Novice query.

[Hampstead]

I’m looking at a second hand telescope. 

It states astronomical magnification x500 and terrestrial magnification x40. 

why would they be different?

 Thank you in advance. 

[Space Hopper]

Terrestrially, you are looking through a lot more stuff, ie, rising air currents, heat plumes etc, pollution and other things so this limits what you can see clearly without the image breaking down.

Looking upwards at the stars things are a bit clearer, as long as you are not looking too low down where you'll get the same issues as above. An example of this is the moon when its low in the sky, which will look a bit distorted by our atmosphere.

Ignore the 500x bit. Thats just marketing hype to entice you  in. Generally as a guide, use the aperture of your scope in mm, then double it. This will give you a realistic high end magnification upto about 250x max.

[Carbon Brush]

If you tell us what telescope it is, we can offer informed opinions👍

Oh and a warm welcome to the best astronomy forum.

 

[Nyctimene]

Because it is very likely rubbish. Many so-called "beginner scopes" are advertised with abnormal high magnifications. I'm guessing, it's a "refractor" telescope with a lens at the upper end of the tube. Usually, the mounts of these scopes are flimsy, so a lot of disappointment is to be expected.

If you could post a photo, especially of the specifications label, it would be helpful to give you more advice.

I'd steer away from this scope. Buy from a renowned retailer after  reading a lot in the "Beginner" section on here.

Enjoy the journey - and a warm welcome here!

Stephan

[allworlds]

Proper astronomical telescopes have aperture and focal ratio (or length) as their main specification, not aperture which in any case depends what eyepieces you use. (Spotting scopes are usually specified like binoculars, lowmag-highmag x aperture.)

So what you state isn't promising. And the only reason I can think that the "terrestrial magnification" would be different would be the use of an erecting eyepiece, which is something some infamously bad telescopes do.

[Moon-Monkey]

Buy your scope from an experienced telescope shop like FLO yes it will sometimes be marginally more expensive but you know that any product they sell will be fit for purpose and the after care will be there 🙂

[JOC]

11 minutes ago, Moon-Monkey said:

Buy your scope from an experienced telescope shop like FLO yes it will sometimes be marginally more expensive but you know that any product they sell will be fit for purpose and the after care will be there 🙂

Ditto above.  Post what you intend to buy on here first and get some good advice, that way you won't have expectations raised only to crash and burn and waste your cash.  Also, look here:

 

before you buy anything at all - even if you just look at the pictures on the first page.  I own a reflecting telescope with a mirror that is 8" (approx. 20cm) wide and a focal length of about 1.2m - bought after taking advice on SGL,  that's probably way more capable than what you are currently looking at.   On a good night I can see the sorts of images that are in the tiny planet pictures in that thread and about x200 to x240 is about the maximum that is useable for me to get those views.  In the UK you won't get much joy going much closer IME.  Thus, it seems unlikely that the telescope you are looking at is fit for purpose given it's optimistic descriptions.

Edited October 9, 2022 by JOC