Planet did not get bigger

[alan tan]

Hi all,

Pls advice me. I have a celestron se8 and I veiw the planet with 25mm eyepiece, then I change to 13, 8 and 6 mm eyepiece. The planet dont seem to be bigger as expected and I cannot see the contrast.
Can bros advice me whether my scope or eyepiece got problem?

Rdgs

[Mariner]

By planet, one would assume you're talking about Jupiter? Is your focuser working properly?

The FL of the 8SE is 2032mm so with your 6mm EP, the power should be well over 300X. You won't get a really clear view unless the seeing is very good but if you don't see a significant change in the size of Jupiter from the 25mm, then perhaps you're aiming at the wrong target.

If on the other hand, you're looking at say Mars or Uranus, then your expectations may be abit too much.

[alan tan]

Hi,

I start to focus wih 25mm ep then the 6mm ep. I tried to focus using 6mm ep but it is blur image and planet is not significantly big. I think I am viewing Jupital if not wrong.

Pls advice.

thks

[Mariner]

Hi Alan,

Can shed some light on what brand/type of eyepieces you are using? Perhaps you can approach someone staying nearby to help check out your setup. Or better yet, bring your setup (or just the EPs) to one of the sidewalk sessions so that the others can assess the issue.

However, base on my own limited experience with a 6SE (smaller scope), the jump in image size for Jupiter between a 25mm and 6mm EP is significant but not to the extent of seeing a big globe in the 6mm. Depending on the type of 6mm EP you're using, you may not get as sharp an image as you would like.

[weixing]

Hi,
25mm on C8 is around 81x and 6mm is 338x, so it's should be significantly bigger.

By the way, what is the colour of Jupiter you saw and did you see any feature on it?? My guess that you aim at the wrong target.

Have a nice day.

[cloud_cover]

In the 25mm on a C8 Jupiter should be clearly a planet, a small ball and not a pinpoint of light. You probably would even see its 2 major equatorial bands
One thing though: Stars don't grow any bigger when you increase power. They remain pinpoints of light but as you increase power, you may notice a halo of light around brighter stars. This is known as the airy disc and is due to diffraction of light about your telescope tube circumference and the central obstruction.
I'm wondering if you could have been looking at Alderbaran, a nearby star in Taurus that also appears and orangy-red. Alderbaran is quite big star and it may appear to have some volume plus a reddish halo (airy disc) which may appear as an indistinct haze.

[alan tan]

Hi Mariner,

The ep I brought it from ebay by name of coolmann01. he said it is "NEW! CELESTRON 6mm PLOSSL Multi-Coated FITS ALL 1.25" Telescope Eyepiece Lens". He said it is same quality as Omini series. I bought 4 ep from him.

Hi Weixing, Cloud cover

Using 6mm ep should have bigger image, that is also what thought, but it did not turn out as expected.

The color of jupital is yellowish using 25mm ep with 2 smaller planets beside and also using 13mm ep I see 2 lines on the planet which make me think that it is Jupital. Maybe I aim wrong target but again the image should be much bigger right?

BTW, is there a fix day/time for sidewalk sessions ?

rdgs

[Gary]

Hi Alan. Congrats on getting a telescope!

I suspect you may have over-estimated how big planets look like in a 8" SCT . Perhaps this is your first view of Jupiter through a telescope so you have no previous image size to compare it with. Try viewing it through telescopes that are smaller than 8" with the same eyepieces and compared the image scale and contrast of the planet(s).

One way to definitely proof there is nothing wrong with the magnifying and light-collecting ability of your telescope is to observe the Moon through it with your 25mm and 13mm. Or you may try that on terrestrial objects too.

Do monitor the Events & Observations section of this forum for announcement of public stargazing events. These events organised by forum members are usually not fix and very dependent on the weather even when a date and time is decided in advance. But since most of us are only free to do stargazing in the weekends, so it is semi-fix in that sense.

The Science Centre Observatory has a more regular date and time as in their weekly friday sessions and for Galaxy Community Club, Fridays and Saturdays. But do take note they are also weather dependent. You may follow their twitter for the latest updates as to whether those sessions are on or off on the actual day.

There is also a regular 3rd monday of the month public free stargazing talk at Toa Payoh Public Library followed by live impromptu stargazing session outside the library.

This coming Saturday is Earth Hour day. There should be at least of couple of public stargazing sessions in Singapore. So do make good use of this opportunity!

Good luck and hope to observe with you someday! 8" SCT is quite a capable telescope for its price.

[Mariner]

Hi Mariner,
The ep I brought it from ebay by name of coolmann01. he said it is "NEW! CELESTRON 6mm PLOSSL Multi-Coated FITS ALL 1.25" Telescope Eyepiece Lens". He said it is same quality as Omini series. I bought 4 ep from him.

See, that's the thing about ebay, the sellers will tell you anything to sell you everything.

An F/10 scope like the 8SE is very forgiving with most EP types so in theory plossls will work fine. However, I find that the sharpest planetary views I got were from my orthoscopics and brandons.

[weixing]

Hi Weixing, Cloud cover

Using 6mm ep should have bigger image, that is also what thought, but it did not turn out as expected.

The color of jupital is yellowish using 25mm ep with 2 smaller planets beside and also using 13mm ep I see 2 lines on the planet which make me think that it is Jupital. Maybe I aim wrong target but again the image should be much bigger right?
rdgs

Yes... that's Jupiter. It's should be bigger if you compare 25mm and 6mm in your C8, but may be your expectation of "bigger" is too "big"...

Anyway, the below is a website that will simulate view in scope and eyepieces:
http://www.telescope-simulator.com/inde ... &Itemid=58

1) Select "Jupiter" in the Object Data field.
2) Select "8" SCT f-10" in both Telescope field.
3) In the eyepiece field, one select "Meade S3000 Plossl 25mm" and the select other one as "Meade S4000 Super Plossl 6.4mm"... this two eyepieces are similar to your 25mm and 6mm.
4) The magnification below should read 80x for the 25mm and 313x for the 6.4mm.
5) The website will show you the comparison simulated view of both eyepiece for Jupiter... you can see the size different.

Have a nice day.