Frequently asked questions (FAQ)

You can also 'Ask an astronomer' if you can't find the answer to your question.

Mt Stromlo and Siding Spring Observatories

Information on the history, research and facilities of the observatories is on this web site in the RSAA and Public information areas. In particular, check out About UsResearch and Observatories pages.

One of the most common questions is, "Can I look through your telescopes?"

We do have some small telescopes that are used for public nightsprivate bookings, and education programs. These are being housed in small domes. 

Sadly, all of the large research telescopes at Stromlo were destroyed in the firestorm of 18 January 2003.

Latest astronomy research findings

Astronomy is a rapidly-growing science. New discoveries are being made almost every day. Some of the results of research at RSAA are found in our News page. Many observatories around the world have similar archives.

There are several web sites and blogs that produce daily summaries of results published world-wide, e.g.

  • Universe Today has a summary of recent findings, a comprehensive archive of past articles, and a "What's up this week" column.
  • Astronomy Now is similar and has a link to Spaceflight Now, a site which summarises results from current space missions.
  • Sky and Telescope, run by the magazine of the same name, is a good all-round site for amateur astronomers. It has a news archive, interactive star chart, observing guides, and an extensive archive of the magazine articles.
  • NASA has a huge range of web sites covering everything from the current breaking news to resources for teachers and students. NASA news and events and Science@NASA will keep you informed of NASA doings.
  • Astronomer and skeptic Phil Plait's Bad Astronomy blog (previously hosted at Discover until 2012 and then at Slate until 2017) covers news and information about science and astronomy and debunks common misconceptions and myths.

What do those strange words mean?

Astronomy, like all professions, has developed its own jargon. If you need to know what a word means there are many on-line astronomy dictionaries available, e.g. NASA's Imagine the Universe Dictionary and, especially for children, the Kid's Astronomy Dictionary.

If you need more information, you could try one of the many "Ask an Astronomer" sites; a Google search will give you hundreds to choose from.

Lights in the sky

There are some simple steps in finding out just what that bright light or object you saw actually is/was (and turn your UFO into an IFO). The easiest is to become familiar with the night sky and learn when bright planets, meteor showers, comets, etc are visible. This is difficult for city dwellers as the bright streetlights are blotting out our view of one of nature's grandest spectacles.

Eclipses and aurorae are the most spectacular things you can see with your naked eye. They will be dealt with after we look at those confusing moving objects.

If you see anything in the sky that you can't identify, note the time, direction of movement, brightness and any changes. Then ask yourself "Is it moving fast, or just moving very slowly westward?"

Note that there are several non-astronomical possibilities such as aircraft, flares, high-flying birds and weather balloons; these are not discussed here.

If moving fast, the astronomical possibilities are ...

... meteors ...

These range in brightness from faint, short streaks ("shooting stars") to fireballs bright enough to cast shadows. Meteors are chunks of rock and/or metal left over from the time the Solar System formed. They collide with the Earth and usually burn up high in the atmosphere. The speed of the collision is around 20 to 50 kilometers per second; this generates a lot of friction which heats the air and causes it to glow, as well as burning all or most of the meteor. Occasionally bigger ones can survive the passage through the atmosphere and hit the surface. They are then known as meteorites.

On an average night an observer with a dark, cloudless sky can see around 10 meteors per hour. At certain times of year meteor showers occur; during these times many more meteor can be seen. A meteor can travel in any direction and is only visible for a few seconds.

Good sources of information on meteors are:

... or satellites.

These man-made objects are not really astronomical, but are one of the most common causes of phone calls to the observatory. They show as "moving stars". Depending on the height of their orbit they can appear to move fairly slowly, taking minutes to travel across the sky, or they can be much faster and take only tens of seconds. Some satellites now fly in clusters, giving rise to many UFOs-in-formation reports.

Since many satellites have huge solar panels, depending on the angle between the observer, the satellite and the Sun, satellites can fade, blink, increase in brightness and appear to wobble slightly. One group, the Iridium satellites, produce spectacularly bright short-lived flashes if the angle is just right. Iridium flashes generate many calls reporting supernovae. Supernovae are exploding stars; they do brighten suddenly, but stay bright for weeks or months, not seconds.

To find out what bright satellites are visible from your area and the times and direction to look in, use the programs on the Heavens-Above web pages, or those of the Visual Satellite Observer's Home Page. You can set these up for your exact location.

If moving slowly, the astronomical possibilities are ...

... stars and planets ...

Venus, Jupiter and Mars at its brightest, between them account for most of the "UFO" calls to the observatory. Bright stars, particularly Sirius and Canopus, also confuse some people when making their first appearances for the year.

