A Calendar of Astronomical Events


(This 1138th Buffalo Sunday News column was first published on January 13, 2013.)


Recently Bruce Caley wrote to suggest that I write a column about astronomical events occurring during 2013. I find this a compelling idea as I am just now in the process of annotating my own calendar for the year, copying birthdays and anniversaries in the new calendar from last year's. (If I don't do this, I end up invariably guessing the date of our anniversary wrong.) Thus this task will fit in perfectly for me and I recommend it to you as well.


It is appropriate in any case to associate astronomical events with the calendar for the calendar itself is largely defined by astronomy. The year corresponds to a revolution, the time it takes our Earth to pass once around the Sun. Because the year takes 365.2422 days to complete one of these orbits, we have leap year adjustments. Since 2013 is not divisible by four, this will not be a leap year and our calendar will have 365 days. (Very few of us will be around when that rule is next contradicted in 2100.)


Our day corresponds to a rotation of the Earth around its axis. And our month corresponds at least approximately to one of the moon's cycles through its phases. As this takes 29.53 days, twelve of these lunar months is 354.36 days, more than ten days short of a year.


Canadian science and science-fiction author, Edward Willett, has this to say about months: "Early societies corrected their lunar calendars by throwing in an extra month or days as necessary. There were literally hundreds of variations of these 'lunar-solar' calendars; the Jewish calendar, still in use, is one of these. The Roman Empire originally used a lunar-solar calendar, but it ended up in a hopeless mess because the people charged with keeping the calendar started fiddling with it to lengthen their terms of office or hasten or delay elections." And he adds, "Calendars change; politicians do not."


Two binding adjustments essentially fixed our modern calendar of months, days and years: the first by Julius Caesar in 45 BCE, the second by Pope Gregory, whose mathematician Christopher Clavius developed the rules, in 1582 CE. These rulings were named for their sponsors as the Julian and Gregorian calendars. We continue to live under the latter today.


Only the week has no connection at all with nature. It is associated with Judeo-Christian tradition and the Biblical story of the Earth's creation in seven days. Although most of us consider this number of days in a week universal, historically there have been "weeks" of length varying from three to ten days.


Here are the few local astronomical highlights that occur this year.


April 28: Saturn will be at its closest approach to Earth and its face will be fully illuminated by the Sun. This is the best time to view and photograph Saturn and its moons.


May 28: Conjunction of Venus and Jupiter. The two bright planets will be within one degree of each other in the evening sky. The planet Mercury will also be visible nearby.


October 18: Penumbral Lunar Eclipse. The Sun, our source of natural light, has width. For that reason, two kinds of shadows occur on the side of the Earth away from the Sun: a cone of complete shadow is called the umbra and the region partly hidden is called the penumbra. In this case the eclipse will be penumbral (partial) and will occur at about 7 p.m. Another penumbral lunar eclipse will take place on May 25, but so little of the Moon will be in shadow that it will not be noticeable.


Meteor Showers: April 21-22, Lyrids (20); May 5-6, Eta Aquarids (10); July 28-29, Southern Delta Aquarids (20); August 12-13, Perseids (60); October 21-22, Orionids (20); November 17-18, Leonids (40); December 13-15, Geminids (60). The number in parentheses represents the maximum number of visible meteors expected each hour.


Full moons will occur on January 26, February 25, March 27, April 25, May 25, June 23, July 22, August 20. September 19, October 18, November 17 and December 17.


On the first Saturday of each month Buffalo Astronomical Association members sponsor a public night of viewing at the society's Beaver Meadow Nature Center in North Java.


When this column was published, several readers pointed out that we may have two comets visiting this year: PanSTARRS in late February and early March and ISON in November and December. PanSTARRS, named for the Hawaiian telescope on Maui through which it was first observed, may be visible at twilight low and near the western horizon. ISON may be visible near daybreak and could be spectacular. I have used the word "may" because there is a reasonable chance that either or both will break up before they get close enough to see. Stay tuned.-- Gerry Rising