A telescope's job is to gather light. In this case, bigger is better (but within justifiable costs and consideration of who is going to be using the telescope). In addition to gathering more light, a larger diameter can give better resolution of detail. To compare the light-gathering power of two telescopes, take the square of their diameters (in the same length units) and divide the larger number by the smaller number. This will tell you how much more light the larger telescope will collect.
Have a favorite planet or planetary satellite you would like to view. Then the Solar System simulator is for you. This NASA/JPL site allows you to create a simulated view of these bodies from different perspectives. For example, you can choose to see the Earth from the Moon, or Saturn from Jupiter. You can choose a time in the past or future for your view in order to see how the relationships between the bodies change over time. You'll find the simulator at
Don't be taken in by advertising concerning telescope magnifying power. Magnifying power is usually about fourth or fifth on a list of important considerations, preceded by things like how much you want to spend, how much light-gathering you can get for that amount (the light gathering ability is the most important item about telescopes and is related to the area of the light-gathering optical part of a telescope, known as its objective), stability of the tripod or mounting used, and finderscope attached to the telescope.
The magnifying power, or magnification, is a comparison between the focal length of the light-gathering lens or mirror, the objective, to the focal length of the eyepiece. The same eyepiece can yield different magnifications for different telescopes if the focal lengths of the objectives of those telescopes are different. To determine the magnification of a telescope, simply divide the focal length of the objective lens or mirror of the telescope, usually given in millimeters, by the focal length of the eyepiece you wish to use, usually also specified in millimeters. The focal length of the objective is often stamped on a small plaque attached to the telescope or listed in the instruction booklet that came with the telescope, while the lenses usually have their focal length stamped on them.
There is a maximum magnification that any optical system can produce. Increasing the magnification beyond this limit simply results in fuzzy images. To determine the optimal or maximum magnification, one rule of thumb is to multiply the clear aperture diameter (in inches or millimeters) of either the objective lens (the front lens) of a refracting telescope or the objective (large) mirror of a reflecting telescope by 50x/inch or 2x/millimeter. Any eyepiece used with a telescope that exceeds this magnification value will probably give poor images.
With the holidays around the corner, it is not unusual to begin thinking about telescopes under the tree. When you begin shopping, deciphering the terminology used and trying to determine what is and is not important can make your head spin. So, over the next few tips, we'll present some information about telescope buying and tell you some of the terms to be familiar with. First consideration: Think of this purchase as an investment, not just the satisfaction of a child's (or inner child's) wishes. Plan on setting aside a couple of hundred dollars or more, but also consider who your purchase is for. Young people tend to have short attention spans, and if the scope isn't easy to set up and use, it may spend more time in the closet than out under the stars. Just as you would think through and become informed about any major appliance purchase, do the same for a first telescope.
So where can you find information about which telescopes are among the best quality and values and which ones lag? You might want to visit the sci.astro.amateur Usenet newsgroup to see what others have to say about their experience of different brands and to learn which brands you might want to avoid.
There is an interesting site for young people, from grade school on up, hosted by the High Energy Astrophysics Science Archive Research Center (HEASARC), part of NASA. Called Star Child, it contains information on a variety of astronomy-related topics divided into two sections, one for younger and one for older readers. To check out the site, point your browser to
An interesting site to visit to obtain views of the Earth and Moon at a particular moment in time and from different perspectives is called the Earth and Moon viewer. You can create maps that show the light and dark areas on Earth at a particular time, look at the Earth at that time from the Moon and even from the Sun. There are some other interesting options available, including the ability to view the entire Earth with timely cloud patterns superimposed on it. Point your browser to
Be sure to consider the tripod upon which a telescope is mounted when comparing telescopes for purchase. It should be sturdy enough to handle the weight of the telescope itself, but it should also be sturdy against vibrations from passing cars and trucks. A nice telescope mounted on a spindly legged tripod is not much better than a poorly constructed telescope on a very steady tripod. In fact, the latter case might at least allow you to see something with care, while all you may see in the former are dancing images.
With all of the hoopla about asteroids and comets threatening to rain destruction upon us from the sky, it is nice to know that there are a couple of sites that can give you the latest information on Near-Earth Objects (NEOs). One such site is the Near-Earth Object Program site at You'll find information on updates of recent discoveries, spacecraft missions planned or in progress, and a nice frequently asked question (FAQ) file with a lot of information and definitions.
An additional site on Near-Earth Objects or NEOs, with some different information in some cases, is the Asteroid and Comets Impact Hazards site, located at
To find your way about the surface of the Earth, you can refer to latitude and longitude. The former is the angle one is north or south of the equator; the latter is the angle east or west of the prime meridian that passes through Greenwich, England.
Right Ascension and Declination offer the same opportunity for locating objects in the sky. Declination is much like latitude: It is the angle north or south of the celestial equator. And the celestial equator is the projection of the Earth's equator on the sky.
