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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

In September 2012 – let Venus be your guide to the Beehive, crescent Moon, and Zodaical Light

Once again, Venus steals the show in the morning sky this September, while Mars and Saturn dance low in the southwest in the early evening. Jupiter crosses over into the evening sky, but just barely – it is still better seen during the early morning hours. In my book, the most fascinating and attractive naked eye challenge of the month will be seeing Venus  in the midst of the Zodaical Light – those minute solar system dust particles that in their own special way and time can mimic the display of the Milky Way.

Check out this wonderful photo of the Zodaical Light – and keep in mind that it was taken through the thin air and superbly dark skies of a mountain observatory and benefits from the camera’s ability to do a better job of capturing faint displays than our eyes. Still, it gives us a good idea of the shape and size of what we are looking for when we seek this elusive glow in our skies.

Zodiacal Light Seen from Paranal, European Southern Observatory.

Now I know the predawn hours are not for everyone, so let’s deal first with the continuing show in the southwest where Mars and  Saturn are still visible low in the sky shortly after sunset – and they still team up with Spica to make an interesting combination. What’s more interesting, however, is as the month goes on Saturn and Spica head  for the horizon pretty quickly while Mars will hold its own for the next several months, hanging out near the horizon and letting the background stars slide behind it.

On September 1, 2012 Mars, Saturn, and Spica will be near the horizon – but visible – 45 minutes after sunset in the west-southwest.

Prepared from Starry Nights Pro screen shot.

For the rests of the month Mars will remain at roughly the same altitude – betwen 11 and 13 degrees above the horizon about 45 minutes after sunset. However, Saturn and Spica swiftly fall out of sight. By mid-month Spica is a mere two degrees above the horizon and Staurn – barely visible – at about 7 degrees high. (Using binoculars will help locate it.)  By the end of September Spica has set at this point (45 minutes after sunset) and Saturn is a mere two degrees above the horizon – most likely too difficult to find.  But Mars’ rapid orbital motion carries it eastward as seen against the background stars which all appear to be moving westward – towards the horizon – because of the orbital motion of Earth.

Venus and the Beehive

Prepared from Starry Nights Pro screen shot.

From about September 9-18, 2012  you can watch Venus pass close enough to the Beehive (M44) star cluster for both to appear in the same low power binocular view. The most interesting view will come on the morning  of September 12 when they are joined by  a crescent Moon. Center Venus in your binoculars, the put it in the right side of the field of view and you should be able to see the Beehive. Put it in the left side of the field of view and you’ll see the Moon.

Oh – and on October 3, 2012 Venus will have an incredibly close visit with first magnitude guidepost star, Regulus. In fact they will be so close for those in mid-northern latitudes that  I doubt you’ll be able to separate them with the naked eye, though they should make a nice binocular – or telescopic – double! They should be about 8-minutes of arc apart – which means they’re closer together than Mizar and Alcor, the famous test of eye sight in the handle of the Big Dipper. I think you will separate them with binoculars, but the large difference in magnitude – Venus is -4.1 and Regulus about 1.3 = could make this a serious challenge. I should add, however, that Venus is moving quickly and  exactly how far apart the two  appear on this particular morning will depend on your location. If I move to the West Coast i get a larger separation. 

Basking in the Zodiacal Light

Prepared from Starry Nights Pro ecreen shot.

The second half of September 2012 will be a good time to start looking for that most elusive of Solar System sights, the Zodiacal Light – and Venus will help!  You actually have a brief window when it’s visible starting about two hours before sunrise and going to about  80 minutes before sunrise. After that the twilight will drown it out. Draw a line between first magnitude Regulus – near the horizon – and Venus. This line will tilt to the right (at least from mid-northern latitudes) and the Zdaical Light will be located along it since that is pretty much the line the ecliptic takes and the ecliptic marks the plane of our Solar System.  The ecliptic marks the general area where you are going to find most Solar System bodies – planets, moons, asteroids – and yes, tiny specks of dust that make up the Zodaical Light.

You don’t need a totally clear horizon to see the zodiacal light, or binoculars, but you do need total darkness and that means little-to-no light pollution and no  – or very little – Moon. In Septmeber 2012 the last two weeks fit the bill – from about Sept. 14-28. I feel I have a good shot at it from my favorite ocean-front observing point where I have a clear horizon to the east with no cities to create light domes there. Mornings in September and October –  or evenings in February and March – are the best times for folks at mid-northern latitudes to look for the Zodaical Light.

The Zodiacal Light is roughly the same intensity as the Milky Way, so if you can see the Milky Way from your chosen location, then you should be able to pick up this faint glow. Like the Milky Way, it stretches over a good deal of sky. It is widest near the horizon and gets narrower as it rises towards the zenith. You want to look for this starting 120 minutes before sunrise, but I advise you also allow at least 15 minutes to half an hour for your eyes to dark adapt. (For projects like this I frequently keep a red flashlight near my bed and use it to preserve my night vision when I get up.)  If you try to look for this later, you may confuse it with twilight. What we are seeing is sunlight reflecting off interplanetary dust particles – dust particles that orbit in the same plane as the planets – the area we call the zodiac – and thus the name for this phenomena, Zodiacal Light.

How high? How bright? How wide? All this depends on your conditions – and even in an area where theere is little or no light pollution, it will vary. All nights are not equally transparent.  But you do want to avoid the Moon and it will come back into the equation by the 28th – but don’t worry. If you miss it this month, October and November are also good months to see it. And if you wish to see it in the evening sky, March and April are good.

If you see it, reflect on this explanation from Wikipedia:

The material producing the Zodiacal Light is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth’s Moon, each particle would be 8 km from its neighbors.

For the metrically-challenged (that includes me) that means one dust particle every five miles! And each particle is tinier than a bird shot – way tinnier than a BB. And that causes all that light?! Awesome!


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