To pick a good stargazing site, several factors are important. You want to travel as far away from city lights as possible in order for the sky to be as dark as possible. You also want the immediate vicinity of your observing location to be as dark as possible in order for your eyes to fully adapt to the dark. (This process takes up to 30 minutes but can be undone in a second, so once you settle in to observe the sky you want the all lights to stay off.) Finally, you want to get above as much of the atmosphere, dust, and haze in order to get a good view, so high altitude helps.

Unfortunately, the lights of Phoenix pollute the sky for hundreds of kilometers around. You can get some relief by driving an hour or two out of town. You can head north or east to the state parks or the national forests, or south or west on I-10 and then take an exit on a remote road. If you can get away from direct view of lights (especially headlights of passing cars) so that your eyes can stay adapted to the dark, your view should be unspoiled. You will get the best view of the night sky if you go much farther out of town and north to the high country of Arizona.

First, check the Sky and Telescope Sky at a Glance webpage. Here you will find information on where the planets, the Moon, and the occasional comet or meteor shower is in the sky. A very common sighting is the planet Venus, which can get as bright as an airplane but can hang mysteriously in the sky for hours after sunset or before sunrise. Due to an optical illusion known as autokinesis, Venus can appear to bob and weave in the sky. This effect is due to small motions of the eye muscles and not because Venus itself is moving. (In fact, this effect accounts for many UFO sightings.) If you suspect your mystery object is Venus, check again an hour later. If the object has somewhat risen (in the morning) or set (in the evening), then you are observing Venus.

Second, recall whether the object moved across the sky fast or slow:

• Faster that an airplane? It might have been a meteor. Meteors can be very faint or extremely brilliant, depending on the size of the meteoroid that is striking Earth's atmosphere.
• About the speed of an airplane or slower? You might have observed a satellite. They can appear as faint star-like points of light moving among the starry sky or they can flare to brilliance if you caught the Sun reflecting off the surface of the satellite.
• Does it appear stationary and only moves when you watch it for many hours? You are likely looking at something far out in space. It is stationary with respect to the stars, but moves on the sky as Earth turns. It is best to check the Sky and Telscope page above or check SpaceWeather to see if there is any exciting objects in the sky you may have caught. The planets visible to the naked eye are Venus, Jupiter, Mars, Saturn, and Mercury.

Finally, if none of this helps explain what you saw, contact us! Call 480-727-7010 or write to astro.info@asu.edu and we'll try to give you an explanation. If you call or write, please provide as much information as you can: what direction in the sky? what time was it? what color? how bright? how much and how fast did it move? was it near a recognized constellation or star? did you see the object with the naked eye, through binoculars, or through a telescope?

The U.S. Naval Observatory Astronomical Applications Department maintains a Data Services webpage that contains very accurate and extensive information on:

The best website for up-to-date information on what's going on in near-Earth space is the NASA SpaceWeather site. It includes a current view from space of the Sun and information on the solar wind, as well as information on solar storms. It also includes predictions for Earth-Sun interactions like aurorae (aka the Northern and Southern Lights). The site also includes photographs of recent celestial events. SpaceWeather also has information on Near-Earth asteroids and recently (re-)discovered comets as well as current and upcoming meteor showers. The website also has links to many NASA news items and other informative space-related websites.

While there are a few bright comets that return regularly (Halley returns every 76 years), most are visible once in a thousand years (Hale-Bopp won't be back for 2300 years). In short, the brightest comets tend to show up on their own schedule. The NASA SpaceWeather website and the Sky and Telescope magazine Sky at a Glance webpage are both good sources of up-to-date information on the sky.

The International Dark Sky Association is an organization devoted to informing the public about light pollution. This isn't just a matter of having darker skies to enjoy, but providing better illumination at lower cost and less wasted electricity, reducing light that leaks into unwanted areas, and reducing glare and improving safety. It's important to everyone!

The Heavens Above website is an excellent database of information on satellites like the International Space Station, the Iridium constellation, the Space Shuttle in orbit, and many others. This website provides information on satellite sighting opportunities when you specify your location on Earth. Or you can specify a location on Earth and a date and time and the webpage will search for possible matching satellites. All satellites are shine by reflected sunlight, so the best time to watch for satellites is a few hours before sunrise or after sunset.

