Monthly Archive for 一月, 2007

Ancient Greek Astronomers Were Smart

Ancient Orrery

Look at the mysterious antique above. It’s the orrery made by ancient Greek. This device is made of bronze and encased in wood. It was found by divers off the Mediterranean island Antikythera in 1900. Thus, it is also called Antikythera Mechanism.

It enabled astronomers in the second century BC to predict the movements of the Moon and Sun, along with lunar and solar eclipses. It could recreate irregularities in the Moon’s motion due to its elliptical orbit. It also helped Greek astronomers to predict the location of the known planet. I guess this was the tool that made ancient Greek astronomers GODlike.

Why Does Larger Newtonian Have Faster Focal Ratio?

This is an interesting question, isn’t it? I only know about this today and I want to share it immediately.

Larger Newtonian (reflector) has a faster focal ratio. As you know, focal ratio is the value of focal length divided by diameter of primary mirror (aperture). So, that means faster focal ratio telescope has a relatively shorter focal length. Why does a large Newtonian (eg. 8″ Newtonian) have a fast focal ratio? The focal length of the Newtonian and refractor is almost nearly the length of the telescope. If a 10″ (250mm) Newtonian has a focal ratio of 10 (f/10), the length of the OTA is most likely over 2.5m. How can a single person handle such a bulky telescope? That’s why large Newtonians are always built to be “fast”.

What about the small aperture Newtonian? Manufacturer always made them slower and the secondary mirror is directly involved in this matter. When a Newtonian has a large secondary mirror, its focal ratio will be smaller in value. If a Newtonian has a small primary mirror but relatively big secondary mirror, the center obstruction (CO) is too great which will results in lower contrast images as well as observing. However, a large Newtonian won’t have much lower images because its center obstruction is relatively small.

The same theory applies to refractor too.

Best McNaught Photos! [Updated!]

Although I haven’t seen McNaught myself these days, the spectacular images around the webs pleased me very well. I have been collecting the best McNaught photos for my very own collection but sharing is always a better attitude. :) Enjoy!

New Addition!

Kevin Crause New Amazing Photo!
Author: Kevin Crause
Location: Mossel Bay, Western Cape, South Africa
Date: 20 January 2007
Photo Details: Nikon D2X, 80mm lens, f/2.8, 20secs, ISO800
Description: This is probably the longest tail I have seen!

Crause
Author: Kevin Crause
Location: Mossel Bay, Western Cape, South Africa
Date: 17 January 2007
Photo Details: Nikon D2X, 120mm lens, f/5.3, 9secs, ISO200

Pieterse
Author: Hannes Pieterse
Location: Bloemfontein, South Africa.
Date: 16 January 2007
Photo Details: Canon 30D, 300mm, f/8, 2secs, ISO800

Penning
Author: Hannes Pieterse
Location: Bloemfontein, South Africa
Date: 18 January 2007
Photo Details: Sony Cybershot DSC-P93A, f/2.8, 25secs, ISO100

Crane
Author: Steve Cranne
Location: Cape Town, South Africa
Date: 19 January 2007
Photo Details: Canon 300D, Canon 50mm lens, f/1.8, 8secs

McNaught C2006/P1 – The Brightest Comet In Centuries?

McNaught C2006/P1 continues brightenning and it’s now visible at daytime sky! Isn’t it really amazing? It’s now the brightest comet in 40 years and continue challenging the Ikeya-Seki in 1965 to be the brightest comet in centuries!

Go outside and stand in the shadow of a building so that the glare of the sun is blocked out. Make a fist and hold it at arm’s length. The comet is about one fist-width east of the sun. This is the instruction by SpaceWeather.com Beware of the sunlight, it will cause severe damage to your eyes if you stare at it with your naked eyes.

Possibly The Brightest Comet This Century – McNaught C/2006 P1

No astronomer is going to keep himself in front of the monitor when this super duper comet shows up. McNaught 2006/P1 is brightenned so rapidly as it nears the Sun. From what I see from the photos taken by amateur astronomer, the short exposure photos are really breathtaking! It’s short exposure! That means the our sights are quite similiar to the photos. Below is the skymap by Space Weather.

