Ken Rejko and Glenn Smith
| Sky Calendar |
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| Glow along the horizon and the light pollution of the
huge hotel and casinos of Atlantic City can't completely hide the splendor of Venus, Mars,
and Jupiter. Ken Rejko and Glenn Smith |
Galaxies swarm in the spring sky, and the planets make for early evening targets.
The planetary gathering at dusk reaches its best in April when Mars, Jupiter, and Saturn all lie within a 5° circle. Jupiter is the brightest and first to appear in the luminous evening twilight, shortly after sunset. Look west to find the three planets trailing in the sun's wake. Once you have located the planetary trio, check out their comparative brightnesses. Jupiter shines at magnitude -2.0, Saturn at 0.3, and Mars comes in at 1.4. High above, in Taurus, lies the magnitude 0.8 "eye of the Bull," Aldebaran. Its ruddy hue imitates Mars.
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A mere 6° separates Jupiter and Saturn on April 1. On April 5, look for the very young moon entering the evening twilight scene - but don't wait too long because the moon quickly slips away, below the horizon. The following day, on April 6, Mars passes within 1.1° of Jupiter, with the growing crescent moon lying 3° south of Saturn. Jupiter and Saturn roll deeper into the twilight each night, but Mars appears to linger. On April 11, the three planets form a beautiful equilateral triangle, followed by Mars passing 2° north of Saturn on the 16th. The next time these planets become so close is 20 years from now, on March 26, 2020.
Before Jupiter and Saturn are lost in the solar glow of twilight, use your telescope to reveal their splendor - the fine belts and zones of Jupiter and its dancing retinue of moons, the delicate ring system around Saturn. Watch them early on in the month because they quickly become harder to see as the two giant planets move into conjunction with the sun early next month. Mars will hang on for another two months because it orbits the sun faster than the two giant planets and hence almost keeps pace with Earth, but, as always, Earth, on the inside of the orbital racetrack, creeps far enough ahead for Mars to appear on the far side of the sun from our perspective.
The three planets soon abandon the evening sky, leaving the winter stars to hang alone above the southwestern horizon two hours after sunset. Taurus the Bull sinks in the west just after the planets, escorted by the lovely star cluster, the Pleiades. Orion, southeast of Taurus, makes its exit. Rigel sets first, leaving Orion's fine belt of three equally bright stars lingering for a while until they succumb to Earth's rotation, to be followed soon after by Betelgeuse. In the ensuing two hours as we approach midnight, Gemini begins to sink also, with the feet of the Twins dropping below the horizon first.
While Taurus and Gemini are still up, a casual glance shows that the ecliptic runs right through these constellations; the line rises steeply from the horizon. The ecliptic in this position improves the possibility of viewing the reflected glow of sunlight off billions of particles of dust that lie in the plane of our solar system left by eons of cometary passes. Called the zodiacal light, this glow is somewhat fainter than the Milky Way, but from observing sites far from city lights, and especially from altitudes above a thousand feet, the cone of light along the ecliptic is unforgettable. Moonless nights during March and April are the best times in the evening to view its ethereal glow, but there are always other opportunities if clouds or light pollution hamper your chances this spring. If you live in an area that is surrounded by manmade skyglow, don't forget to look for the zodiacal light when you are on vacation, camping, or visiting friends and family in a rural location.
The full moon on April 18 is the first full moon after the spring equinox, so it determines the date of Easter, which occurs on the following Sunday, April 23. Since the previous full moon occurred only hours before the spring equinox, this "moveable feast" of Easter falls on one of the latest possible dates, which can range from March 22 to April 25. On the 18th you'll find the full moon rising right after sunset, lying among the stars of Virgo, not far from Spica. The first quarter moon occurs on April 11, and last quarter moon lands on April 26. The growing crescent moon crosses the Hyades star cluster in Taurus the Bull on April 8, but the event is only visible from the Japanese and Australasian side of the globe. Observers in that part of the world will witness a number of enchanting occultations of stars in the Hyades by the moon.
A bright gibbous moon interferes with this year's April Lyrid meteor display, which runs from April 21 to April 23 (which also marks the Christian holidays of Good Friday to Easter), but the following new moon will later benefit next month's Eta Aquarid shower.
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Following the constellations along the ecliptic, after Gemini, we come to Cancer the Crab, a faint grouping that houses M44, the Beehive star cluster. In Latin the cluster is called Praesepe, which means "the manger." The fine galactic cluster contains about 40 stars visible in binoculars.
Next to Cancer and farther along the ecliptic to the east lies Leo the Lion. Regulus is its brightest star, which lies high in the south at 10 p.m. local daylight saving time. Above Regulus floats an easy pattern of stars to find, the inverted question mark - a line of stars that marks the "sickle" asterism. Five degrees to the west of Leo is a star well-known as a Mira-type variable star, R Leonis, an easy binocular object that reaches its peak in late April. Is it visible to the naked eye? (See "Familiar Friends," page 67.)
