Spring is springing! On the upside, the evening weather is warming up, so observing is much more pleasant. On the down side, however, the days are getting longer so it does not get dark enough to observe until much later than it did before we stepped into Daylight Savings Time last month. This drives astronomers nuts – it is either too cold are gets dark too late. No matter what the season, a determined observer will get outside to see what is going on.
Last month I highlighted two zodiacal constellations (Gemini and Taurus), and two other notable constellations (Orion and Canis Major). I will continue to focus on northern hemisphere constellations, because these are the ones that can be readily seen from our northern latitude. I will also point out the zodiacal constellations, because they have a special importance. In their astrological (not to be confused with astronomical) context, each of these twelve constellations represent one of the twelve signs of the zodiac. Also worth noting is that the twelve zodiacal constellations are directly related to the Sun’s passage among the background stars in twelve month (annual) cycles. The circle that the Sun traces through these constellations in its annual cycle is called the ecliptic. It is also interesting to note that the Moon and planets are always located on or near the ecliptic and among the twelve zodiacal constellations. Last month’s Scope Out provides brief description of aids that can help locate a constellation and identify its stars.
Auriga (The Charioteer)
Our first constellation this month is Auriga. It is located above (north and west of) Orion’s head, and it can best be located by identifying its brightest star, Capella, with a planisphere or smartphone app. The brighter stars form a distinct pentagonal asterism. Three open star clusters (Messier M36, M37, and M38) are easily located with a modest telescope.
Cancer (The Crab)
Cancer is a constellation of rather dim stars that can be difficult to see in light polluted skies. This constellation is not much to look at, but I do want to include it because it is one of the zodiacal constellations. It is located about half way between Pollux in Gemini and Regulus in Leo. If Cancer’s stars are not visible, try using binoculars, and then look again once you have located various stars in the constellation.
Leo (The Lion)
Moving east (to the left) along the ecliptic away from Cancer is another zodiacal constellation, Leo. Leo is a rather distinct constellation featuring the bright star Regulus. The head of the Leo presents a sickle shape, or a backward question mark to some, with Regulus at the base. For those observing with telescopes, there are several Messier galaxies located in Leo: M65, M66, M95 and M96. The Leo Triplet is a close grouping of the galaxies M65, M66 and NGC3628 that can be seen together in a single telescopic field of view.
Ursa Major (The Great Bear)
Ursa Major is located high in the northern sky this month. Its brighter stars form an easily located asterism (a grouping of stars that forms a recognizable object, but is not a constellation) known as the Big Dipper. The dipper’s handle is the bear’s tail, and the bowl is the bear’s hindquarter. Upon closer examination and in a darker sky, all of the constellations stars add to the dipper to form a distinct and complete bear. The two Big Dipper bowl stars opposite the handle are the pointer stars that guide the eye to Polaris, or the north star. There are several Messier objects within Ursa Major for observers with telescopes.
Ursa Minor (Lesser Bear)
Similar to Ursa Major, Ursa Minor contains another recognizeable asterism called the Little Dipper. Some of the dimmer dipper stars can be difficult to locate in city skies, and the other stars forming the bear might be impossible to see. Polaris, the constellation’s brightest star, is found at the end of the bear’s tail, or at the end of the dipper handle. This star is thought by some to be significant because it is the brightest star in the sky. We learned last month that Sirius in Canis Major is actually the brightest star. An observer can verify that Polaris is not the brightest star in the sky by locating it, and comparing it with other stars in the rest of the sky.
Polaris (The North Star)
Polaris’ special significance is that it is the Pole Star, located very near the point at which the Earth’s northern axis intersects the celestial sphere. As a result of this unique location in the sky, Polaris will appear to remain stationary all night while all of the other stars will appear to rotate around it. You may have seen star trail images that illustrate this effect. Another implication of Polaris’ unique location is that it is a measure of one’s latitude. From Ashton, MD for example, Polaris appears 39.15° above the horizon, which corresponds to Ashton’s latitude on a map or globe.
SOLAR SYSTEM OBJECTS
The Sun is about half way between vernal equinox and summer solstice in May, so the days continue to get longer. The rate at which the days get longer tapers off at the Sun approaches solstice next month.
