StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

APRIL 2018

APRIL STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

Print Large Sky Charts For 10 p.m. EDT: NORTH | EAST | SOUTH | WEST | ZENITH

Current Solar X-rays:

Current Geomagnetic Field:

1128 APRIL 1, 2018: What a Night!: As conditions have become a “little warmer,” it is that time of the semester when my students begin to learn the operation of our computer driven telescopes, as well as to start to make observations through them. Before they get to use our high-end scopes, I tease them with an introductory lab where they have to make a drawing through a very inexpensive telescope. Actually, these instruments were produced by the International Astronomical Union (IAU) for the celebration of the 400th anniversary (1609-2009) of Galileo’s first observations made through a telescope of his own construction. Galileo did not invent the telescope, nor was he the first to make astronomical observations using a telescope, two big misconceptions that people carry along with them about the Italian physicist and entrepreneur. Galileo was, however, the first to publish his observations in the Sidereus Nuncius (Sidereal Messenger or Starry Messenger) in 1610, and that brought him fame, fortune, and eventually the Inquisition to his doorstep. Although Galileo’s refractors were probably the best in the world at the time, Galileo would have given his right arm to have been in possession of an IAU telescope that was more optically perfect. The goal was to make a million telescopes and deliver them mainly to kids who lived in third world countries. Some were to be sold at $20 a pop with Moravian acquiring 15 of them, 10 through donations. So imagine 20 students making their first telescopic observations, standing like sea captains, or kneeling with their telescopes against a railing while trying to draw an object which is upside-down along with the left and right interchanged. Optically, this is called an inverted and perverted (I kid you not) image. The lab then continues with a gripe session where students note their frustrations as well as a section where they can suggest improvements to their telescopes. The night my Monday/Wednesday crew was on the Collier Sky Deck, March 19, was extraordinarily clear and relatively mild. Two days later, we were experiencing nor’easter number four, and the college closed at noon. As the sun set nearly due west, you could turn around and see the Earth’s gray shadow distinctly rising in the east. It looked as if there was an imminent storm approaching. Above the gray was a diffuse line of pink, the projection of sunlight, reddened by its passage through Earth’s atmosphere (Rayleigh scattering) from the point below the horizon where the sun was setting. About five minutes before sundown, through binoculars I was able to spot Venus, Mercury, and the ultra-thin crescent moon. My students easily caught Venus, as well as the moon about five minutes after sundown, but it took a little more time, perhaps about 15-20 minutes before Mercury revealed itself against the deepening twilight. As it got darker and my students began to use their smartphone flashlights to complete their drawings, I turned one of our smaller, very portable telescopes towards the moon to reveal a better view of earthshine to my students. Earthshine is the light from a nearly full Earth, which appears about 80 times brighter from the moon than the moon appears from Earth, illuminating the part of the moon which is not getting direct sunlight. It looks ghostly to the unaided eye, but through the eyepiece of a telescope gulping in hundreds of times the amount of light that the normal eye sees, my students saw the darker seas (basins) against the brighter highland regions in the earthshine portion of the moon. It was one of the best earthshine views that I have ever witnessed—all in one night, ironically all from light polluted center city Bethlehem.

1129 APRIL 8, 2018: The Sky is Screaming Spring: I’m just going to say it, “Spring is in the heavens,” regardless of the cooler than normal temperatures that we have been experiencing in the Northeast. It is obvious to me that the higher sun angles are at least warming the ground causing the buds and bulbs to stir. My perennials, day lilies and mums, are currently several inches in height, and the grass in my backyard has started to green, all indications that despite the overly chilly conditions, Mother Nature is awakening. I also saw my first robin this week. What does the National Weather Service predict for climatological conditions from May through September? Remember, climate is what you expect; weather is what you get! Look for higher than normal temperatures and higher amounts of precipitation throughout this period for the Northeast. So a hot and muggy summer may lie ahead. One consistent aspect of springtime that can always be banked upon is the sky. It is right on cue with the vernal constellations beginning to dominate in the east. Ninety minutes after sundown, look northeast, mid-sky, and you’ll notice the “Drinking Gourd” or Big Dipper, cup up and handle down, beginning its slow tilt into its upside-down position which occurs during late spring. Although the Big Dipper is not an official constellation, it is certainly American, born and raised. It was never recognized by the International Astronomical Union, the worldwide congress of professional astronomers, when in 1928, the IAU partitioned the sky into the 88 modern star patterns that we use today. The reasoning was simple. Other cultures and countries saw the pattern of the Dipper uniquely. The Dutch called it the Steel Pan; the British thought that it appeared like a plough, while the Germans saw it as a wagon or wheelbarrow. Everyone could agree on the Greco-Roman drawing of a bear, which was how Native Americans also interpreted the pattern. When you view the Dipper, you are observing part of a much larger grouping of stars called the Ursa Major Moving Cluster. Only the two end stars of the Big Dipper, Dubhe and Alkaid, are not included. Astronomers know that the inner five stars were born from the same nebular cloud because they all have a common motion in space. Another celebrity of the cluster is Sirius the Dog Star, the brightest luminary of the nighttime heavens, now low in the southwest. View the middle star in the Dipper’s handle. That’s Mizar. If your vision is 20/20 and you are viewing from a suburban locale, a fainter star, Alcor, should be visible just below and to its left. Mizar and Alcor are thought to be a true gravitationally bound double, separated by a distance of 1.1 light years or 6.5 trillion miles. Alcor has an invisible red dwarf companion orbiting it, but Mizar, through the eyepiece of a small telescope, splits into two stars of almost equal brightness, making it one of the easiest double stars to observe telescopically. Each of those two luminaries which look like a single star with the unaided eye, in turn is a double, bringing the Mizar-Alcor system to six stars in all. Following the arc of the handle of the Dipper brings you to Arcturus and continuing onward to Spica (low in the southeast at 8:30 p.m., better by 10 p.m.), two bright stars which are bastions of springtime. Even if the air feels like early March, the sky is screaming spring.