Satellites in low Earth orbit are at least 130 kilometers (81 miles) above Earth's surface. Lower than this, the satellite experiences too much air resistance and falls back to Earth immediately. A satellite in low Earth orbit completes a revolution in about 1.5 hours travelling about 17,000 kilometers per hour. The International Space Station is in low Earth orbit and the Space Shuttles are limited to low Earth orbit (despite movie depictions to the contrary). Satellites in low Earth orbit are easiest to see because they move rapidly against the background stars. Satellites in higher orbits travel slower, so they take longer to complete one revolution. A satellite that takes 24 hours to orbit Earth is in a geosynchronous orbit. That is, the satellite goes around Earth as rapidly as Earth rotates, so the satellite appears to stay above a region on Earth's surface. Most communications and weather satellites are in geosynchronous orbits so they can communicate with or observe a particular region on Earth's surface. However, geosynchronous satellites are hard to see from the ground because they do not move relative to the background stars. To find viewing opportunities to see a satellite, visit the Heavens Above website.

It will be decades before space travel becomes common or affordable. While some millionaires can afford a trip to the International Space Station, most people don't have the $20 million that Russia is charging for a visit. The main problem of going to space is that the U.S., Russia, and Europe use disposable launch vehicles. The rocket is used once to put people or a payload into orbit, but then it burns up in Earth's atmosphere after the rocket runs out of fuel. Imagine how expensive it would be to buy a new car for every trip to the grocery store! The U.S. Space Shuttles are reusable, but it is very expensive to repair and ready them each time for launch, so the problem isn't really solved. NASA and other organizations are working on newer launch vehicles but it will be a few years before we see them fly.

Another problem of going to space is that you must bring everything with you: the air, the water, the food. Imagine going to a place that doesn't have any air or water, and nothing grows. Once you arrive, you can't just step out and take a breath of fresh air! A trip to Mars could take as long as 6 months. All the air, water, and food must be brought along. Until all those supplies and people can be lifted easily and cheaply to orbit and beyond, it will be too hard and too expensive to go vacationing in space.

The Sun is the nearest star. It is 150 million kilometers (93 million miles) from Earth. Light takes 8.5 minutes to travel this distance. The Sun is an average type of star. Some stars are very much bigger and brighter than the Sun, many other stars are quite a bit fainter and smaller. The Sun and the Solar System is about 5 billion years old. The Nine Planets website is an online encyclopedia of information about the Solar System.

The phases are due to the angle with which we view the sunlit Moon. The Moon does not produce its own light, it only reflects sunlight. Half the Moon is always in sunlight (the day side) and half in darkness (the night side) just like Earth or any planet or moon. If the Moon is in the direction of the Sun, during the day we see mostly the night side of the Moon. This is a New Moon or a crescent Moon. If the Moon is in the direction opposite the Sun, during the night we see mostly the day side of the Moon. This is a Full Moon or a gibbous Moon. Chris Dolan at the University of Wisconsin has written a nifty program to illustrate the phases of the Moon. For best results, set the "point of view" to "Both". Sun, Earth, Moon are on the left; Moon phase is on the right. Tap the "animate" and "stop" button a few times and compare where the Moon is in the left diagram to how the Moon looks in the right diagram.

Contrary to popular thought, there is no permanently dark side (or light side) on the Moon. From any point on the surface of the Moon, you would see a sunset and a sunrise half a day apart, just like on Earth. However, a lunar day is 655 hours or 27.3 (Earth) days long. This is also the time it takes the Moon to complete one orbit around Earth. Since the Moon orbits Earth and rotates in the same amount of time, one side of the Moon permanently faces Earth and one side faces away. These are called the lunar near side and the the lunar far side. Until the advent of spacecraft, no one had ever seen the lunar far side. All of the Apollo landings occurred on the near side.

The Moon is 384,000 kilometers (230,000 miles) from Earth. The closest planet is Venus, 45 million kilometers at its closest. For more information about a particular planet or moon, visit the Nine Planets website.

The nearest star is Proxima Centauri, the faintest member of a triple star system. Proxima (meaning nearest in Latin) is 4.2 light-years from the Sun. (For comparison, it takes 8.5 minutes for light from the Sun to reach Earth and about 10 hours for light to travel from one side of the Solar System to the other.) The other two members of this triple system, alpha Centauri A and B, are close together at 4.3 light years from the Sun. The stars that make up the familiar constellations like Orion or Cassiopeia are a few hundred or a few thousand light years away. So next time you look up at the night sky, remember the starlight you see could be far older than you!