Just as it did in April, the Moon will begin the month as a thin waxing crescent just after sunset above and to the left of the sunset point on the western horizon. Each subsequent evening the Moon will have moved a little farther east, and away from the Sun. Notice too that the crescent will have grown a little wider each evening. The Moon will reach 1st quarter (right half illuminated) on May 6th, full Moon (completely illuminated) on May 14th, last quarter (left half illuminated) on May 21nd, and finally the new Moon (no illumination) arrives on May 28th and the cycle repeats into next month.
The month of May presents a special opportunity for planetary observers. By late month, all five planets that were known to the ancients can be seen. Later in this month’s Scope Out, we will follow the Moon through its 28-day orbit as it visits each of these planets at least once, and one planet will be visited by the Moon a second time before the month is over.
The best viewing of Mercury this year will be during its May evening apparition. It can be best viewed near the end of the month, shortly after the sunsets on the western horizon, above and to the south (left) of the sunset point. The month begins with Mercury’s angular separation (elongation) from the Sun being quite small, which makes viewing difficult due to the Sun’s glare. While it is close to the Sun, Mercury will follow the Sun into the horizon, setting shortly after the Sun does. As the month progresses, and as Mercury moves through its orbital journey around the Sun, the elongation angle increases each day and Mercury emerges farther from the Sun’s glare. The peak viewing opportunity will be a few days before and after May 25th, the date upon which Mercury will have reached its greatest elongation from the Sun. This means that Mercury will be the highest above the horizon and it will set about two hours after the Sun. After May 25th, Mercury’s the elongation angle will decrease over the next few weeks, and it will rapidly disappear back into the Sun’s glare.
Venus remains a morning star throughout the month. It is the brightest object in the eastern sky in the pre-dawn hours, above and to the right of the sunrise point. It will slowly decrease in brightness as its elongation from the Sun continues to decrease. Venus also becomes smaller and less bright as the month progresses, even though more of the illuminated portion of Venus’ disk as viewed through a telescope increases. These changes are all attributable to Venus moving away from Earth as it proceeds along its orbital path around the Sun.
Mars remains in Virgo, and is already well above the horizon at sunset. As this planet is past opposition, Earth is speeding past Mars, and Mars begins to dim as the apparent size of its disk decreases. Telescopic views will be better earlier in the month.
Jupiter‘s position at sunset will be moving closer to the western horizon each evening as the month progresses, and the ability to observe Jupiter in the evening will soon be lost as its orbit takes it to the far side of the Sun as seen from Earth. In a few months, Jupiter will appear on the other side of the Sun as a morning object.
Saturn, the ringed planet, viewed through a telescope is the most breath taking of all the planets. It can be easily found because it is located in the constellation Libra, where it stands out as the brightest object in a region with very few bright stars. Similar to Mars last month, Saturn will rise after sunset in the beginning of the month, and will have already risen at sunset by month’s end. Saturn reaches opposition on May 10th, reaching its peak brightness and largest apparent disk size this year.
As Saturn cycles through its 29 1/2 year orbit about the Sun, we on Earth will alternatively see the top (north face) of Saturn’s rings for roughly half of its orbit, and the bottom half (south face) of Saturn’s rings for the other half. As the view transitions between upper and lower halves of the rings, our view will be edge on, and the rings will seem to have temporarily vanished. The last edge-on view was in 2009, at which time our current view of the north face of the rings began opening up. Even before Saturn’s rings fully open in 2017, our present view is pretty spectacular.
DEEP SPACE OBJECTS (DSOs)
The Great Orion Nebula and Pleiades, which are readily observable with the unaided eye, were pointed out last month in the constellations Orion and Taurus. There are a few more DSOs that can be seen without magnification, but generally only in very remote areas under a near-perfectly dark sky. Most of the remaining 108 Messier objects, however can be seen with the aid of binoculars or a small telescope. I will focus on these objects this month and in the months ahead.
First, look for the pretty open star cluster, The Beehive Cluster (M44), in Cancer. This was the first star cluster that I observed, and it left with me the impression of tiny diamonds on a black felt cloth. Interestingly, M44 is actually brighter than any of Cancer’s stars, but is difficult to see unaided in less than perfectly dark skies. The cluster is located in the center of the constellation, so locate it by looking half way between Pollux and Regulus.
Next, lets locate a galaxy. Find The Whirlpool Galaxy (M51) by locating the three handle stars of the Big Dipper. Take a line from the middle star to the end of the handle. Now take a 90-degree turn toward the inside of the handle, just under half the distance between the two stars. Look for a small, diffuse fuzzy blob. Not impressive, even in a larger amateur telescope, but you will have observed your first galaxy! Images of the Whirlpool Galaxy in Wikipedia reveal that it is a spiral, face on galaxy.
