Gfamily

I'd reckon that the difference can safely be disregarded. What's the reason for the confusion?

Hi @gamermole - a couple of suggestions - * have a look on gostargazing.co.uk to see if there are any Astro Societies near you or any Astro Events where people are likely to have telescopes with them. This should give you a chance to have a look through a range of 'scopes, as that will help you get an idea of what you want to look at, and thus, what telescope will do best for you. * similarly, I don't know if you're one for camping, but if you are I would thoroughly recommend going to a Star Party before you get yourself a telescope. Again, people are likely to have a range of telescopes, and if you ask, they will mostly be happy for you to have a look through them (assuming they're not using them for imaging). You don't need to own your own scope to go, and there should be a good variety to consider. The only downside of Star Parties is that they are usually located in places with skies that are significantly darker than average, so you need to be aware that smaller scopes may well not perform so well at home. The first telescope that I was generally happy with was a Synscan 127 Mak, and if I want to look at the planets or close up on the Moon, that's the one I go for; however, I get far more joy from my little 72mm Refractor for looking at open clusters and galactic nebulae - the wider field of view helps to find the targets in the first place, but not only that, it helps to put them into context. Both of these go on my AZ-GTi mount - which is very reliable and easy to use - a particularly neat feature is its ability to track targets even if you haven't completed an alignment - if you can find it and get it centred by eye, then you can select "Point and Track" and it will keep it in the field of view for hours.

My first thought is that it was a true telephoto lens, where the primary doublet would have a shorter focal length than 300, and the negative lens would extend the focal length, giving a shorter than 300mm distance between the primary and the image plane. However, there is very little difference between the nominal 300mm focal length you mention and the 289mm shown on the technical spec. This makes me think that the second element is effectively a coma corrector for the relatively wide aperture f/4.1 lens, and the effects on any ray diagram would only be minor adjustments to the off axis image.

It's been cloudy today, but using eclipse glasses yesterday and on Wednesday, the big Sunspot was definitely visible.

I got a sheet of proplex* from Wickes for about £5 for a 2.4 X 1.2 m sheet. Cut to size and use sticky velcro pads to hold it closed. * twin walled sheeting used by builders to protect flooring. Lightweight, flexible, folds flat when not in use. Hard to think of anything easier.

I remember the predictions of a very quiet Solar Cycle for #25. https://www.swpc.noaa.gov/news/solar-cycle-25-forecast-update Yet it looks like we're potentially heading for the most active cycle on record.

You can take any image and add straight lines to it to make separate 'zones' for different types of program shortcuts Then, in Windows Explorer, right click on the image and select the 'Set as desktop background' menu item. Then drag the icons into the appropriate area

If you have a laminator, it is easy to print onto paper and make a fairly resilient mask that way. I made my own yesterday - used an online generator which i printed out and laminated. I then cut out the white bits with a craft knife and steel rule. I then cut around the mask, leaving 4 tabs that I can use with an elastic band to attach to the OTA (a 72mm refractor in my case)

Haven't been able to find any ray diagrams for it, but there's information here that might be of interest https://joseph-tang.blogspot.com/2017/11/tair-3-300mm-telephoto-lens.html https://allphotolenses.com/lenses/item/c_857.html http://photohistory.ru/1207248188998898.html (in Russian)

Try this page http://www.astronomycafe.net/FAQs/q1890x.html And this formula cos(A) = sin(d1)sin(d2) + cos(d1)cos(d2)cos(ra1-ra2)

This isn't the reason.

It's because the daytime ecliptic is low in the winter and high in the summer. Conversely, the nighttime ecliptic is high in the winter and low in the summer. When you saw the sun it was in the daytime, and when you saw the moon it was nighttime.

This link works https://www.eso.org/public/products/papermodels/papermodel_0005/ (15 hour construction time!). But your link was useful as it also gave a link to constructing a paper model of an ALMA dish https://www.eso.org/public/products/papermodels/papermodel_0001/

... that Saturn's moon Titan made a very rare transit of the Crab Nebula. This allowed the Chandra X-Ray Space Telescope to make an X-Ray image of Titan's atmosphere, data which was later used to help interpret the data captured during the descent of the Huygens probe in 2005

I can't give any specific advice, but would point out that NZ is known as 'The Land of The Long White Cloud' for a reason. We were there for 3 weeks in December a few years ago, and only had two evenings where we could do any astro - and one of those was clear for just 30 minutes. By the way, if you go to the Christchurch Museum, they have an element of the scale model of the Solar System that was created at Otford in Kent for the millennium. On the scale of the model, Christchurch is the right distance for the location of Ross 154 in Sagittarius.

I got a Manfrotto 028 Tripod on ebay a few years back and it goes to over 7ft There's currently one on sale with about 15 hours remaining https://www.ebay.co.uk/itm/325465606999 I was lucky that there were two similar auctions going on at the same time with about 5 minutes between their closing time - the first went for considerably more than the second, and I was bidding on the second one so paid less than £75. As a tripod it's intended for Studio use, but works well outside - very solid and rather heavy as a result.

Apparently, the computer network used by the Atacama Large Microwave Array was the victim of a ransomware attack in October, and is only now coming back on stream. It's estimated that the effective loss could be valued at over £1.5m per week. Cyber security matters. https://physicstoday.scitation.org/do/10.1063/PT.6.2.20221212a/full/

We bought a copy and had it signed by Andy when he was doing a signing at Jodrell Bank a couple of weeks ago. They have an exhibition of selected images on display for the next few months. It's an extra reason for going.

Turns out it's a bit more complicated than that...

MrsG caught me imaging Mars a few hours before the occultation. By 'eck it was cold. Not the weather for getting first light on a new camera

The last visible in the UK was something like 70 years ago, so two in 120 years is still 'pretty rare'. Globally, I guess they are more frequent than that, but (like total solar eclipses), for a specific location they are relatively rare

This evening saw Chris Lintott give the December Lovell Lecture at Jodrell Bank - he's very good! The next Lovell Lecture is on 19th January. Given by Prof Christopher Conselice and will be Origins: The Big Bang To Intelligent Life And Everything In Between. https://www.jodrellbank.net/events/professor-christopher-conselice-origins-the-big-bang-to-intelligent-life-and-everything-in-between/

The box we had from them last week says "May Contain Snow" - haven't dared open it yet.

For the Moon, you shouldn't have any problem getting it in the field of view, but for planets, it'l be worth boosting the exposure or the gain right up high. The focus is likely to be way out, so the image of the target will be bigger (and more diffuse) than you might expect, so boosting the gain should allow you to see the out of focus image - even if it's slightly outside the field of view of your sensor. ETA - once you know roughly where the focus point is, it'll be time to switch to a nearby bright star and use a Bahtinov mask to refine and lock down the focuser.

What are you trying to focus on? Start with something bright - the Moon if it's visible, or Jupiter (or even a distant streetlight). If you know you have something bright properly centred in the field of view, then you can start adjusting the gain and the exposure to get the image on the screen.