APRIL 2013 NIGHT SKY CALENDAR
April begins....and for us, that means we are only eight weeks shy of spring and we already have that bounce in our gait. To celebrate the sunny season and all the joys and ecstasies that the cruelest month can proffer, we'll post what we intend to be a mood-catapulting odyssey through the spring night sky. Whether or not it turns out to be more cheer than catapult will depend on the scribbles on the passenger evaluation card.
A couple notes: we've introduced a gratuitous new event prominence scale. Instead of a pick event, we assign "Gold," Silver" and "Bronze" to events we considered the most impressive, second most impressive and third most impressive, respectively. So much happens above us (and below us, for that matter) that selecting just one occurrence as a pick event was near impossible.
Also, April is Global Astronomy Month, as designated by Astronomers Without Borders. Watch for special additions to certain DA's throughout month four in commemoration of this distinction.
And, now...finally...to the April Night Sky Calendar.
MONDAY, APRIL 1
MERCURY AT APHELION
The April Fool's event is not exactly a spectacle of flame and fanfare. World One reaches aphelion, the point of greatest heliocentric distance. Or, to phrase it in a way not intended to discourage undergraduates, Mercury is at its farthest point from the Sun during this orbit. Mercury's orbit is elliptical, a geometric shape whose points are not equidistant from a common center -the definition of a perfect circle. As Mercury revolves about Sol, the former's distance from the latter varies from a near point (perihelion) to a far point (aphelion). On April 1st, Mercury will venture 68 million kilometers (42 million miles) from the Sun. As its average distance is approximately 36 million miles, its aphelion value is significantly higher than average when measured proportionally.
WEDNESDAY, APRIL 3
LAST QUARTER MOON
The last quarter moon rises around midnight and sets around noon, on average. The next phase position is NEW, when the moon will occupy the same sky region of the Sun and is therefore invisible.
MONDAY, APRIL 8
MOON 6.6 DEGREES NNW OF MERCURY
One will find the waning crescent moon and Mercury a few fingerwidths apart in the eastern pre-dawn sky. Interesting note: if viewed telescopically, Mercury also appears as a crescent! Since Mercury is inferior (closer to the Sun), we'll never observe a "full" Mercury. Like Venus, the other inferior world, Mercury proceeds through a limited phase cycle. Galileo's observation of Venus' crescent through his own telescope lent him more evidence that the Sun, not Earth, occupied the solar system's center.
WEDNESDAY, APRIL 10
The Moon is not visible when it's new, unless it happens to cross the Sun's face during a solar eclipse. At other times, the Moon passes either north or south of the Sun. This new moon marks the beginning of lunation cycle 1117. Within a couple nights, one can see the waxing crescent moon in the western early evening sky. The next lunar phase is FIRST QUARTER.
FRIDAY, APRIL 12
Just because we neglect Pluto in the "Planet Watch" section doesn't mean we can't mention it in the calendar every so often. Pluto is stationary, meaning that its apparent westward motion "stops." Pluto will then appear to reverse course toward the east. This reverse trek, called retrograde, is an illusory movement resulting from our own perspective. As we watch Pluto from a faster moving world, it seems to turn around when we pass it. Eventually, it will seem to stop again before resuming prograde motion. One cannot observe Pluto without a particularly powerful telescope, but were one to track its motion over weeks, one can now expect to now begin a new retrograde loop.
SATURDAY, APRIL 13
MOON 5.3 DEGREES SOUTH OF PLEIADES
Throughout the last few months, we've included information pertaining to these moon-Pleiades encounters. When the Full was full or at a large gibbous when venturing near the Pleiades, we might just as well have ignored the event as the Pleiades can be difficult to observe. However, seeing the crescent moon close to this star cluster is pure eye confection. Find the crescent moon and the Pleiades Star Cluster in the western evening sky.
SUNDAY, APRIL 14
MOON 2.2 DEGREES SSE OF JUPITER (BRONZE EVENT)
The giant world has certainly had its days over the later autumn and winter. Now, it is well over in the west when darkness descends. See Jupiter and the waxing crescent moon early in the western evening sky.
