And the winner is... (10 June 2009)
The Australian Gemini Office is pleased to announce the results of the Gemini School Astronomy Contest. The contest provided an opportunity for Australian high school students to suggest a target that would be imaged by the Gemini South telescope, one of the world's largest optical telescopes.
The contest entries were evaluated by a special panel drawn from professional astronomy, science education, and journalism. The judging panel was impressed by the high quality of all of the entries, and applauds the efforts of everyone who participated. Based on the dual criteria of aesthetic appeal and scientific reasoning, the panel made the following selections:
First Prize:
- Daniel Tran, supervised by Mr. David Lee, from PAL College, Cabramatta, NSW, who suggested imaging the "Glowing Eye" planetary nebula, NGC 6751.
Runners-Up:
- Stewart Wright and the Forest Lake College Astronomy Club, supervised by Mr. Ian Lightbody, from Forest Lake College, Forest Lake, QLD, who proposed imaging the star Eta Carinae.
- Year 10 "The Universe" class, supervised by Mr. Chris Nielsen, from Sacred Heart College, Kyneton, VIC, who suggested a planetary nebula called SMC N70.
By submitting the winning entry, Daniel will have his target observed by the Gemini South telescope, and the final picture will be put together by specialists from the Gemini Observatory. This image, which will be acquired sometime in the next few months, will then appear on the cover of Australian Sky & Telescope in early 2010.
In addition, all three groups will be able to participate in a Live From Gemini interactive videoconference, connecting the classrooms to scientists in the Gemini Observatory control room.
We hope that you will continue to follow the progress of the "Glowing Eye" nebula imaging, as we will be updating this contest News page throughout the process of the observations moving from the proposal phase, to the acquisition of the images, to the unveiling of the final result.
Congratulations to Daniel, the runners-up, and everyone else who participated in this International Year of Astronomy event!
Read about Daniel in stories from the Fairfield Champion (30 June 2009) and the Fairfield Advance (11 July 2009)
The Phase II Process (24 June 2009)
The transition from having a good idea for an astronomical observation to seeing those observations executed at the Gemini Observatory involves a process known as "Phase II". Gemini has a wide array of different instruments that measure the light coming from the night sky in different ways. As a result, there are lots of instrument settings that need to be correctly adjusted in order for the telescope to collect the data the astronomer wants. The computerized systems that control the telescope's operation also allow for every moment of the night to be used in an efficient manner, even modifying which program is being observed based on the weather conditions at the time. By creating a detailed observing plan, the observatory can ensure that the data being taken will meet the astronomer's specifications. These instructions are contained in the "Phase II" file. ("Phase I" was the initial proposal process.) Below, we'll discuss some of the reasoning that went into the Phase II file for the winning contest entry.
The winning target for the contest is the "Glowing Eye" nebula, a planetary nebula located about 6,000 light-years away from us. Despite the name, a planetary nebula doesn't have anything to do with a planet. (The name originates from the fact that the nebulae looked a bit like giant planets in the small telescopes used in the 1700s.) Rather, a planetary nebula is a cloud of ionized gas that has been thrown off of a star as the star nears the end of its life.
We know from other nebulae, and from earlier studies of this particular
nebula, that most of the light we see is emitted in narrow emission
lines. Light from the Sun is mostly emitted in a continuous spectrum,
so if you split the light through a prism, you see a smooth transition from
red to orange to yellow and so on (like a rainbow seen when sunlight gets
split through the prism of a water droplet). In contrast, a planetary
nebula's light is contained in emission lines--very narrow ranges of color,
with almost no light coming out between the lines. The specific colors
or wavelengths of the lines correspond to the particular chemical
elements in the gas. For example, we know that Hydrogen has a strong
emission line at a wavelength of 656 nanometres (a nanometre is one
one-millionth of a metre). The image below shows examples of a continuous
spectrum and an emission line spectrum.
Because we know precisely at what wavelengths the strongest lines in the nebula will be emitted, we can fine-tune our images to focus on those wavelengths. By taking an image with a filter that only allows certain wavelengths to pass through, we can obtain a picture of just the elements we want to see. For the contest image, we'll be using the elements Hydrogen, Sulphur, and Oxygen, all of which have strong emission lines. And Gemini has a special filter for each of them.
So that covers the topic of how we want our instrument set up. What else
do we need to specify for the Phase II file? One very important item is
the question of where to point the telescope. We have the coordinates of
the target--its street address in the sky--but how do we keep the
telescope pointed in the right place? The telescope weighs tens of
metric tons and is located at the top of a windy mountain, but it has
to precisely counteract the effects of the Earth's rotation in order
to produce a sharp image. How precisely does it need to maintain its
pointing? If you hold your hand at arm's length, the width of your pinky
finger is about 1 degree of arc. There are 60 arcminutes in 1 degree, and
60 arcseconds in 1 arcminute, so that makes 3600 arcseconds across the
width of your pinky. And the telescope will hold its position accurately
to better than 1 one-hundredth of an arcsecond, or less than one
three-hundred-thousandth of the span of your pinky. It's able to do this
amazing feat by taking an image of a nearby "guide" star once every 5
milliseconds, measuring the star's position, and making tiny adjustments
to the pointing. Therefore, in the Phase II file, we also need to pick a
guide star not too far from our target that's bright enough to monitor. We
use all-sky catalogs of bright objects that have been compiled by other
telescopes in order to select the best one. The image below shows the
area around our planetary nebula.
This is a low-resolution picture produced by an all-sky survey, and the
nebula lies at the center. The blue outline shows the area that will be
covered by our Gemini images. Each side of the blue square is about 5.5
arcminutes long. The solid red box highlights the guide star we have chosen.
The guide star sensor can reach anywhere within the dashed red box, and
we've rotated the instrument so that our guide star is inside the dashed
red box, but outside the blue box. That way, the guide star sensor won't
cover up any part of our image.
The final component we need to determine for the Phase II file is how long each exposure should be. The detectors in astronomical instruments are similar to the ones in digital cameras. So if we expose for too long, the image will be saturated and won't look very nice. But, again like digital cameras, it takes a few moments to store each image after the shutter closes, so we could waste a lot of our precious telescope time if we take a lot of very short images. Based on our experience, we've decided on exposures of 60 seconds each as a starting point. But we've also asked whoever will be taking the images to make sure that they aren't saturated.
With all of the details of our observations put into the Phase II file, it then gets double-checked by the experts at the observatory. Once the plan gets approved, the observations are placed into the observing queue, just waiting for the right weather conditions to be executed. The three aspects of the weather that concern us are the phase of the Moon, the amount of cloud-cover, and the atmospheric turbulence. When the Moon is full, the whole sky is brighter, which makes it harder to see faint targets like our planetary nebula. Therefore, we've asked for the Moon phase to be near first or third quarter. For the cloud-cover, we've asked for clear skies. Observations of some bright objects can be done through a bit of cloud, but we want a nice, clear image of the nebula. Finally, we don't want too much turbulence in the atmosphere. When we see stars twinkling, that's due to the disordered churning of the Earth's atmosphere, and it causes images to be blurry. So we have requested better-than-average atmospheric conditions to produce a sharp image of our object.
Even the most basic Gemini observations go through the steps described above: picking an instrument setup, selecting a guide star, and choosing an exposure time. It can take some effort to get everything set up correctly, but it's definitely worth it in order to obtain the data you want.
Return to main contest page.
Australian Gemini Office, ausgo -@- aao.gov.au
The Australian Gemini Office (AusGO) is operated by the Australian
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