Volume 8 Number 2 Spring 2004 PocketThe Planetarium Astronomical Information Newsletter of the Planétarium de Montréal

The Starry Sky — Spring 2004

R T H O N

CEPHEUS

Deneb

PERSEUS CASSIOPEIA

CYGNUS

MINOR

Capella

LYRA URSA URSA

Polaris Venus

DRACO

Vega AURIGA

30/04 Mars 30/04 BOREALIS CORONA

HERCULES Saturn

Castor 30/04 E

GEMINI URSA T

A MAJOR May 24 S

S

May 20 E

T OPHIUCHUS Cor Caroli Pollux May 16 BOÖTES W CANES May 14 VENATICI May 12

Procyon

CANIS

T MINOR

Arctur A

E

SERPENS LEO CANCER N us t

Regulus May 10 e Map: Marc Jobin / Planétarium de Montréal m

o Jupiter C May 8

May 6 VIRGO June 4June 2May 31May 29 May 26 May 25 LIBRA Spica Comet LINEAR CORVUS HYDRA This Star Map is Accurate on… HYDRA (Eastern Daylight Time, except where mentioned otherwise) How to Use this Map March 21 at midnight EST The above map represents the April 6 at midnight night sky as it appears at the indicated April 21 at 11 p.m. times, and remains usable several hours SOUTH May 6 at 10 p.m. before and after.. Hold the map up to the sky May 21 at 9 p.m. in front of you and turn it so the direction you are facing appears at the bottom. Lines iden- Phases of the Moon tify the contellations. The light band outlines the Milky way. (Eastern Daylight Savings Time) except * = Eastern Standard Time) Full moon Last quarter Seasonal Milestones March 6 at 18:14* March 13 at 16:01* April 5 at 7:03 April 11 at 23:46 The spring equinox occurs on March 20 at May 4 at 16:33 May 11 at 7:04 01:49. The summer solstice will take place June 3 at 0:20 June 9 at 16:02 on June 20 at 20:57 EDT. Spring 2004 will New moon First quarter last 92d 18h 08m. planetarium.montreal.qc.ca March 20 at 17:41* March 28 at 18:48* On the night of April 3 to 4, we April 19 at 9:21 April 27 at 13:32 switch to Daylight Time: Clocks move May 19 at 0:52 May 27 at 3:57 ahead one hour. June 17 at 16:27 June 25 at 15:08 The Pocket Planetarium 2 Spring 2004 The Sky This Spring

Winter’s planetary parade continues this spring, featuring Venus, Mars, Jupiter and Saturn. And a brief appearance by Mercury provides a rare opportunity to see all five “naked-eye” planets at once. But among this star-studded retinue, Venus definitely outshines them all.

Venus steals the show known as a “solar transit” (see page 4). by nightfall, so the optimum time for It should come as no surprise that Venus certainly captures the eye, observing it gets earlier and earlier. At Venus is the third brightest celestial but through a small telescope it offers a the end of March, Jupiter culminates in object — surpassed only by the Sun truly fascinating show. In fact, the south at about 22:30. By the begin- and Moon. Throughout winter Venus the planet’s changing ning of May, the planet has already was the dazzling “evening star” — the March 31 aspects are easy to observe. culminated at twilight’s end, and is first star-like object to appear in the Because Venus’ orbit brings then best observed right after dark. west at twilight — and it will continue it closer to Earth this spring, Jupiter is another choice target for to grace the sky until May. its apparent diameter will telescopes. Even small instruments This apparition of Venus is increase dramatically. At the same time, reveal the four moons discovered by extremely favorable. Toward the end of the planet’s illuminated portion Galileo (the total number now surpass- March, the planet appears 46 degrees will change from a quarter May 1st es sixty!) and some of the planet’s from the Sun — its greatest solar sepa- phase to a thin crescent. atmospheric cloud bands. ration. On top of that, the line joining In just a month-and-a- The Moon’s monthly orbit regularly Venus and the Sun forms a very steep half, a spectacular transfor- carries it near the giant planet in the sky. angle to the horizon. As a result, Venus mation unfolds! At the end of On the night of April 2 to 3, the gibbous is very high in the evening sky at the March, Venus’ disk is exactly half lit Moon is situated 3 1/2 degrees to the left beginning of spring. In fact, during this and measures 24 arcseconds of Jupiter; on April 29, the Moon is 3 1 period, the dazzling planet sets 4 /2 May 15 across. However, by mid- degrees above the planet; and finally, hours after the Sun! May its apparent size dou- the first quarter Moon is near Jupiter While the winter constellations drift bles to 47 arcseconds, and once again on May 26 and 27. progressively toward the western hori- it takes on a classical cres- zon, Venus moves eastward among the cent shape with two distinct Saturn — one last look stars. This explains why the evening “horns.” This spring, Saturn is situated at the star seems to remain at about the same During the waning days of center of the constellation Gemini, just place in the sky night after night. Along May, Venus grows even May 31 to the upper left of Orion. Right now the way, Venus passes the Pleiades — a larger: As its crescent gets Saturn’s rings are wide open, which magnificent star cluster in Taurus. On progressively thinner, its makes it — without doubt — one of April 2 and 3, the two objects are less disk swells to nearly one the most beautiful sights in the sky. A than a degree apart. If you follow this minute of arc (1/60th of a small telescope reveals the rings easily, celestial encounter you can see how degree)! Unfortunately, by this time but a larger instrument truly shows the much Venus moves from one evening Venus is very close to the horizon, and planet in all its glory. to the next. observing conditions deteriorate rapidly. Don’t wait too long! In May, con- In fact, Venus’ motion also brings it On March 24, at nightfall, the cres- ditions for observing the ringed planet seemingly closer to Mars: By April 25, cent Moon is just two degrees to the deteriorate rapidly. By then it is too low the two planets are just 5 1/2 degrees left of Venus — a spectacular sight not on the horizon to view clearly, and by apart. But then, Venus loses ground to be missed! The Moon also appears early June it disappears completely in and slips from its celestial perch — near Venus on April 22 and 23, and the Sun’s glare. slowly at first and then progressively again on May 20 and 21, but on these The crescent Moon is near Saturn faster. In May, the evening star quickly occasions the two are not nearly as on the evenings of March 28, April 24 loses altitude and disappears in the close. and 25, and again on May 22. On this Sun’s glare by the end of the month. A final occasion, Mars is also in the pic- few days later, on June 8, Venus is in Jupiter at its best ture: The two planets are just 1 1/2 inferior conjunction. At this point the Jupiter spends the coming months degrees apart on May 25. planet’s orbit carries it exactly between beneath the constellation Leo. The the Sun and Earth, which will result in a giant planet was in opposition on Mars — engulfed by the Sun rare (and widely anticipated) event March 3. This spring it has already risen Mars remains visible this spring Spring 2004 The Pocket Planetarium 3

