Saturn At Its Best And Brightest

Saturn is at opposition today and brighter and closer to Earth than any time this year. Illustration: Bob King

Although clouds blanket the region, I know that 10 miles overhead the sky will be clear tonight, and Saturn will shine at its brightest for the year. As discussed in Friday’s blog, the planet reaches opposition today. That’s when it and Earth line up on the same side of the sun. The difference between closest and farthest distances in 2011 comes to 191 million miles – more than twice Earth’s distance from the sun. This extra nearness makes Saturn is about 1/2 magnitude brighter now than in October, when Earth’s on the other side of the sun from the planet.

Saturn is a gigantic sphere composed mostly of hydrogen and helium some 9 1/2 times larger than Earth. The 2,980-mile-wide dark gap is called Cassini's Division. Credit: NASA

Saturn’s current magnitude is 0.3, making it a near match to Procyon in the constellation of Canis Minor the Lesser Dog. In six months, after our two planets have parted company,  it will have faded to 0.7.

Because Saturn’s axis is tipped like Earth’s, we see the rings open up, close and open up again during its 29.5-year-long orbit around the sun. Currently the rings’ north face is tipped toward us and will be until 2025.

In recent years, the ring plane has been nearly edge-on and looked like a toothpick stuck through Saturn’s olive-like globe. They’ve been opening up this year and in April will be tipped 9 degrees to our line of sight. That’s wide enough to see the dark gap called Cassini’s Division that separates the outer Ring A from the inner Ring B. I’ve spotted it through my scope several times over the past week, when the air’s been steady enough to magnify around 100x.

Saturn's ring tilt varies over the years because its axis is tipped nearly 27 degrees to its orbit. As it orbits the sun, we first see the north face of the rings, then a view of the planet edge-on, followed by a view of the south face. Credit: Tom Ruen

In the coming months, the ring tilt will narrow slightly to a minimum in June and then begin to slowly open again for the remainder of the year. Patience is a must for seeing the rings at their maximum opening of 27 degrees; that won’t happen until October 2017.

The rings, which are made of highly reflective chunks of ice, contribute greatly to the planet’s overall brightness. In the winter of 2031-32, the south face of Saturn’s rings will be nearly fully open at the same time the planet is at opposition. And that happens right around Saturn’s perihelion or closest approach to the sun. Combined, the two factors boost its magnitude to -0.5 , brighter than Arcturus or Vega!

Saturn is easy to find around 9-10 p.m. local time in early April. Face east and look for three bright stars that form a large, long triangle. Saturn is the 'star' at the top right apex. Photo: Bob King

Saturn rises at sunset in Virgo the Virgin tonight and remains visible all night long. As each day goes by, the planet rises four minutes earlier, ascending higher in the southeastern sky throughout the spring.

Take some time the next clear night to enjoy the ringed world at nightfall this month. While it’s star-like to the naked eye, carefully-focused 10x and higher power binoculars will reveal the planet’s oblong shape, made so by the shape of the rings. To see the ring(s) itself clearly and cleanly separated from the planet, you’ll need a telescope that can magnify 30x on up.

By all means, put a telescopic view of Saturn on your ‘bucket list’. It’s the most cosmically beautiful object in the universe.