Forum Replies Created
-
Posts
-
The diagram above starts at 31st December 1954 and ends at 25th March 2020. (Bit difficult to read). It shows little apparent variation in magnitude.
Seems I was getting excited over nothing. A colleague of mine emailed me some AAVSO information including the attached graph. Maybe in poorer sky conditions with the star near the limit of visibility,it appears to be fainter… I just don’t know.
This post piqued my interest so I did a little research:
My Research From ‘Wikipedia’ : This star has an excess emission of infrared radiation, indicating the presence of circumstellar matter. This forms a debris disk around an orbital radius of 16 Astronomical Units from the star. This radius is unusually small for the estimated age of the disk, which may be explained by drag from the Poynting–Robertson effect causing the dust to spiral inward.
From another internet site:
William Creed
Thursday, 2nd March 2017 5:58:14 AM
When I was a kid in around 1955 to 1969 that star was very visible in the night. Why has it seemed to fade over the 20 some years.
And another site:
Is it just me or is the star that connects the dipper with the handle fading out
There are no clouds its a cold , clear night
For those that can , step outside and observe
I have never come across this beforeIts barely there if at all(Feb 2013)
Finally Patrick Moore, in his book ‘Stargazing’ in 2001, at page 25 states:
“Old astronomers of more than 1,000 years ago stated that it was as bright as the other Ursa Major stars. Either they were wrong or (less probably) Megrez has actually faded about a magnitude since then.”
My question – Is it another case of dust obscuration – now becoming more rapid ???? Trouble is, at 57 degrees north it is just about inaccessible from here in Brisbane Australia…
Hello all – from Australia, – where we are in a similar lockdown. Just before it ‘hit the fan’, I had purchased a 150mm F8 Skywatcher ED to replace the Celestron standard achromatic refractor of the same specifications and I am doing some testing as weather permits. (Cloudy time of year.) Anyway I have posted some images on my page on this website. I am the process of preparing a ‘powerpoint’ where the images of the various stellar objects are aligned and follow each other on subsequent slides … amazing to watch the O & B stars flare up with the achromat. Soon the Moon will come around again for my occultation work.
Apart from the other concerns, the downside is that my wife is also cooped up and this means more little jobs are found to do around the place… particularly out in the yard…
This takes me back. I bought this lens and its big 800mm F8 brother in later 2012 and did a fair bit of testing with them and produced three powerpoint presentations about them. I purchased them because they were cheap, cheap, cheap and I just LOVE bargains! (Just email me on peteranderson53@bigpond.com and I will email them to you. Total size under 10mb. On both lenses I was worried about precise focus because it is deadly. I had visions of building a little adjustable frame for precise focussing, but finally settled for my Neanderthal option, namely sticking a removable adhesive rubber furniture pad across the focussing ring when I had achieved precise focus. However if the lens cools down significantly, the focus will shift a tad. Some poor fellow took such a lens to a solar eclipse, and, you guesssed it, the focus shifted, and there was a gorgeous longer exposure of the corona, badly out of focus!I found the 500mm great apart from this focus problem. With the 800 mm, I could not get it precisely sharp at first and sent it back but was told it was within parameters. I feel it was partly the good old focus problem and atmospheric issues, as well as the lens. After all, you cannot expect astronomical quality – you gets what you pays for – if you are lucky!
I dusted off the 500mm lens for the recent July partial eclipse of the Moon because it was very low in the sky and any longer focal length would have been wasted. (image attached). (I used my adhesive rubber furniture pad to keep focus under control.)
Just a thought. If you are concerned about contrast of the image, try to always use the lens hood that comes with it, which you can reverse over the lens (with a bit of padding) when storing it.
I have never had a problem with correct focus across the field as the powerpoint will illustrate, so I can’t help you there. If I had a problem, I wouldn’t trust my neanderthal skills to take it apart and try to fix it, but as my wife will tell you, I am not really a handyman….
Interesting. The drawing is mirror reversed, which since it was too early for the ubiquitous Schmidt – Cassegrains, suggests a diagonal mirror/prism was used with the refractor when the drawing was made.
