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SKY REPORTER: May 2011

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SkyData

Sunday May 1st the Sun is within boundaries of the constellation Aries. In New York City that morning civil twilight begins at 5:25 a.m. Eastern Daylight Time, followed by sunrise at 5:55. The following evening sunset is at 7:52, and civil twilight concludes when the Sun is six degrees of arc beneath the horizon at 8:21 p.m.

On the last day of the month, civil twilight begins at 4:55 a.m. with Sunrise arriving at 5:27. The Sun sets that evening at 8:20, followed by the end of civil twilight at 8:52 p.m. The Sun’s direction then is within boundaries of the constellation Taurus. During May times between sunrise and sunset each day increase by 56 minutes.

Primary lunar phases this month are: New Moon, Tuesday May 3rd at 2:51 a.m.; First Quarter, Tuesday the 10th at 4:33 p.m.; Full Moon, Tuesday May 17th at 7:09 a.m.; and Last Quarter, at 2:52 p.m. Tuesday May 24th.

This month average overnight temperatures recorded near lovely Belvedere Castle across Central Park West from the American Museum of Natural History, rise from 49 degrees Fahrenheit on the first of May to 59 degrees on the 31th.

SkyCast

During May the planets Mercury, Venus, Mars, and Jupiter are located near each other in the predawn sky, offering an alluring arrangement of lights. Venus and Jupiter present their usual bright aspects, but binoculars are needed to spot Mercury and Mars against the glow of morning twilight. A clear view towards the eastern horizon is needed to see this unusual planetary grouping. Such configurations are beautiful can be fine subjects for photography provided you use a tripod and have some control over exposure times.

On May 1st Venus rises at 4:53 a.m. and by 5:30 in brightening twilight, it reaches an altitude of 6 1/2 degrees of arc, about ten degrees to the right of a thin waning crescent moon. (Remember your fist, seen with an arm fully extended, has an angular length of about ten degrees of arc.) These mornings, along a slanting line downwards to the left of Venus are: Mercury, Mars, and Jupiter. At 5:30 a.m. May 1st, Jupiter is only about two and a half degrees of arc above the horizon and has a magnitude of minus two. Venus is at magnitude minus 3.9. Mars, with a magnitude of 1.25 is less than a moon diameter to the upper left of Jupiter, and Mercury’s magnitude is 0.90. The visual magnitudes of both Venus and Jupiter exceed that of any star in the night sky, and the current brightness of Mercury and Mars are comparable to first magnitude stars such as Spica and Deneb. However, due to lack of contrast in brightening pre-dawn conditions, the planets are not nearly as vivid as they would be if viewed in a darker sky.

This early morning assembly of four planets continues in the eastern sky throughout May. A half hour before sunrise Tuesday May 31st a waning crescent moon will again be low in the eastern sky, with Venus about five degrees to its right, elusive Mercury just a degree and a half above the horizon and below the moon. Mars is four degrees to the upper right of Venus, and Jupiter 16 degrees to the upper right of Mars.

If the sky is clear on the evenings of May 3rd and May 5th, observers in the New York Metropolitan area should have fine opportunities to view the International Space Station pass nearly directly overhead.

On Tuesday evening May 3rd the Space Station is expected to become visible to observers, in the New York area with a clear view of the sky, low in the northwest at 9:09 p.m. The craft will look like a single bright star moving slowly from northwest toward the zenith as it gradually brightens to magnitude minus 3.7 (nearly as bright as Venus!) Due to local obstructions, you may not have a sight line to the craft for a minute or two, until it is closer to the zenith. The craft will be at a point almost directly overhead at an altitude of 218 miles at 45 seconds past 9:11 p.m. Thereafter the space craft will gradually fade in brightness as it moves toward the southeast. At about 52 seconds past 9:12 p.m., the Space Station will suddenly disappear from view as it enters Earth’s shadow at a location in the sky near Saturn and the first magnitude star Spica.

Accurate timing is critical. Even a phone’s clock may be off by a minute of two. Obtain excellent timing accuracy by referring to the U.S. Naval Observatory’s Master Clock.

Tuesday May 4th, a thin crescent moon may be seen as evening twilight fades. At about 8:30 p.m. the lunar crescent is located ten degrees above the western horizon about half way between the Pleiades open star cluster and first magnitude Aldebaran, brightest star in the constellation Taurus.

ISS as seen from Space Shuttle

The International Space Station as photographed from the Space Shuttle in 2010

STS-130 Crew, NASA


Another good opportunity to see the Space Station (and the Space Shuttle Endeavor if it is launched on Monday May 2nd) will be the evening of Thursday May 5th if the sky is clear. Moving from the northwest to a point nearly overhead, then toward the southeast, times for the crafts’ visibility are: low in the northwest at 8:22 p.m., near zenith passage at 50 seconds past 8:24, then the Station will disappear low in the southeast at about 8:28 p.m.

Additional predictions and charts showing Space Station visibility from the New York area may be found on Heavens Above. Data for other locations are also available.

