A Z-lightful evening ‎

I looked up this past Saturday night at the end of twilight and faced one of the best zodiacal light cones I've ever had the pleasure to see. The next week and a half will be the last time this spring for a good look at this expanse of glowing comet dust visible in the west 1 1/2 - 2 hours after sunset.

The zodiacal light is centered on the path the sun, moon and planets take through the zodiac constellations. The zodiac basically defines the flat plane of the solar system where all the planets revolve and many comets as well. Comets shed dust from their tails when they swing through the inner solar system. The dust motes are suspended in space and illuminated by sunlight creating a delicate cone-shaped glow visible in a dark, rural sky towards the end of evening twilight. Because the zodiac is still steeply inclined to the horizon in April, the zodiacal light stands high enough about the horizon haze for good visibility. By May the path is lower, and while the zodiacal light is still present, much of it is lost to atmospheric extinction. June, July and August are even worse. Not until fall mornings will the light be seen with relative ease again.

I just happened to be on a hill at a dark location Saturday and was totally taken with the scene. I imagine that flat, wide-open spaces like North Dakota, the light must be even more remarkable. To find the zodiacal light, get to the darkest sky you can. As dusk gives way to night, look for a large, wedge-shaped glow about as bright as the Milky Way standing at an angle to the western horizon with the Seven Sisters Cluster near its top. You might at first think it's a "light dome" from a distant town but its shape and direction of tilt distinguish it from manmade glows.

The reason I needed a hilltop viewing post was to seek Comet Machholz which was discovered in late March by long-time amateur comet hunter Don Machholz. As described in an earlier blog, an amateur discovery is a rare bird in this day of automated sky surveys so I thought it worthwhile to pay attention to Don's find. The comet was low, low, low in Andromeda and despite careful and continuous observation during late twilight I had absolutely no luck seeing it. Comet Machholz was not only faint but the thick, hazy air near the horizon proved a further obstruction.

There are times we amateur astronomers seek a particular object on repeated occasions for hours and in the end never see it. Sometimes we're disappointed but generally not because we know we've tried, pushing both eye and equipment to the limit. There's satisfaction in that as in other endeavors in which you've done your best but haven't always achieved the expected outcome. You either try again from a darker sky, use a bigger scope or go on to another opportunity. As in life, new opportunities always come along in sky watching.

Today the Cassini spacecraft in orbit around Saturn makes another flyby of Titan, the only moon in the solar system with a dense atmosphere. Every time Cassini eyes Titan up close it creates better maps of its intriguing surface dotted with hundreds of lakes of liquid methane and carved by channels and rivers of the same. In a quick one-two punch, early Tuesday evening the craft will make a very close pass to Dione, another of Saturn's moons. In addition to photographs, the onboard instruments that detect moving particles will look for any activity on or near the moon.

Today's successful predawn launch of the space shuttle Discovery (right) made for a spectacular sight for those lucky enough to be there. The shuttle is now in orbit and will dock with the International Space Station (ISS) early Wednesday morning at 2:44 a.m. Central time just before the ISS' first predicted pass over the Duluth region at 5:54 a.m. Inside the shuttle's cargo bay is a module named Leonardo, a pressurized "moving van" of sorts that will be attached to the station temporarily on April 7 and returned to the shuttle's cargo bay Thursday, April 15. The module is filled with spare parts, supplies, new crew sleeping quarters and science gear that will be transferred to the station's laboratories. This is the final compliment of laboratory facilities that will complete the station's overall research capabilities. NASA is getting everything in order before the final shuttle flight later this year. Tomorrow I'll have a complete set of viewing times for watching the pair in the early morning hours.

On a final note, a fairly bright naked eye star will be occulted by a faint asteroid tomorrow morning for those living in Los Angeles, parts of Nevada, western Montana, Idaho or near Calgary and Edmonton, Alberta. The star Zeta Ophiuchi will disappear for a few seconds when the asteroid 824 Anastasia passes directly in front of it. Since Zeta's about as bright as a Big Dipper star, fortunate sky watchers can watch the occultation with their bare eyeballs. No scope needed.