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JANUARY 5, 2020: Belelgeuse: Where Have You Gone?
Friend, Adam Jones, e-mailed me the other day saying I should write an article about Betelgeuse because its brightness has significantly diminished since October. I went out with binoculars to check Adam’s observations, and he was correct. Where have you gone, Betelgeuse, the Alpha star of Orion the Hunter? Like Stevie Nicks’ popular hit, “Edge of Seventeen,” red Betelgeuse, a supergiant star plagued with congestive heart failure, is on the “edge of going supernova,” and its variability is part of the opening act before the main event which astronomers are anticipating could occur between now and one million years into the future. If you face Orion the Hunter with its three belt stars, mid-sky in the south around 11 p.m., Betelgeuse is the bright—well not so bright right now—red shoulder star found on the Hunter’s left side. It should be about as vivid as the luminous blue supergiant, Rigel, which represents the foot of Orion, but looks more like his knee and is catty-corner from Betelgeuse. Betelgeuse is a semiregular variable star. When it was first cataloged by the German lawyer and astronomer, Johann Bayer (1572-1625) in the early 17th century, it was brighter than Rigel, and thus, became the Alpha star of Orion (Alpha Orionis) in his star atlas,
, published in 1612. Betelgeuse varies in brightness by about two magnitudes, from being the sixth brightest star of the night to somewhere around the mid-forties. When I observed it recently, it may have well been fainter than that. I judged its brightness similar to Saiph’s, actually the tip of Orion’s sword, but looking more like the other knee across from bright Rigel. That put Betelgeuse at about +2.1 magnitude, still very easy to see with the unaided eye, but out of place with the way Orion normally appears. Magnitude, or the way that astronomers classify the brightness of stars, is a counterintuitive concept. First, the fainter the star, the more positive the magnitude. Betelgeuse at magnitude +2.1 is much fainter than Rigel at approximately +0.2. Since +0.2 is a more negative number than +2.1, Betelgeuse is the fainter star right now. The other challenge in understanding magnitude is that the difference between one magnitude represents an intensity variation of 2.51. A difference of five magnitudes corresponds to an intensity change of 100. The dissimilarity in magnitude between Rigel and Betelgeuse, if my magnitude estimate is reasonably correct, is 1.9, corresponding to an intensity difference of nearly 6, and perhaps putting Betelgeuse at the point of an historic low. If you want to try to make a brightness estimate of Betelgeuse, use the map posted online (or attached as a PDF) with star names and magnitudes indicated at https://astronomy.org/StarWatch/January/index-1-20.html#1-5-20. Use binoculars, but defocus them so that Orion’s stars look like large disks and find the luminary which most closely matches the brightness of Betelgeuse. If you don’t own binoculars, but wear glasses to correct for far vision—myopia, observe without them, noting which diffuse star blob in Orion is about the same brightness as Betelgeuse. Feel free to e-mail me your results. It’s a lot of fun, and you’ll be contributing to science in the meantime. On New Year’s Day, I estimated the magnitude of Betelgeuse at +1.9. Clear skies!
