I don't like maths but it's time to get serious with my observing. Tracking down faint fuzzies (galaxies, nebulae, etc) is tricky at the best of times, but even more so when you are hunting for the Herschel objects, most of which are very faint. The tried and tested way is to star hop, ie, start from a star you know and work your way across to progressively fainter stars till you find the target, or more likely don't find the target.
Working in the dark is the first difficulty. You can use a faint red light to read star charts and descriptions, but it's amazing how unhelpful they often seem to be when you are in the field. Also, the charts show the stars in the position they actually are in the sky but the finderscope (the little telescope on top of the big telescope) inverts the image left to right and top to bottom. You use the finderscope in conjunction with binoculars, which don't invert in any direction, but then the telescope view is inverted left to right but not top to bottom.
Binoculars = N up, S down, E left , W right,
Finderscope = N down, S up, E right, W left,
telescope = N up, S down, E right, W left.
Since all stars look pretty much the same, it doesn't take long before you are driven mad by this.
There's also a description you can follow to star hop to the target. Remember this little globular cluster the other day, NGC 6229?
Here's the instructions I followed to find it: (O'Meara's Guide to the Herschel 400)
"Find star 52 Herculis, which is 7 degrees north of 3.5 magnitude star Eta Heculis. It forms the north eastern apex of a near equilateral triangle with the 4th magnitude stars Sigma and tau Herculis. Move 40' north-north east to 7th mag star alpha. Now make a slow sweep 1 degree north west to a pair of 8th mag stars oriented north northwest to south-southeast and separated by 5". NGC 6229 is only 5' east-northeast of the pair."
You can easily lose an hour this way.
What helps a bit is knowing what a degree, a minute (1/60th of a degree) and a second (1/60th of a minute) looks like through the binoculars and scope - in other words what the field of view (FOV) is - but each time you change the lens, the FOV changes too. I've finally worked it all out properly, rather than just guessing all the time. Here goes:
15X70 relelation binoculars: FOV 4.4 degrees. The moon is half a degree, so you could fit 8 moons side by side.
My telescope has a 10" (254mm) diameter mirror, and its focal length is 2500mm. That means light from astronomical objects are brought to a focal point 2.5 m from the lens.
But, you say, the scope isn't 2.5m long.
(Previous post 4 years ago)True, but it's a Cassegrain Schmidt scope, which uses a convex secondary mirror and a corrector plate, which, simply put, "trick" the main mirror into behaving like one of a much shorter focal length. Or as I said on the previous post, even more simply put, the scope's wearing glasses.
Without the glasses the tube would need to be this long!
Magnification is a product of the focal length of the main mirror and the lens used.
Here's my main deep sky lens. It's a super quality lens, the 40mm TeleVue Plossl. (review of all the lenses here). Cost: £110, now, though can't remember what I paid 23 years ago for it.
(modelled, as always, by the ever-helpful UniM)
Its focal length is 40mm. 2500mm divided by 40mm = a magnification of 62.5X
The apparent view of view of this lens - ie how big the circle of light is when you look through it with the naked eye, is 43 degrees. The actual FOV (AFOV) is the FOV divided by the magnification, because obviously, if you magnify something eg 10 times you zoom in 10 times and can only see a tenth of what you could previously.
So, 43 degrees divided by 62.5 magnification gives a field of view of ... 0.688 degrees. The moon is half a degree, so through the scope using the Plossl, the full moon will almost 3/4 fill the field of view.
You can see the value of knowing this for faint fuzzy hunting. When the instructions say "make a slow sweep 1 degree north west from star Y, you know how far to go. To move the star from the centre to the edge of the FOV = 0.35 degrees (half of 0.688) and then you need to move the same distance again twice, ie a total move of 0.35 x 3 = 1 degree. Sorted!
This is my mid-power lens. The Meade MA 25mm, 40 degree FOV. It's not a particularly good lens apparently (£33 new: a lens for the "price-conscious amateur." That's me) but it's a proper workhorse, and has served me well for 23 years. Leaving it in a wet garage for 3 years hasn't made it prettier but also, luckily, hasn't affected its performance.
I'm sure you can work out the magnification now:
2500mm / 25mm = 100X.
And the FOV is 40 degrees so AFOV is 40 / 100 = 0.4 degrees. The moon, then would completely fill the view through the scope
This is my top lens: the Meade Series 5000 UWA (Ultra Wide Angle) 6.7mm lens, costing £170. 275g of quality glass.