And Mercury Makes Five! Mercury is the hardest planet to Until about April 6, the five plan- events are certainly not common. observe with the naked eye: It’s close ets known to ancient observers can be Face west about 45 minutes after to the Sun and never far above the seen in the evening sky at once. While sunset. Brilliant Venus is, by far, the horizon. As a result, the tiny planet is not considered extremely rare, such easiest to identify. But if the sky is only visible at dusk or dawn, and only clear and unobstructed, you’ll also March 31, at dusk for brief periods of time. Jupiter one hour after sunset notice Mercury somewhat closer to However, as spring gets under- Saturn Capella the horizon and slightly to the right. way, Mercury favors us with an excel- Mars is above Venus and to the left, lent apparition. To see it, just look while Saturn is higher still, about two toward the western horizon, from thirds of the way between the horizon March 23 to April 6, about half-an- and the zenith. Note that the four hour after sunset. The tiny planet will Betelgeuse planets fall, more-or-less, on the same be brighter toward the beginning of Mars imaginary line — a fact that will no this period. A quick word of advice: An Aldebaran The Pleiades doubt help you with your search. ordinary pair of binoculars can help To locate the fifth planet, you’ll you find Mercury in the glow of twi- Venus light. have to stand with your back to the first four. Jupiter is the very bright Five planets at once “star” shining in the east. Along with This apparition of Mercury provides an the Moon, also visible during this peri- excellent opportunity to observe all od, and the Sun (whose presence is Mercury five “naked-eye” planets at the same 10° indicated by the glow of twilight) you time. Mercury joins Venus, Mars, will see before you all the wandering Saturn and Jupiter, which were all visi- celestial bodies known since the dawn ble throughout the winter. WEST of humanity…