Events come and go, but are interesting to observe. Event durations can vary from an instant to seconds, minutes or days, or even longer. Examples include eclipses, certain planetary arrangements and alignments, meteor showers, and transits of the Sun. One must know when, where, and how to observe an event in the night sky in order to experience it. Most events covered here provide insight into how the Solar System actually works.
May 24th – A New Meteor Shower?
Earth is predicted to pass through the path of Comet LINEAR on May 24th. LINEAR is a small comet that was discovered just a decade ago. It has a relatively short period, returning to the inner Solar System every five years, and travelling no farther away from the Sun than Jupiter. As a result of LINEAR’s orbit being perturbed during its last encounter with Jupiter, the path of its orbit now crosses the path of Earth’s orbit. Meteor showers occur when Earth crosses the orbital path of a comet, because stony debris are left behind as the icy comet evaporates when heated by the Sun. Since this is Earth’s first pass through this rather compact debris field, some astronomers are predicting a brief but spectacular meteor shower that begins at 2am on May 24th. Look for the peak, the highest number of meteors per hour, at around 3am, and the shower should subside by 4am. To observe, a darker sky is better because fainter meteors can be seen. The origin is near Usra Major’s ‘nose’, so watch a point about half way between the origin and the zenith (the point directly above your head). Be sure to dress warmly and sit in something comfortable, like a reclining lawn chair.
Various Dates – The Moon’s Planetary Conjunctions
When two Solar System objects arrive at their closest approach to one another as viewed from Earth, they are said to be in conjunction. This month I will examine the Moon’s close approaches to all five of the visible planets that were known to the ancients. As both the Moon and the planets are in constant motion, the actual conjunction is represented by an instant in time. Because of their slow apparent motion, the close approaches (visits?) can be observed for many hours before or after a conjunction.
As previously mentioned, the planets and the Moon never wander far from the ecliptic. One implication of this fact is that as the Moon completes its 28-day orbit around the Earth, it will be in conjunction with each of the planets once. This month, the young (thin) crescent Moon will first visit Jupiter near the western horizon in Gemini on May 3rd (closest) and 4th. Try to observe on both evenings and note that the Moon has moved eastward. Also note Jupiter’s position among Gemini’s stars, perhaps by making a sketch of Gemini that indicates Jupiter’s position. This sketch will come in handy near the end of the month.
Next up is a very interesting series of close encounters with three bright and colorful objects (Mars, Spica and Saturn) in the east at dusk on May 10th through the 14th. There are lots of things to observe over the course of these five evenings. First, the waxing gibbous Moon will grow larger each evening until it reaches full Moon on May 14th. Next, note that its location is a little farther east each evening. These two phenomena are the result of the Moon moving along its orbital path around the Earth, which changes its angle relative to the Sun. Also note that the point at which the Moon became full last month was closer to Mars (read about the lunar eclipse in April’s Scope Out), and this month the full Moon occurs closer to Saturn. This eastward slide of the full Moon from one month to the next happens because of the Earth moving along its orbital path around the Sun. And finally, note the distinct colors of the three objects: Mars is red, Spica is blue, and Saturn is yellow. The Moon will be near Mars on May 10th, and between Mars and Spica on May 11th. It will be between Spica and Saturn, but closer to Spica on the 12th, and closer to Saturn on the 13th. And finally it will be on the eastward side of Saturn on May 14th, the last evening of this string of encounters.
Another rewarding and challenging opportunity to observe the Moon arrives near month’s end as it transitions from a thin waning crescent in the eastern sky at morning, to a thin waxing crescent in the evening sky in the evening. First, observe the Moon as a thin waning crescent on the eastern horizon during its close encounter with Venus just before sunrise in the pre-dawn hours of May 25th. A careful observer might see an even thinner crescent very low on the horizon and closer to the sunrise point the next morning. After this, the Moon cannot be seen because it is lost in the Sun’s glare as it approaches new Moon (conjunction with the Sun) on May 28th. A young Moon (thin waxing crescent) emerges from the Sun’s glare on May 30th, and can be seen very low on the western horizon near Mercury. On the next evening, it will appear a little higher above the horizon, and it will once again visit Jupiter. Check the sketch that you made at the beginning of the Month. Has Jupiter moved among the stars since its last visit with the Moon on May 3rd and 4th?
© 2014 James R. Johnson.