Gary A. Becker map using Software Bisque's
JANUARY 12, 2020: The Sun: A History of Warming
Around 4.6 billion years ago, an event occurred in our galaxy, perhaps a supernova, which triggered the collecting of gas and dust to form a star cluster, similar to the Pleiades, found in Taurus the Bull and currently visible in our night sky. The ultraviolet radiation from those hot, young cluster stars began clearing the nest of leftover gas and dust that created them, causing secondary pockets of higher density to form which collapsed gravitationally to establish a new generation of less massive stars; one of these was our sun. Over the next several hundred million years, the cluster evaporated, its outer member drifting away first, eventually leaving the sun on its own, orbiting the galaxy with its entourage of planets, moons, and smaller objects. A star is an object that is changing matter into energy within its core, spontaneously converting less massive elements into more massive ones. The matter composing the star wants to decrease its size due to gravitational attraction. This is balanced by the outward radiation and gas pressure created by the energy being produced within the core, trying to expand the star to become larger. When these two forces are in balance, the star is said to be in hydrostatic equilibrium and stable. In the case of low mass stars like the sun, hydrogen is being converted into helium at the loss of almost 5 million tons of matter per second, but it wasn’t always that way. In the beginning the sun was about 30 percent less luminous than it is today, and it was in this environment that life began on Earth and also probably on Mars. Sol’s surface temperature was higher, but its luminosity was lower, implying that the sun was physically a smaller star. During the intervening 4.5 billion years, the amount of helium in the sun’s core has been increasing. Because helium is more massive than hydrogen, the helium has gravitated towards the center of the core where it is squeezed and heated due to compression. This has slowly increased the activity of the thermonuclear furnace in the sun’s core to produce helium at a slightly faster pace, causing the outflow of energy to quicken and the sun to react by slowly expanding to maintain its stability. Surface temperatures have dropped slightly because the density of the outer layers of the sun are expanding, but the increased surface area has overcompensated for this slight decrease in temperature causing Sol to become more luminous. This will not become the red giant phase of the sun. That happens much later, in about 5.5 billion years, and will involve hydrogen burning in a shell surrounding an inert helium core. It is simply the sun adjusting its size for the increased hydrogen core burning due to the small rise in core temperature as a result of helium compression at its center. Currently, conditions should be in balance on Earth, notwithstanding the negative human contributions to global warming, but in a billion years or so, the sun’s increased luminosity will be great enough to raise temperatures to the point where the oceans will boil, and all life as we know it will cease on the Earth. For the moment it is imperative that we solve the human component of global warming, but it is interesting to note that built within the genetic, evolutionary code of all low mass stars like our sun is a natural tendency to warm throughout their lifespans, a condition over which humans have no control.
JANUARY 19, 2020: “I’m a Girl Watcher!”
She’s a hottie and guaranteed to give you cold feet if you plan to watch her. Venus, goddess of beauty, is dominating the chilly southwestern January sky after sundown, sometimes looking like the distant landing lights of a plane. When I was a kid growing up in the 50’s, it was known that Venus was a cloudy world, and that its atmosphere contained carbon dioxide. Speculation was ripe for the imagination. Was it like a steaming rainforest containing exotic forms of life or was it a dry, windswept desert devoid of all moisture? The latter is closer to the correct picture, but with some major revisions. Today we know that Venus’ beauty is only skin deep. Starting at Venus’ yellowish cloud tops resides a goddess who would bake, crush, dissolve, and poison any human or creature that tried to descend to her surface. Venus is the ultimate runaway greenhouse saga with an atmosphere of nearly pure carbon dioxide (96.5 percent) released through volcanic activity, causing surface temperatures (860 degrees F.) to exceed those of the hottest parts of Mercury by over 60 degrees F. Venus’ greenhouse dilemma is caused by solar radiation absorbed at its surface and then reemitted as infrared (heat) energy. This infrared radiation gets reabsorbed by the carbon dioxide atmosphere and is unable to escape easily. It is similar to cloudy nights on Earth being generally warmer than clear nights where infrared energy can radiate directly back into space. On cloudy nights water vapor or water ice acts as the greenhouse agent causing heat to escape at a slower pace, artificially raising temperatures. Atmospheric pressures of slightly over 90 times that of Earth and winds mix the air to create even temperatures between day and night, including the polar and equatorial regions. There is no way to escape the Venusian oven anywhere on the planet. Venus’ surface pressures are crushing, equivalent to having 0.6 mile (one kilometer) of water over an individual, enough to compress some volcanoes on Venus’ surface to features that are called “pancakes.” Whether Venus could have had a brief period where water flowed on its surface is debatable. Because of Venus’ higher initial temperature, water vapor (H
O) would have risen to higher altitudes and have been broken apart by the sun’s ultraviolet radiation (photodissociation) with most of hydrogen lost to space. However, water vapor plus sulfur dioxide, also released through volcanic activity, plus free oxygen would have also combined to form sulfuric acid droplets which astronomers know today represent the bulk composition of the several cloud (haze) layers surrounding the planet. On Earth, rain water dissolved carbon dioxide from the atmosphere, returning it to the surface where it formed carbonate rocks, coral, and other shelled sea life. Venus, crushed by over 90 atmospheres of mostly carbon dioxide, poisoned by the carbon dioxide itself, baked by the scorching temperatures created by the most efficient greenhouse effect in the solar system, and dissolved by the sulfuric acid clouds makes the goddess of beauty, in personification, someone to avoid dating at all costs. Keep your distance, but enjoy her beauty visible in the southwestern sky in the deepening twilight after sundown.
JANUARY 26, 2020: