Archive for October, 2012
A group of amateur astronomers using the Foulkes Telescope think that they have seen Comet 168P/Hergenrother start to fragment.
Here’s the path of the Comet from now until the end of November.
Just above the Square of Pegasus and to the right of Andromeda.
Location shown at midnight on the dates shown. Click on image for bigger view.
Images of Comet 168P/Hergenrother taken by the team possibly showing a fragment breaking off.
This could explain why it suddenly brightened a number of weeks ago from 18th to 10th magnitude as it passed its closest to the Sun.
All that remains now is for us to keep an eye out on it and see what happens next.
Comets, always fascinating, certainly unpredictable.
Taking images of the night sky doesn’t have to be complicated and you don’t need any specialist equipment to do so.
Following this guide will allow you to produce images for yourself without having to take out a second mortgage just to take many fabulous and rewarding images. It can be done using the simplest of photographic equipment.
1. A camera.
Any camera that is capable of taking an exposure of more than a few seconds exposure is capable of taking images of the night sky. Small compact cameras sometimes have a Program or Night Landscape mode. This automatically sets a long exposure of a few seconds and focuses the camera at infinity.
Some nice constellation images can be taken this way. The image below was taken using such a camera using Night Landscape Mode and shows Taurus quite nicely and the star colours of Aldebaran, Betelgeuse and the Pleiades Star cluster.
A DSLR has far more flexibility in what you can achieve, so is the preferred option if you can afford one. There is a lot of dispute on the Internet regarding the different makes of DSLR that are ideal for taking astronomical images. Most people seem to regard the Canon range as being the best, with lots of talk of the Nikon stripping out data when it takes an image. If you have a Nikon or other make of camera, excellent images can still be taken regardless of the make. Most of my images on this Web Site have been taken with Nikon cameras, so there is no necessity to change camera if you already have one to hand.
However there is a lot of third party software available for the Canon range, so if you are considering buying your first camera, I would recommend a Canon for this reason only.
Make sure that you set your camera so that it does two things:
1. Doesn’t use long exposure noise reduction.
2. Saves the resulting image as a RAW file.
(I save my images as both large JPG and RAW, you will see why later).
Also set the ISO setting to at least 400 or preferably more (800-1000).
The higher the ISO setting the brighter the resulting image and the fainter the object you record in less time, but you also get more noise on your image.
The lower the ISO setting the darker your image, and the longer the exposure needed to see faint objects, but you do get less noise on your image.
2. Lenses. The lens you use will determine what you capture. A wide angle lens ~20mm will show a wide expanse of sky (i.e. a wide field of view). A 100mm lens will show a much smaller field of view. A variable focal length lens will enable you to frame different constellations better, but the quality and f-ratio is normally less. A bigger F-number will produce a fainter image, and will need a longer exposure.
3. A sturdy tripod. Holding the camera still is essential. You need something that will hold the camera steady for the extent of the exposure. You don’t necessarily need a full sized tripod. A Gorilla Pod, or something like it, can also be used. A mount like this is light and portable and will enable you to mount the camera on any convenient sturdy support. I have managed to take Milky Way shots with my DSLR on holiday this way, with the camera supported on the back of a Sun lounger.
4. A means of making long and multiple exposures. Many cameras are only able to make exposures of up to 30 seconds on their own. To take images of faint objects, you need to make exposures of a minute or more. To achieve this, you can buy accessories which can be used to make longer exposures. These can be as simple as an infra-red release which will open the shutter when first pressed, and close the shutter when subsequently pressed. An attachment for the camera can be more complicated and will enable you to program the camera to take a number of images one after another. This method of taking images is almost essential unless you want to stand there and keep releasing the shutter manually. As I know from experience, this does become somewhat tedious after a few hours.
Taking Your images.
Now we have really come onto the business end of things. Let’s assume you’ve got your camera mounted on a tripod and are out under a clear sky. Pick an area of sky you are interested in and point your camera towards a familiar constellation. If you have a variable focal length lens frame your chosen area of sky accordingly.
At this stage you need to know two things:
The shorter the focal length of lens used, the brighter the image and the less star trailing is visible.
The longer the focal length, the fainter the image and the more star trailing is visible.
Take an exposure of about 20 – 30 seconds. You may find when you look at your resulting image, that the stars are more than pinpricks. Even if you set your lens to infinity (which is where the stars are) your lens may still not be properly in focus. You may need to experiment a few times and adjust the focus to get really pin sharp stars. Once you have achieved proper focus, you can now take your images.
Take a number of exposures of the same object and vary your exposure in each one. Take images using 10 seconds up to 1 minute exposures, increasing each exposure by 10 seconds. Inspect each image and note at which exposure you can start to see star trailing.
You will have then found the maximum exposure you can take before trailing is visible with that focal length lens. (As a rough guide if you use a 20mm lens you can get away with about 45 seconds exposure before the star trailing as a result of the Earth’s rotation starts to show).
Once you have found this, take a number of exposures at that same setting, pointing at the same chosen point in the sky.