Surprisingly, some people do not realize that the sky is not the same every night. Because the Earth is orbiting the Sun, stars rise and set around 4 minutes earlier each night. This means that the stars that are visible now in the early evening will be in the daytime sky in 6 months time; the winter and summer skies are completely different. Planets move against the background stars, so are not always in the same place in the starfield. Venus and Mercury also have the extra confusing trick of swapping from morning to evening objects and back again in regular cycles.

Moisture, dust, smoke and turbulence in Earth's atmosphere causes planets and stars to appear to change colour, to change brightness and flash, even to jiggle around. These effects are more noticable as the planet is rising or setting. Venus is staggeringly spectacular when seen low to the horizon through a murky or damp atmosphere; every time it reappears in the evening sky it generates a UFO panic.

The only way to check if the bright yellow/orange/red light is a star or planet is to get to know the sky and recognize the critters. This takes time and practice. There are a multitude of books, star charts and software available, the only trap is that some of them only deal with the northern hemisphere sky, so check before buying.

Heavens-Above has a star chart generator on the "Astronomy" pages. This allows you to generate a star chart for any location on Earth at any time for centuries in the past and future. It also shows the positions of the planets. Similar on-line sky charts are available from many sites, e.g. the Sky and Telescope Interactive Sky Chart.

Rise and Set times for the Sun, Moon and Planets are published in most major newspapers. Most sky chart programs give them, or you can use our calculator.

... or comets.

That's right, comets. Despite the Hollywood hype, comets are slow movers as far as the eyeball is concerned. You can often only see movement over hours or nights of observing. Most of them are also rather faint and unimpressive, looking like faint fuzzy blobs. Very few are spectacular large, bright objects with long tails. Most of the excited callers reporting seeing a comet have in fact seen a large bright meteor (a bolide); these are bright, move fast and have long tails of glowing air and meteoric debris. Most comets are found by survey telescopes, satellite observatories, or dedicated amateur astronomers.

Comets are left-overs from the formation of the Solar System. They are balls of dust and ices in orbits that take them between the outer and inner regions of the Solar System. As they get close to the Sun the ices melt and form a "coma", a large shell of flourescing steam around the body (the nucleus) of the comet. The solar wind blows material from the coma to form the tail, which always points away from the Sun no matter which direction the comet is travelling in.

Gary Kronk's Comet and Meteor Shower Pages lists comets that are currently visible (to small telescopes) and gives images and history. He also has links to many other websites of interest.

What about asteroids?

Asteroids are very faint and hard to see without a telescope. If you see a big, bright one it's probably too late to run....

Rings around the Sun and Moon

Light passing through (or reflecting from) ice crystals, water droplets and dust in the atmosphere produces all sorts of effects. One of the most commonly seen is the "ring around the Sun" caused by sunlight being scattered and refracted by ice crystals. To learn about these strange and beautiful spectacles, visit the Atmospheric Optics site.

Sheer spectacle: aurorae and eclipses

Occasionally nature turns on events that can only be described as "awesome". Chief among these are aurorae and eclipses, both solar and lunar.


Aurorae are the result of charged particles from the Sun being trapped by the Earth's magnetic field and channeled to impact the upper atmosphere in a region surrounding the Earth's magnetic poles. This causes the oxygen and nitrogen in the atmosphere to glow, producing the Aurora Borealis, the Northern Lights, in the northern hemisphere, and Aurora Australis in the southern. Aurorae are normally seen only from high latitudes, above 55 degrees, but at times of high solar activity they may be visible in mid-latitudes as well. Your chances of seeing an aurora are better the further north or south you travel.

Aurorae usually produce a display of rapidly varying red, green and yellow glowing patterns in the sky. Streamers , rays and curtains of luminosity are produced about 100 km altitude and can extend for over 1,000 km in the east-west direction.

Information on Solar activity (sunspots, solar wind, etc) and its effects on Earth is available from several web sites. Spaceweather includes galleries of aurora images, and the Australian IPS site includes aurora predictions for our hemisphere.


Eclipses occur in the relatively brief times when the Sun, Earth and Moon are exactly lined up.

If you have ever seen a total Solar eclipse you know that it is one of the most awe-inspiring experiences that you will ever have. If you have not seen one, then do so. You will never forget it. Lunar eclipses are also spectacular, but don't have the total sensory impact of Total Solar eclipses.

