Invitation to the Principal. Outreach program for local schools. I live in the Hills
District of Sydney, NSW where I have a telescope in our front yard. Well it's a little
...
Astronomy Outreach An Invitation to Schools in the Hills District
10 ft Dome
Telescope
Invitation to the Principal
Outreach program for local schools I live in the Hills District of Sydney, NSW where I have a telescope in our front yard. Well it's a little bit more than just a 'scope. There is a fairly decent-sized 12” SchmidtCassegrain telescope permanently mounted in a 10 ft diameter rotating fibreglass dome. Attached to the 'scope is a dedicated astronomical video camera which provides a live view of astronomical objects on a TV screen. This allows for easy group viewing of the night sky and no longer is it necessary for visitors to take turns squinting through an eyepiece and maybe needing to keep readjusting focus to suit their eyesight. And because the camera is especially good at multiplying the signal that it receives from the telescope, faint fuzzies such as galaxies and planetary nebulae that were barely visible in the eyepiece now stand out clearly on the TV screen. In effect, the camera doubles the telescope's aperture giving the equivalent of 24” diameter. And that in most anybody's terms is a large 'scope. My purpose here is to say that the telescope is freely available for use by schools in the Hills District. The following notes will give some background information and guidance as to matters that need to be taken into account. What objects can be seen? Pretty much the full range of astronomical objects can be viewed. The Moon, planets, comets (when available), stars (single, double and multiple), star clusters (open and globular), diffuse nebulae, planetary nebulae and galaxies. The camera is monochrome only which means that the TV view is not in colour. But that is not really a problem as only very few objects display colour when viewed through an eyepiece. When is the best time to view? The first thing to note is that viewing is best done after the end of twilight. A fair rule of thumb would be that twilight ends about half an hour after sunset. In the winter when the Sun sets earlier, viewing can start earlier. Obviously the opposite is true in summer. The second thing is that when the Moon is “up” its glow pretty much drowns out faint deepsky objects. So the first choice you need to make for a particular session is do you want to view the Moon or deep-sky objects? For most practical purposes it is not possible to view both on the same night. Viewing the Moon The most interesting part of the Moon to view is along the terminator (the line that divides the sunlit side from the dark night-time side) because there the Sun is shining sideways-on to the mountains and crater walls revealing them in sharp relief. And since the terminator slowly moves across the Moon's disk the view constantly changes from night to night. Taking children's usual bedtime into account, the best Page 1
time to view the Moon is in the eight days starting at four days after New Moon. At seven days after New Moon the Moon is at first quarter when the terminator divides the Moon's disk into two halves. On that date the Moon will be due north (and therefore highest in the sky) at 6 o’clock in the evening (7 o’clock during summertime). Viewing deep-sky objects The period from three days after New Moon until two or three days after Full Moon is best avoided for deep sky viewing in the early evening. Over the course of the year as the Earth orbits the sun the night sky slowly changes from night to night. For viewing purposes the year can conveniently be divided into four parts, each of three months. Different constellations will appear high in the sky at each three months interval. Objects are best viewed when they are more than 30o above the horizon. Although some objects close to the South celestial pole never set below the horizon and could in theory be viewed at any time of the year, the sky glow from Sydney usually prevents that when they are much below the South celestial pole. All of which means that visitors can expect to see a range of new objects at each visit only if they leave an interval of at least three months between visits. Because of our southerly latitude and obscuring trees on my northern horizon, the telescope cannot reach objects that lie north of declination 35o N. For example, the large Andromeda galaxy M31 does not rise above my northern tree line. But that still leaves a lot of sky in view and the range of objects that are visible is plentiful. What will a visitor see? The combination of the telescope and camera gives quite a narrow field of view. On the TV screen the image measures 10½ arc-seconds by 8 arc-seconds. To put that into perspective the full Moon measures about 30 arc-seconds across. So the TV image is considerably smaller than the full Moon. This has its benefits and drawbacks. The high magnification means that small objects such as planetary nebula, globular clusters and most galaxies are rendered quite large and fairly easy to see on the TV screen. But larger objects, such as the Moon, some diffuse nebulae, open star clusters and the Magellanic Clouds cannot be viewed all at once and it is necessary to move the telescope across them to see them in parts. The quality of the screen image is somewhat grainy. There is no doubt that the image can usually be improved when captured with the video camera and later subjected to postimaging processing. Nevertheless the live TV view is still quite acceptable. The camera allows “snapshots” of the live view on the TV screen to be captured. This allows a permanent record of the session to be kept and the snapshots can be immediately transferred to, and taken away on, a memory stick brought by a visitor or the group organiser. This may allow the night's viewing to be discussed in class later on.