Right Ascension is like longitude, but it is measured in hours rather than degrees. The reference point is the Vernal Equinox, that intersection point between the Sun's path in the sky, the ecliptic, and the celestial equator, where the Sun would appear to be moving from south to north. It marks the location of the Sun on the first day of Spring for the northern hemisphere. When the Vernal Equinox is on the meridian, all objects also on the meridian are assigned 0 hours of Right Ascension. Then, as the Earth spins, carrying new objects past the meridian, new Right Ascension values can be assigned based on the time that has passed since the Vernal Equinox was on the meridian, until it returns there again.
Proper alignment of a telescope with setting circles and a list of the Right Ascension and Declination of objects can help one find objects in the sky that might not be visible to the naked eye.
To get a sense of the scale of the local neighborhood, imagine the Sun the size of a dime. The closest star system to the Sun, Alpha Centauri would be about 325 miles away. And the brightest star in the sky (and fifth in terms of distance from the Sun), Sirius, would be about twice that distance away.
Recently, a couple of comets were discovered that might reach naked-eye visibility during 2000. The first to pass us by is called Comet 1999 S4 Linear, while the second is Comet 1999T1 McNaught-Harley. For finder charts and expected passage dates, point your browser to Dale Ireland's Astronomy Page at
Mr. Ireland is an amateur astronomer with various interests in astronomy, and he has selected additional links that reflect his interests.
On November 30, 1950, Elizabeth Hodges was hit by a 5-kilogram meteorite. Apparently, she was taking a nap on her living room sofa when the space invader ripped through her roof, hit the floor, and bounced, hitting her on the side and leaving a very dark bruise on her side.
Ever wonder what it might be like to approach a black hole? Well, there is a site that might take you to the very edge. Visit the Virtual Trips to Black Holes and Neutron Stars page at
There is a handy calculator on the Web that takes the current date and tells you what phases of the Moon soon follow, what meteor showers may be available soon, the next lunar eclipse, and planet location information. Just go to Astronomy Calculator at:
There are some nice Moon-planet combinations visible in the skies of December. The Moon will be north of Venus in the morning skies of December 3 and north of Mercury on December 6. Telescope users may see the Moon close to Neptune on the 11th, and those north of South America may see the Moon occult Neptune. The Moon will pass close to Mars and Uranus on December 12th. It will actually occult Mars at 19 hours Universal Time, as observed from eastern USA, northeast South America, Central America, northwest Africa, the British Isles, and Western Europe. Telescope users may see it occult Uranus as observed from central South America. A waxing gibbous Moon will pass south of Jupiter on the 18th and south of Saturn on the 19th.
During a visit outdoors about 8:00 p.m. local time, you still have a chance to spot constellations quickly if it is clear. Near the zenith, on your meridian (a line from due south to your zenith point overhead to due north), you will find the constellation of Andromeda. Shaped like the letter A, sweeping toward the east, is a group of stars, the Andromeda Galaxy. That distant fuzzy patch of light will be very close to overhead at that time, making it easy to spot from a dark site with your naked eye. The light from it has traveled from the galaxy to you over a period of about 2.2 million years, so that we would claim the distance to be about 2.2 million lightyears from us.
During December, the Space Shuttle Discovery is expected to be involved with a repair mission of the Hubble Space Telescope. You can follow the progress of the mission as it unfolds at the following Web site:
Mercury makes its best appearance in the morning skies for northern observers during the month of December. It should be best seen in the early part of the month, reaching greatest western elongation, that is, its greatest angle west of the Sun as we observe it, on December 3.
December marks some firsts in the space race between the United States and the former USSR. The Soviet Union's Mars 3 was the first spacecraft to land on Mars, doing so on December 3, 1971. On that same date, two years later, the United State's Pioneer 10 flew past Jupiter. On December 4, 1978, the US's Pioneer/Venus Orbiter became the first spacecraft to successfully orbit Venus. On December 14, 1962, the US's Mariner 2 flew past Venus to become the first interplanetary spacecraft. On December 15, 1970, the USSR's Venera 7 was the first spacecraft to softly land on Venus and the first to softly land on any planet. And, on December 24, 1968, the US's Apollo 8 became the first manned spacecraft to orbit the Moon. Also, during December 1993, astronauts aboard the Space Shuttle Endeavor completed a round of repairs to the Hubble Space Telescope, greatly improving its ability to provide quality images and spectra.
There are some notable birthdays of individuals associated with astronomy during the month of December, including Annie Jump Cannon (December 11, 1863), who pioneered work in the classification of stellar spectra. Tycho Brahe (December 14, 1546) is credited with being one of the greatest naked-eye observers prior to the invention and use of the telescope in astronomy. Sir Isaac Newton (December 25, 1642) is known for his laws of motion and of gravity, along with his work in optics. The invention of the telescope design that now bares his name, the Newtonian reflector, had an impact on much of modern astronomy. Finally, Johannes Kepler (December 27, 1571) discovered three empirical laws describing the motion of the planets, based on the observations of Tycho Brahe.
Need to gain weight? Lose weight? Then maybe you should get around. Visit other planets. But, before you do, you should get some ideas of where to go to achieve the weight change you desire. You can start by visiting Your Weight on Other Worlds at:
The Sun is approaching a maximum in its activity. Images of the Sun at different wavelengths can yield a lot of information about the Sun during this time period. To see some of the recent images of the Sun and compare them across different wavelengths, visit the Solar Data Analysis Center at NASA Goddard Space Flight Center and follow the links to current solar images.