Contrary to what the name implies, a light-year is a measure of distance not time. Simply, a light-year is the distance that light travels in one year. Since light travels at 300,000 kilometers per second (186,000 miles per second), a light-year is a very large distance, about 9 trillion kilometers (5.9 trillion miles). Because of its large size, the light-year is a convenient measure of astronomical distances. On average, the stars are separated by distances of a few light-years. Even on this scale, however, the Universe is large. The center of the Milky Way is 25,000 light-years away, the Milky Way is 100,000 light-years across and it is 2 million light-years to the nearest large galaxy, the Great Andromeda galaxy.

A parsec is also a measure of distance, about equal to 3.26 light-years. It is defined as the distance at which a star will have a parallax of one arcsecond. A star's parallax is its apparent motion relative to the background stars when the star is viewed from opposite sides of Earth's orbit, or six months apart. (You can visualize this effect by holding your finger steady out at arm's length and looking at your fingertip out of each eye separately.) Using a bit of trigonometry the distance to the star can be determined from its parallax. The concept of parallax originated with ancient Greek astronomers. However, the parallaxes of stars are very small angles, less than one arcsecond. (An arcsecond is the apparent size of a nickel viewed at a distance of 4 kilometers or 2.5 miles. 60 arcseconds is equal to one arcminute, and 60 arcminutes is equal to one degree, and 360 degrees is equal to a complete circle.) Because the ancient Greeks did not have telescopes, they were unable to see the tiny parallaxes of the stars. This lead them to the conclusion that the stars were fixed on the celestial sphere. In reality, the stars are much more distant than the ancient Greeks ever imagined. On average, stars are about 1 parsec from their neighbors.

It is estimated that the Milky Way galaxy contains about 100 billion stars. Of those, a few thousand are visible to the naked eye. The stars visible to the naked eye are either very nearby, very bright by themselves, or a combination of the two.

Each galaxy is made up of millions or billions of stars. There are many billions of galaxies. So the number of stars in the whole Universe is LARGE, probably larger than 1,000,000,000,000,000,000 and the number may be infinite!

The Solar System, which includes the Sun, the planets, and all the comets and asteroids, is somewhere between 4.5 and 5.0 billion years old. We know this from a combination of our knowledge of the Sun and the ages of rocks here on Earth and those rocks returned from the Moon. All of the planets formed at about the same time, so we can't say which planet is oldest or youngest. If you'd like more information about the Sun and planets, The Nine Planets website is a good starting place.

One answer is no. The surface of the Moon and the planet Mars have been tested for life. No life was found. Many other objects in the Solar System have been investigated from orbit. There are no obvious signs of anything that we would identify as life.

Another answer is yes, perhaps someplace we haven't tested yet. The chemicals that make up life on Earth are common in space, in comets and meteorites, and probably exist on the surfaces of other planets here or around other stars. Now searches for life center around liquid water since every form of life on Earth needs it to survive. It is reasonable to suppose that other life would need liquid water too. The Moon, Mercury, Mars, the moons of Jupiter, Saturn, Uranus, Neptune, Pluto and its moon Charon, comets, and some asteroids all have some quantity of frozen water on their surfaces or underground. Other bodies, like Jupiter's moon Europa, are suspected to have liquid water below the surface. Interstellar gas clouds contain large amounts of water vapor, so water appears to be universal. But only one world, Earth, is known to contain large amounts of liquid water. In years to come, with more powerful telescopes and more advanced robot explorers, we may find that some of the planets or moons in the Solar system or around other stars have oceans and lakes like Earth, but at this time Earth is unique in this way.

A galaxy is a "city of stars", composed of many stars, but also gas and dust. A small galaxy may have a few million stars. The largest galaxies may have trillions of stars. Spiral galaxies have stars and gas that rotates in a pancake-like shape, like the galaxy NGC 891. When a spiral galaxy is viewed face-on, the spiral arms are visible, like the galaxy M51. Elliptical galaxies have stars that orbit the center in no particular direction, so they look like a fuzzball of stars. The giant galaxy M87 is a good example of an elliptical galaxy. Many galaxies harbor giant black holes in their centers.

The Milky Way is the spiral galaxy that contains the Sun. It is visible under dark skies to the naked eye as a band of fuzzy light stretching from horizon to horizon. This panorama shows the whole sky, with the Milky Way sweeping through the southern sky on the left and the northern sky on the right. We see the Milky Way like this because the Sun and the planets in orbit sit inside this vast collection of stars and gas. This panorama shows the Milky Way undistorted, as it would appear from out in space. If we could see the Milky Way galaxy from the outside it would look something like the galaxy M83. The Sun is located near one of the outer spiral arms of the Milky Way, about two-thirds of the way out from the center.