If the Moon moves exactly between the Sun and Earth, it blocks off the sunlight producing a Total Solar Eclipse. During totality as the shadow of the Moon passes across the surface of Earth - for a period of up to 5 minutes in the best case - the sky darkens, the temperature drops and the ghostly glow of the solar corona flashes into view. Totality is preceeded and followed by Partial phases while the Moon is covering only part of the Sun as it moves into (and out of) exact alignment. The partial phases can last for around an hour before and after totality. Solar Eclipses can only occur at New Moon.

As the shadow of the Moon on the Earth is only a few hundred kilometers wide at best, and the path traced out by the moving shadow is up to a few thousand kilometers long, solar eclipses are only visible from a narrow strip of the Earth's surface. Each eclipse track is different, so keen eclipse-watchers travel all over the world to see them. Words cannot describe the impact of the event; make it a priority to see one.

Lunar eclipses occur when Earth passes exactly between the Moon and Sun; the Moon passes through Earth's shadow. This can only happen at Full Moon. During the eclipse the shadow of Earth gradually covers the full Moon, producing crescent partial phases. At Totality the Moon is completely in shadow, but in most cases is not completely "blacked out" as the Sun's rays are diffracted by Earth's atmosphere and the result is that the Moon appears a deep red colour. As Earth's shadow is much larger than that of the Moon, Totality during Lunar eclipses can last for an hour or so. A full eclipse including the partial phases lasts for hours.

All that you need to know about eclipses, both solar and lunar, can be found on the NASA Eclipse Home Page. This contains full information on eclipses past, present and future. It also includes full information on Transits of Mercury and Venus across the Sun.

Information for school projects

The web is a goldmine of information on all subjects. There are sites, however, that are full of pseudo-science posing as science. The best way to avoid disinformation is to stick to sites from reputable organisations, like the ones listed on this page. Most astronomical and space science institutions have educational resource areas full of project material. The first step in finding it is to learn to use a good search engine.

Most of the requests from Australian students come from primary students looking for material on planets. Some good starting points are:

Both these sites have links to images and information about spacecraft missions.

For answers to specific questions, you can try one of the "Ask an Astronomer" sites; a Google search will give you hundreds to choose from.


Queries fall into two main groups: information about the telescopes at specific observatories, and "What sort of telescope should I buy?"

Information about the big research observatories and telescopes can be found on their institution's home pages. A page of quick links to the largest optical telescopes on the planet is provided on the Nine Planets BigEyes page. A web search will turn up similar information for radio, X-ray, Infra-red, telescopes.

Buying a first telescope can be an exercise in frustration. The sad fact is that most of the telescopes sold in department stores and camera shops are next to useless for looking at the heavens. Telescopes need to be powerful enough to see more than a good pair of binoculars will. The power depends on the collecting area of the main lens or mirror, so this has to be significantly larger than that of your binoculars. Price rises fairly rapidly with the size of the optics, so go for the largest aperture your wallet can stand and remember, "Pay peanuts, get monkeys".

Forget department stores and buy from a store that deals in telescopes and optical equipment. Advice from your local amateur astronomical society can save lots of problems; check them out in your local directory of clubs and associations.

A great introduction to the problems of, and solutions to, buying a telescope is provided by the editors of 'Sky & Telescope magazine’

Starting in astronomy

Once again, the editors of 'Sky and Telescope' say it pretty near perfectly, so read their Astronomy Basics for an introduction to amateur astronomy.

Astronomy is one of the few sciences where amateurs often make a significant contribution to research.

Why do astronomy?

Astronomy is the ultimate science, combining (at least) physics, chemistry, geology, biology, engineering, and computer science. It investigates the history, physics and chemistry of the Universe. It has shown the way that the chemicals necessary for life have been produced from hydrogen atoms by stars. It shows us how we and our planet fit into the overall scheme of the Universe, and is actively seeking signs of other life "out there".

Astronomy performs an important educational service for our nation. As an exciting science that anyone can enjoy and even do useful research in, astronomy stirs scientific curiosity in thousands of young people every year. Many scientists first became interested in science through astronomy.

From the dawn of civilization, astronomy has provided important stepping stones for human progress. Astronomy has been vital to all of the ancient civilizations. Buildings (pyramids, ziggurats, burial chambers, stonehenge and similar megalithic structures, etc are all aligned to the rising, setting or culminating points of celestial objects. Planting and harvest times were calculated by heliacal rise/set times (constellations rising/setting at sunrise/set). Sirius was a "prime marker" for the Egyptians, Venus for the Maya, the list is huge.  Australian Aboriginal people were amongst the earliest astronomers.

