Jump to content

Walking on the Moon

Novice attempt on Uranus - first light for ages


Recommended Posts

[Spoiler - I did not positively identify Uranus]


I pulled my 8.5" f/7.6 DIY dob out of storage on Saturday - washed the mirror (it looks pretty well gubbed with a few inch-diameter patches of oxidisation, smaller patches of missing coating, scratches, etc), substituted a 12" lazy susan for the old stiction-y formica and cutting board az bearing, removed some weight from the stand, re-purposed an old smartphone with Skeye and other apps, added a phone holder to the scope for push-to, started building an observing chair - generally waiting for clear skies.

At 1900, I pulled the scope out back - one nearby street light gave me enough light to see what I was doing. I found a level-ish patch of ground and had a quick flick around the only objects I knew where to find - the Double Cluster, Pleiades, either M36 or M38 I'm not sure. My 8yo son had a look with me, but the temperature was falling to zero so he turned in.

After a rough alignment on the phone with Polaris and Aldebaran, I pointed to where Uranus was supposed to be. The phone confirmed I was nearby but I had no idea what I was looking for. It was a bit laggy with jitter around +/- 0.5 degree, so helpful but not all that great.

I had two low power eyepieces to choose from - a Vixen NPL 30mm (50deg AFOV) and a generic 40mm Plossl (~40deg AFOV). I dislike looking through the latter, so I used the 30mm - I'd bought it to improve a cheap 3" reflector and is currently my favourite EP. The focuser is 1.25", made from plastic plumbing parts and a couple of other bits - turn to focus. I now know that the 30mm in the big dob gives me a FOV of just under 1deg at ~55x mag, but I didn't know that then.

I hunted around and saw a few stars, a couple looked blueish but often the phone would show me I'd strayed way off. I kept going back. Nothing looked like a disc at that power and I needed to get some context. I went inside, loaded Stellarium and sketched out some adjacent star patterns, trying to put together a plan for hopping around from "flat trapezium" to "triangle" pointing towards "line of three", a "cross" and such things. Bear in mind that I didn't know the FOV I was dealing with.

I couldn't complete my star hopping. I could find the start point reliably, or at least what I believed was my start point, but with everything upside down, differing magnitudes, nearby stars I hadn't sketched and no idea of the FOV, I never got past step 2. I studied Stellarium again, tweaked my steps, but still no further.

I picked a field that over my time observing I had convinced myself contained Uranus - half a dozen obvious points of light and a dozen or so others that were easy enough to ignore - I was able to find this portion again with the 30mm if I lost it - "flattened triangle in lower right, one to the left, two above", phone indicating I was more or less centered.

I have two other lenses - a cheap 11mm (80deg AFOV) and a TMB Planetary II 6mm (58deg AFOV). At ~270x with a lively new az bearing, the 6mm was a bit much to say the least. To use the 30mm, I screw my focusser nearly all the way out - the 11mm is nearly all the way in. With the twitchy az bearing, changing eyepieces was a challenge - just undoing the lock screw pushed the scope off. ~150x mag with the 11mm, half a degree FOV if I'm getting all that.

I studied everything in this portion with the 11mm, but it's cheap and doesn't focus well at all. Nothing that didn't look like a slightly fuzzy point, no discernible disc. (I know I need to re-collimate the scope - perhaps that EP will improve then.) I went back to the 30mm and wound down before giving up at about 2200, only then realising how much frost had settled on the scope and on my coat.


I went inside to follow up - I set up my telescope and EP for an occular view in Stellarium but didn't think it showed enough stars, so I googled for a star chart. I picked out jrtorres' triatlas PDFs - chart C260. I took the coordinates for Uranus and EP FOV from Stellarium and stared blankly at the chart, trying to follow my own star-hopping steps from earlier. I changed tack after discovering I could download additional star files for Stellarium. I created a dummy EP with twice the AFOV for a bit more context, as I know I wasn't centered on Uranus. Again, I tried to hop. I tried to find the portion of sky I was familiar with when I thought I was near. I played with absolute and relative scales, light pollution, magnitude limits - trying to see what I saw in the scope. I failed.


I still have no idea whether I saw Uranus or not, and have been unable to identify exactly where I was looking when I thought I was close. I think I've learned a few things, though.

  • it helps to know what your EP and scope is showing you in terms of FOV, magnitude, etc
  • it helps to know what the portion of sky you're looking at is supposed to look like
  • using two EPs which focus at opposite ends of the focuser travel is annoying
  • cheap EPs and/or a narrow AFOV makes your DIY scope feel like a bit of a let down
  • I need a bit more friction on the az bearing
  • the mirror, despite its poor condition, still seems to perform well enough for now
  • I could do with another EP in the box, 20mm or so
  • digital setting circles will no doubt improve on the phone app - I'm waiting for the parts to arrive


However, Jupiter in the 11mm looked as crisp as I've ever seen it this morning, though apparently too bright without filter for an afocal video.


I'll try it all again another night.

  • Like 6
Link to comment
Share on other sites

  • 3 weeks later...

Uranus and neptune can be quite tricky to find without setting circles or go-to. I've found printing the relevant stellarium page and drawing on the expected view circle for the finder scope helps a lot because it gives you a scale for the star patterns you're looking for. Once you have it centred in the main scope 270x and an 8.5" should have no trouble showing the disc if you can take care of the bearing issue you mention. It's great that people are still making and using DIY scopes. To me at least it adds a lot to the enjoyment of the hobby :)

  • Like 1
Link to comment
Share on other sites

I have only found Uranus by manual searching with an EQ mount. I had Stellarium beside me. The starhop was not easy at all. Easy to miss where you are. But eventually I was able to see it. It is not bigger much than a star (without magnification), but it is blueish. Maybe you just didn't recognize it?

  • Like 1
Link to comment
Share on other sites

Great write up :thumbsup:

I now completely cheat by using 'push-to' on my 2nd scope :) But, there was definitely a much better sense of achievement, and the thrill of the hunt, when star hopping like I used to with my Telrad and finder scope.  At times frustrating, it often took me more than one session to find a target! But I knew the sky better... now I feel like a fraud - I see more, but it's not the same!!

  • Like 1
Link to comment
Share on other sites

It can be a great help to find the outer planets when they are in conjunction with an easier to find object. I noticed in the January issue of Astronomy Now that Uranus is described as being 35 arcminutes south east of zeta Piscium. That distance is roughly the angular diameter of the moon and the star is around mag 5. Also zeta Piscium appears to be an optical double star, which might help to know that you have found the star. The separation of the stars is 23 arc seconds, roughly the size of Venus at the start of January. So with your 30mm, once you have found the star, all that is needed is a slight nudge south east and Uranus should be centred. Then a print out of the fov zoomed in to about 1 or 2 degrees could pinpoint Uranus. A newtonian without a star diagonal should simply produce an image that is upside down.  Once that is done, up the magnification to see if you can discern any colour ( blue/green) or disc.

Also I`ve noticed that on the 12th of January, Neptune will be about a Moon`s width east of Venus, so that might be worth a try as well.

  • Like 1
Link to comment
Share on other sites

Uranus is an easy spot in my 8x56 binoculars and my 9x50 finder scope, once you have found it :icon_biggrin:

I found it by following a star hop in my binos, from the main 2 stars in Aries almost in a straight line down to Uranus.


There are 2 very distinctive triangles of stars, Uranus is in the higher of the 2 triangles. Unfortunately from my location the stars in Pisces are nor very prominent on most nights due to the light pollution. So i found this method work very well. seeing it through the binos helped massively.

I am sure you will get a positive identification next time.





  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.