Directly overhead

[bluesboy]

Hi Guys

I was trying to look directly overhead at the Galaxy M101 in Ursa Major over the weekend. I had real trouble trying to see anything through the sighting scope or the main scope. I wondered if Newtonian scopes were designed for directly overhead or do I need a Dob?

[Stu]

Viewing directly overhead can be a challenge in various scopes, even dobs. It gets very difficult to manouvre them when pointing straight up. Refractors too can be challenging as the eyepiece ends up low down.

Was your problem getting the scope positioned or just that you could not see M101? I ask because it is a notoriously difficult object to see, it is large and faint, and gets washed out easily by any light pollution. It's often easiest from a dark site with binoculars.

Stu

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[NGC 1502]

If trying to find M101 from a town, it's quite tough.  From my back garden in Southend I've only bagged it a few times, on transparent and moonless nights in the spring, with my 10" Dob.

Here's a star hop from Alcor / Mizar http://www.ne.jp/asahi/stellar/scenes/object_e/m101.htm  scroll down for that.

Using a Dob (or any alt-az) to view directly overhead is not convenient, it's called "Dobson's hole"........takes a bit of practice.

Regards, Ed.

[scarp15]

Zenith or aiming close to the zenith with a dob is a little tricky to coordinate but doable with practice. Looking for objects directly overhead is desirable, as this can be the darkest part of the sky, particularly useful at this time of year or in moderate light pollution.

M101 itself requires a dark sky and can be quite diffuse, keep trying and you will get it eventually.

[NGC 1502]

Link to Dobson's hole http://www.ct-astronomer.com/large_dobsonian.htm scroll down to "viewing at the zenith"

Regards, Ed.

[Moonshane]

Yep. Good old Dobson's hole!

[bluesboy]

There was me thinking I was being dense. Dobson's hole. Excellent. Yes I had trouble getting the scope in a good position to view and then had trouble trying to manoeuvre the scope when I did get to a position suitable. On my knees trying to sight was fun, glad I had a whiskey as an excuse. Maybe try again at the other object in that part of the sky. Cant remember its M number though

[AlexB67]

If you have a convenient spot in your garden with any bit of a slope on it, a good workaround for the Dob hole near zenith, I never used an EQ mount, apart from it messing up aligment  I presume it may work  with other mounts too ? I have one area with a dedicated slope in my garden since I like observing near zenith, but I do not like the Dob hole so my solution is move the Dob hole away a bit from zenith for easier navigation on a surface with a slight slope 

[Stu]

If you have a convenient spot in your garden with any bit of a slope on it, a good workaround for the Dob hole near zenith, I never used an EQ mount, apart from it messing up aligment I presume it may work with other mounts too ? I have one area with a dedicated slope in my garden since I like observing near zenith, but I do not like the Dob hole so my solution is move the Dob hole away a bit from zenith for easier navigation on a surface with a slight slope

The EQ equivalent is looking at or around Polaris, same sort of principle. I think my mount instructions suggest setting up non polar aligned if you want to view in that area and tell the goto that's what you've done, it has to work harder but manages ok. Same type of thing as setting up a dob on a slope (or popping a brick under one side of the base???)

Stu

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[bluesboy]

I have an EQ2 mount, I did shorten the back standing leg and lengthen the height to see the sight scope but then had trouble seeing through the eyepiece. Something I am going to have to work at.