1130 APRIL 15, 2018: Finger Angles: A bright meteor flashes across the inky black sky and disappears behind a distant tree line. Did the fireball fall among the trees or did it go much farther? I had an incredible experience similar to this when I was up in Springfield, Vermont back in the ‘70s at an annual telescope making conclave called Stellafane. I was actually observing meteors with friends that evening on a grassy field with about 500 other individuals, most of whom were looking at the heavens through their telescopes. Suddenly there were screams and shouts, hundreds of them, and I remember, somewhat startled, sitting up in my lawn chair, the whole field lit up much brighter than the full moon, the grass a distinct green. I saw my long shadow moving slowly from left to right. It was in back of me. I flipped around in my sleeping bag to catch with hundreds of others a huge sputtering fireball low to the horizon, brighter than the full moon, disappearing behind a stand of trees. It was the brightest fireball that I have ever witnessed, possibly as luminous as 20 full moons, an event not soon to be repeated or forgotten. The meteor did not land in the treed forest but continued on its path into Canada where it was calculated that it did reach the ground as a meteorite. I caught about the last 30 degrees of its motion before it vanished. Besides the sheer euphoria of seeing such an event, it is important to note as many details as possible in order to understand the phenomenon. One datum is the path length. Witnesses have the tendency to state the length of the path across the sky as “It went 15 inches or two yards before it disappeared.” Unfortunately, that is a meaningless concept because the sky is a dome or hemisphere over our heads. We measure “distance” across the heavens as an angle. The horizon surrounding us is a full circle of 360 degrees, while the “angular measure” of an arc from the horizon through the zenith to the opposite horizon is 180 degrees. You can learn the separation between certain stars to help with these measurements. As an example, the angular distance between the two pointer stars of the Big Dipper is just over five degrees, while the measure of the three stars that form the belt of Orion the Hunter have a separation of just under three degrees. You can also create angles with your fingers held at arm’s length. The accuracy is a little less because arm lengths and finger thicknesses vary, but it is much more precise than using feet, inches, or meters, etc., to describe an event which has crossed the sky. Your pinky equals 1 degree; your index finger, 1.5 degrees; your three middle fingers held together, 5 degrees; a fist with the thumb on top, 10 degrees; and finally, your pinky and thumb stretched as widely as possible, 20 degrees. From common experience think about the angular diameter of the moon, then go out sometime during the next two weeks when the moon is visible and observe which one of the above combinations of fingers, excluding the 20-degree suggestion, represents the angular diameter of that big ole moon visible in the nighttime sky. I guarantee you’ll be surprised.