During the evening of Mother’s Day Sunday May 8th the waxing crescent moon is about ten degrees south of Pollux, slightly brighter than its neighbor Castor. They mark the heads of Gemini, the celestial twins of Hellenic mythology.

May 10th and 11th, the moon is near Regulus, a first magnitude star that is the brightest in the constellation Leo.

The waxing gibbous moon is in the constellation Virgo Friday May 13th and Saturday May14th. It then forms a triangle with Saturn and the first magnitude star Spica.

The Full Moon of Tuesday May 17th at 7:09 a.m. is traditionally called the Full Flower Moon or Corn Planting Moon. That evening moonrise is at 8:48 p.m. in New York City. That night the moon is less than five degrees of arc from red giant Antares, brightest star in Scorpius. Although red is the most intense visual color produced by this star, the blend of all its emitted colors makes it appear beige to the eye. Therefore, when you see Antares, don’t expect it to look “stop sign” red!

During the early morning hours of Sunday May 29th, the waning moon is less than five degrees of arc from bright Jupiter, currently near the border between the constellations Aries and Pisces.

At five a.m. Saturday May 30th, a narrow waning crescent moon is again near an interesting configuration of Venus, Jupiter, and Mars. Mercury is then lest than two degrees above the horizon and very difficult to see in the brightening sky.

SkyLore

At the start of May the brilliant star Arcturus is high in the east as twilight fades and this month it progresses towards the meridian, the sky’s center stage. Among stars visible from the latitude of New York City, Arcturus is second only to Sirius in apparent brightness. From late spring through early autumn Arcturus, in the constellation Bootes, is the most brilliant stellar feature of the evening sky. The visual prominence of Arcturus allows it to be seen even from the center of town, as long as no artificial lights shine directly into our eyes. During evenings of May with the help of binoculars, or away from urban centers with unaided eyes, the second magnitude stars of the Big Dipper may be seen high in the northern sky. This, the most famous of star patterns, may then be used to visually link several features of the spring sky. As you trace the Dipper, note how its handle curves. That enables us to extend the handle’s arc, indicating a line toward Arcturus. Continuing the imaginary curve further south leads eyes to first magnitude Spica, brightest star in Virgo.

Another use of the Big Dipper’s shape is to imagine its bowl filled with water. If a hole were punched in the bottom of the bowl, the water would flow onto the back of Leo the Lion. However, during evenings of May the Big Dipper is seen apparently “upside down” in the northern sky. Therefore we need to use extra imagination to visualize water flowing from the bottom of its bowl toward the zenith, then “down” in the direction of the constellation Leo, in the southern sky.

The striking pattern of Big Dipper stars, the “Arc to Arcturus,” and subsequent “Speeding to Spica” may be easier to trace if you can recline while observing stars around the zenith. If you are looking up from heavily illuminated parts of the city, remember that use of binoculars make it easier to locate many stars invisible to unaided eyes. With field glasses it is rather easy to outline stars of the Big Dipper, even from the center of Manhattan (As long as you don’t include bright terrestrial lights in your binocular’s field of view).

If you have exceptionally keen vision, you may notice a star located at the bend of the Big Dipper’s handle has a very close faint neighbor. Binoculars will make this pair clearly visible. The brighter member is named Mizar and the fainter component is Alcor. If you have a telescope available you may notice Mizar itself is a double star. The components of this telescopic pair, Mizar A, a second magnitude star and Mizar B at magnitude 4, are 76 light years from Earth. They stars have a separation of 15 seconds of arc; equal to about 1/3 the apparent diameter of Jupiter as seen from Earth.

Constellations of spring evenings are in general not as spectacular as those of winter such as Orion and Taurus. This is because during evenings of spring the region of the Milky Way Galaxy’s northern pole is near the center of our sky. It is a region with far fewer visible stars especially those that are bright and young. During winter we face a relatively nearby region of star formation, having many bright young stars, centered in and near Orion.

Along with its absence of many brilliant stars, spring evenings also lack an abundance of interstellar dust and gas clouds. Such nebulae and the bright stars they spawn are more typical of the Galaxy’s disk, the section of the Milky Way most visible in the middle of our sky during winter and summer evenings. This dearth of interstellar dust around the Galactic Poles allows us a less obstructed view outward to beyond the Milky Way’s confines, toward distant realms of intergalactic space. Therefore sky regions surrounding the north Galactic Pole are areas where distant systems of galaxies may be well observed. The pole of the Galaxy is within boundaries of the faint constellation Coma Berenices, west of Arcturus, about half way between the Big Dipper‘s Bowl and Spica.

As noted above, Arcturus is a star of considerable brightness, seemingly contrary to an absence of other bright spring stars. Arcturus is however not an actual member of the disk‘s stellar population. It is currently just passing through that disk and is moving contrary to the general orbital flow of the Sun and most other neighboring stars. It may be that Arcturus, currently 37 light years from the Sun, is a former member of a small galaxy that long ago, perhaps before the formation of our Solar System 4 1/2 billion years ago, was attracted to the Milky Way, then torn apart as its stars joined with those of the much larger Galaxy host.

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