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Sky Happenings February 2008
Moab UT (at City Hall)
38O34’ N Latitude 109O33’ W Longitude
4048 ft - 1234 m
The Sky for February 2008
By Faylene Roth
Sunrise and Sunset Times for
February 2008

DAYLENGTH
Sunrise and sunset times are calculated for a flat horizon. Actual times may vary depending upon the surrounding landscape. The period of daylight lengthens by one hour and four minutes during February. Twilight extends daylength by several hours. Civil twilight provides adequate light for movement and begins about one-half hour before sunrise. Nautical twilight reveals shapes but not detail and begins approximately one hour before sunrise. Astronomical twilight illuminates the sky with a faint glow. It occurs about one and one-half hours before sunrise. The same progression applies to dusk.

MOON HAPPENINGS

February begins with a waning crescent moon in the early morning twilight. On February 3, the fading crescent rises with Jupiter and Venus in the southeastern sky along the tail of Scorpius. On the morning of February 4 a very faint crescent hangs directly below the two planets. After New Moon on February 6, the moon returns to the evening sky. On Februaary 13 a first quarter moon approaches very near the Pleiades. On February 15 a gibbous moon moves to within one degree of Mars after midnight. The Full Moon rises on February 20 at 5:51 pm. A total lunar sclipse begins at 6:00 pm. On February 25 a waning moon moves across the sky after midnight below Spica in Virgo. On February 29 look for the last quarter moon in the southeastern morning sky near bright orange Antares in Scorpius.

LUNAR ECLIPSE

The first stage of the lunar eclipse of February 20 will have begun by the time the full moon rises above the cliffs surrounding Moab. However, the entire period of totality, the 51 minutes when the moon is totally darkened by the Earth’s shadow, will be visible as long as skies are clear. The moon enters the partially illuminated region of the Earth’s shadow, the penumbra, at 6:00pm as the sun is setting in the western sky (the beginning of civil twilight). At 6:43pm (halfway through nautical twilight) the moon should be in full view as it begins to disappear into the umbra, the dark central shadow cast by the Earth onto the moon. Totality begins at 8:00pm in a dark sky (one-half hour after the end of astronomical twilight) and lasts until 8:51pm. By 10:09pm the moon will have moved out of the umbra. At 11:17pm it moves out of the penumbra and the eclipse is complete. Viewers must be east of the Rocky Mountains to see all stages of the eclipse.

ASTERISMS
The Hyades and the Pleiades feature prominently in the winter sky. Locate the Hyades by identifying the five stars that form the V of the bull’s head in Taurus. Look 10 degrees (width of your fist at arm’s length) northwest of the Hyades to locate the 6 visible stars of the Pleiades. Although they are easily recognized star patterns, they are not constellations. They are known as asterisms. Asterisms may be a sub-part of a constellation or derived from neighboring constellations. Common asterisms include the Great Square of Pegasus, the Big W of Cassiopeia, the Northern Cross in Cygnus, and the Summer Triangle of Aquila, Cygnus, and Lyra. Most asterisms are composed of stars that appear in the same region of the sky but are not near one another in distance. The Pleiades and the Hyades are unusual because they are star clusters, groups of stars that move together and have a common origin in time and space. The Hyades, 151 light years from Earth, contain several hundred stars. At 625 million years old, these stars are only one-eighth the age of our five billion year old sun. (Aldebaran, the brightest star in Taurus, is not part of the Hyades star cluster.) The Pleiades is 440 light years away with more than 1,000 stars that formed only 100 million years ago.

VISIBLE PLANETS

Jupiter - rises within minutes of Venus in the early morning twilight of February 1; the two planets appear one-half degree apart (less than the width of your little finger held at arm’s length), their closest approach for the year; Jupiter precedes Venus in the morning sky for the remainder of February; located in Sagitarius in the southeastern sky at dawn shining brighter then most stars at magnitude -1.9.

Mars - high in the night sky throughout February,; moves eastward through Taurus; on February 13 compare the red planet’s color to the orange light of nearby Aldebaran; continues to fade in brightness as Earth rapidly moves away along its inner orbit.

Mercury - visible after February 24 from a high vantage point at morning twilight about five degrees (three fingers widths held at arm’s length) above the horizon; in conjunction with Venus on February 27; shines at magnitude 0.2, less bright than Jupiter which is higher in the morning sky.

Saturn - rises with Leo in the evening sky; situated near the moon during the lunar eclipse on February 20; reaches opposition (nearest point to Earth) on February 24 when it shines like a full moon at magnitude 0.2, as bright as Rigel at Orion’s foot.

Venus - brilliant morning star (magnitude -3.9) can be used to tell time throughout February; rising between 5:30 am and 5:45 am, Venus should clear the surrounding cliffs soon after 6:00 am; in conjunction with Jupiter on February 1.

WHY THERE ARE NO GREEN STARS
Stars that burn hot and fast appear blue. Main-sequence stars with average lifespans and moderate temperatures appear white or yellow. Expanding giants and supergiants have cooler surface temperatures and appear orange to red. The light emitted by a star usually covers a range of wavelengths that indicates its temperature. Any stars that emit light in the green range would also emit light in the adjacent yellow to blue range. The color-receptors in our eyes perceive this mix of wavelengths as yellow to white. Use the key at the upper left of the star chart to discover the array of colors displayed in the winter sky.

MAJOR CONSTELLATIONS OF FEBRUARY

Overhead
Auriga
Canis Minor
Gemini
Orion
Taurus

Northward
Cassiopeia
Cepheus
Ursa Major
Ursa Minor

Eastward
Cancer
Leo

Southward
Canis Major
Hydra
Lepus

Westward
Andromeda
Aries
Perseus

The winter sky features an array of star colors. Blue stars are Rigel in Orion, Regulus in Leo, and major stars of the Pleiades. White stars are Sirius in Canis Major, Procyon in Canis Minor, and Castor, one of the twin stars in Gemini. Pollux, the brighter twin, shines yellow-orange. Aldebaran, in Tauras, shines orange. Betelgeuse, at the tip of Orion’s club, shines. red.

Hold the star chart high above your head and match the compass directions to the direction you are facing.
Adjust the star chart by orienting Ursa Major (Big Dipper) to match its position in the sky.

The star chart approximates the night sky from astronomical twilight to midnight. As the night and the month progress, the constellations will shift toward the northwest.

Primary Sources: USGS, U.S. Naval Observatory, http://www.fourmilab.ch/yoursky/

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