If you have trouble viewing this newsletter, click here. Welcome again to our monthly educational newsletter with features on exciting celestial events, product reviews, tips & tricks, and a monthly sky calendar. We hope you enjoy it!
Starry Night® is known around the world as the most popular software for classroom and desktop astronomy. But you might be surprised to know it’s fast becoming an important tool for planetarium visualization. “Starry Night® Dome” is used in planetariums around the world as a real-time three dimensional virtual universe, taking students on tours of the heavens. The dome version of Starry Night® is the graphics engine for the SciDome Digital Planetarium, a video system designed to project computer graphics onto a 180 x 360 degree, hemispheric planetarium dome. SciDome is made by Spitz Inc, of Chadds Ford, Pennsylvania one of the world’s largest suppliers of planetarium systems. Spitz is an appropriate choice to offer a Starry Night® based planetarium system: Over their 60-year history, they’ve installed traditional planetarium instruments (known as “opto-mechanical star projectors”) into thousands of planetariums around the world. Spitz planetariums can be seen in museums around the world, though their specialty is planetarium theaters for schools and colleges (there are over a thousand school planetariums in the US alone). As these older educational planetariums begin to show their age, a “digital upgrade” to the computer-based SciDome is a logical next step. Utilizing a custom fish eye projection lens and high resolution digital projectors, SciDome accurately maps the Starry Night® universe onto the immersive planetarium dome. Starry Night®’s database of stars, galaxies, 3D models and other deep sky objects is realistically projected in an immersive full-dome theater environment. “Starry Night® is the perfect platform to teach students about the complex universe we live in.” says Scott Huggins, Marketing Director for Spitz. “The space science curriculum is so comprehensive, there’s almost nothing we can’t show. It offers a thousand times more teaching capability than traditional planetarium projectors.” Planetariums all over the world are adopting Starry Night® as their astronomy display medium. There are over 40 SciDome owners in diverse locations like Malaysia, Italy, Turkey India and the United Arab Emirates, as well as in dozens of locations in the US. “For us, the most important feature of Starry Night® is the compatibility between our Dome systems and the educational versions students use in the classroom,” says Huggins. “For the first time in planetarium history, students are actively interacting with the planetarium system. If a student makes her own visuals in Starry Night®, it’s simple for her to show them to other students in the spectacular, fulldome setting of a planetarium”. For more information about Spitz and SciDome powered by Starry Night®, visit www.spitzinc.com. After his discovery of Jupiter’s moons, Galileo turned his telescope to the other planets. Mars and Venus were not well placed for observation and the appearance of Saturn puzzled him, but he concluded that there were no moons around the other planets. Discovery Two: The Phases of Venus In September of 1610 he received an offer from Grand Duke Cosimo de Medici to move to Florence. Eager for more discoveries, Galileo turned his attention back to Venus. At that time, Venus was an “evening star” and Galileo’s poor optics showed little more than a fuzzy blob. But the very fact that Venus showed no evidence of a crescent was a blow against the Ptolemaic system. According to the geocentric system of Ptolemy, Venus was always between the Earth and the Sun and so could only show a crescent phase. Of course, there was always the possibility that Venus gave off its own light and hence no phase effect would be seen. By mid-December, Venus showed a half-moon phase and Galileo was convinced that Venus did indeed show phases. In a letter to Cosimo’s brother, Galileo preserved his priority of discovery by including a Latin anagram which could later be unscrambled. Galileo’s drawings of the phases of Venus. Why did he not announce his discovery then and there? At half-lit phase, Venus has a small angular diameter and the fuzzy image presented by his optically poor telescope was not at all convincing - especially to a non-believer! It wasn’t until the crescent phase became obvious that Galileo deciphered his anagram. You can follow Galileo’s footsteps by examining the appearance of Venus in the late summer to early winter of 1610 by downloading the file Venus1610.snf and running time forward. And just what did Galileo find puzzling about Saturn? Stay tuned for the next article to find out. Herb Koller The stars and constellations don't change position any more rapidly than the continents on Earth, and we can measure those with a fixed grid (latitude and longitude) so we should be able to build a similar grid system on the