Search the AusGO:
Public Links
Astronomer Links

Frequently Asked Questions about Gemini and AusGO


What is Gemini?

The Gemini Observatory is an international partnership. Seven countries (Australia, the USA, the UK, Canada, Australia, Argentina, Brazil, and Chile) combined together to build and run two of the world's largest and most powerful telescopes: Gemini North (located on the extinct volcano Mauna Kea, on the Big Island of Hawaii), and Gemini South (located at Cerro Pachon, in the Chilan Andes). The two telescopes are virtually identical, and together they provide astronomers coverage of the whole sky, north and south. Gemini North began doing science in 2000. Gemini South made its first science observations in the latter part of 2001. At the end of 2012 the United Kingdom withdrew from the Gemini partnership.

Why the Name?

The telescopes are named after the constellation Gemini, "The Twins" because there are two identical, twin telescopes.

Who Owns Gemini?

Giant modern telescopes such as Gemini North and Gemini South cost around A$100 million or more each. As such, they are too expensive for most universities or individual countries to own and operate. Instead, they are typically built and run by international consortia. Gemini is built and run by an international partnership of Australia, the USA, Canada, Argentina, Brazil, Chile, and (prior to 2013) the UK. It has two offices, one in Hilo, Hawaii, the other in La Serena, Chile.

Astronomers and engineers from all these countries helped design and build the telescopes, and astronomers from all these countries get to use them. Each partner country has a national Gemini office which supports users in that country.

The Gemini Observatory partners, funding agencies, and partner shares are currently:

The partner share of each country reflects how much they pay towards building and running the telescopes, and determines the share of the telescope time that astronomers from that country get.

In addition, 5% of the telescope time goes to Gemini staff, 2% to the Director of the Gemini Observatory for Discretionary Time proposals, and 10% to the telescope hosts, in return for providing the telescopes their homes: the University of Hawaii for Gemini North, and Chile for Gemini South. Some telescope time is also reserved for engineering work, commissioning new instruments, and as a reward for instrument builders.

Why are the Gemini telescopes important?

Gemini is the only pair of telescopes giving full coverage of both the northern and southern skies. The telescope locations are superb. Mauna Kea is the best observing site in the Northern Hemisphere. At 4200 meters, it towers above 40% of the Earth's atmosphere and most of the atmospheric water vapour that hinders infrared observing. Cerro Pachón, 2700 meters high, sits within the dry mountains of the Atacama desert.

With light-collecting mirrors 8.1 m in diameter, the Gemini twins are among the world's largest telescopes working at optical and infrared wavelengths. Just as you can make photographs from visible light, you can use detectors to make images from infrared "light". Infrared radiation allows astronomers to see through the smoky dust particles that wreathe forming stars and many other parts of our Galaxy.

The Gemini telescopes are the best in the world for making infrared images, and are capable of making pictures even clearer than those of the Hubble Space Telescope. This is made possible by new technologies ("adaptive optics") that allow the telescopes to compensate for the distortion of light as it passes through the Earth's atmosphere.

Gemini observations will help answer questions about how stars and planets form, the structure of the Milky Way and other galaxies, and the age and evolution of the Universe.

What's the magnification of the Gemini Telescopes?

In good conditions, the Gemini telescopes can magnify things about 2000 times.

But this isn't really the right question to ask. You could easily build even a lousy telescope with a similar magnification, and many retail stores sell telescopes just like this. But these telescopes just magnify a small blurry picture into a bigger blurry shaky picture: you don't see anything new. What really matters is how much detail you can see in the pictures taken by a telescope. With the human eye, if your eyesight is good you can make out details as small as 0.03 degrees (120 arc-seconds). A good pair of binoculars will drop this to around 12 arc-seconds. A good amateur telescope will do much better (though many telescope sold in non-specialist shops don't): you'll usually be limited not by the telescope but by blurring in the atmosphere, to around 1-2 arcsec. Gemini gets around 0.5 arcsec regularly, and with adaptive optics can get images as sharp as 0.05 arcsec.

How far can you see with the Gemini Telescopes?

About 12 billion light years, so far. But again this isn't really the right question to ask. The universe is transparent, so even a small telescope can see things practically all the way back to the Big Bang, if only they are bright enough. Where Gemini wins is that it can see things much fainter than is possible with smaller telescopes, and can see them in more detail.

