Follow the Zodiacal Light

zodiacal light reflecting off dust in solar system (Photo credit: Wikipedia)
Many people may be away from home for the Pesach holidays, perhaps even at dark sky locations. If so, look to the west shortly after nightfall to see the elusive Zodiacal Light. It is a bright pyramid shaped cone,  wide at the bottom near the horizon, tapering to a peak at the top. It will be marked by a line connecting the bright planets Jupiter, closer to the horizon, and Venus to the above left. The line conecting these two planets passes through the ecliptic, the plane of the earth's orbit around the sun. The other planets and our moon lie within a 5 degree radius of the ecliptic, so they are never far from it. The ecliptic is called the Zodiac by astrologers, and for the same reason the sun, moon, and planets are always found within the constellations of the Zodiac.

Tonight Jupiter is in Aries and Venus is in Taurus, Venus having just put on a magnificent show passing the star cluster, the Pleiades, last week. The Zodiacal Light is a dim, elusive cone of light that is the reflection of sunlight from billions of grains and dust that lie in the plane of our solar system. The earth is constantly bombarded by these throughout the day and night, but most are too small to show as meteors. Consider them to be motes of cosmic, solar system dust that light up as they reflect the light of the sun at evening. Now is the best time of year to observe the Zodiacal Light, since the plane of the ecliptic makes an almost 90 degree intersection with the horizon, lifting the Zodiacal Light high in the sky and making it readily visible from dark, clear skies. The path of the ecliptic is marked by Jupiter and Venus, so the zodiacal light should appear along the line connecting them. Go outside and have a look and let us know if you can spot the Zodiacal Light. When you do, remember you are seeing a light show put on by the dust that fills the plane of the planets' orbits around the sun.

The Zodiacal Light, as it appears along the line connecting Jupiter and Venus, shortly after dark tonight, April 8, 2012

A Red Letter Observing Night

Zodiacal Light via WikipediaLast Tuesday night we had the Tellers and the Zamchecks under the stars and enjoyed some unique observing experiences. As I was showing them the Milky Way one of them (it was Michael Teller who deserves full credit for this observation) pointed to the horizon and asked, "What's that?" "That", as it turns out was the Zodiacal Light, a phenomenon I had never seen before.

I remembered talking to one of the astronomy graduate students at the Wise Observatory in November, and he remarked that he had seen the Zodiacal Light for the first time from Mitzpe Ramon that month. The Zodiacal Light is a fan of light that rises from the horizon toward the sky following the path of the Zodiac, or ecliptic, and is caused by the reflection of sunlight from dust and debris in the plane of the solar system. It takes a very dark, clear sky and unobstructed horizon to see it, together with circumstances of the position of the sun and ecliptic that I won't go into here. It was awe inspiring to see the band of the winter Milky Way, our galaxy, overhead with the band of the Zodiacal Light, our solar system next to it, and us standing on earth in between, our place in the cosmos clearly seen.

This alone would have sufficed to make for a red letter night. But wait - it gets better. Jupiter is a favorite telescope object right now, high overhead on an early winter's night. For the third time this year Jupiter appears quite close to Uranus as seen from the earth, just 1/2 a degree or the width of the full moon distant, and visible in the same low power telescopic field. (Although the positions of the two planets appear close in the sky as viewed from the earth, this is just an optical alignment. In reality the two planets are 15.21 astronomical units apart, or 1,414,530,000 miles. Yes, over 1.4 billion miles.) It was a wonderment to see the dark-striped disk of creamy Jupiter with three of its Galilean moons alongside, while just above it and to the side rode aquamarine Uranus like a small bubble in the black sky. I will never forget this beautiful sight, and almost refused to surrender my place at the telescope to our guests.

This photo, taken in September during an earlier conjunction, is a good approximation of the view in our telescope of Jupiter, its Galilean moons and Uranus on Tuesday night. Our colors were more intense. (Photo credit: Jin Lu) Click for full size image.

The sights made everyone giddy with excitement, so when I mentioned that Saturn would be rising about 12:30 AM, we decided to reconvene the group then and go up for another look. This was also my first view of Saturn for this season. It did not disappoint. Not only were the rings magnificent but we could also see Titan, Saturn's largest moon, and possibly a few other smaller ones.

As the last quarter moon rose in the sky with Saturn, the moon beams stuck us and for a moment we became "lunatiks". The group broke into a spontaneous snake dance across the hard rocks of the desert. 

A little night music 

Exhausted but well satisfied with our night's observing, we returned home.

Tellers, Zamchecks and that wiley old moon.

Keep on looking up!

Related articles

• Night Sky: Uranus to Align With Jupiter This Week (space.com)
• Mystery of the Zodiacal Light solved (Sky & Telescope)