Along with lunar eclipses and meteors, conjunctions — two or more bright celestial objects appearing close to each other — rank as one of the night sky's most remarkable recurring phenomena visible with the naked eye.
Seeing the moon near a bright planet always grabs our attention, but planetary conjunctions can also be show stoppers, especially if you watch the movement of the planets over time among the background of stars.
Conjunctions are one of nature's optical illusions, making it appear that celestial objects are extremely close to one another. That's only from our perspective, though. In reality, they're millions of miles apart.
Just picture a celestial track-and-field stadium from a bird's-eye view. Each planet has its own lane, just like a runner competing in a sprint or relay. The sun is in the middle of the stadium. The planets race around it, with Earth in Lane 3. The earth's location on the track relative to the other planets determines which runners (planets) we see in our line of sight.
This analogy illustrates why planets vary in their visibility and why they are not always visible at the same times each year. They migrate from the evening sky, to not being visible, to appearing in the morning sky.
Conjunctions are not rare. Since 2003 we've averaged five planetary conjunctions a year that are less than one degree apart, the width of your little finger at arm's length. 2013 will feature six.
Why so frequent? The planets and the moon travel near and along an imaginary line we call the ecliptic. It represents the apparent path of the sun in our sky from our perspective. With the planets and moon moving in space at different speeds with different-size orbits, it's just a matter of time until two or more planets are positioned so they look to be extremely close to each other from our perspective.
Venus and Saturn take their turn Monday morning. Since July, Venus has dominated the morning sky. Venus can currently be found in the southeast for about two hours starting at 4:30 a.m. in the constellation of Virgo the Maiden.
Back in July, Venus formed a morning conjunction with Jupiter that placed the two planets at an apparent separation of five degrees, about the width of three fingers at arm's length. Last March the same two planets were three degrees apart during the evening hours.
In August, three degrees separated Mars and Saturn.
This time around, Venus and Saturn appear less than one degree from each other. Many telescopes will show the two in the same field of view. Take advantage of Saturn's visibility, as its rings are at their most tilted, or opened, in six years.
Without a telescope, keep an eye on the sky and watch Venus and Saturn slowly moving against the background of stars. Come Nov. 30, Saturn will be farther from the horizon, whereas Venus will be closer. With a closer look, you may even see Mercury, which rises at 5:40 a.m., hanging low in southeast.
So after this holiday weekend, I encourage you to gaze at the sky for a remarkable planetary conjunction Monday morning. And if you're not a morning person, you can still enjoy the view of Jupiter in the east after sunset.
This is Cosmic Mike wishing you an astronomical day. For more celestial news and events be sure to "Like" my Cosmic Mike page on Facebook.
Mike Smith is senior astronomy educator at the North Museum of Natural History and Science in Lancaster.
cosmicmike@northmuseum.org
