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Stardate
08:31:97
Saturn rises above the eastern skies this week, offering viewers a chance to glimse the planet's mighty ring system starting at about 9 pm. Arguably the most beautiful object in the solar system when viewed by amateur astronomers, Saturn is now chasing mighty Jupiter across the late summer skies. Saturn orbits the Sun at a distance which varies between about 1,350,000,000 km and 1,500,000,000 km (between 843,750,000 and 937,500,000 miles) from our parent star. This is a distance equal to nine to ten times greater than the distance between Earth and the Sun.
Keep in mind as you are reading about rising or setting times of objects from any astronomical source that the times listed are based on an ideal horizon, which is most often not the case. Because horizons vary, astronomers and astronomical software have no idea of what local rising and setting times will be.
To figure out your local rising or setting times, there are two
ways to go about it. The first involves going out to the area where you
do most of your observing, and measuring how high the horizon is in different
directions. Since the Earth turns at 15 degrees per hour, objects seem to
arc across the night sky at a speed of one degree every 4 minutes. Therefore,
if you find that your eastern horizon is, for instance, 10 degrees above
the true horizon, then objects rising above that horizon would be seen,
from that area, 10 times 4, or 40 minutes after the time listed. If your
western horizon is 5 degrees from an ideal horizon, than an object setting
there would set 5 times 4, or 20 minutes before the time listed.
The second method is to simply wait until an easily recognizable object such as Saturn comes over a given horizon, and record the difference between the listed rising or setting time, and when the object was first seen from your location. Then, any object rising or setting on that horizon would differ by that same amount of time. By this method, you can also find the angular height of your horizon. After all, if an object rises 40 minutes after the time listed, than that horizon must be 40 divided by 4, or 10 degrees from a perfect horizon. Saturn will be 10 degrees above the horizon by 10 pm, and will be found about 11 degrees to the south of due east.
If the Earth turns at 15 degrees per hour, and Saturn rises at 9pm, why is it only 10 degrees above the horizon at 10pm, and not 15 degrees above? The answer lies in the the fact that objects create an arc as they travel across the sky. Since the Earth turned 15 degrees in that hour, and Saturn only climbed 10 degrees during that time, a little trigonometry reveals that the orbit of Saturn is inclined nearly 42 degrees to the horizon. Look for Saturn as a bright, magnitude 1.4 object low to the east/southeast about 10 pm.
The rings of Saturn are among the objects which enjoy the greatest popularity among amateur astronomers, and Saturn is the most highly requested object to view at star parties. The rings of Saturn were first glimpsed by Galileo in the year 1609, who described the planet as having "ears". The fact that the rings of Saturn are seperated from the planet, and encircle it was first deduced by Christian Huygens in 1659. There are several gaps in the rings of Saturn, the largest of which can be easily seen by even very small telescopes or binoculars, and is known as the Cassini division. It is named after Giovanni Cassini, who discovered the gap in 1675. When the Voyager 1 spacecraft passed by Saturn in 1979, it revealed the rings to be made of many thousands of grooves and gaps, similar to a phonograph record.
Next week, we'll take a more in-depth look at Saturn, and the week after that, a study of Saturn's strange, giant moon Titan.
Clear skies, and good viewing.
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