The Astronomical Information on Your Star Certificate

All Name A Star Live customers receive a Star Certificate, such as the example below, displaying the name of their star, a personal message for their gift recipient, and astronomical information about their star. But what exactly is this astronomical information, and what does that information represent?

The astronomical information appears toward the bottom of the certificate. In this example, the "Catalog Number" for this star reads "TYC 6200-1058-1." The letters "TYC" stand for the "Tycho" catalog of stars, which is simply a list of stars commonly used by astronomers. The letters "TYC" together with the numbers that follow those letters constitute the scientific name, so to speak, that astronomers have given this star within the Tycho catalog. In short, the star's scientific name is "TYC 6200-1058-1."

Astronomers use a number of star catalogs. Some of the most popular star catalogs include the Tycho catalog (TYC), the Hipparcos catalog (HIP), the Smithsonian Astrophysical Observatory catalog (SAO), and the Henry Draper catalog (HD). A given star can be listed in each of these catalogs: Thus, any given star can

Photograph of Polaris, the North Star. Polaris is actually a trinary star system: All three stars of the Polaris sytem appear here. Credit: NASA

have several different scientific names. Let's take the case of a star listed in the Tycho catalog as TYC 4628-237-1. This star has multiple scientific names, including HIP 11767, SAO 308, and HD 8890. But most people know this star simply as "Polaris" or "The North Star."

The star in our example – TYC 6200-1058-1 – just happens to appear only in the Tycho catalog. However, in a certain sense, it appears in one other catalog: Name A Star Live's list of stars, where the star is named "Melissa."

Beneath the Catalog Number on the star certificate you'll notice the "Constellation" of the star. Just as we divide a continent into clearly-defined areas called "nations," astronomers divide the night sky into clearly-defined areas called "constellations." Each constellation has its own boundaries within which are located countless stars. In our example the star known in the scientific community as "TYC 6200-1058-1" is located within the area of the night sky called "Libra" (which just happens to be one of the constellations of the zodiac).

The "Visual Magnitude Indicator" is a measure of how bright the star appears in the night sky. The lower this number is, the brighter the star is. In our example, TYC 6200-1058-1 (Melissa's star) is magnitude 11. A 12th magnitude star would be dimmer, and a 10th magnitude star would be brighter. On a clear, moonless night, far from city lights, the dimmest star a human with normal eyesight can see is a star of magnitude 6. (So to see Melissa's star one would need to use a telescope.) Most of the stars one sees in cities are stars of magnitude 3 or lower. Stars can have magnitudes that are less than zero. For example, the brightest star in the night sky is the star "Sirius" (TYC 5949-2777-1), which is magnitude -1.4. By comparison, the full Moon is magnitude -13, and the Sun is magnitude -27. The ancient Greeks invented

North America as seen from space at night. Due to light pollution from urban areas, in order to see dim stars one must travel far from city lights. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

this visual magnitude system, ranking the stars they could see with the naked eye from 1 through 6, with 1 being the brightest and 6 the dimmest.

Finally, the "Right Ascension" and "Declination" values found on the star certificate are the astronomical coordinates of the star. Geographers use an imaginary grid of longitude and latitude lines to locate positions on Earth. For example, New York City is located at longitude 73º 58’ West and latitude 40º 47’ North. Similarly, astronomers use an imaginary grid of lines called "Right Ascension" and "Declination" to locate positions in space. Declination is measured in degrees, minutes and seconds, and Right Ascension is measured in hours, minutes and seconds. In our example, Melissa’s star (TYC 6200-1058-1) is located at Right Ascension 16h 1m 37s (read as "16 hours, 1 minute, 37 seconds") and Declination -15 º 13' 11" (read as "negative 15 degrees, 13 minutes, 11 seconds").