Nik271

Well done, Malcolm! Its one of these features where everything has to come together - correct illumination, good seeing, quality equipment and of course, a sharp-eyed observer 🙂

Thank you both, I'm glad if my observations help others! In turn I get a lot of ideas for future observations from fellow SGL-ers, this is what I like most in this forum. Yesterday the night was clear but not so transparent. I spent most of my observing time on Jupiter but still had another look at NGC 604, this time with my biggest scope,the Skymax 180. I have to say Maks are well suited for this target. The extra aperture and magnification (about x180) helped to see it even clearer. It looked a bit like like a planetary nebula or a very dim globular. I tried my UHC filter this time. It helped a little as the nearby star became dimmer. The nebula looked a bit larger with the UHC. I coudn't see any structure to it, I guess its needs a proper light bucket for close inspection. Encouraged by seeing this one I'm going to try NGC 206 next, a star forming region in M31. From what I can find this one is tougher since it is more diffuse and probably more affected by light pollution. Also it is a star association , not a nebula and filters will not help for it. Keep looking up, Nik

I want to share my first observation of a nebula in another galaxy: NCG 604 in M33. This is often quoted as the brightest and easiest extragallactic deep sky object to observe and accessible to even small telescopes. It is a giant molecular hydrogen cloud in M33 which dwarfs anything in our own galaxy: it is estimated to be 1500ly in diameter, for comparison the Orion nebula M42 is only 25ly across. Well, in the past couple of nights I gave it a try and can confirm that it can be seen even in a 4 inch refractor from a suburban location (my garden is listed as SQM 20 but I suspect it is brighter). In fact because it is a small condensed object (1 by 2 arcminutes) I consider it even easier to spot than M33 itself. The first stage is to get to the location of M33. I use my finderscope, start at Alpha Trianguli and use stepping star to get to a lozenge of 8-th magnitude stars which contains M33. Once in the general area I switch to my widefield EP (24 Hyperion EP) to locate a distinctive quadrilateral at one corner of lozenge. Its easy to distinguish as its courner star ( the one towards the centre of M33) is a wide double. Stepping on the side of the quadrilateral towards the double and one step beyond gets you to a 11-th magntiude star. NGC 604 is a dim glow next to it. I could only see it with averted vision and a medium magniication, x70 to x100. The first night I used my 4 inch refractor and it was barely detected. The second night I used my 127 Skymax and it was easier to see occasionally with direct vision due to the extra aperture. I'm sure more aperture will make it even easier. NGC 604 is listed at 14-th magnitude but I don't believe this. I would estimate it at perhaps 12-th magnitude, which is the limit of my 4 inch. I also tried a UHC filter but it made everything too dark. It may work if you have a larger scope. Anyway, if you haven't tried this one, give it a go! I never thought it possible with my scopes and location. Clear skies! Nik

NOAA has updated its forecast for the current solar cycle 25 peak. Previouly they expected it to peak in 2025. The new forecast predicts an earlier peak in 2024. Good news for the solar eclipse watchers in April 2024. Also earlier peaks traditionally mean a stronger cycle. https://www.weather.gov/news/102523-solar-cycle-25-update?fbclid=IwAR0vxB_sgrEOMxNAC5JQizXA2YnUqNNWek4Mcdc25hbVn0lfuVcAZCyuQKw Interestingly the past few weeks have been very quiet from what I have seen.

The weather held here too, and the seeing improved from poor initially to good in the past hour. I could use up to x160 on Jupiter. Io was visible at the start and then near the end once it approached GRS and the edge of the planet. Watching the shadow move was mesmerising, I have been outside for the whole of two hours just watching it . Now time for a toasted crumpet 🥶

According to Stellarium at 22:25 both Io and its shadow will be passing over the GRS. I hope the clouds stay away until then!

I'm going to watch the shadow transit of Io tonight. Shadow contact is at 20:30 shortly followed by Io itself moving across Jupiter very close to its shadow. I've set up my Skymax 127 and fingers crossed the weather is cooperating so far🤞

I think the limit of resolution for both scopes is not their aperture but the atmospheric seeing conditions. In most locations the seeing introduces 2 arcsecond blur over a long exposure, whereas the resolution limit of 100mm scope dictated by aperture is just 1.3 arcseconds. In principle C11 should produce a less noisy image but again after noise reduction any advantage of this will be trumped by the seeing.

Managed to see Rima Sharp for only the second time. The seeing cooperated briefly at about 10pm and in short periods I could even resolve the bends in the northern parts. With Skymax 180 at x220. Aristarchus region also looked superb. Mons Rumker was like giant semi-melted marshmallow on the terminator.

Cool! It will be a nice sight, one crescent occulting another much smaller crescent. I may try to image this, weather permitting. My DSLR has been sitting idle for a few months...

Plain wooden sheds are naturally well ventilated. Those with insulated cavity walls and the metal boxes/shipping containers style are the ones to watch out for excessive humidity.

