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SkiesIdaho
Skies
December 2007
Vol. 4 No. 12
Idaho Skies is a column for beginning amateur astronomers and those interested in astronomy. Suggestions about the column are gladly accepted by the columnist, at paul.verhage@boiseschools.org
This month look for the star Aldebaran, the lucida of Taurus the Bull. It’s half way up in the sky when you face towards the east. The star is pale orange in color and forms the apex of the “V” of Taurus (where it represents the eye of the bull).
Aldebaran is a large orange star. With a diameter 38 times larger than the sun’s, it would reach to the orbit of innermost Mercury if it replaced the sun in our solar system. Its orange color means its surface temperature is cooler than our yellow-colored sun and is therefore, less intense per square area. However, its larger size and greater surface area combine to emit 150 times more light than the sun. Aldebaran is larger than the sun because its core contains more helium from its fusion of hydrogen. Since helium is denser than hydrogen, it squeezes the core harder and hotter. The increased temperature and pressure is high enough to fuse helium ash into carbon and oxygen. The “ignition” of helium caused its surface to swell out and cool to the orange star it is today. If you were born in 1942 then Aldebaran is your birthday star this year because the light you see tonight left Aldebaran 65 years ago. Aldebaran points the way to two star clusters, the Hyades and Pleiades. Aldebaran looks like it’s a member of the Hyades, but it’s really 350 light years closer to Earth.
December begins with Saturn just two degrees above the moon. The moon and Saturn rise around 1:00 AM on the 1st. At two degrees a part (equivalent to four lunar diameters), they can both be seen together in binoculars.
Also on the 1st, the moon is at last quarter. Therefore, the moon won’t rise until around midnight on the 2nd. This means the evening sky remains dark until then. That’s perfect for those wanting to see faint objects in their binoculars or telescopes during the evening.
As you drive to work on the morning of the 5th, you’ll see the moon, Spica and Venus forming a small equilateral triangle. Venus forms the left corner of the triangle, the moon is the bottom corner, and dimmer Spica is the top right corner. Their distances from earth are 90,225,000 miles, 251,400 miles, and 263 light years respectively. So much for appearing close together in the sky.
If weather or technology doesn’t fail us, the European Space Agency’s Columbus Laboratory will lift off for the International Space Station (ISS) on the 6th. Columbus is the largest European contribution to ISS. It’s a 23 foot long module containing ten experiment racks and room for five more. Experiment racks are the size of a phone booth and have all the connections an experiment might need. Even neater, Columbus has four external locations for mounting experiments in the vacuum of space. Astronauts or controllers on Earth can operate the experiments loaded into Columbus.
If you’re a 5th to 12th grade teacher, then you might be interested to know that on the 6th there’s a web seminar designed for you. Go to the website, http://learningcenter.nsta.org/products/symposia_seminars/JPL2/webseminar5.aspx to register for the seminar, Are We Alone?
The moon reaches apogee on the 6th. Its greatest distance from Earth this month is 252,422 miles
Hard to believe, but it’s been 35 years since the last Apollo mission launched for the moon. The target of Apollo 17 was the Taurus-Littrow region of the Moon. In 1972 this region was believed to contain a mix of rocks that were younger and older than any found to date. Astronauts Gene Cernan, Harrison Schmitt, and Ron Evans launched several hours late, but they were still the only night time Apollo launch. Cernan and Schmitt landed with their rover on the moon on the 11th. Schmitt was the only scientist to go the moon, and the last astronaut to step on its surface. Apollo 17 spent three days working on the lunar surface. They drove a total of 19 miles across the lunar surface and collected 243 pounds of rocks. One of the mission highlights was their discovery of orange soil. The orange came from tiny beads of volcanic glass mixed in the lunar soil. Billions of years ago, a volcanic fire fountain emitted the glass beads that the astronauts discovered. It makes one wonder how other things the moon has waited billions of years for us to discover.
The moon is new on the 9th. If you want dark skies all night, then this is your night.
The Geminid meteor shower reaches its peak on the night of the 13th and the morning of the 14th. The meteor shower is a consistently good shower and you can expect to see at least 50 meteors per hour. The only thing keeping this shower from being as popular as the Perseids is that the Geminids take place near winter. Meteors from the Geminids appear to radiate near the star Castor. Castor is the fainter of the two top stars of Gemini. You can watch the meteor rate increase after midnight, that is if you justify being up that early on a Friday morning.