Spectacular when they stream right across the sky and converge on the anti-solar point (see attached – leaving Bora Bora)In fact the big dipper can be seen from Southern Queensland if you time it right. My images on this BAA site show how it was done from Noosa Heads (26 deg S), early evening, in early May 1968. The whole story is told.
From Northern Queensland, add another 10 degrees of altitude… Very easy.
I have an Elger’s Map of the Moon on the wall of my observatory in a glass picture frame, that I put over an old watercolour, and it has ‘lived’ on the wall above the desk these last 39 years. I originally bought it in the late 50’s/early 60’s.Being a lunar observer (occultations mostly), I refer to it regularly for the odd identification and check of terminator etc. etc.
Rukl’s book is good, but this map is ‘in my face’ every night if I need it.
I also bought ‘The Moon’ by Wilkins and Moore, (the book with the 300 inch map). The lunar detail really looks impressive, but it is largely unusable. I can believe the complaints that there is a lot of spurious detail.
Now, as far as the mirror reversed images are concerned (and they can be a pain), there are relatively cheap ‘correct view’ prism diagonals available. Avoid the 45 degree units. Those I have seen are not a great quality and exhibit flares across the field for bright object. Besides they are a pain at high altitudes. But consider the correct view 90 degree unit. The downside is that the light path is 12mm longer than a standard prism. (the 45 degree one is even longer), and the light path is only about 20mm wide due to the nature of the prism. But for standard eyepieces, say 25mm focus and below, the drop off in light near the edges is not really apparent, and an oldie like me does not have to re-learn directions when I use a lunar map or find a star field or whatever. I have one living on my C14 and another on the 150mm refractor. (The other SCT’s till have the standard prisms.)
I don’t know UK prices but a retail Australian suppler has a standard 90 degree diagonal for $39 and the ‘correct view’ unit for $49. This would equate to around 21 and 26 UK pounds. So they are cheap.
Firstly I hope I don’t fall foul of the moderator but it is a true story. Our eldest son, when at university made a batch of wine with some of his mates. Brewed it themselves. They wanted to do it properly so they were casting around for a name for the labels on the bottles. After test tasting it, they settled on the name ‘cat’s arse’, because, one sip and the mouth pursed together tightly like a cat’s …. The more astringent, the tighter the pursing of the lips.
Okay, then fast forward. It is virtually impossible when buying cheaper white wine (say in casks) to get any idea of how astringent it is. This is no guide -fresh white – crisp white – dry white . Champagne has ‘brut’, but white wine nothing… (Here in Australia anyway.) So our family have adopted the ‘cats arse’ scale. A higher number represents more astringent and it has proven very useful. Nevertheless it makes for difficulty in the bottle shop when asking “Where does this wine rate on the …… scale?” Then you need to explain it. I used it just this morning when buying a cask of wine. . Perhaps the scale should be formally introduced.
All I know is that the Australian Jan 19 ‘Sky and Telescope’ printed my story about observing the main stars of Ursa Major (Big Dipper) from Noosa Heads , Aust at 26 deg South as a ‘focal point’ item so I am ‘chuffed’ with it. (See details in my account on this website) Of course we don’t see this lunar eclipse in Australia so the local edition did not cover it. The Australian edition, glossy, 8 per year at 84 pages each draws key articles and reviews from its parent but includes a healthy amount of local content.
The answer is a resounding YES. It depends what you want to do with it and I go back to the film days well over half a century ago. You can take ‘happy snaps’ through the eyepiece of bright objects but in this case mobile phone cameras where the lens size is comparable in size to the exit pupil of eyepieces, are likely more efficient. If happy snapping, get as close as possible without bumping the eyepiece, but expect that you won’t get a full frame, just like in the attached Moon image using this method.
Now, if you remove both camera lens and eyepiece, with luck you can achieve prime focus and this is where it really gets interesting because you will be using the main mirror of the telescope as your lens. If your telescope can track your target – even for only around 30 seconds, by cranking up to say 2000ISO you can get passable deep sky images, but beware that the optics need to be properly adjusted. I have included an image with a 6″ F5 telescope of the Eta Carina area and you can see how the focus falls away on one side due to poor alignment.