1131 APRIL 22, 2018: Constellations: After a couple days of sudden summer like conditions (April 13-14), we are back into the dark ages of winter. As I write these words, it is actually snowing outside (April 17), not that I’m worried about any of it sticking to the ground; but it is still snowing, and the temperature is only 40 degrees F. It also snowed on April 19. The latest I have ever seen it snow in the Lehigh Valley was May 1. I was in junior high school, I believe, in the eighth grade. We are less than two weeks away from that date, and the flakes still keep coming. Generally, I am beginning to spend a lot more time out-of-doors observing with my telescope, but I am still in “the quick dash outside” mode to make sure that everything in the sky is in its place. It has just been too cold and cloudy. Yes, the heavens are all about spring with winter’s stars crowding themselves ever farther into the west and southwest, but Old Man Winter just won’t let go. The constellations that we see gracing the northern and southern hemispheric heavens were not always formalized. In fact, there have been hundreds of different patterns created in the sky. Eighty-eight of them were officially sanctioned in 1928 by the International Astronomical Union, the worldwide congress of professional astronomers that also establishes the rules for naming objects like comets, asteroids, supernovae, variable stars, etc. If you remember, the IAU was also responsible for demoting Pluto from a planet to a dwarf planet in August of 2006. The concept of a constellation to the IAU is different from what most individuals believe a star pattern to be. The IAU could care less about the actual pictures that might be drawn. No official stars create the representations. That is up to your imagination. Instead, the IAU established the official boundaries and names for the constellations, similar to the boundaries of states in our nation or counties within a specific state. All of the stars inside that boundary belong to the constellation, not just the luminaries your imagination creates to construct the picture of what that constellation represents. To further complicate matters, there are numerous star groupings which are considered to be constellations by the general public but are not recognized as such by the professional community. The pattern most frequently mistaken for a constellation by Americans is the Big Dipper. It is, in essence, composed of the brightest members of the Great Bear, the constellation of Ursa Major. Other cultures or nations saw these same seven stars differently—a plough, a wagon, or a steel pan. Groupings of stars such as these are termed “asterisms.” The Little Dipper (Ursa Minor); the Pleiades, located on the shoulder of Taurus the Bull; the belt of Orion the Hunter; and the Northern Cross, part of Cygnus the Swan, are other examples of well-known asterisms often mistaken for constellations. All of these, except for the Swan, are visible right now just after dark. Cygnus is holding out for the warmer weather of summer before it soars overhead.

1132 APRIL 29, 2018: It's Leo Time: The weather has been cooperative enough that both of my Moravian astronomy classes have had the opportunity of viewing the heavens from Shooting Star Farm, a much less light polluted location north of Quakertown, as well as from the Sky Deck, situated on the rooftop of the Collier Hall of Science. Bill Jacobs and Johnny Killwey open up their farm to my Moravian pupils and friends who bring their high-end telescopes for an evening of stargazing fun. My Tuesday/Thursday class had an exceptionally clear evening on April 10; however, temperatures went below freezing before the end of the event. It was definitely long john weather, but the sky was fantastic. One of the star patterns that was especially noticeable was Leo the Lion, high in the south as soon as it got dark. To the Egyptians 4000 years ago, Leo served a practical purpose to everyone who lived along the Nile. When Leo was in conjunction with the sun, it was the “Time of the Lions,” when the sun shone more directly on Egypt, heating the air and baking the ground, compelling the lions that lived in the neighboring hills to seek the refreshing waters of Egypt’s lifeblood for relief. The Egyptians even had a reason for why it became so hot during that time of the year. The sun combined its powers with Leo’s brightest star, Regulus, and the other prominent luminaries of the king of the beasts to produce the summer heat that drove the lions crazy with thirst. At the time of the construction of the Great Pyramid, 2560 BC, the sun actually occulted Regulus on July 12 (Gregorian Calendar) so that the lion was in close proximity to the sun from mid-June through mid-August. Today, the sun passes below Regulus, but it is close to Leo’s alpha star from late July through late September. Why the change? Our calendric system is based upon the tropical year which results from the time interval between two successive crossings of the vernal equinox (first moment of spring) by the sun and not a full revolution of Earth around Sol which is about 20 minutes longer. The westward motion of the vernal equinox transpires because the Earth’s axis wobbles in a nearly 26,000-year cycle called the precession of the equinoxes. By using the tropical year instead of the exact orbital period of Earth, holidays stay in sync with the seasons. Christmas will always remain in step with early winter, but the stars of Christmas will slowly change to become the stars we observe in early summer. That will take about 12,000 years. Check out Leo the Lion by first finding the Big Dipper high in the NE right after dark. Then take the Dipper’s two Pointer Stars, Dubhe and Merak, and instead of using them to find the North Star by traveling left, move to the right in a straight line across the sky until you see a backwards question mark. That is the head and part of the body of Leo. Bright Regulus will be the “dot” at the bottom of the backwards question mark. To the left of the question mark, three stars form a distinctive triangle which becomes the hindquarters of the lion. Putting it all together gives one the impression that the lion really represents the Egyptian sphinx. Check it out! I’m not lying about the Lion or the sphinx. It’s really cool to see!

[April Star Map]

[April Moon Phase Calendar]