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A night hike through the cosmos

on August 17, 2010

The aptly-named Celeste Burrows armed herself with scissors, pens, and a two-inch wide roll of paper on Friday night, ready to lead 12 adults and three children on an unusual journey. She unrolled and cut lengths of paper and handed them out, instructing each person to write “sun” on one end and “Pluto/Kuiper Belt” on the other.

Burrows teaches astronomy at community colleges and at the Chabot Space and Science Center on Skyline Boulevard in Oakland, but on Friday she was dressed to hike, wearing a warm vest and with her pants tucked into her boots. She was ready to guide a simulated walk through the solar system, a roughly four-mile loop through Roberts Park starting at the science center and ending in the dark. Similar hikes combining nature and astronomical lore have been conducted through Chabot in the past, but the opportunity arises infrequently.

Before the walking commenced, Burrows wanted her charges to learn a bit about interplanetary distances by charting out the planets on paper. The exercise clearly showed that no one in the group had much of a clue where any of the planets are in relationship to the sun.

Burrows moved around from person to person, asking what planet they thought went halfway between the sun and Pluto. No one knew. It was Uranus, she said. How about halfway between Uranus and the sun? Everyone was still stumped. It’s Saturn. How about between Saturn and the sun? They were still clueless, though curious, copying from neighbors and waiting for Burrows to fill them in on the next planet’s location.

Saturn and its rings. Photo from Chabot Space and Science Center.

The maps also clarified that most of planets ­– Mercury, Venus, Earth, Mars, Jupiter, and Saturn – orbit far closer to the sun than distant Neptune or Pluto do. Pluto, considered too small to be a proper planet, is located along the Kuiper (rhymes with “hyper”) Belt. About 5 billion miles away from the sun, the belt marks a sort of border for the solar system; it’s littered with many “small” objects including dwarf planets like Pluto, as well as asteroids and leftovers from the solar system’s creation.

After getting an idea of where things lie in the solar system, the hiking group headed out into the woods, accompanied by a sliver of moon slowly rising in the west, as Burrows pointed out. If it had been slightly darker, they might have seen Venus, Mars and Mercury coming into the sky alongside this crescent moon.

But the real purpose of the hike wasn’t merely to stargaze but to try to fathom the layout and scope of the solar system while enjoying dusk in the woods. Burrows asked the group to imagine that the sun was around a meter in size, perhaps the length of one big stride. If the group’s starting point at Chabot was the sun, she said, it would be roughly 46 steps to the first planet, Mercury. The group embarked from the entryway, counting steps across the road toward the trailhead.

One of the smallest in the party, a little girl in a bright pink and purple knit poncho, counted out loud for everyone. The count stopped the group in the middle of the road, at virtual Mercury, the closest planet to the sun. After a quick briefing by Burrows, the group took 48 more steps to Venus. The second planet from the sun is actually the hottest, even though it’s farther from the sun than Mercury. It used to be considered a twin to Earth, being of similar size. However, it swelters at more than 850 degrees Fahrenheit under a thick atmosphere of heat-trapping greenhouse gas, more than 95 percent carbon dioxide.

Forty steps later, when the group arrived at “Earth,” it was about 7:30 p.m. and the actual sun hung low in the sky. Golden light slanted through the redwood trees of Roberts Park onto huckleberry bushes and ferns. Dull thuds from footsteps on dirt and mossy fallen wood were punctuated with cracking twigs and camera clicks. The observatory and its concrete finally invisible a stone’s throw behind the trees, the hike had begun in earnest. Next stop, Mars.

In space, it takes ten minutes for the radio waves traveling the speed of light from Earth to reach the rovers that cruise the Martian surface, and another ten for the waves to get back to Earth. None of the physical objects that humans have sent to Mars – satellites that orbit the planet, or the two rovers exploring its surface – have ever returned: the only Martian objects that we have, come from the rare meteors are knocked off Mars and happen to land on Earth.

A hiker asked, How does that happen? Mars would have to collide with an asteroid of sufficient size to send Mars rock flying off at its escape velocity, the speed that objects need to reach to free themselves of a planet’s gravity, Burrows explained. It’s about 11,300 miles per hour on Mars. (Earth’s escape velocity is about 25,000 miles per hour.)

Passing Mars, the group continued to walk as night fell on Roberts Park. Every year, Burrows explained, our planet bravely plows into clouds of space dust, the trails left behind comets away in other parts of their orbits. When this detritus–mostly ice and pebbes–hits our atmosphere, it burns up. At night, the larger of the glowing particles are visible to the naked eye, appearing as streaks across the sky as they fall to earth.

Late last week, meteor buffs everywhere looked to the sky to catch the fantastic showers caused by the Perseid meteors, an event that happens every August as Earth intersects the detritus left by the Swift-Tuttle comet. The comet itself is on its way out to the edges of the solar system and won’t return for 116 years. Unfortunately for those hoping to catch a glimpse of the Perseid meteor shower during Friday’s hike, a solid fog began to roll in along the distant ridges as the group arrived at a mock Jupiter.

Roughly an eighth of the distance between the sun and Pluto, sits the solar system’s biggest planet, Jupiter. “If someone was looking at our solar system from some alien place they would describe it as ‘the sun, Jupiter, and some scruff,’” Burrows said.

Jupiter’s distant next-door neighbor Saturn looks almost as large, though, if you add its huge rings, she said. However, Saturn, as an object of scientific interest, is somewhat eclipsed by its many moons. Two of the 62 moons of Saturn that have been discovered so far—Titan and Enceladus—show evidence of liquid matter, which might indicate a potential for life, as does the presence of carbon. Titan has rivers of liquid ethane and methane, organic gases on Earth but both containing carbon. Enceladus shows simple organic compounds, too, and may hide liquid water below its frozen surface.

Solar-Go-A-Round Exhibit. Photo from Chabot Space and Science Center.

From the Earth, it takes a bit less than an hour for light to reach Saturn. For the hikers, it took a similar amount of time to reach virtual Saturn. And for an actual robotic spacecraft, the Cassini-Huygens mission, the journey from the Earth to Saturn took seven years. Fortunately for those participating in Burrows’s guided hike, it didn’t take quite so long to return back to Chabot, where, on a clear night, Saturn and the closer planets can be viewed through the observatory’s telescope, open to the public until 10:30 p.m. on Fridays and Saturdays.

It’s the last chance for Chabot visitors to see the center’s Solar-Go-Round exhibit, a virtual tour of the solar system, which closes forever at the end of the month. It will be replaced by Bill Nye’s Climate Lab, an exhibit about climate change and energy.

Upcoming events at Chabot are listed here.

Lead image: Diffuse nebulae called M42, sometimes visible to the naked eye. Photo courtesy of Chabot Space and Science Center.

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  1. Laurel Kornfeld on August 17, 2010 at 9:40 pm

    Pluto is not too small to be a “proper planet,” as dwarf planets are planets too, in spite of the controversial IAU decree. Only four percent of the IAU voted on this, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. Under this definition, our solar system has 13 planets and counting: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.

  2. Anrica Deb on August 17, 2010 at 10:34 pm

    Laurel, Thank you! What a wonderful explanation of what it means to be a planet. -Anrica

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