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I seem to remember commenting on
https://britastro.org/observations/observation.php?id=20201122_230000_68e4171212c0b467
and Martina responding to my comment. Neither comments appear to have survived the transition to the new regime.
No big deal but perhaps it is indicative of something that might be?
OTOH, perhaps advancing senility has damaged my memory.
It doesn’t seem to matter much whether you use a Newtonian or a Cassegrain. That from personal experience and from reading the metadata attached to many images on the web.
What is by far the most important is that the telescope tracks the sky properly. Getting everything mechanically balanced makes the mount’s job much simpler!
Having an autoguider is not essential but certainly makes life immensely easier. Without it you need to have a very well set up and high quality mount and/or take lots of short exposure subs then throw away any which show unacceptable trailing.
A few glitches. In another tab right now I have https://britastro.org/observations/user.php open. It shows me “Showing images 1 to 40 of 8972” rather than just my own uploaded images. Curiously enough, when I first went there after logging on it did as I expected.Although it is clear how to filter by object name, it is not at all apparent to me on how to search by username.
Next was an attempt to find my Barnard’s star upload to see whether animated GIFs work. Setting the search to “Stars” and Library to “Member Images” resulted in a different set being displayed, some of which were tagged as stars. The majority (an image of the “Copernicus area” for instance) did not. Adding “Barnard’s Star” into the object box did not change the results found.
Logging out and logging in again fixed the first problem. I then went to the Barnard’s Star image and found that the animated GIF now works perfectly. Brilliant! However, the comment is now incorrect but if I try to remove it an error response is given
Papers exist on how to convert between the Gaia G, RP and BP measurements to other wide-band systems such as Johnson-Cousins. For example, see Appendix C and its two tables from https://arxiv.org/pdf/2012.01916.pdf for a detailed account.
I have a large number of unfiltered images with stars between 8th and 22nd magnitude, taken with two different CCD cameras. Perhaps I should measure them and see how well they correlated with DR3 values.
What is your budget, roughly?
Are you wedded to any particular optical design (Newtonian, CDK, etc) and any particular mount (alt-az, GEM, fork …)?
Why does it have to be a closed tube? I used a Beacon Hill 18″ Dob very successfully back in the late 80s with a fabric shroud to keep out background light. It had the advantage of no tube currents.
http://beaconhilltelescopes.org.uk/ are still in business and they still ship up to 12″ with a solid tube. You could ask about larger ones.
(though the need to include a decimal point when defining well known lines is ugly)
I know what you mean. It is so much prettier to write 5889.950Å and 5895.924Å than 588.9950nm and 589.5924nm. It means you get to use a non-ASCII character. 😉
To be serious now: my work was done with a spectrograph with a resolution in excess of 300,000. The sodium D lines were separated by about a centimetre at the focal plane. Decimal points were essential, even when using wavenumbers (cm^-1) because the centroids of narrow lines could often be measured to better than 0.01cm^-1.
I used cm^-1 as an energy unit for a few years when doing my DPhil research.
In those units red is about 15000, yellow about 20000 and violet about 25000.
I grabbed copies of AotDS V1,2,5,6,7 a few days ago while they were still available from astroshop.eu, though V6 will not ship until the new year.
Well pleased with them, but the text badly needed a proo-freader [sic] before printing. Now wondering whether to create a list of errata and make it available — assuming that no-one has already done so (I haven’t checked).
Now wondering what will become of vols 8 through 23-ish.
A more serious response this time.
In my view, the arrow of time would not stop, abruptly or otherwise. Everything other than photons, neutrinos, electrons and positrons would have decayed (we do not presently know enough about dark matter if it exists and supersymmetrical particles — if any — to know whether they are stable). However, positronium atoms would still be around, albeit with a typical size of a parsec or more. Plenty of opportunities for them to interact and form structures. So what if it takes petayears for each interaction?
I like Douglas Adams’ take on this:
“In the beginning the Universe was created. This has made many people very angry and has been widely regarded as a bad move.”
At the consumer / beginner level I suspect that the EA telescopes are the future, in the same way that smart phones became the future of the Polaroid Instamatic.
Those who wish to play with the big boys and girls are very likely to have diffraction-limited adaptive optics, automatic plate-solving, DSS charts (or their successors), the Gaia DR4 astrometric and photometric catalogue, and multiple photometric filters with associated analysis data & software built into their scopes as standard. I suspect that cameras which image in the main near-IR atmospheric windows will also become mainstream at an amateur level.
We are going to have to agree to disagree on bias images. As an amateur photometrist I often take Light exposures which vary between a second or few to a minute or few — roughly two orders of magnitude — for each sub. Bright stars saturate in less than five seconds; faint ones are barely measurable after stacking an hour’s worth of subs.
Taking bias frames is a matter of a few minutes work in my experience. Each image has essentially zero exposure time (almost by definition) and at most a few seconds download time. Also in my experience, processing bias frames is essentially cost-free in most (all?) software. After co-adding the bias images to create a master bias, flush their subs to recover the storage.
Very strongly agree with the advice about taking a good number of dark, flat (and bias!) frames to average out the noise. I generally use somewhere between 10 and 100 depending on my patience and the brightness in each filter of the fluorescent panel used for the flats.
You may have gathered that there are almost as many opinions as photometrists…
As far as charts are concerned Aladin and DSS are both free and far in excess of what printed media can realistically provide. I use them all the time and print off what I require as and when it seems like a good idea.
It is more the replacements for Burnham’s and Annals of the Deep Sky with which I am concerned.
I love the smell of old paper in the morning. It smells of contentment. I own many astronomical publications, a few of which are over 200 years old though very few can honestly be described as useful except in very unusual circumstances.
True. I had overlooked the possibility of actions such as detection of outbursts and period searching in time series of observations. Crazy, really, because I generally go unfiltered when observing exoplanet transits.
Hi Darren,
It is truly pleasing to learn of someone who wishes to do science as well as art!
I would strongly recommend getting a Johnson-V filter. It is by far the most used photometric filter and although it is possible to emulate its results by taking images in several other filters at the same time, that process is really not recommended unless you have no choice. It requires more exposure time with complicated calibration and data reduction processes to give inferior results.
Until your filter arrives you can spend your time productively working through the data reduction process on whatever images you have to hand. The results will not be compatible with measurements made in standard pass bands but you will learn much about what needs to be done. There are all sorts of niggles that need to be dealt with, as I have learned the hard way.
