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David Levy's Guide to Variable Stars, 2nd Edition by David H. Levy

By David H. Levy

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Additional resources for David Levy's Guide to Variable Stars, 2nd Edition

Sample text

Thus, the 1950 and 2000 positions differ somewhat from that of 1900. Why do we use the old 1900 positions? The answer is based in the rise of variable-star astronomy at the turn of the century. The discovery of so many new variables created a need for a logical system of designations, and the coordinate system provided it. We know that the actual positions for each star are different now, but changing the designation to keep up with it would introduce needless confusion. 2 Variable In this column we name the variable star.

Using months and years would make this a tiresome question to answer. We know, however, that the Julian day of the second observation was 2444660, and that the day of the first was 2439551. By simple subtraction we conclude easily that the second observation was 5109 days after the first. Julian days are measured from noon to noon, UT. Universal Time is the time used in Greenwich, England, and to convert your standard time to it you need to subtract or add a number of hours. Don’t forget that the number changes if you switch to daylight time.

When it blossoms, the quality of your observations, whether they involve describing a tree or the brightness of a star, will increase dramatically. After Sir William Herschel discovered the planet Uranus in 1781, he described how the quality of his instruments enabled him to make detailed observations at high magnifications. Even today such powers are practically unheard of, and the astronomers of his time questioned his ability to see at such gargantuan magnifications. Herschel replied with confidence: ‘‘Seeing is in some respects an art which must be learnt.

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