Magnification: 2500/6.7 = 373X!
FOV = 82 degrees, so apparent view is 82/373 = 0.22 degrees. Notice that it gives almost 4X the maginification of the MA lens but still gives over half the field of view of the MA.
Summary (for me,as much as for anyone else)
How marvellous! While writing this post I stumbled across this eyepiece, which I'd never used before.
It turns out to be a really super one for deep sky work. It's 125 magnification but is wide angle and gives an AFOV of over half a degree, significantly more than my 'workhorse' 100 mag. lens
Ah, I do love a planetary nebula. It's "a kind of emission nebula consisting of an expanding glowing shell of ionized gas ejected from old red giant stars late in their lives. The word 'nebula' is Latin for mist or cloud and the term 'planetary nebula' is a misnomer that originated in the 1780s with astronomer William Herschel because when viewed through his telescope, these objects appeared to him to resemble the rounded shapes of planets. Herschel's name for these objects was popularly adopted and has not been changed. They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years."
Last night the skies were clear and dark, and I managed to bag these two beauties. My astro-sketching is definitely improving; this is a good approximation of what I actually saw last night.
And the Blinking Nebula is so called because when you stare at the central star the nebula seems to disappear, but reappears when you use peripheral vision.
Agian, this is a pretty good impression of what I saw:
This is the best map I've ever seen for identifying how much light pollution is in your area.
You can zoom right in. Live in London? forget dark skies; you live in permanent light. Old house in Hatfield marked with the circle. No wonder I could never see anything apart from Moon planets and the brightest stars:
New home: I'm not allowed to say exactly where we live - UniM fears kidnapping - but suffice it to say we are in the square and on the edge of one of the blue regions. Happy days! Skies seem pretty dark just from the garden and I still haven't had the chance to get out into the countryside to see how much better it is there.
Back in December 2007, I started the Herschel 400 challenge. Here's what I said at the time:
I've recently embarked on The Herschel 400. This is a long-term astronomy project to identify 400 galaxies, star clusters and nebulae. Sir William Herschel was the top astronomer of his day; with the help of his sister Caroline, he discovered and catalogued over 2500 deep sky objects in the 18th Century. Many of these objects are too faint to be detected by amateurs, so in the late 1970's the Ancient City Astronomy Club (ACAC) in Florida created a list of 400 of the brighter objects to develop and test the observing skills of "advanced astronomers living in the Northern Hemisphere." (I'm not saying I'm an advanced astronomer at the moment, but I will be by the end of it!)
In theory, it could be done in a year but realistically, it's likely to take 2 - 3 years. There is a great account here by someone who took 18 years.
I set up a new blog to record my observations and managed around 50 or so objects but then gave up. It became just too demanding to dismantle the the huge scope and drag it into the car to drive 40 + miles north of Hatfield in search of half-decent dark skies, especially when, as often happened, the sky clouded over on arrival, or it was too windy to set up. Stupidly, I deleted the blog, sure that I wouldn't complete the challenge and moved on to other things.
Well now 7 years on, I live in those dark skies and I'm starting over again! This time I'm going to record every observation, and post it up either here or on another new blog. Ideally I would use the big scope, the 16" diameter one, but it's not on a driven mount ie you have to hold it in place and the object quickly drifts. This makes observing difficult, drawing very difficult and photography impossible, so I'll start with the 10" and see how we go. I've not yet experienced fully dark skies from the new garden yet, as the summer skies never get complely dark, but current indications are that it's going to be fantastic, so I'll be able to sit in the comfort of my own garden tracking down and recording all the 'faint fuzzies' in the H400. Marvellous! I won't start properly until the MA is finished, which will be in early September, but I've already bagged a couple. Here's the globular cluster (a tight ball of stars) NGC 6229. It looked exactly like this through the eyepiece:
Its magnitude (brightness) is around 9.4. The faintest stars visible to the naked eye from a dark sky are around 5.5, and each increase in magnitude number equates to a drop in brightness of 50% , so this cluster is er 16X too dim to be seen with the naked eye. It lies outside the milky way, at a distance of 102, 000 light years.
