Fellow Chicago Astronomers...

I received a very nice note from a gentleman I met at a party last year. He is just starting out in astronomy and got a very nice scope.

Hi Joe!

I was out looking at the stars this evening. I'm still very much a novice...just learning to use the scope. I bought a 10 inch dobsonian with the star finder (though I haven't had much luck getting that to work). I did have luck finding Saturn, Mars, and the M51 galaxy though!

Just out of curiousity, should I expect to be able to see the spiral in M51 with a 10 inch dob in Chicago? I was only able to see the two bright stars next to each other - I could not make out any definition. I was observing using a 10mm Sirius Plossl eyepiece.

I'm also curious if you have any must have reccomendations. One thing I'm considering is shelling out some dough for eyepieces....I really want to get an eyepiece in the 4-8mm range so that I can make out more definition in planets. I'm willing to spend a few hundred dollars if the money really makes a big difference in quality. I've read that barlows are good for beginners but more advanced observers prefer a really good eyepiece to using a barlow (thus I'm reluctant to buy a barlow).

Very Grateful,
Dave

Dave...

Congratulations on joining the ranks of citizen astronomers, prying the secrets from the cosmos.

A Ten inch Dobsonian is a fine instrument, not only excelling in Deep Space Objects, but for general observations as well. The light gathering aperture of the 10" mirror will allow you to funnel dim photons traveling over hundreds of light years right into your retina and marvel at the sights.


First, on the Star Finder -



First, using a 10mm eyepiece in the scope, center a terrestrial object in the scope and don't move it...... Be it an antenna on a building, smokestack or whatever...you want the object not to be moving, so as to accurately match the cross hairs on the finder to the center of the eyepiece on the main scope or Optical Tube Assembly (OTA). If you try doing this on a star, the rotation of the Earth at 1000 MPH, will soon move the star..and frustration sets in and you have to start all over. Now, with the target centered in the eyepiece - use the small adjustment screws on the finder. Move them slowly one at a time, until the target is smack in the middle of the crosshairs of the finder. Check if the target remains in the center of the eyepiece often as you are doing this.

In time, you will be able to align using stars quickly, but not recommended to start with. This procedure will need to be done frequently before your observation sessions.

Also in regards to star finders....

A Zero-Mag Star Finder is good too have. I have them on all my scopes - and the tool places a red circle reticle on a plastic screen projected onto the sky to help you locate objects easier & faster. I use the "Rigel Star Finders"...



There are others as well, and I use this one too - on my smaller C5 SCT...



There is also the Telrad, but I find those too big & clunky.



Viewing -

The planets will offer great views in your 10" dob. Saturn, being the most spectacular - with her ring system nearly edge on now, it's still a great sight.



Mars is rather anticlimatic, and as it's speeding away from us now, it's disk is getting smaller each night.



Jupiter, (now visible in the east before sunrise), will show you great bands and four of it's brightest satellites in a row.

But....

High magnification is not usually the name of the game.

Astronomers stick to low magnifications most of the time, (40mm to 17mm to maybe a 10mm). A few factors come into play here:

1- Sky conditions -

Rare is the perfect, deep and clear night for observing. The blanket of air above our heads is usually turbulent, causing our targets to boil, wave and blur. using high magnification eyepieces just increase these awful views.

2- Field of View (F.O.V.) -

As you increase the magnification, you are also decreasing the FOV of the telescope. Sometimes, this makes the object hard to find and especially...hard to keep up with, if using a Non-motorized scope, as most dobs are.

3 - Dimming -

Also, as one increases the magnification of the selected eyepiece, it also dims the objects. Nothing is free - and indeed you can magnify greatly an object, but it will dramatically lose it's brightness.

When sky conditions are near perfect and we have a bright enough object, then we can kick up the magnification to bring out details on planets, split double stars cleanly and dive into lunar craters...



Enjoy these opportunities when you can.

Now, for galaxies....they prefer low magnifications - as they are relatively dim to view and large. A high magnification eyepiece is not recommended, but rather a low one, like a 25mm or so.

Using a technique called "Averted Vision", astronomers can observe the fainter parts of an object in the telescope, by looking to the side of the target in the eyepiece. This allows the photons to strike the more sensitive parts of the retina, thereby allowing more detail to be observed. It takes some time to train your brain to see this way, but once you do, it will open up a whole new way of seeing.

M51 is quite the cool galaxy...



Open faced to us, we can enjoy the spiral arms in this Hubble image. But at best, with our own modest scopes and eyes, we get mostly this...



And usually just a grey wisp of a target.

The Andromeda galaxy is similar and a ghostly oval patch to the eye.




And the older we get, the less sensitive our eyes get. The two "Bright stars" you saw there Dave, were the cores of the galaxies...! Very cool...



Eyepieces -

Every astronomer should have at least three basic eyepieces...

a 25mm

a 17mm

and a 10mm

Now, you can get a 40mm eyepice, which will provide very low power, but a great large field of view. Excellent for star clusters, galaxies and slowly exploring the sky. I have one and it's one I use often - especially showing the public the Moon. And then you can go for higher powered eyepieces such as a 6mm, 4mm or even a 3.5mm. They have their place, (mostly limited to planetary & lunar observing), and are great with a scope your 10", but you will find that they will not be used as frequently as the others.


This brings us to the Barlows -



Barlows are a must have. A 2x Barlow will double your magnification on any eyepiece, without having to purchase more eyepieces. A 25mm will be a 12.5mm and a 10mm a five. Again, nothing is free, and you will be including another layer of glass between you and the object...which "steals" a little bit of the brightness and definition, through reflections, refractions...and a bunch of other "tions".

But, get one.

Plossl eyepieces are good. Not the best around, but they are affordable and take abuse. Naglers & TeleVues are among the best...but are quite expensive...and deservedly so. If you can get 2 inch eyepieces...even better. Much more preferred over the 1.25 eyepieces commonly used. They offer a very wide FOV and brighter image. The 2" eyepieces display a quite comfortable wide Field of view...and they are like looking thru a spaceship's porthole...


Comparing a 1.25" eyepiece on the left to 2" eyepieces on the right...you can see the dramatic difference in size.

We use 2" eyepieces at the Adler Planetarium and one of my Chicago Astronomer members has some that I use from time to time. They are great! Warning: Some of them are quite heavy and may throw your Dob off balance.

Get yourself a Star Atlas/map, a red bulb flashlight and your set.

There are always more toys to get and it really never ends, but I would be happy to assist you in offering my advice before you buy.

Also...look around this site, as there is a lot of content here on the many joys of urban astronomy including observation sessions, equipment and experiences.

And of course Dave, a warm welcome to join me and the Chicago Astronomer crew on our observation sessions. Post your astro adventures on this forum, as we would like to follow and assist.

And, let me know if you wish to be included in "The Chicago Astronomer" email notifications on upcoming events and activities. You can also follow the action on Twitter: www.twitter.com/astronomerjoe

Ain't astronomy fun?