Two Comets in the Springtime Sky It’s rare to learn of the appearance of southern hemisphere, we’ll have to where it will disappear in June. a potentially bright comet more than a wait until the final weeks of their visit Will comet NEAT become bright few months in advance. Yet this to see them from our northern lati- enough to see with the naked eye? spring, two comets will be visible at tudes. Some predictions are optimistic, but the same time: Comet NEAT (C/2001 Comet NEAT will appear first, forecasting a comet’s brightness is dif- Q4) discovered in August 2001, and above the southwest horizon during ficult due to many uncertainties: comet LINEAR (C/2002 T7) discovered the evenings of early May. After May Disappointments are common. One in October 2002. Though they will be 5, it should be high enough to see thing is sure, the first half of May will ideally placed for observation from the with ease. On that date NEAT will be see NEAT at its brightest after which, it 9 degrees to the left of the bright star will fade from view as it slowly heads Sirius, which serves as an excellent ref- away from the Earth and Sun. in the west at twilight. Its fren- erence point. Both objects will be 8 Comet LINEAR will be much hard- zied eastward rush among the stars degrees high about 30 minutes after er to spot. It will become visible during carries it from Taurus into Gemini on sunset. The comet’s tail will extend the final days of May, and will remain May 7, and it skims by Saturn on May toward the left and be parallel to the just a few degrees above the west- 25. horizon. southwest horizon. Unfortunately, On the evening of March 25, the Over the following nights, NEAT LINEAR will only be observable during 1 crescent Moon is just /4 degree to the will gain altitude, which should afford twilight, about an hour after sunset. right of the Red Planet; and the two an excellent view against dark skies Since its brightness will already be are just a few degrees to the left of the after twilight. On May 10, the comet declining, the best chance to view it is Pleiades star cluster. On April 23, Mars is situated 6 degrees to the left of the at the end of May. Technically though, is located 2 degrees below the lunar star Procyon. On the night of May 14, the comet will remain in telescopic crescent; and on May 22, the Moon is comet NEAT passes two degrees sight until July. situated below both Saturn and the below the magnificent Beehive star Just as LINEAR becomes visible, Red Planet. cluster (M44) in the constellation comet NEAT will be situated between But the Sun finally catches up to Cancer. This is a sight not to be the legs of Ursa Major, and will still be Mars, and it sinks into the glow of twi- missed! Finally, NEAT will continue its reasonably bright. Two comets for the light by mid-June. northbound route into Ursa Major, price of one? Why not! Good observing! The Pocket Planetarium 4 Spring 2004

An historic event On June 8, Venus Passes In Front of the Sun A very rare event is due to happen this spring! For the first time in 122 years, Venus will pass directly between the Earth and Sun. For several hours, the planet will appear silhouetted against our daytime star.

Every 584 days, Venus passes between Americas, the transit will already be about 1/32nd of the Sun’s diameter. the Earth and Sun: This is known as underway at sunrise. Using special protective filters, those inferior conjunction. Normally though, In Montreal, when the Sun rises at with good eyesight should be able to Venus’ orbit carries it either above or 5:06 EDT, Venus will be more than half see the silhouette of Venus with the below the Sun’s disk. But on rare occa- naked eye. sions, when the inferior conjunction N In order to fully appreciate the occurs in early June or early December, event, a telescope or binoculars are Venus’ alignment carries it directly in suggested, but they must be equipped front of the Sun. This is called a with a special solar filter. The Sun’s transit. image can also be projected on a Transits of Venus usually occur screen with a pair of binoculars or

tical at Sunrise in pairs, eight years apart: Each acts 3 and 4 small telescope. In this case, a filter pair is separated from the next by Ver should not be used. However, the t Cont either 105 1/2 or 121 1/2 years, in setup must be monitored at all alternating sequence. The last E Vertical a W times to ensure that no one acci- transit of Venus was in 1882, so dentally looks through the optics. no living person has seen one! Contact 1 If you miss this transit of During the 18th and 19th cen- Contact 2 Venus, the next one will occur on turies, a number of expeditions June 6, 2012. After that, you’ll Contact 4 were mounted to observe the transit Contact 3 have to wait until December 11… Traj of Venus from the four corners of the ecto 2117! ry o f Ve globe. At that time, such events were nus Happy observing! considered extremely valuable, scientif- Research, text and illustrations: ically speaking. The transit of Venus Marc Jobin offered a unique opportunity to calcu- S Translation: Louie Bernstein late the distance between the Earth and the Sun. With this measurement, it was way through its passage across the Important Warning then possible to determine the distance solar disk. But the final portion of the of all the planets in the solar system, transit will be the most interesting. Great care must always be taken and even the closest stars. From 7:05:18 to 7:25:18, the planet when observing the Sun: Intense Today, the distance to the planets will cross the edge of the Sun — a total solar radiation can cause instanta- is measured with great precision thanks of 20 minutes. These times are referred neous burns, and permanent damage to radar. The transit of Venus is now of to as contacts 3 and 4. During this to the retinas. When observing the interest only because it is rare, and time, the Sun will be 20 degrees above Sun directly, either with the naked because of the history it evokes. the horizon. Elsewhere in Quebec, the eye, or a telescope, one must always exact time of egress will vary by several use specially designed solar filters. Transit 2004 seconds, depending on the observer’s For more information on the On June 8, 2004, Venus will cross the location. transit of Venus, and safe solar Sun’s disk in roughly 6 hours and 12 observing, log onto our website at minutes. This transit will be visible in its Observation entirety throughout Europe, and most During its transit, Venus will appear like www.planetarium.montreal.qc.ca of Africa and Asia. In the eastern a perfectly round, black dot measuring

The Pocket Planetarium is a seasonal information newsletter published by the Planétarium de Montréal, 1000, rue Saint-Jacques, Montréal (Québec) H3C 1G7 Texts and illustrations are excerpted from , the newsletter of la Société d’astronomie du Planétarium de Montréal, and are published with permission. Text and illustrations: © 2004 Planétarium de Montréal. Dépôt légal — Bibliothèque nationale du Québec et Bibliothèque nationale du Canada (ISSN 1703-3098)