McNaught C/2006 P1

After I get the permission from the author of the photos, I will post them up here.

Omega AstroFilters – Hubble’s Filters

Narrow Pass Band Nebula Filter by Omega Astrofilter

Omega AstroFilters is the supplier of NASA Hubble Space Telescope filters and the Mars Rover. So, you know that there is no doubt of the quality issue. I can’t say much on this though as I haven’t tried their filters yet. Hopefully, I will get a free Mars Rover poster.

I will get a NPB, Narrow Pass Band Nebula Filter. It’s a Ultra High Contrast type filter which is great for observing small and fainter emission planetary and nebula and a variety of bright nebula.

What’s more they have? VHT (Very High Throughput Nebula Filter) designed for small scope, HPOIII (High Performance OIII) for emission and reflective nebula and GCE (Galaxy Contrast Enhancement Filter) for galaxies.

Visit them at Omega Astrofilters!

Remove The Corrector Plate Of LX90

Going to put it back

It’s so interesting to disassemble a telescope especially those have a very precise and big gears. I’ve disassembled my computer since I was 8 and 8 years later I disassembled my LX90. I will tell you how to do so step-by-step. However, take it at your own risk, I will not responsible for any damage done to the telescope. I suggest that you read all the procedures before you do anything. If possible, read one more before you start and it’s advisable to print this article with you or leave your monitor on when you are doing your work.

In the Part I, I’m going to tell you how to disassemble the corrector plate. The photos below are clickable for a larger version.

Remove the screws on the black housing

(1) First, unscrew every screw on the black housing in front of the OTA. There are 4 on the top and 3 at the bottom. The screws have to be unscrewed by Allen Wrench. I have 3 from Meade when I bought the scope.

Unscrew the screws on the specification ring

(2) Afterthat, you have to remove the screws on the ring which have the specification of the telescope. Please make sure that you don’t point your scope down at this moment just in case the corrector plate fall down and result in severe damage.

Unscrewing done!

(3) Caution! Although you have all the screws undone, don’t remove the corrector plate now or you will regret for life.

Make a marking

(4) Now, check whether the Meade engineer made a marking over the edge of the corrector plate and the black housing. If he did, continue to the next step. If not, you have to do your own marking. Make sure that it’s visible!

(5) Do you see 6 pieces of cork slices filled in the gap between the corrector plate and the housing? I suggest removing them before you proceed to remove the corrector plate. After removing them, hold your hand on the secondary mirror (the center obstruction) and turn the scope down. If the corrector plate doesn’t fall down at this moment, try the way below.

(6) You suppose to see 2 big gaps, don’t you? I used a knife which was small enough to fit into the gap and insert it to the maximum (the knife holder may touch the corrector plate now). Use the way that you open a tin with a spoon to remove the corrector plate. I heard a loud “boom” when I successfully remove it. Do you still have the secondary mirror mounted on the corrector plate? You better have it untouched because once it’s removed, you can’t put it back precisely. You have to call UPS and pickup the item back to Meade. Haha… Frankly speaking, I did remove it accidentally. Luckily, I made a marking on the screws that hold the secondary mirror. Luck really plays an important role. I was able to put it back almost the same as before.

LX90 without corrector plate

(7) Okay, the corrector plate is removed. What shall I do next? I did cleaning of the corrector plate and removing of a toothpick which was ACCIDENTALLY dropped into the OTA via the baffle tube.

The Secondary Mirror

(8) Let me show you the back of the corrector plate which faces the primary mirror.

(9) No more, I am going to put the corrector plate back now. I restore the cork slices first. Wish you a happy removing! :D

Offline For Week

Attributed to the damaged submarine cable (Asia Pacific Cable Network 2) which plays an important role in Asia internet, I was unable to access my blog hosted in U.S. That’s why the blog wasn’t updated for week.

In this period, I have removed the corrector plate of my LX90 and pictures will be posted soon with guidelines. The process was quite scary to me.

A good news here. This blog will be optimized soon for a better reading environment.




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