This weekend offers stargazers one last good opportunity to pull out their telescopes and view Saturn's narrowing rings before they go dark and Saturn slides down into the evening twilight.

Normally you can see Saturn's glorious rings through a telescope. But about every 15 years, they seem to disappear. This is due to a change in the orientation of Saturn compared to Earth. When the rings are edge-on to the Earth, they are very hard to spot because they are less than one mile thick.

The rings won't become precisely edge-on until Sept. 4, but don't bother marking your calendar. Saturn will be so close to the sun that no one will be able to see the rings wink out.

Look for Saturn this weekend as soon as possible as night falls around 10:30 p.m. The ring world will sit about 13 degrees above the western horizon. You will have only about 20 minutes to view the almost edge-on rings before Saturn sets.