Occultations, conjunctions, eclipses, oh my!

2015 has certainly been a year for celestial alignments! As we go to press, there will be a total lunar eclipse tomorrow (September 27th), which I told you about last month. In brief, the sun will set at 6:44 with the moon rising already in partial eclipse. Totality begins at 7:11 and ends at 8:23 p.m. This will be the fattest eclipsed moon we will ever see, because the moon will be at the closest point in its orbit (perigee).

Tehachapi already enjoyed a total lunar eclipse last April, plus two in 2014. It’s easy to think they’re a regular event. In fact, being correctly positioned for a decent total lunar eclipse isn’t that common at all; the 2014 eclipses were the first ones of the decade, and this one will be the last until 2018 January 31. (We’ll also need to get lucky with the January weather!)

Lunar eclipses occur when the moon passes through the earth’s shadow. In other words, the earth comes between the sun and the moon. The flip-side is the solar eclipse, where the moon passes between the sun and the earth, casting a narrow shadow on the earth--so narrow in fact that (unless you’re really lucky) you have to travel to a place where the fast-moving shadow is going to be. The next nearby solar eclipse will be in 2017. On the morning of August 21st, a 71 mile-wide path of strange darkness will come crashing onto the Oregon coast at supersonic speed. After streaking east across the Rockies, the shadow’s path turns southeast across the Great Plains, passing just north of Nashville, and across South Carolina. By mid-afternoon, the totality path will be moving fast across the Atlantic, where ships loaded with nerdy tourists like me will be waiting.

Believe me when I tell you that it’s not too early to find a spot you like along the path of totality and make a reservation! People from around the world will be flocking to this event. The venerable Astronomical League is already planning to have their annual convention in Casper, Wyoming, right on the shadow’s path. To decide where and how you want to enjoy this special astronomical event, you can begin by going to http://eclipse.gsfc.nasa.gov/. Scroll down just a bit and click on the big blue globe that takes you to a special site for the 2017 solar eclipse. (Do you like country music? I recommend Nashville! If it were in January, I’d join you; but August!!?? You know how much I love heat and humidity.)

When planets line up, we call them conjunctions. Since all of the planets revolve about the sun in more-or-less the same plane, this happens all the time. Yet, we can’t help but want to make something of it. Why is it that we’re so much more moved when two planets set side-by-side instead of one-at-a-time? Perhaps Luke Skywalker knows.

You will recall the planetary kegger that was underway as summer began. Jupiter was the host, with Venus and Mars the guests of honor. Together they slipped behind the setting sun last August. The party appears to be going strong as they reemerge in the morning twilight. Through my telescope it appears that their attire could use a little pressing--but, maybe that’s just atmospheric turbulence.

Venus can’t be missed in the crisp morning sky. You’ll find Mars lagging down and to the left, with Jupiter even further down and left. With each passing day, Jupiter rises out of the murky twilight and into the comfort of the darkness. Along with first-magnitude-star Regulus, they make a very impressive parade. Jupiter will rise swiftly throughout October, skirting Mars on the seventeenth by less than one-half degree. From the 22nd to the 29th, Venus, Jupiter and Mars will all fit within a single binocular field.

Mercury will try to join the parade, but won’t rise very high before falling back toward the sun at mid-month.

As the moon rises on October first and second, it will have the Hyades star cluster behind it. On the morning of the second, first-magnitude-star Aldeberan will be occulted by the moon. That is, the moon’s orbit around the earth will take it directly in front of Aldeberan. With as many stars as there are in the sky, you’d think that sort of thing happens all the time. In fact, it’s quite uncommon for such a bright star to be eclipsed by the moon, because there aren’t that many bright stars along the moons path.

Indeed, this particular occurrence can be observed from only a small fraction of the earth’s surface. So, if you’re up, have had your first cup of coffee, and can find west, you might want to go out at about 6:39 to see Aldeberan wink out along the moon’s edge.

The Hyades, at a distance of only 153 light-years, is the closest star cluster to us. Yet, being so close, its stars appear somewhat spread out, making the cluster appear rather unclustered. To us it’s simply the nose of Taurus, the bull. But a closer examination reveals an interesting and lively part of our galactic neighborhood.

The best way to examine the Hyades Cluster is with binoculars. A telescope will allow you to examine individual components, but it takes binoculars to capture the entire scope of the cluster.

Aldeberan, being only sixty light-years away, isn’t actually part of the Hyades Cluster. Lying only about half-way there, it will make a fine waypoint for the first intrepid explorers of the cluster (in circa 3015).

Clusters are where stars are born by the bushel. On vast scales, interstellar gas and dust are slowly pushed and pulled together by gravity into huge clouds. Within them, smaller (though still massive) clouds form knots where the hydrogen density is sufficient to start nuclear fission--stars begin to form. Swirling eddies within the cloud cause local rotation around these protostars where planets and other bodies eventually form. The rest is history...and we’re very much part of it!

These nebulae (Latin for cloud) can be seen all around us in various stages of development. The most primitive would be your basic interstellar dust cloud (example: The Great Rift). As stars start to form, gas and dust are consumed in the process, as well as blown away from hot newborn stars (ex: M42, the Great Orion Nebula). As more stars come to life, the cloud dissipates and a shining open star cluster like the Hyades Cluster remains.

It should be noted that quite nearby is another famous open star cluster: The Pleiades (aka: M45, the Seven Sisters). Lying nearly three times the distance of the Hyades, it has a much tighter grouping. However, the cluster still takes up way too much sky for most telescopes and is best appreciated with binoculars.

Long ago our Solar System was quite probably part of such a star cluster as we left the cradle all those billions of years ago. Unfortunately, our ‘cluster-mates’ have long since parted company and drifted off into the galaxy. Perhaps our cosmological detectives can identify some of them one day.

The moon passing in front of the Hyades, or occulting Aldeberan, is really nothing more than a chance alignment of the stuff in the sky. Planets bunch up in the sky and then spread out. The moon passes in front of the sun and slips into the earth’s shadow on a regular and predictable basis. Critical decisions of global import have been made based on the word of astrologers reading portents from one celestial alignment or another--even to the present day, I’m sad to say.

Yet, I don’t say that these happenings should be dismissed as meaningless. We give them meaning. We identify and mark these unusual opportunities just so that we can bear witness to unique moments in space-time. There’s no need to attach mystical, metaphysical, or magical significance to them; they’re just fine excuses to reflect upon our place in the Universe, and our inevitable voyage to these limitless vistas. And when we get together to share the excitement of these events, we’re celebrating how we’re all in this voyage together.

Almanac

The Draconid meteor shower will peak the night of October 8-9. They are unpredictable and rarely offer more than a handful of meteors per hour; but the Draconids have been known to produce meteor storms and slow-moving fireballs. At least the moon won’t be a problem.

The Orionids will peak the night of October 21-22. This shower often peaks at around twenty meteors per hour. There will be a waxing gibbous moon, but it will set at 1:33 a.m.--just in time for prime time viewing!

October 11-25: Zodiacal Light is bright in the east an hour or two before dawn.Sunrise/Sunset: 6:48 am/6:38 pm (Oct. 1st)