Many commonly used devices and techniques have been developed from those pioneered in astronomy.

  • Trigonometry was invented by Hipparchus, a Greek astronomer;
  • The adoption of logarithms was driven by the needs of astronomical calculations;
  • Calculus, the basis of all modern science and engineering mathematics, was invented by Sir Issac Newton for astronomical calculations; 
  • Einstein developed his Theories of Relativity as part of his mathematical model of the Universe.

Astronomy provides the navigational and timekeeping techniques that allows explorers, sailors and aviators to explore our planet. Navigation and geodesy have always been dependent on astronomy. Positional astronomy measures the changing positions of the stars. Because of the precession of Earth's axis, star positions change with time so that you can't use catalogues from even a few years ago for accurate navigation. The positions of stars are used for celestial navigation and for laying out the absolute grid that current GPS systems and satellite navigation depend on. All of the navigation systems in use (except dead reckoning) link back to the stellar grid.

Before atomic clocks, time was measured by transit observations of stars. Transit observations are still used to calibrate the clocks and measure earth rotation variation, etc.

Digital cameras and imaging software were developed by astronomers (from Vietnam war sensing equipment) to overcome the slow speed and non-linear response of chemical photography. Higher speed means you can see fainter quicker. Linear response means that if you use twice the exposure time you collect twice the light recorded, making calculations from the data much simpler.

Digital images also mean no messy chemicals to use in processing; the image is available almost immediately for storage, inspection or further digital processing. Much time is saved between taking the image and being able to act on the information contained in it. This may not be so vital for astronomers, but for medical and industrial imaging it really does save lives.

Image enhancement and restoration techniques were developed to get the maximum information out of extremely faint images. It means that you can easily adjust things like the brightness, contrast and dynamic range of an image. The photos you used to toss away because the exposure was wrong can usually be saved if they are digital or digitized. Ordinary people use it to make second-rate images usable. Science and industry use it to get the most out of an image, e.g. forensics, where the information may only be contained in a faint stain or mark. There is now lots of software available for image processing; all of them use developments of the algorithms that first appeared in astronomical software.

From radio astronomy we get several systems that are used everyday in modern TV and radio receivers/transmitters. They include data correlation and signal processing, sensitive microwave receiving systems, high gain antenna and low noise receiver technology. All of these provide better performance for less power usage.

Cryogenics are used in both radio and optical astronomy to cool receivers and cameras for long periods at stable temperatures and are now vital for spacecraft, engineering and biological sciences.

Remote sensing of the Earth from satellites (looking back at home) uses imaging and spectroscopic equipment and techniques developed for/by astronomers to look out into the Universe. These remote-sensing satellites are vital for everything from weather forecasting to detecting and measuring the effects of global warming.

The current space age, which brought us the communication and weather satellites upon which we depend each day, would have been impossible without the fundamental knowledge of gravity and orbits discovered by astronomers.

The X-ray scanner (e.g. at airports) uses image scanning techniques developed for x-ray astronomy.

Computer Assisted Tomography (CAT scanners); the infrared scanners used in hospitals to find tumours, which have a hotter temperature than the rest of the body, came out of the technology and software developed by astronomers looking at infrared radiation from distant stars and galaxies.

Predictions of the effects of Solar activity. The Sun sustains all life on Earth. Charged particles are emitted from solar flares. These bombard the Earth, interfering with communications systems, electric power grids, and even the yields of semiconductor chip production. Solar astronomy predicts such events and thus saves industry millions. All life on Earth depends on the Sun. Even in its present stable state it deals out some doozies. Big solar flares produce a burst of electromagnetic radiation plus a burst of high-energy electrons and atomic particles. If the flare is aimed our way, these particles hit the Earth's magnetic field and are funneled in along the field lines toward the magnetic poles. This produces a huge electrical surge that overloads power circuits and produces general mayhem. The classic case was in 1988 when one knocked out the power grid in eastern Canada for several days. One of the prime jobs of solar observatories is to detect, record and measure flares and let the relevant bodies know when to switch satellites into "safe" mode and to stand by the circuit breakers.

Astronomers study nuclear processes in stars, both stable and unstable. Stars are the only large, long-lived nuclear reactors we can safely study. Remember, "Solar IS Nuclear". If the problem of safe, reliable nuclear power is ever solved, a huge proportion of the answer will come from astronomy.

As a science that deals in fundamental research, it is impossible to put a dollar value on astronomy or to predict just what it will discover. The only thing that can confidently be predicted is that it will continue to produce surprising and spectacular insights into our amazing Universe, and to generate many useful spin-offs along the way.