WEDNESDAY, APRIL 17
MARS IN SOLAR CONJUNCTION
Again, nothing to see here. We consider this to be a wholly academic event. Were we able to see the solar system from a point "above" it, we'd observe Earth on one side of the Sun and Mars on the other. We call this configuration "superior solar conjunction," as Mars is on the Sun's far side. "Inferior solar conjunction" refers to the configuration when a planet is between Earth and the Sun. The superior planets, those more distant from the Sun than Earth, can only enter superior solar conjunction. The inferior planets, those closer to the Sun than Earth, can enter both inferior and superior conjunction.
THURSDAY, APRIL 18
FIRST QUARTER MOON
The first quarter moon rises around noon and sets around midnight. Yes, the Moon is as visible during the day as it is as night, even though we often associate the moon with the night sky. One can easily find the Moon in the daytime sky, as well.
THURSDAY, APRIL 18
SUN ENTERS ARIES
Throughout the year, the Sun appears to progress through thirteen constellations comprising a retinue called "The Zodiac." The Sun's motion through these star patterns is an illusion: Earth moves around the Sun and therefore the latter just appears to occupy the thirteen zodiac patterns each year. These constellations are Pisces the Fish, ARIES THE RAM, Taurus the Bull; Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Maiden, Libra the Scales, Scorpius the Scorpion, Ophiuchus the Serpent Charmer, Sagittarius the Archer, Capricornus the Seagoat, and Aquarius the Water Bearer.
MONDAY, APRIL 22
LYRID METEOR SHOWER PEAKS
What?! No bronze, silver or gold for a major meteor shower? Well, April 2013 won't be a great month for the Lyrid meteors. The term astronomers use is "unfavorable," in reference to meteor showers that aren't really worth the trouble. The big issue is lunar light interference: the nearly full moon will make meteor observing a wee bit difficult.
THURSDAY, APRIL 25
Some Eastern Hemisphere observers (i.e. not us) will witness a partial lunar eclipse. A part of Earth's shadow will envelope part of the full moon. While not as impressive as a total lunar eclipse, such partial events are still lovely sights for the astronomically minded, as they occur because our one Moon traipses into Earth 800,000 mile long shadow cone!
THURSDAY, APRIL 25
MOON 3.5 DEGREES SSW OF SATURN (SILVER EVENT!)
A glorious sight: planet six and the full moon traveling together in the sky. See the most distant world and the nearby moon proceed hand in hand throughout the night.
SUNDAY, APRIL 28
SATURN AT OPPOSITION (GOLD EVENT!!)
Saturn rises when the Sun sets and is visible all night! We designate Saturn's opposition as the pick event as the ringed world will shine so brightly and remain in our sights from dusk till dawn. While Jupiter sinks, Saturn rises.
MERCURY: Mercury is a morning planet through most of April. We lose it by the last week. See the little world growing brighter in the pre-dawn eastern sky. Of all the visible planets, Mercury is typically the most elusive because it remains so exasperatingly close to the Sun. VERDICT: If you're awake before sunrise, see Mercury in the east! Best to try during mid month.
VENUS: Under the sea foam and "No, nothing's bothering me, I'm fine! And if that's Adonis, I don't want to talk. Go away." VERDICT: Poor Adonis..no Venus this month.
MARS: The war god world seethes in the cavern, forging sword and spear with his equally dyspeptic compatriot Vulcan. And, damn is it difficult to draw out the conversation when all you have to say is, "Mars isn't visible until June." VERDICT: Not even reading this entry is worth it. Mars admirers have to wait until summer.
JUPITER: Jupiter's "star" is fading. Find it in the western early evening sky. Though still the brightest planet visible this month, Jupiter descends in the west and consequently becomes all the more difficult to find. VERDICT: Still a good sight for early evening observers. Jupiter vanishes in late May, only to return to the morning sky in July. So, catch it while you can.
SATURN: (PICK PLANET) Mythologically, Jupiter (Greek Zeus) overthrew Saturn (Greek Cronos) and consigned him to languish in Tartarus for all eternity. This month, Saturn has its revenge as it snatches the pick planet diadem from its bloated show-off neighbor. While Jupiter remains bright and beautiful in the western evening sky, Saturn rises in the early evening in the beginning of the month; and around sunset at month's end. Saturn is at opposition on April 28th, so it will remain visible all night! VERDICT: After a winter of impatient bit champing, we finally see Saturn rising to greater prominence. While Saturn will remain conspicuous throughout the spring and summer, it will be at its maximum brightness for the year by the month's end. A splendid time to see Saturn, especially if you have telescopes or even binoculars.
*Yes, for what it's worth, we regard Pluto as a planet.