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Reasons To Believe Home PageI hope you caught a glimpse of Comet Hyakutake. My sons thought it looked like a faint fuzz ball, but I thought it looked pretty spectacular. Of the several comets I've seen since I started star-gazing (at age 8), none has matched the dimensions of this one. On March 23 the comet's head alone covered an area as wide as four moons, and the tail stretched out much farther.
Did you know that Hyakutake was discovered by an amateur astronomer? An amateur is someone who watches the sky for fun with homemade equipment, a pair of binoculars, a catalog- or store-bought telescope, or no equipment at all. Nearly half of all known comets have been discovered by amateurs—including kids and teens. Many novae (exploding stars) have been discovered by amateurs, too. Since professional astronomers (those who are paid to study the sky) typically focus intensely on one object or one type of object using one or more of several complicated instruments, they have little time to scan the heavens, and they are grateful for the work of amateurs.
Amateur astronomers make their greatest contribution in measuring the brightnesses of variable stars, stars with a brightness that increases and decreases at regular intervals. Every year sky-watchers of all ages all over the world record hundreds of thousands of measurements of thousands of variable stars. When I was in high school, I was part of that group. I turned in hundreds of measurements every year to the American Association of Variable Star Observers in Cambridge, Mass. Other amateurs and I helped professional astronomers better understand the physics of stars.
Some variable stars can be studied without any special equipment at all. If you read this issue's "Science in the News" articles, you'll see that measurements of Cepheid variable stars played an important role in strengthening the evidence for God's creation of the universe. Cepheid variables get their name from the constellation Cepheus, in which the fourth brightest star, Delta Cephei, was the first-discovered pulsating variable. By estimating its brightness once or twice a night for three or four weeks, you can determine its pattern and interval of variation. Astronomers can convert your measurements of this pulsation period (time span) into a calculation of how far away the star must be.
If you'd like to measure Delta Cephei's pulsation period, here's how—providing you live anywhere above 30 degrees south latitude. (This project will be easier for Canadians, Europeans, and most Americans. At their northerly latitudes, this star is visible all night long; it doesn't rise and set.) First, find Delta Cephei in the north part of the sky to the right of the bright W-shaped constellation called Cassiopeia. The star map connected with this article will help you. You'll see that the stars around Delta Cephei are all steady in brightness, and our map gives each a number for its brightness (the smaller the number, the brighter the star).
Next, estimate how bright Delta Cephei appears compared to stars a bit brighter, a bit dimmer, or about the same. For example, if it seems halfway between the brightness of the star labelled 4.6 and the star labelled 5.2, write down 4.9. Be sure to record the time and date of your observations and estimates. Because this star goes through its pulsation cycle over several days, measurements need be made only once or twice a night. If you get rained out or clouded out, don't worry. The gap in your notations can be filled in with measurements in future days and weeks.
Once you have enough measurements collected to see the pattern and period, you can plot them out on graph paper, marking the brightness numbers on the vertical lines and the days (and times) on the horizontal lines. The number of days between the brightness peaks or brightness valleys is Delta Cephei's period of pulsation (or oscillation).
Reasons To Believe will award a $25 gift certificate (toward items in our catalog, including the new CD-ROMs) to the first person fifteen years old or younger who sends in an accurate data report. That report must include these three things: 1) your actual brightness estimates over a minimum of three weeks, 2) a plot of those estimates on graph paper, and 3) your determination of Delta Cephei's pulsation period. Adults are welcome to participate, too, but just for fun, not for the prize.
You'll soon see that Delta Cephei is not the brightest variable star in the sky. A star in Perseus is considerably brighter and its variations much more dramatic. This star is regularly eclipsed by a much fainter star. In the next issue of Facts & Faith, I'll propose a project involving this "binary" variable star.
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