Forty years ago, when I was in graduate school, a big goal in astronomy was to discover a planet or a planetary system about another star.

Back then, searching for a planet involved taking many photographs or photographic plates of a suspected star over decades. This collection of plates was measured very precisely using special microscopes that could detect a very slight wave in the star’s motion. This slight wiggle was a sign that an orbiting planet was pulling and tugging on the star.

As one observatory detected this tell tale variation, a rival observatory with comparable images would announce that its plates failed to collaborate this discovery. With the advent of large reflecting telescopes at a number of observatories, research interests shifted towards distant deep space objects. Then even bigger telescopes came into use as well as the Hubble Space Telescope.

In 1991, the first planet beyond our sun was found. Instead of being around a sun-like star, the planet was orbiting a pulsar, a rapidly spinning neutron star. A neutron star is the remnant of the core of an exploding heavyweight star (type II supernova). The problem with a planet orbiting a pulsar is that the supernova explosion would have vaporized any nearby planets!

Presently, some astronomers think that after the explosion, there would be a disk of debris about the core that may allow the formation of planets (generation II planets, in contrast to the original planets (generation I). Since this discovery, astronomers have learned that this pulsar has actually three planets orbiting it. These planets were not found by direct observation but by variations in the timing of the radio pulses from the pulsar.

Since 1995, the discovery of planets orbiting other stars has been dominated by two teams of researchers, one in the United States and another in Europe. Both groups use the Doppler effect, the lengthening or shortening of light waves by motion away or towards us.

The spectroscopes used to detect the Doppler effect in starlight can detect motions as small as 3 meters/second (about as fast as most people can walk). (A meter is 3.28 feet.) A majority of the 300 plus new planets were discovered this way. When a planet orbits a star, it causes the star itself to move along a much smaller orbit at a low speed that can be measured.

A more recent technique to detect planets about other stars is by the very slight dimming of a star’s light as a planet passes in front of the star (an event called a transit). There are very sensitive light meters that can pick up a dimming of a star’s light by one part in thousands. This transit effect can be used with rather modest telescopes. About 50 of the new planets discovered have been through the transit method.

A more exotic way of detecting new planets is through microlensing, where the nearby star bends the light of a distant bright star into two very close images on either side of the star itself. The microlens effect causes a brightening of the distant star over a broad peak. But if there is a planet around the nearby star, it causes a small pip in the light curve of the distant star.

Most of the new planets found are comparable in mass to our biggest planet Jupiter, but in a tight orbit about their stars. These planets would be very hot and slowly evaporating. The present methods used tend to favor the detection of heavy planets in tight orbits about their stars. But some discovered planets have bigger orbits.

The heavy planets would likely have dense atmospheres, not suited for life as we know it. But planets comparable in size to the Earth and within a star’s habitable zone (where liquid water could exist) would be the mostly likely planets to have life. The next generation of space telescopes may detect these kind of planets.

Today is the first day of summer, our longest season. Tomorrow the moon swings from the morning to the evening side of the sun (new moon). At this time, there will be a total eclipse of the sun in Southeast Asia and the China Sea. (The next total solar eclipse for America will be in August, 2017.) By Wednesday, June 24th, the crescent moon will be easy to spot in our 10 p.m. western dusk.

There are four planetarium programs open to the public on the summer skies and assorted topics, one this evening at 7:30 p.m., this Wednesday at 7:30 p.m., this Friday at 7:30 p.m. and the following Monday at 7:30 p.m. The program is “All You Wanted To Know About the Summer Skies,” lasting about a half hour. The Planetarium is in Tawes 302 at Frostburg State University . Call (301) 687-4270 for road directions.

Bob Doyle invites readers’ comments or questions; leave a message at (301) 687-7799 or email him at rdoyle@frostburg.edu .