Ok, the plan is to record all the Messier objects (previous post) over the next year. Here's my first, the open cluster, M34:
If you don't look too closely you might think it's a photo, at least for a few seconds (or maybe I'm just kidding myself). Anyway, it's actually my first attempt at a "sketch" using Photoshop. I recorded the postion and brightness of stars at the eyepiece using pencil and paper, then photographed the result and used the paintbrush tool on Photoshop to make it as realistic as possible. The main stars at least are pretty accurately placed. Why digital sketching? Astrophotography is a very exacting and time-consuming business, and deep sky imaging is exponentially more tricky than planetary work, so given my lack of spare time at the moment I'm settling for this way of recording what I see. Actually it's very exciting to get back to 'proper' observing and let the photons hit the eye rather than the sensor. Lots more to come!
"It's a thing for attaching a thing to" says David.
I think that's close enough for the chocs.
I've always wanted to mount my binoculars but didn't know how to go about it, but now I have my universal adapter it's a piece of cake:
These are 15X70 Revelation bins. Think astronomy has to be an expensive hobby? Think again! These are now on Amazon at £53 including delivery. The 70mm objective lenses and 15 times magnification give amazing views of star clusters and also show dozens of galaxies and nebulae. My plan is to use these in conjunction with the 10" scope to find and record all the Messier objects over the coming year:
The Messier objects are a set of astronomical objects catalogued by the French astronomer Charles Messier in his "Catalogue des Nébuleuses et des Amas d'Étoiles"("Catalogue of Nebulae and Star Clusters"), originally published in 1771, with the last addition (based on Messier's observations) made in 1966.
Because Messier was interested in finding only comets, he created a list of non-comet objects that frustrated his hunt for them. The compilation of this list, in collaboration with his assistant Pierre Méchain, is known as the Messier catalogue. This catalogue of objects is one of the most famous lists of astronomical objects, and many Messier objects are still referenced by their Messier number.
The first edition included 45 objects, with Messier's final list totaling 103 objects. However, Messier 102 was not reported correctly, bringing the total to 102 objects. Other astronomers, using side notes in Messier's texts, eventually filled out the list to 110 objects.
It's interesting to see how the media covers science and space stories. It seems they either skip over them in seconds ("boffins land a spaceship on a comet! And now on to sports news") or they completely misrepresent a story. Today's 'supermoon' falls into the latter category. There are pictures like this in the press:
Mark J Terrill/AP
Well, it's only "surreal" because they used a big lens.
Here's my pic, taken half an hour ago.
Marvellous! But the magnification is 80X...
The moon is usually around 30' in apparent diameter. That's half a degree. Your little finger at arm's length covers around 1 degree, so half a little finger will block out the moon. Tonight the moon is around 14% bigger. That means it's around 1 mm bigger as measured by your finger at arm's length. It's a lovely sight tonight, and about 30% brighter than usual:
But stories like this in the Independent are frankly insulting.
And the Express article here is just plain silly. They actually quote the Bible: Joel 2:10 states: “Before them the earth quakes, the heavens tremble, the sun and the moon grow dark and the stars lose their brightness.” They then say some believe this could trigger the "End Of Days."
The Bible gives terrifying warnings of impending doom signalled by rare and foreboding cycles of the moon. Well, yes, but these cyles aren't rare, they happen every 13 months...
"Pastor John Hagee, author of the controversial book Four Blood Moons, maintains messages in the Bible say God “does actively control the sun, the moon and the stars in order to speak to us”.
He said unusual lunar patterns are a signal “that something is about to happen that will change the course of history”.
Er, well that's as may be (controversial = barking mad) but this isn't unusual, it's part of a regular cycle. Read more about the pastor here. It's funny but scary, as he's one of the most influencial religious figures in the USA.
More from the Express (shame on you) The supermoon is coincidentally timed to virtually clash with an annual explosion of ‘fireballs’ due on Tuesday.
Exposion of fireballs? Oh you mean the dust-sized particles which form the Perseid meteor shower?!
Then the Bishop of Greater London is quoted as saying there is nothing to fear and is seeking to "allay fears over an impending armageddon."
Words fail me.
Here's my vid of the moon tonight. Amazing how fast it's moving (real time) . Maybe Pastor Hagee is onto something....
Although I'm under self-imposed 'house arrest' in order to complete the Masters, I do pop out occasionally. I had a quick wander around the Paxton Pits a couple of days ago and got some nice close up footage of this common UK bird. What is it? I expect everyone to know, but if not, click on the link below. (Oh dear, I say "common" but a quick look on the RSPB site says it is now a Red Status bird, meaning it's in severe decline)
Alan T sent in this great photo of a dragonfly.
"I’m no expert obv. Nice bright one though, at Worth Matravers in Dorset."