The Geminids began appearing about 150 years ago, before that, there’s no record of them. Their hourly rate has been increasing since their discovery and has maintained its high hourly count for several decades now. Several decades from now, the Geminids will disappear when their orbit no longer crosses Earth’s orbit. The parent of the Geminid meteor shower appears to be a dead comet called 3200 Phaethon. Astronomers discovered the former comet, now asteroid, in 1983.
It’s rotten to think that humans last walked on the moon 35 years ago on the 13th. On December 13, 1972, the Apollo 17 lunar module, Challenger, lifted off from the moon. It successfully docked with the Apollo Command Module, America, in lunar orbit and returned to Earth on the 19th.
Mariner 2, the first American spacecraft to make a flyby of another planet, passed Venus 45 years ago on the 14th. Mariner 1, also targeted for Venus, launched before Mariner 2, but its booster failed before it could enter Earth orbit. Its backup, Mariner 2, spent 3-1/2 months cruising to Venus. The three foot across spacecraft with its 15 foot across solar array passed 21,600 miles from Venus. It measured the planet’s magnetic and radiation fields and its temperature. Mariner 2 discovered that Venus rotated slowly backwards and had a very dense and hot carbon dioxide atmosphere. Perhaps due to its slow rotation Venus had no magnetic field and did not trap solar radiation into a belt surrounding the planet. After passing Venus, Mariner 2 continued returned data for another two weeks. The dead spacecraft is currently orbiting the sun.
If you can find dark skies, then you can see an asteroid. On the 15th, aim your binoculars, or better yet, small telescope, on the moon at around 7:00 PM. One moon’s diameter below the moon is a faint star. That star is actually Pallas, the second asteroid astronomers discovered (in 1802). Binoculars can see stars appearing half as bright as Pallas, but you’ll still need dark skies to see the asteroid well. The chart below will help you locate the asteroid. When you see Pallas, you’re looking at an asteroid 163 miles across (the second largest asteroid) and 229 million miles away. For comparison, Pallas is roughly as wide as the distance between the cities Meridian and Burley.
Science fiction author Arthur C. Clarke celebrates his 90th birthday on the 16th. Clarke is best known for his science fiction story and movie, 2001: A Space Odyssey. However, did you know Clarke also invented the geostationary communication satellite? His concept for placing three radio communication satellites in 22,000 mile high orbits was published in the magazine Wireless World shortly after the end of World War II. Satellites orbiting Earth 22,000 miles above revolve around the Earth once every 24 hours. That makes then appear to stand still above the Earth’s surface. Three such satellites can see each other and relay radio transmissions to anywhere on Earth, except to the poles. Today geostationary orbit, or Clarke orbit, is one of the most popular pieces of real estate in space. Clarke currently lives in Sri Lanka.
The moon is at first quarter on the 17th. If it’s not too cold, take some time to look at the moon through your binoculars.
Earth passes its closest to the red planet on the 19th. Every two years and two months, Earth catches up to Mars. During those times Mars appears it brightest in our sky. So look for a bright orange star that rises in the east near sunset. That’s Mars and it’s only 54 million miles away.
On the night of the 21st, the Pleiades (the Seven Sisters) is 1-1/2 degrees to upper right of moon (or three lunar diameters). This would be nice in binoculars, but since the moon is nearly full, its light will wash out some of the cluster’s fainter stars.
Eight minutes after midnight on the 22nd, the sun reaches winter solstice for the northern hemisphere. In other words, winter begins for Idaho. If you were to watch the time and position of sunset for the last few weeks, you’d see that the sun had stopped rising later morning and farther south. In other words, at the solstice, the sun’s daily changes in time and position come to a stop. In a few weeks, we’ll begin noticing that the sun is rising earlier and farther to the north. The days will get longer, but it will take the atmosphere and ground some time to catch up to this change.
The moon is also at perigee on the 22nd. Its distance from Earth, which is its closest distance for the month, is 224,200 miles
On the evening of the 22nd and morning of the 23rd, the Ursid meteor shower reaches its peak intensity. This shower appears to radiate near Ursa Minor, or the little Dipper. That means the shower is visible all night. However, the shower tends to be weak, so you shouldn’t expect to see more than 10 meteors per hour from this shower. Perhaps in another six years though, we’ll see a meteor per minute from this shower. That’s because the Ursids fluctuate in intensity every 12 years. Unfortunately, this year, the full moon’s light wipes many meteors in this shower, so don’t worry if you’re too busy to observe it.
The moon is full on the 23rd. The full moon in December is often called the Long Night Moon, or Moon before Yule.
