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Skywatching

Conjunctions and 'rising worms' in space

Movement of planets

On March 2, the planets Venus and Jupiter were within half of a degree of each other in the western sky after sunset.

That is closer together than the width of the full Moon. They are still fairly close together but getting a bit further apart every night. These close encounters, known as conjunctions, are a beautiful consequence of the way the planets move around the Sun in their orbits.

Conjunctions between the planets, along with eclipses of the Sun and Moon, and the movements of the Sun, Moon and planets among the stars, were familiar to our ancestors. Even though they did not understand what was going on, they could predict astronomical events precisely.

Back in those remote days, the science of astronomy had not yet separated from the pseudo-science of astrology, and events like conjunctions, eclipses and the positions of the planets among the stars were widely regarded as portents. This is probably why two royal astronomers were executed by their angry King for not telling him an eclipse was due. The predictive skills of those ancient astronomers came from the combination of painstaking observations and the identification of patterns and rhythms in the movements of objects in the sky.

All the known planets orbit the Sun in concentric, almost-circular orbits. Starting from the Sun, we have Mercury that races around the Sun in about 88 days, Venus, with a lap time of 225 days. Our planet takes a year (365 days) to complete one trip around the Sun. Continuing outward there is Mars (687 days), Jupiter (12 years), Saturn (29 years), Uranus (84 years), and Neptune (165 years).

Since all the planets are orbiting in almost the same plane, it is inevitable that from our position on Planet 3, on occasion we would see pairs of other planets lying in the same direction, appearing close to one another even though in reality they are far apart.

If all the planets orbited in exactly the same plane, close encounters between planets would be very common, with planets passing precisely in front of another. However, because the planets do not orbit precisely in the same plane, these encounters are very rare, and close encounters like the one we have just seen (unless it was cloudy) are pretty rare too.

Our ability to comprehend the motions of the planets has been made complicated by our being forced to make our observations from one of those planets, spinning on its axis as it orbits round the Sun. This means planets appear to move in one direction among the stars, and then reverse course for a while before returning to their original directions.

Because these motions repeated, our ancestors decoded their rhythms and used that knowledge to predict future movements, conjunctions and other events.

It is likely our first astronomical observations involved our noticing the rising and setting points of the Sun moving to and fro along the horizon during the year, and using them to fix the seasons. The cycle of phases of the Moon gave us our first concept of the mo(o)nth and the beginning of a calendar. From there it would have been very human to look more deeply at the rhythms of the sky and the timing of events like conjunctions and eclipses, and in doing so give birth to what would become astrology and the science of astronomy.

Each year contains about 13 lunar cycles, running from new Moon to the next new Moon. Many peoples around the world named each lunar cycle after some important local event.

Somebody named the current lunar cycle the "Moon of Rising Worms", when worms hibernating deep in the ground wake up and come up to start the new season's work.

If so, the people who named that Moon were certainly not living in Canada.

•••

• Venus and Jupiter still lie close together, low in the southwest after sunset. Mars lies high in the south.

• The Moon will reach last quarter on March 14.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, B.C.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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