Now I could rabbit on at length, but the question is what you specifically want to do with it so I will leave my comments there. (If
you wish, you could visit my account site and check out more images. Virtually all are DSLR images.)Like many others I have not seen it. I tried several times in early December – I am 27.5deg South and 153 deg East, but did not see it and then the clouds rolled in. However, though in the hills, I live only 10km from the centre of a major city to my east and the sky is not dark. (At zenith mv 5.3 to 5.4 at best.) I had simply tried in the area using binoculars and 8X50 finder scope and nothing ‘popped out’. People well in the country- and here I am talking 200km away, saw it as a faint fuzz blob with a brighter core and shorter focus lenses recorded it as such.
Now, I am not a great fan of comets though there have been some spectacular ones. Ikeya Seki in 1965, Bennett in 1970, Halley maybe during the Total Lunar Eclipse on 24th April 1986, Hyakutake in 1996, and so on. Though it hung around for a while I wasn’t impressed by Hale-Bopp, though McNaught in January 2007 was great. Now there were many others in this period, some I missed due to cloud, but no others ‘seared’ into my mind.
My experience in looking for comets is to deduct around 2 to 3 magnitudes from the stated brightness and then start looking, since much of the brightness is the fuzzy surrounding coma and a combined magnitude is the one given.
This is particularly so with comets approaching close to the Earth because, being closer the coma is so much more extended. IRAS Araki Alcock in 1983 as it travelled north to south in the evening sky, looked like a fuzzy ill defined tennis ball several degrees across – just a large fuzz blob with no discernable nucleus. Very disappointing!
The diminutive but very active nucleus of Wirtanen only grew a narrow and faint tail but given the geometry (it was effectively at ‘opposition’ when closest), the tail would have been largely obscured by the fuzzy diffuse coma directly in front from our line of sight.
Anyway, for me, clouds again intervened around the time of closest approach. (You see our summer has much more rain and cloud.)
So I didn’t see Wirtanen either, but I don’t think I missed much.Just a few comments from the ‘peanut gallery’ as it were.
In 1978 our Association (Astronomical Association of Queensland) in Brisbane, Queensland Australia (27.5 deg south 153 deg east) conducted a light pollution survey which we repeated in 2018 forty year later.
Needless to say, the membership was generally lethargic, even for something as simple as this involving simple naked eye observing, but we got enough results to show that as the city grew skies deteriorated. The mean limiting magnitude in 1978 was 5.5 and in 2018 it was 4.6. My personal site deteriorated from 5.8 to 5.4. By this statement you will see that it was not a simple ‘star count’ which provides limited information, and in a large area like Orion there can be miscounts and double ups. Besides spanning (from the UK) over 15 degrees in altitude, extinction will play a factor. (See later comments).
However I would like to make my point that we tried to do this as scientifically as we could. The ideal would be to have a scientific device to properly measure it, and the next best would be to have a roving team who would first meet and test their eyes so that they could add a ‘correction factor’. Then they would visit key sites and take the readings. However this sort of exercise is costly and you have to operate with those funds and volunteers that you have.
Anyway, what we did was publish a map of Scorpius with the brightness of the stars marked. This was to be our reference.
The sightings were to take place within one half hour of 9pm during a specified moonless week in July when Scorpius would be nearly overhead. This way we avoided contamination from shopping centres and stuff near the horizon as well as extinction at lower altitudes.
The instructions were to get dark adapted, and first identifying stars that were easy to see, then moving to ever fainter ones until they were no longer visible. A bit of ‘averted vision’ might be used but not ‘wishful thinking’. I remember reporting 5.3 okay and 5.4 with a ‘following breeze’.
Now people’s eyes change with age. There is a grey/green cast which develops and reduces contrast and changes the colour balance. (Fixed by cataract surgery.) So without cross-checking, which in an amateur society is probably difficult, you will have to take the results on faith. There is also the factor that some people like to ‘talk up’ how good their site happens to be, but though you know who they are, you can’t reasonably address this.
I just supply all of this for interest. Orion is easy to identify. It straddles the celestial equator so from your locations would at best be under 40 degrees altitude on average and at a reasonably altitude would be in the South East- South- South West quadrant. If sites had bright developments in that direction, it would badly skew results.