sky for mapping purposes. This will give us a map that is independent of the local horizon and zenith. The first thing we need are some fixed points. The sky appears like a spinning sphere outside the Earth (really, we're the ones spinning), so there are two of these. They're overhead when viewed from the north and south rotational poles of the planet. (Not coincidentally, 90º away from these poles is a line that runs all the way around the sky directly above Earth's equator.) One of our coordinates the sky equivalent of latitude, called declination is measured with respect to these celestial poles and celestial equator. Here's the view from mid-northern latitudes the north celestial pole appears partway up the sky, neither overhead (as it would be if you stood at the North Pole) or on the horizon (if you were standing on Earth's equator). We now need a celestial longitude. On Earth, the arbitrarily chosen line of zero longitude (the Prime Meridian) runs from the north to the south pole and through the Greenwich Observatory in London. But we can't just project that line onto the sky the way we did with the poles, because it sweeps around the sky once every day as the Earth turns. We need to find a fixed point on the sky and draw a line between the celestial poles, running through that point. The one that was chosen was one of the two points (the equinoxes) where the Sun's path on the sky (the ecliptic) crosses the celestial equator. The Sun sits on the celestial equator on the first day of spring and the first day of autumn. (In this illustration it's late March, and the Sun has passed the equinox.) This zero line of celestial longitude is called the celestial meridian, and the longitude coordinate on the sky is called right ascension. Declination is measured north or south of the celestial equator. Like latitude, it's expressed as a number between 0º and 90º, with a qualifier of north (positive) or south (negative) to tell you which hemisphere of the sky you're looking at. Right ascension is always measured in one direction, eastward from the celestial meridian. Sometimes it's given in degrees, but the most common standard is to express it in hours. One hour east of the meridian is 1/24 of the whole way around the sky. Just as with maps on Earth, a star chart will have these coordinates marked so that you know the orientation and scale of the chart. You can see the celestial coordinate grid in Starry Night® by pressing G on your keyboard, or opening the Options › Guides tab on the left side of the screen. Brenda Shaw Florence, Italy, is the home of many museums, some of which contain the greatest works of art humanity has ever produced. It’s easy to overlook the small Institute and Museum of the History of Science, which looks not unlike a small warehouse, but this museum, which I visited in 2006 on my way home from viewing the March 29 eclipse in Libya, houses many treasures of the history of science. As an astronomer, I was particularly excited by the contents of the display case dedicated to Galileo Galilei. This contains the only two surviving telescopes made by Galileo, plus a grisly relic: the mummified remains of Galileo’s hand. In the eighth year of the 17th century, the idea of a new invention called a telescope was percolating throughout Europe. Spectacle makers in several locations, notably Hans Lipperhey in the Netherlands, discovered that by combining two lenses of different focal lengths they could make a device which magnified and brought distant objects closer. Though most saw this as a new tool for use in warfare, a few applied this device to science, using it to study the heavens. Most notable of these early telescope users was Galileo Galilei in Padua, Italy. The son of an eminent lutenist, Vincenzo Galilei, he had long been interested in science. In 1609 he built his first telescope, and soon became one of the leading makers of telescopes, demonstrating and selling his telescopes in the various courts of Italy. He apparently made many telescopes, but the only two that survive are the ones in this museum. His discoveries formed the basis of the “new astronomy,” which he popularized through his many books, unusual for the day being written in ordinary Italian, rather than scholarly Latin. He wanted everyone, not just scholars, to learn about his discoveries of the spots on the Sun, the craters and mountains on the Moon, Jupiter’s four bright moons, and Saturn’s mysterious shape. Galileo’s telescopes are simple refractors with objective lenses only an inch or so in diameter. Lenses were hard to manufacture in those days and suffered from severe chromatic aberration, unless they were kept small in size. Chromatic aberration is the spreading of the light into a tiny rainbow called a spectrum, and this plagued all refractors until the achromatic lens was discovered nearly two centuries later. One way of reducing chromatic aberration was to increase the focal length of the objective: Galileo’s