The current distance record holders are quasars and galaxies around 12 billion light years away, but a more distant object may be found at any time, and even if it is discovered by some other telescope, Gemini is sure to be used to study it.

What are the Gemini mirrors made of?

The Gemini telescopes collect light with mirrors, not lenses. Each telescope has an 8.1-m diameter "primary" mirror to collect and focus the light as it comes in from space, and a smaller "secondary" mirror to further focus the collected light. A Gemini primary mirror collects as much light as 2.5 million human eyes! Each primary mirror starts out as a "blank" consisting of 42 hexagonal blocks of ultra-low-expansion glass, fused into one large, thin disk. The blank is polished to extreme smoothness. If the mirror were the diameter of the earth, the largest bump on it would be less than 30 cm high!

The glass mirror blank is coated with a layer of metal only 1/1,000th the thickness of a human hair. The mirror must be recoated every few months. The coating can be aluminium (standard for most telescope mirrors) or silver. The unique silver coating gives a much better performance at infrared wavelengths. The Gemini primary mirrors are only about 20 cm thick. They can be distorted by thermal effects (heat flows) or by gravity when the telescopes tilt. To maintain their precise shape, 120 "actuators" gently push and pull the mirrors back into perfect form. These adjustments are typically only about 1/1,000th the thickness of a human hair.

How big are the Gemini domes?

Each of the Gemini Observatory domes is over 15 stories (45 m) high and weighs more than 600 tonnes. When a Gemini telescope is in use, 10-m wide vents open at the base of its dome to regulate the air temperature above the mirror. This lets the telescope make sharper images.

How much does Gemini cost?

The construction budget for both Gemini telescopes was US$193 million. The annual cost of running the two telescopes is about $US10 million, of which some US$4 million a year is spent on developing new instruments for the telescopes. Each night of observing on a Gemini telescope is worth about US$33,000.

How does Gemini compare with the Hubble Space Telescope?

A large state-of-the-art ground-based telescope such as Gemini can be built for about a thirtieth of the cost of the Hubble Space Telescope. When equipment fails in space it is expensive to replace: each Space Shuttle flight costs about US$500 million. In addition, the time lag between designing the instruments and launching them can mean that some technologies have become dated by the time they are used in space.

It is difficult to launch into orbit a telescope with a mirror larger than 4 m in diameter. An 8-m telescope such as Gemini is about 10 times more sensitive to light than a 4-m telescope. A big, sensitive telescope is essential for certain kinds of work, such as studying the light of faint stars and distant galaxies to determine their properties (such as mass, age and chemical composition).

New technology known as "adaptive optics" means that ground-based telescopes can virtually wipe out the effects of the Earth's atmosphere on starlight, making pictures that can be sharper than those from the Hubble Space Telescope.

Why weren't the Gemini Telescopes located in Australia?

Because Australia doesn't have any really high mountains. Ideally a telescope should be:

All this means that if a Gemini telescope had been located in Australia, its performance would have been substantially degraded. It was thus a no-brainer to put them on higher, drier overseas sites. This doesn't stop Australians from using the telescopes, and it doesn't stop a lot of the construction money being spent in Australia.

Mauna Kea in Hawaii is probably the best well-studied place on Earth for big telescopes, which is why so many are located there. We tend to think of Hawaii as warm and wet, which is true at sea-level on the windward sides of the islands. But the telescopes are at an altitude of 4,200 metres, the moisture is locked below the summit by a strong inversion layer, and the night-time temperature rarely goes much above zero up there - observers always feel funny packing their thick coats for a trip to Hawaii! Cerro Pachon in the foothills of the Chilean Andes is not as high (2,700 metres) but looks more arid than the Simpson Desert, and has the same inversion layer to keep away thermals and moisture.

Recent research suggests, however, that there may be a even better place to put giant telescopes than Hawaii or Chile: the high plateau of Antarctica. Future giant telescopes may thus be located there, in the Australian Antarctic Territory.

How do the Gemini telescopes work?

Former Australian Gemini Scientist Dr Paul Francis at the ANU has prepared this overview of what it takes to keep the Gemini telescopes working perfectly.

