. [Read more...]

A Look at the Earth’s Interior.

Eruption! Our active planet as seen from the Aqua satellite… (Credit: NASA).

(Note: The essay that follows it part of a series of papers I wrote in my quest for my science teaching degree… I always hate the fact that school writing only makes it to two sets of eyeballs, mine and the graders, so I re-worked my writing a bit for the blog format…)

The Earth is the only terrestrial planet that we have the availability to reach out and examine up close. By use of painstaking scientific processes, we can monitor the inner workings of our world and create a model of its interior structure that presents a high degree of accuracy with what is observed. Still; while we live on its surface, we have never penetrated the shell of even its outer crust or sampled its deep interior… just how do we know what’s within?

To map the Earth’s interior perhaps no tool is more essential than the seismograph. Also sometimes referred to as the seismometer, this device is essential for recording and monitoring seismic waves in the Earth’s crust and their passage through the interior. This device usually consists of an internal inertial mass that is deflected relative to an external frame, usually anchored to the surrounding bedrock. As the device is shaken, the mass is moved as waves pass through it, deflecting a needle against a scrolling spool of paper marking the passage of time. Early detectors were constructed during the Chinese Han Dynasty. Modern detectors may be on the classic needle deflection type or digital and utilize the precise measurement of laser beams or a mass magnetically suspended generating a negative feedback loop. Key waves detected are P, or primary waves, S, or secondary waves, and surface seismic waves.  P waves are the initial “push-pull” waves of an earthquake. These are the fastest waves, and thus the first recorded during a seismic event. An elastic wave, P waves can travel through any medium, be it solid, liquid or gaseous. These waves are compressional and can also vary with the subsurface depth of the earthquake. Next waves to arrive are the S, or shear waves. Also known as transverse waves, these are slower moving and can only travel through solid material. Finally, the surface waves are the last to arrive at a given detector, as they are slower moving and generally cause the most damage. If these waves can be recorded by three separate detectors spaced out on the Earth’s surface, a precise epicenter can be pinpointed. Also, the fact that an Earthquake shadow zone is generated where only P waves are seen is prime and well documented evidence that the Earth’s outer core is not solid, but molten. Indeed, the magnetic shear or torsion generated by the interplay of Earth’s iron-nickel solid core, and liquid molten outer core, is further evidenced by our relatively strong magnetic field. In comparison to the Moon and other terrestrial or rocky planets, the interior of the Earth is a dynamic place, and seismology helps us understand this differentiated structure.

(Created by Author).

Elements of seismograph construction may include a digital strong-motion accelerograph or several inter-connected seismometers working to create one coherent output. A classic earthquake will first register on a seismogram as a series of short spikes marking the initial P-waves. Minutes later, the first S-waves will arrive spanning a slightly longer period of time. Finally, the largest and most damaging surface waves arrive. As seen on a seismograph, the timing and spacing recorded at an individual station may vary depending on the depth and distance of the earthquake epicenter.

The science of seismology is crucial to understanding the interior structure of the Earth as well as predicting where damaging earthquakes or tsunamis are likely occur. This study is vital to the whole Earth model because although we cannot directly sample interior layers of the Earth, we can model them by examining the speed and types of waves that transverse the crust, silica rich mantle, and inner and outer cores.

The outer surface of the Earth is composed of tectonic plates that either converge, or subduct one under another, diverge or separate, or strike slip or grind past one another. This type of surface material recycling drives what’s known as the rock cycle. The outer-most rigid crust is known as the lithosphere, which is comprised of the crust and a layer of brittle and solid rock about 100 km thick. This crust is thickest on the continents, and thinnest underneath the oceans. Of special interest is a separation known as the Mohorovi?i? Discontinuity, first discovered in 1909. This boundary between the crust and the Earth’s mantle was deduced by studying the refraction pattern of earthquakes by shallow p-waves.

Farther down, the lithosphere rides along top of the flexible and molten asthenosphere. This layer extends down to a depth of about 400 miles and is mechanically detached from the deep lower mantle. Again, only P-waves can travel through molten regions of the inner Earth; S-waves cannot. This key fact is prime evidence that the outer core of the Earth is fluid, or molten. Likewise, the refraction and reflection of seismic waves can also provide us with a “look” inside the Earth to probe its interior.