The Moon, Mars, and a star cluster are close enough together for your binoculars on the night of the 23rd. The star cluster is M-35 in Gemini and it is three degrees or six lunar diameters west of the moon. Here’s an idea of what they’ll look like in your binoculars.
Mars reaches opposition on the 23rd. Opposition occurs because Earth is in a smaller orbit than Mars. Therefore, every 26 moths Earth catches and passes Mars. When at opposition, Mars is in line with the Earth and Sun.
Close to midnight on the 28th, the moon appears between the planet Saturn and the star Regulus. Saturn is the yellowish “star” seven degrees to the lower left of the Moon. That’s about the width of three fingers when viewed from your extended hand. Regulus is the alpha star of Leo and the Lion and is 2 degrees above Moon. You can see Regulus and the Moon together in your binoculars, but Saturn will be too far away to be in the same field of view.
This Month’s Topic
Many children receive their first telescope as a Christmas present. You can make sure it’s a pleasant experience and one that will last for years by avoiding some of the common telescope pitfalls. The major pitfalls of telescope purchasing are poor quality optics and rickety telescope mounts. There are two minor issues discussed at the end of this article, small finders and poor quality eyepieces.
Avoid telescopes that advertise their magnification as the most important feature. In reality, magnification power is not the most important feature of a telescope. In fact, it’s not even the second most important feature. Astronomical objects tend to be faint first, and small second (many planetary nebulas are an exception). Many astronomical objects are quite large. For example, I can see the Andromeda Galaxy and Orion Nebula quite well with a pair of binoculars at 7 power. So the first consideration for a telescope should the aperture, or diameter, of its objective.
The objective is the main lens of a refracting telescope or the main mirror of a reflecting telescope. The larger the telescope’s objective, the more light it gathers and the fainter the objects that you can see with the telescope. An aperture of at least three inches is required to see the most popular objects in the heavens, but an aperture of six or eight inches makes a better first telescope (if their focal length is short). Telescopes larger than 8 inches tend to be heavy, and as a result, it’s difficult to carry them outside or load them into the car. So unless you’re really gung ho on astronomy, a big telescope will not get used much.
The focal length of a telescope is given in both inches and f-ratio. The focal length is a measure how long the light rays must travel to be brought to a focus. As a result, the focal length indicates how long the telescope tube must be. The f-ratio is the focal length of the telescope given in terms of its objective diameter and is calculated by dividing the telescope’s focal length by the diameter of its objective (be sure to use the same units for the focal length and objective diameter). Popular telescopes have short f-ratios, like F/4.5 or F/6. Telescopes with larger f-ratios are longer in length and therefore heavier in weight. They also have narrower fields of view, making it more difficult to locate objects through the telescope (which makes a good finder scope more important).
A wobbly mount is the second curse of the Christmas telescope. When the slightest breeze makes the image in the eyepiece dance, you can’t detect the details. A solid mount allows steadier views and makes using the telescope much more pleasant to use. It’s not necessary to get a fancy equatorial mount with clock drive for a first telescope. Doing so is sort of like buying a Mazerati for a first car. A telescope that tracks the stars is of no use if you can’t first locate the object you want to look at. Besides, a high quality equatorial mount is heavier and more expensive than a simple Dobson mount (AKA Dob). The Dob is a simple and rock steady mount for reflecting telescopes. It’s easier to use than the equatorial; you just pull the telescope where you want to look. The Dob mount allows you to purchase a telescope with a larger objective.
No matter how good the objective of the telescope, it can’t do the job if the eyepiece is poor. Inexpensive telescopes tend to have eyepieces with plastic bodies and plastic lens. It doesn’t take much to scratch a plastic eyepiece, at which point it become less than useless. High quality eyepieces are made with a metal barrel and glass lenses.
There are two standard size eyepieces. The most popular has a barrel 1.25 inches in diameter and the other is 2 inches in diameter. There is a less popular size eyepiece that you probably won’t find any more, that’s the Japanese Standard eyepiece with a barrel diameter of 0.965 inches. Note that the diameter of the eyepiece barrel is not related to the magnification created by the eyepiece.
The magnification created by an eyepiece is determined by dividing the focal length of the objective by the focal length of the eyepiece. For example, using a 25 mm focal length eyepiece in a telescope with a 1000 mm focal length objective yields a magnification of 40 power (1000 mm divided by 40 mm). The shorter the focal length of the eyepiece, the greater the magnification it creates. An inexpensive way to increase the magnification of an eyepiece is to insert it into a Barlow lens before inserting it into the telescope. The typical Barlow doubles the magnification of the eyepiece.