With the Sun becoming more active, the probability of seeing aurora increases, even in middle latitudes. The Aurora Information and Images page can tell you when it might be possible to see aurora from your area:
The Constellations and Their Stars Web site is a nice site to visit for finding a lot of information about constellations. It even includes a Frequently Asked Questions (FAQ) list. The site also features star maps, as well as a breakdown of those visible each month. To check it out, point your browser to
In addition, PBS Online provides a nice interactive timeline for astronomy, from the Big Bang to possible futures of the universe. Point your browser to
The Galileo spacecraft orbiting Jupiter recently completed the second close pass of Jupiter's intensely volcanic satellite, Io, producing images of much higher resolution than those from the Voyager fly-by missions in the 1970s. To see the latest available images, point your browser to the NASA's Jet Propulsion Laboratory and follow the links to the latest images.
Is it a bird? Is it a plane? Is it a UFO (well, not likely)? To find out, you might check out the Visual Satellite Observer's page. Here you can find information about things visibly moving across the sky. Some may be aircraft, but others may be one of a rich variety of man-made satellites orbiting our globe. These can be interesting to look at. Astrophotographers may want to know of their passage as well, so that an errant satellite doesn't spoil a well-planned photograph.
For another convenient site for spotting satellites from your location, point your browser to the Heavens Above Web site. By entering your latitude and longitude (manually or by choosing from the database), you can get a list of satellites visible on a particular date. It can also help you locate the better-known satellites like Mir and ISS.
Did you get a telescope for Christmas? Then a little time spent checking adjustments and understanding magnification will make it all that more useful. Take the time to get the finderscope and the telescope aligned. This can be done during the day. Simply point the telescope to something easy to spot, such as a light post, treetop, or other such object. Start with your lowest power eyepiece to get the widest field of view in your telescope. Then use the adjustment screws on the finderscope to slowly move the crosshairs to the same object. Once properly adjusted, one can simply aim the telescope by looking through the finderscope and putting the crosshairs on the object. Using higher power lenses during the adjustment phase and thus narrowing one's field of view, makes the adjustment that much finer.
You can use your meridian, the line that runs from due south, through your zenith, the point directly overhead, to due north to help find less obvious constellations. In early January, around 8:00 p.m. local time, you may find the following constellations about the meridian: Eradanus the river winds its way back and forth across the meridian in the southern sky; Fornax the furnace; the eastern edge of Cetus the whale; Perseus the hero near the zenith; then back around to Polaris in Ursa Minor (the small bear); and low on the northern horizon, Draco the dragon.
Do you have a burning question of an astronomical nature? There is a chance it might have been asked in the astronomy newsgroups. It is possible to access the Frequently Asked Questions (FAQ) for sci.astro even if you are not interested in or do not have access to the Usenet newsgroups. Simply go to:
Occasionally, a question of physics may arise in discussing astronomy. A great place to go for quick answers is the Usenet newsgroup sci.physics. You can find the Frequently Asked Questions (FAQ) list for this group at:
The Chandra X-ray Observatory has recently released some new images of Eta Carinae. This unusual star radiates some 5 million times the energy of the Sun and may be near the end of its life. For comparisons of images made by Chandra and other sources, visit the Chandra X-ray Observatory home page at:
Stephen Hawking, famed astrophysicist, celebrates a birthday on January 8. Other January births include those of Robert Wilson, co-discoverer of the cosmic background radiation, (January 10, 1936); Johann Bode, who popularized a mathematical scheme of predicting planet distances out to Uranus (January 19, 1747); John Couch Adams, one of two to successfully predict the location of Neptune (January 21, 1792); and Harold Babcock, who proposed in 1961 the model for sunspot formation linking the differential motion of the Sun and its magnetic field (January 24, 1882).
The Titius-Bode rule was a simple numerical trick to determine the distances to the planets known at the time, according to the Copernican model of the universe. The sequence is a set of numbers beginning with zero, then 3, then doubling each number after that, to get 6, 12, 24, 48, and so on. Then 4 is added to each and the number obtained is then divided by 10. This would yield 0.4, 0.7, 1, 1.6, 2.8, 5.2, and 10, the average distances (to one decimal place) in astronomical units, of the planets known at the time. When Herschel discovered Uranus, and it was found to also follow this rule, an intensive search for a planet at 2.8 AU was initiated, culminating in the discovery of the minor planet, Ceres, on January 1, 1801.
December 22 marks the Winter Solstice, or the first day of winter in the Northern Hemisphere. On this date, the Sun rises farthest south of east, crosses the sky at its closest to the southern horizon, and sets farthest south of west. The ancient peoples often marked this time in their architecture, for once the Solstice has passed, the Sun would begin rising more and more to the north, and before too long it would be Spring and planting season. The Sun reaches this farthest southern point in its apparent annual path in the sky at 7:44 Universal Time.