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On blood moons and tetrads

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lunar eclipse
“Lunar eclipse April 15 2014 California Alfredo Garcia Jr1” by Tomruen – [1]. Licensed under CC BY-SA 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Lunar_eclipse_April_15_2014_California_Alfredo_Garcia_Jr1.jpg#/media/File:Lunar_eclipse_April_15_2014_California_Alfredo_Garcia_Jr1.jpg

There is a lunar eclipse coming the end of this month, and depending on who you ask it is significant for different reasons. In fact, there has been a lot of hype about this particular eclipse (or rather, series of eclipses) in some Christian circles with the term “blood moon tetrad” often being used in conjunction with prophetic claims. I’m certainly not a specialist in Biblical prophecy, interpretation, or the history of Israel, but I can unpack some of the sensationalized terminology here and help sort out the science behind the hype.

Let’s start with the term “blood moon.” The popular press has recently started using this term to refer to a lunar eclipse. Lunar eclipses happen quite frequently, usually twice a year, when the full Moon passes into the Earth’s shadow. This causes the Moon to fade in brightness over the period of a couple hours and often take on a deep red hue due to the Earth’s atmosphere and the way it scatters light.

Consider how the sky looks during a sunset: even though the Sun is hidden beneath the horizon, the atmosphere bends the red portions of sunlight toward us. From the Moon, during a lunar eclipse, the Sun is hidden behind the Earth. The glow of a ring of sunsets casts that red light onto the Moon’s surface, making it appear duly reddish or “blood red.” This effect can be heightened if the Moon is near the horizon, depending on atmospheric conditions.

So what about “tetrad”? There are different types of lunar eclipses. If the Moon only moves partly into the Earth’s shadow, it’s called a partial lunar eclipse. The eclipse of this month is the last in a series of four total eclipses, in which the Moon passes through the darkest portion of the Earth’s shadow. A series of four total lunar eclipses without any partial eclipses between is known as a tetrad. This current tetrad includes the total lunar eclipse of last April as well as the eclipses of April and October of last year.

How rare are such series of eclipses? Glancing through my copy of NASA’s huge “Five Millennium Canon of Lunar Eclipses,” which included information on all lunar eclipses from 2000 BC to 3000 AD, I see that over the past thirty years there was a tetrad in 2003/2004 and 1985/1986 (as well as several lunar “triads”). According to the website EarthSky.org, there will be eight tetrads in the twenty-first century, while the years 1701 to 1899 had none at all. There were five in the twentieth century.

So what does this all have to do with Biblical prophecy? According to some sources, this particular tetrad is unique because it lines up with specific Jewish holidays. Last year, the first lunar eclipse of the series fell during Passover, as did the eclipse of April of this year. Last year the October lunar eclipse was during Sukkot, or the Feast of Tabernacles, which again corresponds with this month’s eclipse.

The important thing to remember though is that the Jewish calendar (unlike ours) is a lunar calendar; its months correspond with the actual phases of the Moon. Both Passover and Sukkot begin on the fifteenth day of the Jewish month, which usually corresponds with the full Moon. And because lunar eclipses only happen when the Moon is full, it’s not strange there would be occasional line-ups between these holidays and a series of lunar eclipses. How occasional? Again, according to EarthSky.org, this has happened eight times since the birth of Christ.

And here’s where the prophet interpreters come in, offering links between the years in which a tetrad of lunar eclipses corresponded with these holidays and important events in the history of Israel. But that’s the problem: history is a complex, messy business, and the human mind is hard-wired to find patterns everywhere, even where they don’t exist. Plus, these “significant events” are subjective: how widely do you want to interpret what events are actually important? The tetrad of 1493-1494 is linked to the expulsion of the Jews from Spain, for instance, but the order for the expulsion wasn’t signed in these years and the persecution lasted for decades. Making 1493-1494 especially significant is arbitrary. And other events that would seem to be significant are ignored: there was no lunar tetrad, for instance, during the Holocaust. Finally, I should add that this whole claim of prophetic significance is offered by individuals outside the Jewish community with little insight or regard into what that community would actually consider culturally or historically important in their own past.

In my mind, searching for codes in the night sky is much less useful than simply appreciating the grandeur of astronomy for what it is. And this month, regardless of prophetic forecasts, we have the chance to witness one of nature’s most impressive spectacles. The “blood moon tetrad” will conclude with the total lunar eclipse beginning the evening of Sunday, September 27th. (If you’re still looking for cosmic coincidents, here’s another one: my birthday is September 27th.)