Page 2
What about the weather? The Moon can be viewed through very thin cloud cover but otherwise viewing is not possible on cloudy nights. Planned visits are always subject to the vagaries of the weather. If it is necessary to call off a planned visit it can always be re-scheduled for a later date. How many people can the observatory accommodate? The dome is 10 ft in diameter. The central portion is occupied by the telescope and most of one half of the remainder contains the furniture and equipment needed to control the 'scope. This leaves only the other half available to accommodate visitors. The optimum number depends on the age group concerned. • • •
2 adults (seated), or 3 to 4 older children (standing), or 5 to 6 small children (standing and/or squatting)
An accompanying adult could stand in the other half of the dome. How long should a viewing session last? That is largely up to the group organiser to determine. For smaller children one hour is just about right. Older children may get more benefit from staying longer, particularly if the viewing session is geared to one or more predetermined topics. Planning for a visit For Moon viewing not much forward planning is required since on any given night the view is largely dictated by the location of the terminator across the Moon's disc. However, if the same group is to view the Moon more than once it would be a good idea to time the visits so that they occur on different days in the Lunar cycle when the terminator will be in different places. Most calendars display the phases of the Moon so it is easy for group organisers to determine on which days the Moon is best viewed in any particular month. Deep-sky viewing sessions can simply take the form of general sky tours of those objects that are currently available at the time. In that case not much prior planning is needed. However more benefit can be had out of a session (particularly for older children) if the group is briefed on a particular topic before they come. For example, the group organiser might discuss the nature of globular clusters and ask the group members to gather information about them (which is easy to do these days with the Internet). Then when the group arrives they will be better able to appreciate what they will see with the telescope. In other words, it is much better if the group organiser dictates the general course of the viewing session. Since the range of available deep-sky objects varies from month to month it would be best if a group organiser could discuss a planned session when making a booking.
Page 3
Who controls the session? I will be on hand to control the telescope and camera settings. I can also, if necessary, act as tour guide. But it would be preferable for an accompanying group organiser to determine the content of, and act as guide during the course of, a session. I have software that lists precisely what objects can be conveniently viewed at any time and date and I can easily provide this information to a group organiser when a session is being planned. What other topics can be discussed? Older children may be interested to learn something about astro-imaging. I can discuss and give some practical demonstration of this fascinating subject. This could involve time away from the telescope at the computer in my house and is particularly suited to cloudy nights. The steps usually involved are : Software Acquisition of initial video file(s) Rejection of unsatisfactory video frames Stacking of retained video frames into one image Bringing out faint details, sharpening, etc.
Gstar4 VirtualDub RegiStax Adobe Photoshop
The next steps You may care to pass this on to any science teacher(s) who may be interested. If necessary, a preview night-time visit to assess the suitability of this offer can be arranged. If you or your staff want to organise one or more visits to the observatory, you are cordially invited to contact me. Please use the Contact Me page on my website davidlloydjones.com
David Lloyd-Jones
Page 4
Live TV View - Moon Mare Imbrium
Live TV View - Moon Southern Highlands
Live TV view
Processed 2 x 2 frames image
Centaurus A (galaxy)
Centaurus A (galaxy)
Live TV View
Processed image
Tarantula Nebula in LMC
Tarantula Nebula in LMC Page 5
Live TV View - M66 galaxy in Leo
Processed image - M66 galaxy in Leo
Live TV View
Processed multi-frame image
Omega Centauri (globular cluster)
Omega Centauri (globular cluster)
Page 6
