the newly licensed Peter Ceravolo trying out his wings andgetting a few aerial snapshots of the Starfest gathering.Rachel, along with her parents and I, attended one moretalk in the afternoon, that by Ivan Semeniuk. He enthusiasticallylaunched into the early history of asteroid discovery, highlightingthe discovery of Ceres nearly 200 years ago, coming full circleto our own opportunity to personally discover Ceres in the fallas it passes through opposition in the Hyades — very close toits original discovery position. Emerging from the main tent,we were dismayed to find the western sky scudded withherringbone clouds in front of a higher icy whitewash. It wasnot a good sign for the evening observing session or for goodweather the next day. Sure enough, over suppertime the Sundisappeared prematurely, taking with it the last clear skies ofStarfest ’98. Final score: Clouds 2.5 nights, Stargazers 0.5 nights(not counting the two clear nights enjoyed by those who camein the days before Starfest).After supper Lief Robinson of Sky & Telescope gave a widerangingtalk on the opening horizons for amateur collaborationwith professional astronomers. He echoed the feeling I have(and I am sure the feelings of many in the hall) that we are inthe “golden age of amateur astronomy.” With widely availablequality equipment, personal computing power, and Internetcommunications, it is now more possible for the amateur toengage in useful, serious research. A particular strength foramateurs is their ability to dedicate extended observing timeto projects, unlike professional astronomers who are sorelysqueezed for observing time. Leif showed many examples ofuseful, exciting amateur astronomy, including sensitizedcamcorder videos of Perseid meteor fireballs (voices on tape inexcited Japanese), and the 4-second asteroidal occultation ofa 2 nd magnitude star. I found the last video even more breathtakingthan the solar eclipse video offered earlier in the day, probablybecause I have tried (and failed) many times to see and timean asteroid occultation. I felt (and feel) duly inspired!By then it was time for a reluctant last look around. Racheland I settled into the Red Light Café for an extended cozy stay.What better pastime is there for clouded out astronomers thancoffee, games and conversational company… and even theoccasional song?The view of the grassy area on Friday instead of Saturday. Joe O’Neil (inwhite shirt at left) is standing by his table of goodies, while fellow LondonCentre member Marc St. Clair (pony tail) is demonstrating his freshlybuilt,Dobsonian, binocular 20-cm telescope.As you might guess, my first Starfest was a lot of fun, eventhough we woke up to thundershowers and drizzly rain on theSunday getaway day. The hot breakfast available from the RedLight Café was especially welcome that morning! My thanksare extended to the folks at the River Place campground forproviding excellent facilities, and to the North York AstronomicalAssociation for organizing and running a wonderful gathering.Next year’s Starfest runs from July 15–19; I am hoping evennow that I will not be doing field work then…Phil McCausland is a planet-watcher and avid stargazer presentlyattached to the London Centre of the RASC, who also has close tiesto the Windsor and St. John’s Centres. In his alter-life he is workingon a Ph.D. in geophysics at the University of Western Ontario. Hehopes that his interests in geophysics and astronomy will soon dovetailtogether nicely.292JRASC December/décembre 1998
ReflectionsDark Morningsby David M. F. Chapman (dave.chapman@ns.sympatico.ca)By the time you receive this issue of the Journal, the dayswill have become very short and the Sun, being low inthe sky, will cast only feeble rays upon the ground (assumingyou are reading in Canada, not lounging in a wicker chair atsome sunny southern resort). For those who rise early to go towork or school, the mornings can be gloomy, even dark. Butreflect on this question: when is the darkest morning of 1999?To make it easier to answer, I’ll make it a multiple-choicequestion:1. December 22.2. January 2.3. October 30.4. None of the above.The most correct answer is number 2, and the subject of thismonth’s column is why I used the adjective “most.”The cycle of Earthly seasons owes its existence to the 23˚.4tilt of the Earth’s equator relative to the Earth’s orbital plane.That is common knowledge, although many otherwise welleducatedpeople remain confused about the origin of the seasons.The seasonal cycle is driven by the annual variation in solarheat delivered to the Earth’s surface at temperate latitudes. Innorthern-hemisphere summer, when the Earth’s North Poletilts towards the Sun, the days are long and the rays from thehigh-altitude Sun are tightly concentrated at the Earth’s surface.In winter, the North Pole tilts away from the Sun, the days areshort, and the rays from the low-altitude Sun are spread overa wider area. For anyone (like me) who habitually rises at thesame early time each morning for work (6:30 a.m.), the cycleof seasons is portrayed by the brightness of the sky: wintermornings are dark, summer mornings are bright, and equinoctialmornings are twilit.Imagine how dull life would be if the Earth’s axis were nottilted! The Sun would rise exactly east at the same time everyday, arc through the sky, and set exactly west twelve hours later.That would be true whatever the latitude, the only variancebeing the elevation of the Sun at noon. As one day would belike another, there would be no seasons. The Polar Regionswould be permanently frozen, the equatorial zone would beinsufferably hot (as now?), and one would have to search outa habitable intermediate latitude where the temperature wouldbe “just right.” (This is beginning to sound like Goldilocks andthe Three Bears!) Following the same train of thought further,consider how the polar tilt — through its influence on theweather — has shaped the history and culture of human lifeon our planet, and how things might have turned out differentlyif there were no tilt.But I digress: this column is about light and dark, not hotand cold, although the two are clearly intertwined. In the celestialsphere, the ecliptic is a great circle inclined at an angle of 23˚.4to the celestial equator. As the Sun moves along the eclipticthrough the year, its declination (angular distance north orsouth of the equator) cycles between +23˚.4 and –23˚.4. Bymanipulating the angular relations found on page 24 of theObserver’s Handbook 1999, anyone who is trigonometricallyadept can work out how the length of the day varies with theday of the year, and how the observer’s latitude influences theresult. (Alternatively, simply peruse the “Times of Sunrise andSunset” section of the Handbook, beginning on page 84.) In theequatorial zone, the latitude is low, and there is only a smallvariation in day length throughout the year. In temperate zonesat higher latitudes, there is significant annual variation in thelength of the day. At the high latitudes beyond the Arctic andAntarctic Circles, the length-of-day calculation can becomesingular, indicating that the Sun may never rise or never set oncertain days.Based on what has been presented so far, it seems obviousthat the latest sunrise (and hence the darkest morning) of anyyear would be the day of the winter solstice, which is December22 in 1999. (After all, it is the day of the year with the fewestdaylight hours.) Not so! The calculation of sunrise and sunsettimes is actually a bit more complicated than working out theday length from the angular relations and dividing it into twoequal parts before and after noon. A correction known as the“Equation of Time” must be applied to the nominal sunriseand sunset times symmetrically spaced about noon. Thecorrection is made up of two components. The largest componentresults from the Earth’s tilt and accounts for the fact that theSun moves steadily along the ecliptic, not the celestial equator;the correction amounts to as much as plus or minus 10 minutesand cycles back and forth twice during the year. The secondcomponent of the correction results from the eccentricity ofEarth’s orbit, and accounts for the fact that the Sun appears tomove faster along the ecliptic when the Earth-Sun distance issmaller (Kepler’s Second Law); the correction has an annualcycle of up to plus or minus 7.5 minutes. The two correctionsconsidered together form a fairly complicated correction formulaby which the Sun can lead the clock by as much as 16 minutesand lag behind the clock by as much as 14 minutes. Evidencefor that is found in the Ephemeris for the Sun in the Handbook(page 76). The time of the Sun’s transit of the meridian (i.e.when it is highest in the sky) is not 12 noon sharp, but variesthroughout the year.December/décembre 1998 JRASC293