telescopes are typically long and skinny, looking more like a walking stick than a telescope. The tubes were made of various materials, including wood and cardboard, but usually not of metal. Because Galileo was selling his telescopes to the aristocracy, they are often beautifully decorated with brightly colored bindings and wrappings. The eyepiece of Galileo’s telescopes is a very unusual one compared to most telescope eyepieces. Rather than being a positive lens, similar to a magnifying glass, it is a negative lens that intercepts the converging light rays coming from the objective and makes them parallel to enter the eye. This has one big advantage: the image is erect; but many disadvantages, especially its extremely narrow field of view. This design survives today only in simple “opera glasses” with only 2 or 3 times magnification. Any more magnification, and the field of view becomes impractically small. Most later telescopes use a design developed by Johannes Kepler which uses a positive lens for an eyepiece, inverting the image but allowing a much wider field of view. The magnification of Galileo’s telescopes was very low by modern standards, with a maximum of about 20 power. It speaks well for Galileo’s talents as an observer that he was able to see so much with such a limited instrument. Even the least expensive beginner’s telescope of today vastly exceeds what Galileo had in both aperture and magnification, as well as freedom from aberrations. Geoff Gaherty A conjunction occurs when two celestial objects are in line as seen from the Earth. The inner planets, Mercury and Venus, can have two different conjunctions with the Sun. These are called superior conjunction, when the planet is on the far side of the Sun, and inferior conjunction, when the planet is on the near side of the Sun. This month we will witness a nice inferior conjunction of Venus as it passes from the evening sky to the morning sky. One of the most useful features of Starry Night® is the ability to view the solar system from different perspectives. This can help us understand what goes on at an inferior conjunction of Venus. First let’s get an overview of the process. Under the Favorites menu choose Solar System:Inner Planets:Inner SolarSystem. This gives you a bird’s eye view of the four inner planets, seen obliquely. Click the Time Stop button and then click on the menu at the right end of the Time and Date box and choose “Now.” Zoom in until the Earth’s orbit fills the window. Choose the “Location Scroller” cursor from the Cursor box, just to the left of the Time and Date box. This lets you move your viewing location by dragging on the screen. Drag downwards so that you get a view looking straight down on the solar systems, so that the planetary orbits appear circular. Note the position of Venus somewhat above the imaginary line joining the Earth and Sun. If you now advance the date one day at a time by clicking on the date and then pressing the up cursor key on your keyboard, you’ll see Venus gradually move into line with the Earth and Sun. The three will line up perfectly on March 27, which is the date of inferior conjunction. You may wonder why Venus doesn’t actually pass in front of the Sun. Use the location scroller to drag upwards on the screen until the Earth’s orbit (green line) becomes a straight line. You’ll notice that Venus is now well above the plane of Earth’s orbit because of the different tilts of the two orbits. This means that for observers in the northern hemisphere, Venus will pass above (north of) the Sun. This gives a special advantage in observing Venus which we’ll get to shortly. Now lets look at how the conjunction appears to an observer on Earth. Use the menu button at the far right end of the Location box to choose your regular viewing location “with Reset.” Stop the time advance and set the time to 12:00 noon. We want to see clearly what’s happening around the Sun, so turn off the halo effects. You do this by right-clicking (Windows) or control-clicking (Mac) on the Sun to open the contextual menu, and choosing Halo Effects:Never. Under the Labels menu, choose “Planets-Moons”. Again, advance the date one day at a time by clicking on the date and using the up-cursor key. Notice how the Sun moves northward in the sky (spring is coming!) and how Venus moves to the right (northern hemisphere) and passes well above the Sun. On March 27 Venus is at its closest to the Sun, just above our line of sight. In the sky, this takes place when Venus is somewhat to the right of the Sun, because of the tilt of the ecliptic in the sky. Wouldn’t it be interesting to see how Venus is illuminated as it passes above the Sun? It’s easy with Starry Night®! Go back to the current date by choosing “Now” from the Time and Date box menu. Stop time as before and set the time to noon. Starry Night® lets us enlarge Venus (or any other planet) in the sky, while keeping the sky itself at normal scale. First, I prefer to see Venus with a cloudy