But beyond the probing of Earth’s interior, the study of seismology is crucial to other applications, both scientific and economic. The study and conduction of seismic waves can be applied to locating large fossil fuel deposits as well as prime aquifers or areas of potential sink hole activity. Again, this utilizes our understanding of the transmission, reflection, and refraction of P- and S- waves through solid versus liquid and gaseous material. Seismology is also used to detect nuclear weapons testing, and to assure compliance with test ban treaties. The liquid outer core is further evidenced by the creation of Earth’s magnetic field. When we look at smaller, cooler bodies such as the Moon and Mars, little evidence for a magnetic field is seen; in fact, the low density of the Moon versus its size is prime evidence that it was once part of the Earth’s crust and mantle ejected by a massive impact. Igneous basaltic rocks brought back from the Moon by Apollo astronauts support this theory. Finally, seismology demonstrates evidence for plate tectonics by showing observational proof that the plates of the lithosphere are active and in motion. Plates snapping back into place or grinding past each other all generate massive amounts of seismic waves in what we know as earthquakes. Over time, these cause the raising of great mountain ranges such as the Himalayas or massive earthquakes such as were recently witnessed in Haiti, Chile and Japan.

In conclusion, seismology and the study of seismic waves are key examples of how we can study something in science without directly examining it. Beyond just scientific interest, this has given us such benefits as the Pacific Tsunami Warning Center that has saved countless lives. As we move out and study other planets in our solar system, knowledge of the interior structure of the Earth will give us some insight into comparative planetary science and just how common or rare a dynamic place like Earth truly is.

Review: The Kaguya Lunar Atlas.

On Sale Now from Springer Books!

You’ve never seen the Moon like this before… On September 14th, 2007, SELENE, or the SELenological and ENgineering Explorer rocketed out of JAXA’s Tanegashima Space Center on her way to the Moon. [Read more...]

AstroEvent: 4x Planets, 1xMoon, and a 12° FOV!

Where have all the planets gone? Four of the five classical naked eye planets are about to reveal themselves this week in a splendid fashion. As Venus sinks morning by morning towards the horizon, expect Jupiter, Mars and Mercury to emerge low in the dawn sky. The action culminates the weekend of April 30th-May 1st, when the waning crescent Moon approaches the grouping… use brilliant Venus as a visual “anchor” to guide your eyes to the fainter planets. On what date will you be able to spot each planet from your location?

[Read more...]

09.04.11: 2010 SO16-A World in a Bizzaro Orbit.

Ever wondered what local space would be like if the Earth had more than one moon? Well, it turns out that we do have several natural interlopers; sort of. Recently, researchers A.A. Christou and D. J. Asher of Armagh Observatory in Northern Ireland reported on the discovery of a unique Near-Earth Asteroid (NEA): 2010 SO16, a 200-400 meter space rock locked in a horse-shoe orbit with Earth.

[Read more...]

AstroEvent(s): Of Occultations & Daytime Stars.

This week brings with it an interesting double-double header. First up is a challenge that comes to us via the Royal Astronomical Society of Canada … sure, you’ve seen Venus near the daytime Moon, and perhaps you’ve caught Jupiter low at opposition just prior to the setting of the Sun… but did you know that it’s possible to catch some of the brightest stars while the Sun is still above the horizon? Right around the first full week of April is a good time to give this a try; your assigned quarry is Sirius in the pre-dusk, and Vega in the post-dawn. Both of these stars are in the negative magnitude range and might just be visible from a pristine site with good seeing. In the case of Vega, a fun project would be to acquire it before sunrise and follow it into the daytime skies either visually or with an equatorial tracking telescope. Sirius, although brighter at magnitude -1.5 may be tougher; in this instance, finding the star in relation to a nearby landmark a day prior at dusk and then trying to acquire it before local sunset may work. I once successfully caught Jupiter in the daytime in this fashion, near opposition from the arming-end of runaway in Kuwait back in 1998. Good luck, and we’ll be attempting this feat of visual athletics right along with you!

But wait, there’s more… this week also sees the waxing crescent Moon pass through some interesting star fields in the constellations Taurus and Gemini. The result is a series of interesting stellar occultations; 1st, on the evening of April 7th, the Moon skims the Hyades cluster and occults Upsilon and Kappa Tauri for viewers in western North America. Kappa is of particular interest as it is a very close (0.1”) double. Even if you aren’t in the target zone, the crescent Moon+Hyades= a good photo op. Three days later, we US east coasters get a shot with an occultation of Zeta Geminorum, otherwise known as Mekbuda. This is another bright star around magnitude +4.0. Mekbuda is also a Cepheid variable with a period of 10.2 days, one of the brightest in the sky. Watching this star wink out and then reappear should be a good replay of last month’s Mu Geminorum occultation… the action for the US East Coast centers around ingress at 9:21 PM EDT and an egress of 10:35PM. The occultation extends up to a graze line cutting across the Canadian Maritimes… good luck, and watch this space for a video after-action clip if successful!

