Here are a few ideas and things to keep in mind.
The Kind of TargetOne approach is to decide what category of object would be interesting to study, and then to identify a particular example.
What kind of target would you like to see in your image...
- a galaxy cluster?
- an individual galaxy?
- a spiral galaxy?
- an elliptical galaxy?
- an irregular galaxy?
- a star cluster?
- a nebula?
The Size of the TargetAn important item to remember is that the instrument used for the contest, the Gemini Multi-Object Spectrograph (GMOS), will produce an image that is 5.5-arcminutes wide and 5.5-arcminutes high. Five arcminutes is about one-sixth the diameter of the Moon. That covers an area much larger than the cameras on the Hubble Space Telescope. So, whereas Hubble is great for seeing the details on small scales, Gemini excels in providing the larger context. The blurring effects of the atmosphere mean that the smallest features that will be resolved in the contest image will have angular sizes of about 0.8-arcseconds. With these constraints, most objects within the Solar System will not make good targets because the images would not be sharp enough. In addition, most stars visible to the naked eye would be problematically bright.
The Coordinates of the TargetTo make sure the object is visible during the contest, you can search for its coordinates on SIMBAD, an enormous online catalogue of celestial objects. The coordinates you want to look at from SIMBAD are the ICRS coordinates on the first line. For example, the entry for M31 reads:
00 42 44.31 +41 16 09.4
meaning its RA is 00 hours, 42 minutes, 44.31 seconds; and its declination is +41 degrees, 16 arcminutes, 9.4 arcseconds. Because M31's declination is greater than 0 degrees, it is not an eligible target for the contest. As a reminder, the coordinate limits are:
1. Right Ascension (RA) greater than 14 hours OR less than 1 hour.
2. Declination (Dec) between -60 degrees and 0 degrees.
Writing Your One-Page ExplanationAstronomers use images to learn about all of the types of objects listed above:
- They measure the sizes of objects and the locations of any companions. This can tell us about the masses of galaxies and the ages of nebulae.
- They study the colors of stars and the brightness at different positions within an object. This can tell us about stellar ages and compositions, and the history of the object.
- They examine the emission and absorption of light from various pockets of gas and dust. This can tell us about the physical processes going on in the gas.
Try to think about the kinds of astronomy images that you find awe-inspiring. Often, these have a range of colours and a mixture of stars, gas, and/or dust. What features do you want your image to have?
For examples of what Gemini and GMOS can do, check out the Gemini image galleries. If an object is already in the gallery, it's probably not a good choice for this contest!
Teachers: If your school has more than two potential entries, consider using the opportunity to re-create the process astronomers use to award telescope time. Allow the students to present a short argument in favour of their idea, and have everyone rank all of the proposals. Then submit the two entries with the highest average scores.
Checking Your Contest Target
Here are some tips for checking your choice for the contest, using the previous winners as examples.
If you already have a target in mind, and want to check if
it's appropriate for the area that can be covered by Gemini's GMOS
camera, try checking the Digital Sky Survey (DSS):
The DSS is an all-sky photographic survey that was taken with two small telescopes, located in Australia and California. Although the images are at low resolution, we can use the DSS to get a rough idea about how well a target will fill the GMOS field-of-view.
The easiest way to examine the results is to click on each of the Preview images. These different images were taken through different filters--coloured pieces of glass that only allow light of certain wavelengths through to the photograph. By looking at light of different wavelengths (red versus green versus blue), we can study different aspects of the target--for example, seeing different kinds of gas or different kinds of stars.
If we examine the images for NGC 6872, we see that the three filters
give somewhat different views of the galaxy, with the bluer filter
(the first image) showing more detail in the outer parts of the spiral arms:
Targets which change their appearance in the different DSS views are likely to be excellent targets for the contest.
Another check you can do with the search results is to ensure that the coordinates, the RA and Dec columns, fall within the range allowed for the contest. Because of the position of the Sun and the latitude of the Chilean mountain where Gemini South is located, only a portion of the nighttime sky is available for the contest.
In this case, the RA (right ascension) and Dec (declination) are 20 16 55.20 and -70 45 36.0, which falls within the allowed range for that year's contest.
The final image that we produced for the 2010 contest can be found here.
A Second Example
In this second example, using the winning target from the 2011 contest, we show how things can go slightly wrong when using the search tool.
The variation bodes well for the image, and in fact, the central region was the area we focused on for the final image.
Why The DSS Search Tool Isn't The Whole StoryOur final example uses the image from our 2009 contest to demonstrate that the DSS tool is just one of the things to consider when choosing a target.
But when the final Gemini image was put together, an terrific picture came from the data, thanks to the interesting appearance both of the main target as well as its surroundings. The moral of the story is that the DSS Search Tool is a helpful guide to picking a good target, but if you have a a good reason for choosing something that looks questionable in the DSS, go for it! But don't forget to the keep the general guidelines about the sharpness of Gemini's images in mind.
Can't Find Your Target in the DSS?If your target isn't found by the CADC's search tool, the RA and Dec will appear as zeroes. The tool will eventually show you a set of images, but with just a few stars in the field. You can overcome this problem by specifying the target's position (RA and Dec) in the CADC's other DSS search tool:
Don't forget to restrict the box size to 5.5!
Need More Help?If you're still having trouble either finding a target or checking one you've already chosen, try contacting your local university astronomy department or amateur astronomy club for advice. Professional and amateur astronomers tend to be extremely friendly folks, who are usually happy to give a little of their time to good causes like helping students explore the universe!
© Australian Gemini Office 2012. Last updated on 25-Jan-2012 17:00:00 EST