Cumberland Times-News

Bob Doyle - Astronomy

July 6, 2013

Pulling, tugging helps us to find other stars

When I was in graduate school at Virginia in the 1960s, I heard Peter Vandekamp, director of the Swarthmore College Observatory talk about a possible planet in orbit about Barnard’s Star.

Of all the nearby stars to our sun, Barnard’s Star has the largest drift across the sky. If Barnard’s Star had a planet, it would be pulling and tugging on this dwarf star, causing Barnard’s Star to have a wavy path across space.

Vandekamp had been observing Barnard’s Star with his 24 inch wide lens telescope for decades, compiling photographic data that seem to show a wavy path. Other astronomers had photographed Barnard’s Star as well and couldn’t find such a pattern.

As science relies on repeatable measurements to verify any assertion, talk about Barnard’s planet faded from view. But most astronomers still felt that our solar system was not unique; single stars as our early sun would be surrounded by a disk of debris that could form into a system of planets.

In the 1980s, infrared telescopes were put into orbit, looking for large disks of debris about nearby stars that would give off heat waves. Such disks were found, further supporting the idea that planetary systems may be common.

But actually observing planets orbiting other stars seemed nearly impossible. The light of the parent sun would be millions of times brighter than the planet’s reflected light.

Directly observing a planet about a nearby star would be analogous to observing a moth around a street light in San Francisco with a telescope as far away as our East Coast.

As the decades passed, there was great improvement in the imaging of telescopes. The best astronomy film used only a few percent of the light particles (photons) to effect chemical change, resulting in impressive images with exposures taken over hours.

With Charge Coupled Detectors (CCD) replacing film, up to 90 per cent of the photons are used to form a digital image. Another improvement was in high resolution spectroscopes, revealing that the colors in star light are crossed by dark lines.

These dark lines are due to changes in the electron levels of atoms in a star’s atmosphere. Using the shifts of these lines, astronomers could measure star motion as small as 1 meter per second (a very slow walk).

Measurement of star light intensity also greatly improved, allowing detection of a change of light intensity as little as 0.01 per cent.

In 1996, a Swiss observing team announced the discovery of a planet orbiting a star in Pegasus. Other observatories had to confirm their data.

An American team operating in California soon announced their own discoveries. The early discoveries were mostly “hot Jupiters,” massive gaseous planets in tight orbits about their stars.

The pulling and tugging of the these planets on their parent star over a few days were easily detected by the line shifts in these star’s spectra (array of colors in the stars’ light).

The next surge of planetary discoveries was found by planets crossing in front of their parent stars. This would cause a gentle dip in the star’s light that would repeat with each orbit of the planet. Even medium sized telescopes owned by amateurs could detect such changes in light.

In 2009, NASA launched the Kepler space observatory whose mission was to monitor the light of 150,000 stars in the star group Cygnus. Kepler has identified 2,700 planets, all subject to confirmation by Earth based telescopes.

In the 17 years of planet hunting, nearly a thousand exo-planets (planets orbiting other stars) have been confirmed.

The next big step is to detect atmospheres about some of these exo-planets and to look for tell tale signs of life such as free oxygen.

Bigger telescopes are now under construction in Hawaii and Chile. Space telescopes bigger than Hubble will be joining the effort to find an exo- planet that has life.

SKY SIGHTS AHEAD: Early tomorrow, the moon will swing from the morning side of the sun to the evening side (New Moon). The moon may be visible as a very slim crescent on July 10 about 9:15 p.m. to the left of the brilliant planet Venus .

On July 11, the crescent moon will be to the left of the star Regulus, marking the heart of Leo, the Lion.

 Bob Doyle invites any readers comments and questions. E-mail him at . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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