The astro-term for this week is Transparency. In terms of astronomy, transparency is the ability for light to pass unhindered through the atmosphere. Pollution, dust, and aerosols all act to scatter light and dim objects. You can have clear skies, but poor, washed out transparency. Generally, the higher and drier you are, the better transparency will be, as evidenced by a deep blue daytime sky and an inky black nighttime sky. This is also an all important factor in success in daytime star-spotting as discussed above.  Transparency is rated 1 to 10, with 10 being the absolute best, and is closely tied with seeing, or the resolution ability based on atmospheric turbulence. I’ve had clear skies and decent transparency after a storm front, only to have poor seeing as the convective cells rolled before my eyepiece!

02.04.11: Stalking an Impact.

On February 11 of this year, Stefano Sposetti and Marco Iten of Gnosca Observatory Switzerland used a Borg 125 ED refractor and a high speed video camera along with a similar setup attached to a Celestron 11 at a separate location to record a flash on the nighttime side of the then just past 1st Quarter Moon.

[Read more...]

29.03.11: Lunar Lava-Tubes.

Living on the Moon will be a tough proposition for future astronauts. With lunar daylight stretching for two terrestrial weeks, astronauts and equipment will have to be prepared for swings in temperature from +120 to -180 Celsius in the shade.

[Read more...]

AstroEvent: The Return of Saturn 2011.

Two of unique planetary events are on our astro-radar this week. The first is an extremely close conjunction between brilliant Venus and faint Neptune on the morning of March 27th. At a mere 9’ minutes separation at 0100 UT, this will be one of the closest planetary conjunctions of the year.

[Read more...]

20.03.11: An Occultation Update.

This Super-moon Sunday, we’d just like to give a brief self promotional shout-out to an astronomical success we had last weekend. Last Sunday we managed to catch the occultation of the 4th magnitude star Mu Geminorum by the waxing gibbous moon from Astroguyz HQ here in Hudson, Florida;

[Read more...]

19.03.11: Our Moon… in Cosmic Rays.

Sure, you’ve seen the Moon countless times, and perhaps you’ve been drawn out, zombie-like to view this weekend’s “Super-Moon,” but have you ever seen the moon in… cosmic rays?  This is but one gem that has come out of NASA’s Lunar Reconnaissance Orbiter (LRO).

[Read more...]

Tricks at the Eyepiece

Sure, you’ve got the gear, you’ve got the ultimate telescope, or maybe you just like to causally observe. But have you ever given much thought as to how to observe? The simple act of looking is so reflexive that most of us do it without a second thought. In the realm of astronomy, however, the use of a trained eye is paramount to enjoying what you’re seeing.

[Read more...]

AstroEvent: Can You Spy the Zodiacal Light?

This week’s astronomy challenge is seasonal for mid-latitude observers. Around the time of the equinox, the ecliptic meets the horizon at a favorable angle and a unique phenomenon may become apparent: the zodiacal light. This diffuse band of light can be briefly seen after sunset or before sunrise from a moderately dark location.

[Read more...]

18.02.11: A Titan(ic) Flyby.

Far out in the depths of the solar system, one of our most distant orbiting ambassadors is completing a flyby of the largest known moon. On Friday, February 18th at 11:04AM EST NASA’s Cassini orbiter will skim the Saturnian moon at a distance of just 2,270 miles above the enigmatic moon Titan.

[Read more...]

Near Earth Objects: Mitigating the Threat.

(Editor’s Note: What follows is a scenario/article along with an original lesson plan re-written for a blog format).

Eventually, it had to happen. With scant warning, the announcement is made that a large space rock is inbound to strike Earth and is only weeks away. The news largely takes the public by surprise; this is the big one, an extinction class event. People are exasperated to learn that little can be done to deflect the large impactor; all that remains is for scientists to predict the precise impact location and for world organizations to attempt evacuations so that some of humanity might survive… [Read more...]

AstroEvent: A Solstice Eclipse!

One of the final astronomical events of the year for 2010 is also one of the biggest. On the night of December 20th-21st, the Moon will undergo a total lunar eclipse. This eclipse will be visible in its entirety for North American observers and at sunrise for European South American observers and sunset for observers in Australia and the Far East. First Umbral contact will begin at 06:32 UTC, and totality will last 73 minutes from 7:40 to 8:53 UTC with greatest eclipse at 8:18 UTC.

[Read more...]