Telescopes need several eyepieces so you can change the telescope’s magnification. The maximum useable magnification of a telescope depends on the quality of its optics. For a high quality telescope, a maximum magnification of 60 times per inch aperture is a good rule of thumb. So expect a good quality six-inch telescope to begin creating poor images if used above a magnification of 480 times. Be very suspicious when you see a two-inch refractor advertising a magnification of 300 power! The really tragic thing is that I have seen telescopes like this.
There’s also a lowest useful magnification that a telescope can create. If the magnification is too low, not all the light gathered by the telescope can enter your eye. When you use too low of a magnification, it’s as if you are using a telescope with a smaller objective. The lowest useable power of a telescope is calculated by dividing the diameter of the telescope (in millimeters) by 7 for young people, and by 5 or 6 for older people.
A telescope’s finder scope or viewfinder is used to point the telescope at the object you want to observe. A viewfinder is a secondary telescope of low magnification and wide field of view. Its wide field of view is centered on the narrow field of view of the main telescope. It’s easier to find an object in the viewfinder than it is in the telescope, especially as the magnification of the telescope is increased.
A good viewfinder has a diameter of 2-inches. A smaller diameter viewfinder doesn’t gather enough light to make a suitable number of guide stars as visible, which makes it difficult to locate faint astronomical objects. Larger diameter viewfinders are useful on large diameter telescopes, but for a first telescope, the 2-inch viewfinder is just what the doctor ordered.
A viewfinder that is not aligned, or doesn’t remain aligned, with the main telescope is a major source of frustration. When the viewfinder is not properly aligned or won’t stay aligned, you’ll end up spending several minutes sweeping the sky with the main telescope trying to locate your astronomical object of interest instead of finding the object in your telescope when you first look through it. So using a poorly aligned viewfinder means that you’ll miss the object of your interest will have to start all over again. Do this enough times and you will give up for the night.
Good places to look for a telescope are the major advertisers in magazines like Sky and Telescope and Astronomy. Two examples of telescope manufacturers you’ll find advertising in these magazines are Meade and Orion.
My recommendation for a good first telescope would be a six inch, f/4.5 of f/6 or an eight inch f/4.5 reflector on Dobsonian mount. It would have one or two plossol (a popular wide-angle design) eyepieces with focal lengths between 12 mm and 32 mm for the 6” f/4.5, 12 mm and 40 mm for the 6” f/6, or 4 mm and 32 mm for the 8” f/4.5.
Good luck with your new telescope.
The Royal Society of Canada, Observer’s Handbook 2007
Baalke, Ron, Space Calendar, 3 October 2007, <www.jpl.nasa.gov/calendar/>
Night Sky Explorer (software)
Kaler, James, Stars: Aldebaran, <www.astro.uiuc.edu/~kaler/sow/>
NASA, Columbus Leaves Europe, Heads for America, 23 May 2006, 3 October 2007, <http://www.nasa.gov/mission_pages/station/structure/Columbus_module.html>
NASA, Apollo 17, 3 October 2007, <http://www-pao.ksc.nasa.gov/kscpao/history/apollo/apollo-17/apollo-17.htm>
Kronk, Gary W., Meteors Online: Geminids, 3 October 2007, <http://meteorshowersonline.com/geminids.html>
NASA, Mariner 2, 3 October 2007, <http://nssdc.gsfc.nasa.gov/nmc/tmp/1962-041A.html>
Wikipedia, Arthur C. Clarke, 3 October 2007, 3 October 2007, <http://en.wikipedia.org/wiki/Arthur_C._Clarke 3>
NASA, Hurtling toward Mars, 3 October 2007, <http://science.nasa.gov/headlines/y2007/21aug_hurtlingtomars.htm>
Kronk, Gary W., Meteors Online: Ursids, 3 October 2007, <http://meteorshowersonline.com/showers/ursids.html>
Occultation of Mars on 24 Dec, International Occultation Timing Association, 3 October 2007, <http://www.lunar-occultations.com/iota/planets/1224mars.htm>
NASA, Mars Opposition, 3 October 2007, <http://mars.jpl.nasa.gov/allabout/nightsky/nightsky03.html>
Wikipedia, Aldebaran, 10 October 2007, 7 October, <http://en.wikipedia.org/wiki/Aldebaran>
Dark Skies and Bright Stars,
Your Interstellar Guide