Astronomy graduate students in the Department of Physics and Astronomy are willing to speak to public or school groups. If you'd like to contact them, please call (480) 727-7010 or write to astro.info@asu.edu. Also, the Saguaro Astronomy Club and the East Valley Astronomy Club have members that can come out to speak to your group.

To get a feel for what types of telescopes are out there and which you prefer, consider "test driving" a few telescopes first. Consider attending a meeting of a local amateur astronomy club. Many members are willing to have newcomers try out their telescopes at a club event. Phoenix has three large clubs: East Valley Astronomy Club, Saguaro Astronomy Club, and the Phoenix Astronomical Society.

The two main types of telescopes are refractors and reflectors. Refractors use lenses to collect the light. Reflectors use mirrors to collect the light. Good quality lenses are much more expensive to manufacture than mirrors so for two telescopes of equal size, the refractor will be much more expensive than the reflector. In fact, refractors larger than about 6 inches diameter are prohibitively expensive for most amateur astronomers. In contrast, a 6 inch diameter reflector will cost about $300-500. Because of this, many astronomical telescopes smaller than 2-3 inches in diameter are refractors and those 4 inches in diameter and larger are reflectors.

In addition to the mirror or lens that collects the light, telescopes have eyepieces that focus the light and provide magnification. Interchangeable eyepieces allow you to vary the magnification and the field of view of the telescope. The focal length of the eyepiece is the important characteristic, usually measured in millimeters. A long focal length eyepiece (perhaps 56mm) will provide a wide field of view and low magnification, while a short focal length eyepiece (perhaps 10mm) will provide a narrow field of view and high magnification. Some telecope manufacturers advertise the high magnification their instrument can achieve, sometimes up to 500x. Unfortunately, observing with magnification above about 300-350x is usually useless because of the atmosphere's blurring effect. Many new telescopes come with an initial set of eyepieces, but the capabilities of a telescope can be expanded simply by purchasing additional eyepieces.

Alternatively, buy a pair of binoculars. Binoculars are very useful for observing the night sky, they are lighter and more portable than a telescope, they can cost much less, and they can be used for other activities like sporting events, nature hikes, and birdwatching. Binoculars are classified by two numbers. The first number, magnification, typically ranges from 5x - 20x. The second number, the diameter of the lenses, typically ranges from 20 millimeters to 100 millimeters. A common pair of binoculars is 8x50, while a large pair of binoculars for astronomy is 15x80. A small pair of binoculars may run $100, a large pair may run as much as $400. A sturdy tripod is useful to hold the binoculars steady.

When selecting a telescope or a pair of binoculars for use in astronomy, there are two rules to keep in mind. First, you want to collect as much light as possible. This is contrary to some advertisements, which focus on the magnification the telescope can achieve. The important measure of a telescope is the diameter of the lens or mirror that collects the light. Second, get a high quality instrument. It does no good if your telescope wastes the light that it collects or produces a distorted or unfocused image. A small telescope may run $200, a larger telescope can be as much as $2000. You can save money by buying a telescope without a clock drive (the device that tracks the motion of the sky). If you don't plan on doing astrophotography, you really don't need to have the telescope track the sky. If cost is an issue, you can track the sky manually.

When buying an instrument, it is generally best to stay away from nature stores, department stores, or camera shops. The staff probably haven't ever looked through a telescope or even know how to properly use one. (There are exceptions, but this is generally true.) Stores also generally don't provide the best deals on astronomy equipment. Instead, pick up a copy of Sky & Telescope or Astronomy magazine at a bookstore and browse the ads. A good online store is Orion Telescopes & Binoculars. Remember, quality costs more. A telescope that sells for $59.99 may appear to be a great buy but is likely to be of such poor quality that you may not be able to see anything through it.

The Department of Physics and Astronomy has its own planetarium in Bateman Physical Science B-wing. For more information on this planetarium, go to its website. In addition to the ASU planetarium, the Arizona Science Center in downtown Phoenix has the Dorrance Planetarium.

Arizona has some of the darkest, clearest skies in the US. There are a number of professional observatories that include visitor centers and tours. The Lowell Observatory, in Flagstaff, and the Kitt Peak National Observatory visitor center, west of Tucson, provide public observing sessions.