When did Australian join the Gemini partnership?

On 18 February 1998, the then Minister for Education, Dr David Kemp, announced Australia would join the Gemini partnership. Through the Australian Research Council's Linkage Infrastructure, Equipment and Facilities (LIEF) program, Australia took a 5% share in the US$193 million project. On 21 August 2001, the Federal Government announced funding under the Major National Research Facilities (MNRF) program for Australia to increase its share of Gemini to 6.2%.

What does Australia get out of its membership of Gemini?

Put simply, access to one of the world's premier observing facilities. In 2006, Australian astronomers received approximately 70 hours on each telescope. However, membership of Gemini brings other rewards and opportunities also. Australia joined the Gemini partnership in 1998, too late to take a major part in designing and bulding the telescopes (we are hoping to avoid this problem in future, by joining partnerships building the next generation telescopes earlier). Since that time, however, Australian astronomers and engineers have played a major part in designing and building the instruments that sit at the back of the Gemini telescopes and record the signals from space. These instruments are crucial to the success of the observatory, and cost a large fraction of the total budget.

The first Gemini instrument built in Australia is NIFS: the Near Infrared Integral Field Spectrograph, that was commissioned in October and November 2006. This remarkable multi-million dollar instrument was built at the Australian National University's Mt Stromlo Observatory. It was destroyed in the Jan 2003 bushfires, but has since been rebuilt, in partnership with Canberra firm Auspace. NIFS takes a spectrum of every part of an object at once, using adaptive optics to remove the blur caused by the Earth's atmosphere.

The second Gemini instrument is GSAOI: the Gemini South Adaptive Optics Imager, which was also built at Mt Stromlo Observatory, and shipped to Gemini South in 2007 where it will be integrated with a new 5 laser adaptive optics system. It will obtain wide field pictures at infra-red wavelengths.

The Australian Astronomical Observatory has also been taking the lead in designing an immense Wide-Field Multi-Object Spectrograph (WFMOS) that could allow Gemini to piece together the origins of our Galaxy, and measure the acceleration of the Universe.

How do Australian Astronomers Use Gemini?

Any Australian scientist can apply for time on one or both of the Gemini Telescopes. You have to write a telescope proposal, which explains what you want to do, and how you plan to do it. These proposals are considered by the Australian Time Assignment Committee twice a year. The most exciting and technically feasible proposals are then awarded time - this may be as little as an hour, or as much as several nights.

The lucky astronomers may choose to travel to the telescope to carry out their observations. Alternatively, they can let the data be taken by Gemini staff, when the conditions are right. In the latter case, they plan the observations in great detail using a computer program, and upload the plan to Gemini's computers. When the weather conditions are right, Gemini staff (some of whom are Australian) will execute the observations. The astronomers can then access their data over the Internet.

Who can apply for Australian Gemini time?

In the spirit of international goodwill, and in the interests of ensuring that the best science gets done, Australia maintains an "open skies" policy when it comes to accepting proposals from astronomers worldwide, i.e. it is not necessary for Gemini proposals to be led by, or even involve Australian astronomers. Unlike AAT proposals, where there is a cap set on the amount of open access time awarded to applicants from outside Australia, the amount of Australian Gemini time awarded to non-Australian applicants is not limited. Nevertheless, the Australian Time Assignment Committee will generally want to see a justification of why the science proposed cannot be done with facilities already available to the applicants. If the proposal includes applicants from other Gemini partner countries but is seeking time only from Australia, ATAC will want to know why the proposal is not being submitted as a Joint proposal seeking time from all partners in proportion to the intellectual involvement of each investigator.

See the ATAC Policies and Procedures document for more information.

What does the Australian Gemini Office (AusGO) do?

The Australian Gemini Office has the job of making sure that Australian scientists get the best possible science out of these amazing telescopes. Our mission includes:

Since 2007, AusGO is also responsible for managing Australia's usage of the 15 nights per year on the twin Magellan 6.5m telescopes in Chile, purchased from the Magellan consortium. As part of this arrangement, two Magellan Fellows are based at Magellan for 2 years each, followed by a third year at an Australian institution of their choice.


Australian Gemini Office, ausgo -@- aao.gov.au