Introduction
Week 6 gives some ideas for individual research and the possible field trips; we will discuss what these are and how you might contribute to research.. Many astronomical apparitions occur over specific and limited sections of the earth so if you live in a remote area, you might be a key observer in recording the occultation of a star by an asteroid. As well, grazing occultations of stars by the moon are visible only from specific locations, and you may wish to be part of a group conducting such research.
Eclipses are of special interest to those who like, and can afford to travel. The next solar eclipse to occur in Australia will be in 2002 December 4 and the best place to observe it will be near Ceduna, South Australia. We will return later to this important event.
At home, you could be an important contributor to established programmes such as the timing of the shadow of the earth when it touches the edge of craters and other features on the moon during a lunar eclipse seen from one complete hemisphere of the earth while the moon is above your local horizon. The next lunar eclipse will be visible in Australia in 2000 July 16.
Stellar occultationsAs the moon moves through the night sky near to the ecliptic, many stars are seen to disappear and reappear behind the moon. This is due to the moon's orbital velocity, which is slower than that of the stellar background, and the same stars are not occulted because of the moon's orbital inclination to the ecliptic. The phase of illumination of the moon provides a variable in these occultations where some disappear behind the dark limb and others at the bright limb. Reappearances are similarly affected and to see a bright star suddenly reappear from behind the dark limb is a rewarding sight.
Observing these events provides more exact data on the size and terrain of the moon, variations in the earth's rotation and orbit, and thus facilitates corrections to our time.
To observe at the telescope, accurate setting-up is necessary, and your location is required for predictions of the time of each occultation of a star for your site are required.
Activity: Here is an outline of procedures for observing and reporting occultations. If you want to try this, you may e-mail me for further details.
Acquire the star and track it to the limb of the moon (it is easier to track the disappearance of magnitude 7 or brighter stars at the dark limb). Try to keep the image of the illuminated moon out of the field of view, so that it is easier to concentrate on the star's image, and use 80 magnification to reduce the field of view).
Use a short wave radio for a time source and record the star's disappearance on a tape recorder.
Extract the exact time of the occultation.
Record the star, time, seeing conditions and method of timing and the source together with your telescope and location details.
Forward your report to the occultation clearing house in Japan.
Again, practice will greatly help to perfect your observations.
Stellar grazing occultationsUnless you have unlimited time and travel funds, it is best to observe grazing occultations near your location. As the star just clips, or grazes, the edge of the moon, it will appear in the valleys of the moon and disappear behind the mountains on the limb of the moon. Therefore, observations by many observers spread along the shadow path will result in multiple "on and off" data at discrete distances from the limb of the moon. With sufficient timings, these data provide the basis for an observed limb profile drawn for comparison with the profile charted by Watts.
Observation procedures are similar to those for occultations, but the set-up must be within the moon's shadow on the surface of the earth. One has the challenge of finding the correct location, setting-up accurately away from home, and hoping that the short wave radio and tape recorder work and that there is no cloud during the time of the graze.
Group expeditions are often held. These are lead by an expert and experienced astronomer to maximise the data, so if you are interested, again please e-mail me for the predictions of grazes near your location.
Solar eclipses
Observing a solar eclipse is one of the most rewarding astronomical undertakings I have undertaken. It usually requires inter-state or overseas travel, plus great care in the preparation of equipment and coordination with other observers.
There are few solar eclipse visible in Australia, but in 2002 December 4, a total solar eclipse will be visible in Ceduna, South Australia. This is your best opportunity to witness a solar eclipse in the next few years and the travel distance should be reasonable.
In this case projection of the solar image as it is occulted (or eclipsed) by the moon is generally satisfactory, but to optimise the image a solar filter fitted to your telescope, video or photographic camera is best. At a total eclipse, filtering is necessary up to totality, but to see the outer corona of the sun, its prominences and solar flares you may remove the filter during totality, and replace it immediately after totality, as soon as the sun just reappears. After totality you can observe the filtered image, but usually the impact of a total solar eclipse is such that you are overwhelmed by the beauty and lose interest in the latter phase.
Solar filters are the key to this observation and aluminised mylar forms a very inexpensive filter if correctly constructed and fitted. Other glass filters can be used, but are usually very expensive. If projection of the sun's image is used, of course there is no need for a filter, and during totality the observer can look safely at the eclipsed sun either through the telescope or with the naked eye.
For the Ceduna eclipse there is considerable information already available and the first link is to Fred Espenak's page. My own page has some details concerning the predicted times of Baily's Beads seen as the photosphere of the sun peaks through the valleys of the moon - a worthwhile observation is to time these beads.
If you live near Ceduna, or if you are prepared to travel to Ceduna e-mail me as soon as possible so that I can provide details of the Canberra Astronomical Society's expedition.
Lunar eclipsesThe place to go for information on lunar eclipses is of course my Lunar Eclipse FINDER page and the linked Home Page, but here is a brief list of eclipses visible in Australia from 2000 to 2004. l Total: 2000 July 16 and 2001 January 9
Partial: 2001 July 5
Penumbral: 2001 December 30, 2002 May 26 and 2002 June 24.
Total: 2004 May 4.
A lunar eclipse is rewarding. as most last for hours as compared to the few minutes in a solar eclipse. Many observations can be made from a complete video record from first to fourth contact when the umbral shadow of the earth leaves the moon. During the passage of the earth's shadow across the moon, the timing of its contact with surface features on the moon can be made, and occultations not possible during full moon (when the eclipse occurs) can be timed. In a total eclipse the moon's colour can be a light pink to a deep red depending on how far it is immersed into the earth's shadow. Photographers can make many interesting attempts to capture this colour change.
Lunar eclipse observations are used to find out how the earth's atmosphere changes in size, how out-of-round it is (its oblateness) and how the atmosphere increases the expected size of the umbra (or its enlargement).
Activity: To obtain information on observing times, predictions of when lunar craters will be immersed or when they emerge from the umbra, look at the FINDER page for the next eclipses visible in 2000.
Questions for reflection
Test your progress by trying to see if you can answer the following questions. If you have any problems e-mail me or put your query on the discussion page.
Why are solar eclipses only visible over a small part of the earth? Why are lunar eclipses visible from one complete hemisphere of the earth?
Where would you find information on the possible occultation of a star by an asteroid? How would you observe such an event from your location?
What is a grazing occultation? How would you observe the graze and what instrumentation is required for an effective observation?
When and why would you use a filter for observations of a solar eclipse?
Where would you find data on stellar occultations by the moon for your area on a particular date? How would you observe these?
In what ways are lunar eclipses of interest? How would you find information on the next lunar eclipse visible in your area and what would you observe during this event?
How would you start on your own astronomical research project and would you participate in an organisation available on the Internet?
Activity
Find the path for the next solar eclipse in Ceduna South Australia
A solar eclipse may be safely observed with moderate telescopes and video or photographic cameras. See if you can find the path limits for the Ceduna solar eclipse in 2002 December 4 and outline your observing plans for this eclipse. E-mail me for help if necessary. In any case, I would be interested in your plans.
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