The full moon rises in the east at sunset that evening. By 9:15 the Moon has begun to enter the darkest portion of the Moon’s shadow, marking the most vivid phase of the eclipse. It will be at its darkest at about 9:45, and the moon will begin to emerge from deep shadow at about 10:20. The Moon will not be completely out of the Earth’s shadow, however, until after midnight. As far as visibility, this will be an easy lunar eclipse to observe—taking place when the Moon is high in the early part of the evening. (Last year I had to make students get up before dawn to spot the eclipse.) So definitely take the opportunity to wonder and ogle, but try not to prognosticate.

This column first appeared in the Kankakee Daily Journal, August 28th, 2015.

August offers a look at Lyra

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When I talk to people about observing here in town, they often bemoan the fact that light pollution makes stargazing all but impossible from within the city limits.

Though it is true that observing from an urban setting doesn’t compare to an experience under truly dark skies, it’s certainly not the case that there’s nothing to see from one’s own backyard or even sidewalk.This month I’ll consider some of the sights in the constellation Lyra, which is almost directly overhead throughout August in early evening.

Lyra is a tiny constellation, but it holds a wealth of lovely double stars that are bright enough to be seen without a pilgrimage to the deep, dark countryside.

The constellation Lyra is easy to find on clear nights. Vega, its brightest star and the brightest star of summer, is nearly overhead at sunset. Vega marks one apex of the famous Summer Triangle, an asterism of three bright stars high in the summer skies. Lyra itself though is small formed of a triangle of stars attached to a larger parallelogram. Classically, the constellation was seen as a harp or lyre.

Lyra

My observations are made with a six-inch reflecting telescope from my own yard in Kankakee, but a smaller telescope will reveal these sights as well. You’ll want to use eyepieces that give a relatively low magnification. (I used about 40x. Calculate the magnification of your eyepiece by dividing your telescope’s focal length by the focal length of your eyepiece. A shorter eyepiece focal length gives greater magnification.)

Sometimes you want higher magnification, as when you’re viewing the planets or the Moon and want to see details, but for the following views a lower magnification is better.

Start your tour with Vega, especially if you’re new to stargazing. A single star doesn’t look much different through a telescope, but this will give you a chance to align your finding scope (if your telescope has one) and test your instrument’s focus. It will also give you an idea of the seeing conditions for the night. If you can focus Vega down to a brilliant, sharp point, and if you can see one or two of its dimmer companions in your telescope’s field of view, you should be able to spot the rest of the objects in this list.

Hop down from Vega to Zeta Lyrae, the dim star where the triangle meets the parallelogram. This is one of the many double stars in Lyra. Double stars are great targets for light polluted skies. Unlike nebulae or galaxies, they are fairly bright and thus easy to enjoy even from one’s own backyard. Through even a small telescope, Zeta Lyrae is revealed to be a wide, uneven double, and many observers report seeing a beautiful color contrast between the component stars.

Moving up to the third star of the tiny triangle that makes up the top portion of Lyra, we find Epsilon Lyrae, one of the most popular double star systems in the sky and an example of why some observers (like me) get so excited about double stars. At 40x you may simply see what looks like a wide pair of white stars. But if you increase your magnification (I used 130x), you’ll see that each of these stars is actually itself a pair of stars. The entire system is known as the “Double-Double.” You’ll need a steady eye and good seeing to split them, but you’ll know if you’ve succeeded by noticing the orientation of each tight pair: they’re inclined at ninety-degrees to each other.

Moving back to a lower magnification, each of the stars at the apexes of Lyra’s parallelogram is a treat.

Delta Lyrae is a wide double star in a diffuse cluster of stars. One of the components is a lovely orange in contrast to the surrounding blue stars.

Beta Lyrae also is a group of colorful stars. (The Ring Nebula is nearby, halfway between Beta and Gamma Lyrae. From my front yard, the Ring Nebula at 70x looked like a faint smoke ring, barely visible.)

