Merry Christmas! Have you received any gift from Santa? Please let me know if you receive any astronomical equipment as your Christmas gift! I received a great artwork from my sister. I would like to share it with everyone. 
Monthly Archive for December, 2006
The exit pupil is the image of the objective that is formed by the eyepiece. It’s where you place your eye to see the full field of view. You can calculate the diameter of the exit pupil by dividing the focal length of the eyepiece by your scope’s focal ratio or you can divide aperture by magnification.
Exit pupil (mm)= Fe ÷ f/# (N) | D ÷ magnification
Fe: Focal length of eyepiece
f/# (N): Focal ratio of telescope
D: Diameter of aperture (mm)
For reflector telescopes, it’s best to avoid exit pupils larger than 7mm or smaller than 0.5mm. Refracting telescopes have no upper limits on exit pupil sizes.
For the full field of view to be seen, the exit pupil should correspond with the dilation of the dark-adapted pupil, which is between 5 and 7mm. The dialation of our dark adapted pupil has to be larger than the exit pupil to see the full field of view. An exit pupil larger than 7mm means that some of the light will be lost outside of the eye’s entrance pupil, no matter what the distance of the eye from the eyepiece.
An important factor to consider a eyepiece is eye relief. This is the distance between the viewer’s eyeball and the eye lens of the eyepiece.
The eye-relief distance is fixed by the eyepiece design and is normally rather exact. A person who wear glasses may have problem to get the full field of view as he cannot reach the correct eye relief point. If his eyes are outside the correct eye relief distance, the field of view is reduced and the reduction depends on the individual and the design of the eyepiece.
Date: 15 December 2006
Time: 0057 UT+8
Venue: Home garden
I was quite lucky that I was able to watch 4 Geminids after the peak (13 December 2006). The interval of the appearance of the first 2 Geminids was around 30 seconds. No equipment was used during the meteor shower watching.
Afterthat, I setup my LX90 to observe the “Tonight Best”. It’s the guided tour written by Meade. Every of the objects observed are Messier Objects. They were M35, M36, M37, M38, M42 and M45 (Pleaides). I was supposed to be able to see M1 (Crab Nebula) but the tour showed me M42 (Great Orion Nebula). M42 was in greenish tone. I would say it’s always the best nebula for visual enjoyment as this is one of the nebula which you can see colour.
M35, M36, M37, M38 and M45 are open cluster. There were really a lot of stars in the view. It’s very fantastic, especially the M37 which has the greatest amount of stars. The arrangement of the amount of stars from high to low is as follow. M37>M38>M35>M36>M45
I observed Saturn as well! The view is not so great as it’s still low in the sky but it’s getting higher and higher, so no worry. The time is coming soon.
Geminids 2004 Taken by Jason A.C. Brock in December 2004
Geminids peaks on the 13 December and 14 December which is the best meteor shower in this year! It’s predicted to be around 120 meteors per hour. That means you would see one or two meteors every minute.
The source of the meteor shower is 3200 Phaethon, a myterious object which is either a comet or an asteroid. 3200 Phaethon is catalogued as PHA as it’s a potentially hazardous asteroid whose path misses Earth’s orbit by only 2 million miles.
The seeing here is quite poor. The dew has affected the scene. I will try my luck tomorrow to watch those left-overs.
SOHO No.1200 Discoverer, Bo Zhou. Image courtesy of Renjiang Xie
1200th comet discovery of SOHO (Solar and Heliospheric Observatory) spacecraft was found by a Chinese amateur astronomer, Bo Zhou. The SOHO No.1200 was a tiny, diffuse, and very faint object. It’s detected in images taken with the spacecraft’s LASCO C2 coronagraph which he downloaded.
From this, we know that we don’t have to own a telescope to do researches or findings. There are quite a number of “virtual telescope” among the internet. I will try to collect as much as possible to benefit those who can’t afford to buy a research grade telescope.
I will create a page of the collection and more virtual telescopes will be added.
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