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Sagan Planet Walk, Ithaca, NY

42° 26′ 22.53″ N, 76° 29′ 48.52″ W

The Sciencenter

The Sciencenter in Ithaca, New York, is a great science museum for children. It’s full of practical demonstrations of scientific principles and hands-on exhibits without being dumbed down. A good way to reach the Sciencenter is to follow the Sagan Planet Walk, a 1.2-kilometer walk through Ithaca that starts downtown and follows a scale model of the Solar System.

But before you go, download the free MP3 tour of the Solar System that accompanies the walk. The tour starts at the Sun and works its way toward Pluto, passing the closely spaced Mercury, Venus, Earth, and Mars. After Mars, the planets become more distant; the next stop is Jupiter, then Saturn, followed by a long gap to reach Uranus. Neptune is even further, and finally at Pluto you arrive at the Sciencenter.

Each planet is represented by a concrete monolith with a picture of the appropriate planet and an explanatory panel. Stop at each planet and listen to the corresponding MP3 on your audio tour.

The Sciencenter is full of things to see and touch. The Saltonstall Animal Room has live animals such as frogs and snakes, and Connect to the Ocean has a tide pool where children can touch and interact with sea urchins, starfish, and more. For the under 4s there’s the Curiosity Corner, where everything is safe for small hands.

There’s also an infrared camera that projects the heat of a visitor’s body onto a large plasma screen in the Mars and Stars section, where you’ll also find more about the planets along the Sagan Planet Walk.

Outside, there’s the Emerson Science Park, where children can clamber over a suspension bridge, a Voussoir bridge that only stays together once the keystone is in place, and a climbing frame made of common geometric shapes. The speed of sound is illustrated with a delay tube—speak into one tube and wait for it to come out the other end. Parabolic dishes (see Chapter 48) are illustrated with a pair of whisper dishes—whisper into one, and a friend hears the whisper on the other side of the park. Other exhibits show the operation of levers and pendulums.

Whether you spend two hours or half a day in the Sciencenter, it’s an ideal spot for kids and science before heading off to enjoy the rest of Ithaca and Cornell University.

Practical Information

Full details of the Sciencenter and Sagan Planet Walk (including the downloadable audio tour) are available at http://www.sciencenter.org/.

Parsecs

It’s common to speak of astronomical distances in light years (one light year being the distance light travels in one Earth year), but astronomers are more likely to talk about parsecs.

A parsec is calculated by first imagining a line connecting the Earth and the Sun and projecting a perpendicular line, starting at the Sun, into space. A triangle is completed by projecting a line from the Earth into space that meets the perpendicular at an angle of 1 arcsecond (1/3600 of a degree). The distance of the hypotenuse starting at the Earth is one parsec, which is about 3.3 light years (see Figure 114-1).

Figure 114-1. One parsec

The distance between the Earth and the Sun is called an astronomical unit (or AU), which is 149,597,870,691 meters. By basic trigonometry one parsec is calculated to be 206,265 AU or 3.09 × 1016 meters.

The name parsec comes from “parallax of one arcsecond” and refers to the stellar parallax method of determining the distance to a star. When a nearby star is viewed at different times of the year, it appears to have moved relative to the background stars because of parallax.

The parallax effect is easily seen by observing two objects at different distances. For example, if you observe a pair of trees in a park—one close to you, and one far away—and move your head relative to the closer tree, a large movement will result in a smaller apparent movement of the distant tree.

In the stellar parallax method a star is observed at two times, six months apart. By spacing the observations at six-month intervals, you ensure that the Earth will have moved as far from the initial point as possible and be on the opposite side of the Sun. Observations of the relative movement of the star from the two positions give the parallax angle, and basic trigonometry (as discussed previously) gives the distance to the star relative to the distance between the Earth and the Sun.

To get the parallax angle, astronomers measure the angle between the star being observed and a distant, fixed star (Figure 114-2). This yields two angles, one for each of the two observations, and the parallax angle is simply their sum. The distant star is assumed not to have moved relative to the Earth, making the star appear at the same angle in both observations.

Figure 114-2. Stellar parallax