The constellation Virgo rises in the east during the evening, and its brightest star, Spica, when joined by an imaginary line to Regulus, delineates the ecliptic well. The "Y"-shaped bowl of stars, a familiar group making up part of the second largest constellation in the sky, lies to the northwest of Spica. North of Virgo's bowl, the faint constellation Coma Berenices houses the North Galactic Pole - the location of the point where an imaginary line extending from the rotation axis of our Galaxy intersects the celestial sphere. This explains the lack of bright stars - we are looking right out of our Galaxy perpendicular to the disk toward deep, intergalactic space. This entire region of sky is dotted with faint smudges of light, star cities, and galaxies. Within Coma Berenices lurks a more local member of the heavens, the asteroid Ceres. Ceres is a few weeks past opposition and an easy binocular object at magnitude 7.0. It lies close to 6 Comae Berenices on April 12. (See "An Asteroid for Binoculars," page 67.)
The brighter members of the Virgo supercluster of galaxies can be found with most amateur telescopes, though a 6-inch scope is ideal. Begin with M59 and M60, two elliptical galaxies that lie 1.25° north of the magnitude 4.9 star Rho Virginis. Discovered by J. G. Kohler while observing a comet in 1779, Charles Messier himself recorded the objects a few days later, and they became two of his designated catalog entries. The pair is visible together in a low-power eyepiece as two small, dim smudges of light. Notice that close to M60 is another dim galaxy, two magnitudes fainter than the magnitude 9.0 elliptical galaxies. Appearing as a fuzzy "star" in 4-inch telescopes, larger scopes will reveal more features of the spiral galaxy NGC 4647 (NGC = New General Catalogue, the listing compiled by John L. E. Dreyer).
Careful scanning of this region, greatly aided by a good star atlas, will reveal eight more Messier objects, along with dozens of NGC galaxies. Choose a night of little moonlight and gaze outward to these star cities millions of light-years away, each one home to many billions of stars.
High overhead, the Big Dipper swings through its upper culmination. It also contains a number of galaxies, though the most famous galaxy, M51, actually lies in the neighboring constellation of Canes Venatici. (See "First Views: The Whirlpool Galaxy," page 65.) Called the Whirlpool Galaxy, M51 lies 3.5° southwest of Eta (h) Ursae Majoris, also known as Alkaid, the star that marks the end of the handle of the Big Dipper. Small telescopes will show a distinctive double patch of light. Scopes larger than 8 inches will begin to reveal the spiral arms.
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During the first two hours after midnight, the summer triangle rises above the eastern horizon, led by the brilliant magnitude 0 star Vega in the constellation Lyra the Harp. Its reappearance also allows for an early look at the beautiful Ring Nebula (M57), lying midway between Beta and Gamma Lyrae. This exquisite and delicate ring appears perfect through an 8-inch scope - lovers of the night sky are always drawn to this planetary for its ability to stun with each return visit.
By 2 a.m. local time in early April, Aquila the Eagle soars above the eastern horizon. Its principle star, Altair, shining at magnitude 0.8, completes the summer triangle. Altair resides 16.8 light-years from Earth, making it one of the sun's closest neighbors. This nearby star was used by Apollo astronauts to help guide their spacecraft. Aquila was the focus of attention last winter when Nova Aquilae 1999 erupted and burst onto the scene reaching magnitude 4.0. It quickly faded and is now beyond view of binoculars. Many remember their first view of the nova while standing out in the cold winter nights of early December. Now that four months have passed, the weather is warming and Aquila returns to us in the morning sky, triggering memories of those nights searching for a new friend. One wonders what surprises Aquila will bring.
Our daytime star is expected to be at peak activity this year. It's almost guaranteed that you will find numerous sunspots on the sun on any day this year. But do take care - observing the sun should never be done casually. The sun is exceedingly bright. Not only can its heat damage an eyepiece, but a one-second glance through any optical device will damage your retina at the back of the eye beyond repair. Pain cannot warn you: The back of the eye doesn't have nerves, so you won't feel a thing.
Safe viewing of the sun is easy - point your telescope toward the sun, ensuring no one has his or her eye near the eyepiece. Use a piece of white card, hold it about one foot away from the eyepiece, and move the telescope around until you see an image of the sun projected onto the card. Now focus the image, and sunspots will snap into view.
Daily monitoring of sunspot positions will allow you to quickly calculate the rotation rate of the sun. Try this for sunspots at a variety of latitudes - you may be surprised by the result. The sun doesn't rotate as a solid object, so rotation periods vary depending on latitude. Around the limb, look for subtle, bright patches in the photosphere near sunspots. These bright features called faculae are slightly hotter than the surrounding photosphere. The sun also dims toward its own edges, known as limb darkening.
Because the sun is a gaseous ball and has no solid surface like a planet, when we view the limb of the sun we are viewing regions higher in the atmosphere than the central part of the disk. The higher photosphere is slightly cooler, so it emits less light. Making solar observing a regular part of your routine will help you get extra mileage out of your astronomy equipment and add many productive hours to your hobby.
Martin Ratcliffe is Director of Theaters at the Exploration Place in Wichita, Kansas. Alister Ling is a meteorologist working for Environment Canada in Alberta.
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