surface, rather than the default, so right-click (Windows) or control-click (Mac) on Venus, and choose “Surface Image/Model:Clouds”. Now let’s magnify Venus. Click on the Find tab on the left side of the screen to open the Find pane. Venus should be the third item down. Use the scroll bar at the bottom of the Find pane to scroll to the right until you see a column headed “Magnification,” which may be abbreviated to “Mag…” This is a column of “sliders” which let you enlarge that particular object. Slide Venus’ slider slowly to the right, and you will see Venus gradually enlarge! Enlarge it so you can clearly see its phase and the “ashen light”: the part of Venus which is unilluminated by the Sun, but which is actually slightly lighter than the sky background. Now advance the date one day at a time and watch what happens to Venus’ phase. It shrinks to the thinnest crescent, and moves around to the south side of the disk as Venus nears conjunction on March 27. Continue to advance the date past conjunction and watch the phase grow and shift around to the eastern side of the disk. It is actually quite easy to observe Venus’ phase near conjunction with a small telescope or even binoculars. As always when observing close to the Sun, you have to take precautions. Because Venus is passing above the Sun, it is very easy to locate yourself so that the Sun is safely hidden behind a roof peak or chimney. Starry Night® will show you the direction and distance from the Sun for any particular day. I have observed Venus myself within about a day of inferior conjunction with an 8-inch reflector telescope. The cusps of the crescent were greatly extended beyond the 180° you would expect, and the ashen light was clearly visible. This month is an especially good opportunity to observe this because Venus will be relatively far from the Sun, over 8 degrees. Clear skies! Geoff Gaherty In honor of the International Year of Astronomy and commemorating the 400th anniversary of Galileo's first gaze through the telescope, Starry Night® Education has prepared a fun, interactive tour to clearly illustrate for your students the impact of Galileo's discoveries on our understanding of the Universe. This free download, complete with interactive exercises and worksheets, will allow your students to:
To download Galileo's Universe now, please click here. After installing, open the SkyGuide pane in Starry Night® and click on the “Galileo’s Universe” link at the bottom of the page. Galileo's Universe will work with any version 6 Starry Night® Education product. If you are currently using an earlier version we offer great discounts on upgrades, and flexible multi-seat lab pack options. To learn more about the many features included in our newest Education packages, please visit us at Starry Night® Education. To discuss upgrade and multi-seat installation options, contact us at 1-877-290-8256. On the night of February 25th, Ceres, the first asteroid discovered and recently reclassified as a dwarf planet, will reach magnitude 6.9. This is the brightest it has been since the mid-1800s and won't be this bright again for over two millennia. At magnitude 6.9, Ceres is within reach of binoculars and small telescopes. Don't let the scale of the diagram above fool you: Hydra is the largest constellation, and covers some 90° of sky. At this time of year, from mid-northern latitudes, it lies along the southern horizon at midnight. To start, M83 is an impressive barred spiral galaxy that, from our vantage point in space, lies almost face-on. Even small scopes should pick up its obvious structure. M68 is a nice globular cluster, 33,000 lightyears away. It's visible in binoculars but a telescope brings out the individual suns. NGC 3242, the Ghost of Jupiter, is one of the finest planetary nebulae in the sky. It's a full magnitude brighter than the more famous Ring Nebula (M57) in Lyra. A small telescope reveals a pale blue disc with diffuse edges and the prominent 11th magnitude star. Due to its high surface brightness, this target takes high magnification quite well: try 200x or 250x to see the football-shaped interior and faint shell. NGC 3115, the Spindle Galaxy, is actually in Sextans. In contrast to M83, this galaxy is seen almost edge on. It's a lenticular galaxy, meaning it's a disc galaxy with very little spiral structure. Sean O'Dwyer Kenneth Stewart took this photo of the Pleiades (M45) from West Haven, UT. Canon 20D with 70-200mm f4.0L Camera lens @ 200mm. A total of 36 minutes of exposure (72 30 second exposures stacked).
RULES: We would like to invite all Starry Night® Education users to send their quality astronomy photographs to be considered for use in our monthly newsletter. Please read the following guidelines and see the submission e-mail address below.
|
MAR 2009
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
You have received this e-mail as a user of Starry Night® or as a registrant at starrynighteducation.com
To unsubscribe, click here.