For near overhead at your latitude in early evening, at present there is Capella, but the surrounding star patterns are not distinctive. Might I suggest using Ursa Major in April-May. Nearly overhead early/mid evening and very distinctive. Just print and distribute a map with magnitudes marked, say in your Journal/Newsletter.
I hope my thoughts are helpful.
Last night I had another ‘lull’ in my occultation observing and moved over my 150mm refractor to check out whether I could see ‘the pup’ with the aperture stopped down to 112mm. (The altitude was around 55 degrees.) Okay, I was a bit cocksure and this attitude (pride comes before a fall), clearly deserves what it gets. The weather has changed here and the moist south-easters are blowing. As a result, though okay for occultations, conditions are not appropriate for splitting difficult double stars. Once again I was enchanted by the exquisite diffraction disc and rings of a refractor, somewhat larger when stopped down to 112mm, but while the disc appeared to remain fairly stationary, the rings, whilst still for the most part sharp and discrete were in constant random motion. Most of the problem was the twinkling type random flashing from the central disk. I increased the magnification to X522, and knowing where to look, with the full 150mm aperture could only maybe say that I glimpsed the pup once or twice. I could not say that I really saw it. At 112mm aperture absolutely nothing. And yet on the other occasion just a few days ago with the same instrument, same eyepieces, it was really easy at high magnification! (report above.)
Now what lesson have I learned? Firstly to reiterate, but this time very strongly, that steady seeing (and a clear sky) are essential. Now obviously altitude will play a significant part in the opportunity to achieve this. Because good altitude is a ‘given’ for me, it is quite unfair to directly apply my observations to those possible from northern Europe.
From the appearance last time in the 150mm I would feel that the original claim of visibility with a 130mm instrument is ‘do-able’ under the right conditions. The difficulty is to get those conditions from England where Sirius at 52N latitude rises to a maximum altitude under 22 degrees even allowing for refraction.
This evening there was a lull in my usual lunar occultation work and I turned my C14 onto Sirius. Now my C14 has always suffered from a slight haze on the inside of the corrector plate, and I have never plucked up the courage to remove and clean it like I did my old C8. Further the alignment of the secondary is tweaked to approximately correct to give good star images but is not perfect and in/out of focus images at high power will testify. So what I am saying is the optics are not perfectly clean nor perfectly aligned. Conditions were relatively steady. So I first of all inserted a standard (40 to 60 degree field) 8mm – 24mm zoom eyepiece. At 24mm (X163) the pup was very difficult to see close to the brilliant image of Sirius. It was easier to zoom in to the 8mm focal length (X489) when it stood out so plainly with black sky all around that I was wondering whether I was looking at the correct star. Zoomed out back to X163, (now knowing precisely where to look), I was able to spot it, by moving my eye around the eye lens a little, to cause the rays emanating from nearby Sirius to avoid this area and so reveal the ‘pup’ very close to Sirius. Re-inserting my standard 25mm eyepiece (X156), I managed to repeat this operation.
Now my views on this are, short of using an occulting bar: Firstly, if using a Newtonian, check that the spikes from the diagonal support will not be in the way.
Secondly, ensure that the conditions are sufficiently good to obtain a sharp and relatively stable star image.
Thirdly, don’t muck around with a low magnification. Go straight to 400 or 500 so that the pup will be a reasonable angular distance from Sirius. Only when thus located, scale back and check out the lowest magnification that you can reasonably see it. I would suspect this to be around X150 or a tad less. There is no point trying to initially pick it up at a low magnification!
As I reported earlier in this thread, these results tonight were very similar to those with my 150mm refractor last March, except that the refractor produced a much fainter image and a whole lot of colour from chromatic aberration.
I will try 150mm refractor with the 112 mm aperture stop to see if I can still pick up the pup.
Now I must confess, that tonight I did not play fair at all. Not only was I using the C14, but you probably don’t want to know the altitude of Sirius at around 11hrs 30min when I observed it. I will tell you anyway… around 65 degrees!
So whatever I have recommended should be taken with a grain of salt when you factor in its altitude from your site.
pP
Try again