I also have had terrible weather all summer, these days I'm pretty happy when able to spot Vega overhead in the evenings 😀 On the positive side on some early morning recently I have had a short windows of clear sky maybe 30 minutes to an hour. My most used scope is now a 70 mm F6 refractor, lightning quick to set up and the weather does not allow for more aperture anyway. Hey I saw both Saturn and Jupiter last night, that counts as a good night for me these days 😀

The good news (for us) is that the starlink satellites burn in the atmosphere after about 5 years. Let's say Starlink aims for 10,000 satellites at any time. So every year SpaceX has to launch 2000 of them, this is about 40 rocket launches just to maintain this number. Maintaining the network becomes linearly more expensive as the number of satellites grows. I personally have serious doubts whether the whole thing can ever be profitable. Terrestrial internet services (including mobile phone networks) are cheaper and generally serve the large densely populated parts of the world already. Starlink core customers are people in remote areas not served by fast net, plus the the digital 'nomads' working on the move. Hard to see how these core customers will be enough to pay for the maintenance of the network in the long run. State sponsored (for example military) applications are extremely uncertain, since the bottom line for such application is - do you have complete faith in the provider of the service? As the Ukrainians found out in case of Starlink - the service can be taken away at any time. I think that in 10 years time there actually may not be so many of these low flying satellites....

The optical axes of the two scopes will need to differ by the parallax of a galaxy measured from two points about 1 meter distant. This is so small that for all practical purposes the axes of the two scopes can be considered parallel. Getting this is not going to be easy at this focal length. Use largest sensor size available, this should give some slack in case of small misalignment.

I believe it was for some evening of mid December 2025. We have some time to get ready for it!

You've done very well for a first DSO session! A lot of these objects look glorious in dark skies and just a grey smudge in city skies. Though the gobular clusters respond well to magnification. I also use RDF for rough pointing. Often I know the area well enough to find my way from there using a widefiled EP in thr Skymax, which gives barely 1 degree view of the sky. Another solution is to use a RACI 9 x 50 finder. Even in city skies this will show you the stars up to 7-th magnitude in a 5 degree circle in the correct orientation. When exploring an unfamiliar area of the sky, I first use the RDF to point roughly in the direction, then I swap the RDF with the RACI and star hop using it with a star map. This is slower bit the success rate is higher. Be careful with M51, it is very hard or near impossible to see in heavy light pollution. M81 and M82 should be possible.

At F7 the objective will need to be 70mm forward in the tube so that the light cone decreases from 120mm to 110mm to fit the diameter of the main tube without vignetting. I expect there is a conical opening of the tube at the objective end, but the lense hood is hiding it in the pictures.

Currently I don't think I have much of a chance of success at Enceladus, the rings ar still too bright and Saturn too low in the haze. The second half of 2025 looks like the best time:

The visual and the astrophotography filters are usually different since cameras see wider spectrum than us and collect photons over long period of time . So the astrophotography filters will be too dim for visual. The one exception is the oxygen iii filter and the nearby H beta line which are sort of fine for both applications. But again the specialist astrophotography Oiii filters will be very narrow band and expensive.

Yes they are, so UHC or Oiii filters help with them. The Crab (M1) is a bit fainter, bit with the advantage that is much higher from the UK. With experience I can see it in 20x80 binoculars in my Bortle 5/6 sky without filters. Don't expect much though, it is just a faint smudge in small instruments.

The sky transparency has been very poor over southern UK recently and the Eagle nebula is not very high over the horizon, only 25 degrees. Did you see the nearby Swan nebula, it's a bit brighter? It may be just the haze and humidity in the air.

If you leave the scope outside to acclimatise in the evening the danger is that it may become significantly cooler than the ambient air by radiating heat into the sky. What I do is drape a towel over the scope, it is very effective at blocking the IR. A tarp for covering motocycles/barbeques is anothe cost effective option.

While waiting for a clear night this recent thread on shadow transits started me thinking, how large the shadows of the Galilean moons on Jupiter really are? Here I'm interested in the umbral shadow, that is the area on Jupiter where the moon creates a total eclipse of the Sun. This should correspond to the dark dots we see in our telescopes. I'm assuming that the penumbral annulus (the partial eclipse area) scatters a lot of light in Jupiter's atmosphere and is not easily visible. Also I'm assuming the shadow cone hits Jupiter surface at close to perpendicular, ( in general the shadow is going to be an ellipse with a minor axis as given below). After a short calculation with similar triangles here are the results: Io: 2970km Europa: 1920km Ganymede: 3520km Callisto: 1380km The first three tally with my own observations: Largest shadow is by Ganymede, then Io, then Europa. The shadow of Callisto is a surprse: despite being the second largest moon it actualy casts the smallest umbral shadow. The reason is becuase Callisto orbits very far out, almost twice as far as Ganymede and its umbral shadow is decreased a lot. Incidentally I have not yet observed a shadow transit of Callisto to confirm this, it seems to pass either above or below Jupiter. Another interesting point is that 1 arcsecond angle to Jupiter from Earth at opposition (4AU distance ) spans about 2900km, i.e. the shadow of Io. We can see even Europa's shadow with small scopes , which shows that the classical resolution limits apply mostly to starlike sources and 'contrast' features can be detected which are much smaller. I'm attaching my calculations if anyone is interested. I didn't compute the larger penumbral shadow diameters, basic geometry shows that it should be larger by as much above the diameter of the moon G as the umbral diamter is smaler than it (i.e. G+(G-U)=2G-U).

Nice! I've tried for Rima Sharp numerous times with my biggest scope, the skymax 180, but I've found it quite a challenge, there was one occasion where I think I saw the northern part in brief moments but can't say it was a definitive view. It's a waiting game for the right moment. Another of my favourite challenges are the trio Armstrong, Aldrin and Collins craterlets in Tranquility. Armstrong is easy, the other two I've seen only a couple of times. I think it's not just the width of the craters but also how steep the incline of the sides, the more shallow is harder.

Europa is the smallest of the Galilean moons and naturally casts the smallest shadow. This has also been my experience observing it. Io and especially Ganymede's shadows are much more obvious to spot. Incidentally I have not observed a shadow transit by Calllisto.