Michael settle, age 13, of clendenis, w. V., for his question:

What is a pulsating star?

No expert has to tell us that most of the stars seem to vary, now brighter now dimmer, like flickering flames. Perhaps the official name for these sparklers is pulsating stars. Not so, say the experts. The antics of a true pulsating star are far more dramatic than a twinkling wink.
The wondrous heavens are populated with a wide assortment of star types    young and old, giants and dwarfs, fiery red and flaming gold, white hot and hotter blue white. Most stars are steady characters and constant by nature. As a rule, the astrophysicists can place a star in a certain class and expect it to stay there. The coolest stars are the m type red giants. The hottest are the 0 type blue white stars. Pulsating stars are odd balls of fire that refuse to abide by this neat system of grades and classes.
When we use our eyes alone to estimate the brightest and the dimmest stars, we are estimating their apparent magnitudes. But objects seem to shrink and dish with distance, and this optical trick is true even of the stars. By apparent magnitude, a dim star may be a distant dazzler, and a brilliant star; may be a modest fellow quite close to the solar system. Estimating true or absolute magnitude is related to distance and calls for skills of both astronomy and physics the special know how of the astrophysicist.
This patient task was made more complex by certain stars that change in magnitude from day to day or even from hour to hour. But there is always a divided reward for a job well done. When the pulsating rhythms were charted, they provided an accurate yardstick for measuring up to 600,000 light years of heavenly distance.
Each pulsating star repeats its own rhythm in a set period which may be hours, days or months. It may start each pulse as a big hot yellow star of class f and advance to the next class as a bigger and brighter, hotter and whiter type star. Its magnitude may vary by perhaps 10, perhaps 300 fold. We do not know why they pulse, but hundreds of these odd stars have been sighted in the milky way and others in distant galaxies.
The figures show that the brightest pulsating stars are those with the longest periods. The magnitude of a star is related to its distance hence, the relationship between the brightness and period of a pulsating star becomes a yardstick. More remote pulsating stars helped the astrophysicists to estimate the distance of the magellenic clouds, the great spiral in Andromeda, and other star systems beyond our galaxy.
Stars that change or seem to change are called variable stars. An eclipsing binary seems to vary because it is a pair of orbiting twins, and at regular intervals one star eclipses and dims the other. Sometimes a modest star explodes into a dazzling nova or supernova. A pulsating star is called a cepheid variable because the first ones were noted in Cepheus, the kennel shaped constellation which is separated from the big dipper by the little dipper and Draco, the dragon.