Thursday, June 21, 2012

Hilal Observation at Port Dickson & types of refractors

‘Hilal’ observation, or otherwise known as the sighting of the new moon, is a traditional Islamic practice where once the new moon is sighted, a new month begins in the Islamic calendar. Now, the tradition remains, and is further pursued by the latest technology and astronomy instruments.

Yesterday, Simpson and I followed prominent Malaysian astrophotographer and our ‘sifu’ William Chin to join the Muslim folks in searching for the new moon. The location is at Klana Beach Resort, Teluk Kemang.

Klana Beach Resort is I think an astronomy-themed resort at Port Dickson. It sports its own observatory with a 24 inch Ritchey-Chretien telescope, the largest of its kind in Malaysia!

Over at the observation deck the folks are starting to set up their equipments. It was sunset and the young Moon is just 10 degrees above the sun. After the sun sets there’s a small window of opportunity to see it before the Moon sets too below the horizon.
The sun sets on the sea, a nice vantage point but there are some clouds near the horizon.
Well there’s no time to lose! William and his gang sets up the 10 inch Meade LX200 telescope in a jiffy!

A note about this ‘smaller’ telescope on top of the Meade. William called it one of the legendary ‘weapons’ in the astronomical world! It is an apochromatic refractor.

Basically there are three types of refractors – chromatic, achromatic and apochromatic. As refractors work around the principle of refracting light, light of different wavelengths gets refracted to different paths when it passes by the lens, sort of like how you played with the triangular glass prisms to make rainbow colours :) This effect is undesirable in astronomy as it makes the image focus at different points. Hence, there exists these types of refractors to counter this problem.

This is a basic lens with no corrections whatsoever. You can see that the different spectrum of the light focuses on different points. To counter this, :

A better lens was designed, named the Achromatic lens. This is now the standard for most entry level refractors including my Astroview 100mm. :) However, as you can see there are still quite some difference between the focal points, and this produces an effect called chromatic aberration where a violet halo will form around bright objects such as the Moon. It doesn’t affect viewing but take note, the colour isn’t real!

Now, to further improve the refracting telescope, another new design was created – the Apochromatic lens, or more usually known as “APO” which now use 3 lenses instead of two to bring all the focus to a point! APO scopes are really awesome scopes, but they come with a hefty price tag not just because the manufacture process is more complicated, but the materials of the lenses (not glass, mind you) are rare and expensive.
Image credits :

The price difference let’s say for an 80mm refractor (both Orion products – ) :
Orion GoScope 80mm TableTop Refractor Telescope (Achromat type)

120 USD
Orion ED80 80mm f/7.5 Apochromatic Refractor Telescope (Apochromatic)

500 USD – note that this doesn’t come with the mount, which can easily cost a few hundred bucks more!

Now this here is a 9 inch apochromatic refractor in Penang, the largest refractor telescope in Malaysia. Guess how much does it cost? :P

After everything is set up they’re ready to go! Many other people are also joining them for the observation, bringing along mostly the same telescopes lol. You can see a radically different one here though – a surveyor’s scope!
The sun sets over the horizon in this computer screen which controls the telescope remotely. In the end, too bad that day we didn’t get to observe the hilal due to too heavy clouds near the horizon. However a trip to see the 24’’ giant RC, as well as getting tips from William for stargazing, is more than worth it! :)

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