But my favorite sight of all in Lyra is a bit off the beaten path and not terribly well known. It’s sometimes called the “Double-Double’s double,” but I think it’s actually nicer than the more famous Double-Double. It’s a pair of double stars, like the Double-Double, known as Struve 2470 and 2474. They’re dimmer than the pair that make up Epsilon Lyrae, but because the components are farther apart they’re easier to split. They also have more marked colors, the brighter components appearing yellow in contrast to the dimmer bluish companions. Moreover, by some cosmic coincident the pairs are orientated in the same direction so they indeed look like almost perfect twin double stars in a single telescope eyepiece. This view alone would be proof enough for anyone who says the city skies are too bright to hold telescopic wonders.

doubles
Struve 2470 and 2474, the “Double-Double’s Double,” image from bestdoubles.wordpress.com.

This column first appeared in the Kankakee Daily Journal.

New Horizons

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108417main_image_feature_267_ajhfullImage courtesy NASA.gov.

Fast, small, cheap, and putting us in touch with the outer reaches of the solar system, the New Horizons spacecraft, which will reach its closest approach to Pluto this month on July 14th, is billed by NASA as the “smart phone” of interplanetary robotic explorers. The fastest spacecraft ever launched from Earth, New Horizons is an example compact, efficient engineering opening the door to new discoveries. This month the probe, launched nearly a decade ago in January of 2006, completes its three billion mile journey, the longest journey ever to a particular object in space.

Besides the technological achievements this plucky probe represents, New Horizons is a step into a new solar system frontier, a glimpse of a region of our own planetary system where we have not yet ventured. The close look at Pluto afforded by this mission is an opportunity for the first time to study the place where the solar system gets weird. Since tiny Pluto was serendipitously discovered in 1930 by Illinois native Clyde Tombaugh, we’ve known that it didn’t quite fit with the rest of the planets. We have small, rocky planets (Mercury, Venus, Earth, and Mars) in the interior of the solar system and large, gaseous planets (Jupiter, Saturn, Uranus, Neptune) on the periphery. Pluto—usually beyond Neptune and much smaller than any other planet—is the odd man out.

Yet it’s only recently that we’ve realized Pluto isn’t alone in its strangeness. Rather, it’s the first known object from a whole new region of the solar system. This region—which is turning out to be filled with small icy objects like Pluto—is known as the Kuiper Belt, and we still don’t know much about it. We do know that Pluto was only the first dwarf planet discovered in this region. Recently Pluto has been joined by the discovery of other dwarf planets beyond Neptune like Eris, Makemake, and Huamea. New Horizons affords the first close look at this strange region of space. Once it passes Pluto, the spacecraft may be redirected to pass another Kuiper Belt object.

Besides the Kuiper Belt, Pluto is itself still an oddity. It will be the first icy planet studied closely, for instance, and may help answer the question of whether certain types of comets are simply objects like Pluto that fall into the inner solar system. Pluto also offers an example of a gravitational oddity: along with its largest moon, Charon, Pluto is technically a double planet. Pluto and Charon orbit a common center of mass between the two objects, making them unique in the solar system by forming a double planet instead of simply a planet and moon.

And then there’s Pluto’s complicated system of newly discovered moons besides Charon. Tiny Nix, Hydra, Styx, and Kerberus have recently been shown to tumble about Pluto in a chaotic system. These miniscule objects have been studied using the Hubble Space Telescope, but New Horizons will provide the first opportunity to study them up close. Indeed, the presence of Pluto’s unexpectedly complex satellite system represents one of the large unknowns of the mission: is the space around Pluto empty or filled with debris that could pose a danger to the speeding spacecraft? The weeks leading up to New Horizon’s encounter with Pluto have been a time of suspense.

New Horizons is a fly-by mission, meaning that it’s not landing on Pluto’s surface (like the Mars rovers) nor is it entering orbit around the dwarf planet (like Cassini around Saturn or Messenger around Mercury). New Horizons will study Pluto from its closest distance of about six thousand miles on July 14th while barreling past the planet at nearly forty thousand mph. It has to be moving fast—it’s had over three billion miles to cover since leaving Earth almost ten years ago.

What sort of things do scientists hope to learn from this mission? For one thing, scientists want to better understand how Pluto “fits in” with the other planets of the solar system. What do its unique properties tell us about the origins and evolution of the solar system? For the first time this month, we’ll get a close look at the strange boundary region of the solar system that we’ve only ever been able to study from afar. As far as the solar system goes, it really is “the final frontier,” and we’ll get our first close views of it this month.

This article first appeared on Friday, July 10th, 2015 in the Kankakee Daily Journal.