Without touching the lens, move the camera to a different point in the sky and take a number of images in the same way. If you do change the focal length of the lens, you will need to check your focus once more before continuing.
Processing Your Hard earned images.
After a few hours you should have a few sets of “almost” identical images on your camera.
Now comes the fun part in getting the data you have captured so it gives you a pretty picture.
I use two pieces of free software to help me process images:
This is a nice piece of software which allows you to add image together. As its name suggests, it enables you to add images together to produce star trail pictures. If your camera is static on a tripod (as yours currently is) the stars are moving across the sky due to the Earths rotation. This means that between each of your exposures, the sky has moved. If you take enough images and put them into Startrails it will show the difference in the stars position and you will see the movement quite easily. The use of JPG’s that I suggested earlier would be better for this as they are smaller images and more easily handled by the Startrails software. To show you how it works, below is a 20 second image of Aquila taken with my DSLR from a dark sky site in Wales. It doesn’t look very exciting, does it? I took 17 images exactly the same and dragged them into Startrails. The resulting image is shown second . That does look a little more exciting now, doesn’t it?
Startrails enables you to see the movement of the stars and produce star trails just using the images you have already taken. You can also see the colours of the stars in an image like this too.
Startrails will also produce an animation of the stars movement as an AIV file as well if you want it.
Deep Sky Stacker (DSS): http://deepskystacker.free.fr/english/index.html
Now things get really exciting. Using the very same 17 images RAW images of Aquila shown above I pulled them into DSS and processed them. Unlike Startrails, DSS looks at the images and determines where the stars are. So when it processes the images, despite the fact that the stars have moved between exposures, it will register the stars on top of one another and add the images together. As a result of this faint objects you can hardly see on the original images are made brighter as the data is added together. the image below shows the result of stacking those same 17 RAW images of Aquila together:
Now you can see the bright band of the Milky Way and the dark rift at the side of Aquila.
If you look carefully you can also see the Coat Hanger in Vulpecula.
I’m sure you will agree that this is not a bad result for a camera standing static on a tripod.
Go on, give it a go.
You won’t be disappointed.
Although it won’t become anywhere near as bright as the two comets expected next year, Comet 2012 A2 (LINEAR) will pass close to The Pole Star in November. Currently in Draco it is about 13th magnitude. It passes close to Polaris on the 23rd of November.
At this time it should have gained a magnitude at about magnitude 12.
By Mid December the comet will be close to the star Alrai (Gamma) in Cepheus.
As it will be so easy to find at this time, I know it’s faint, but go on, give it a go.
Path of Comet 2012 A2 (LINEAR) end of October until the end of the year.
(Comet moving from left to right).
(Click on image for a bigger view).
I attended the Back to Basics meeting at Bedford School on Sunday.
I started the day directing arrivals to the car park. Once that stint was over, I was free to enjoy the rest of the day at leisure.
One couple I spoke to came from south of London.They were complete beginners, and keen to learn more.
When we arrived someone had a PST set up on the lawn where we caught quick views of the Sun in Hydrogen Alpha.
Some small prominences were visible.
The meeting was introduced formally by Peter Hudson.
The speakers were:
So what astronomy can I do? – Martin Morgan-Taylor.
Resources – Bob Marriott.
Solar Observing & Workshop – Peter Meadows.
We then stopped for a very nice lunch in the school dining room.
Lunar Observing & Workshop – Martin Morgan-Taylor.
Planet Observing & Workshop – Michael Foulkes.
Simple Astronomical Imaging – Tony Morris.
Meeting closed by Peter Hudson.
Overall I felt that it was a very good introduction to many of the subjects.
At times I felt that the one or two of the speakers assumed people were a bit more advanced than they thought and took them down paths that were well beyond the basics. This could have confused people even more if they were hoping for some gentle guidance and listening to one or two comments from the audience confirmed my thoughts. But I do realise that it is very difficult to pitch talks like this to the right level.
However, I thought that overall though the day was extremely enjoyable and great value for money.
There was a lot of information given out (a few more handouts would have been more beneficial to take that information away) and a quick poll to a couple of people as they left gave the impression that they had really enjoyed the day and had got a lot of extremely useful information from it.
I must say, as one who struggles to make drawings, I really enjoyed the practice at trying to sketch Jupiter and the Moon. I found that I could “almost” reproduce what I could see on the screen. Whether I could this quite so well at the telescope remains to be seen.
Many thanks to all the speakers who gave their time to talk to make the day extremely enjoyable and also very informative.
And of course the same to members of Bedford AS who supplied the copious amounts of tea and biscuits throughout the day.
This newly discovered asteroid passes close to the Earth on the 12th.
It will approach the Earth to only about 57,000 miles on that date.
Apologies, but I put incorrect details of its position previously.
It is just above Corvus, so very difficult to image, especially from the northern hemisphere…
Minor Planet 2012 TV passes close to the Earth about 2/3 the distance of the Moon this weekend.
The 40m rock will become a 13th magnitude object.
Unfortunately for observers in the UK the object is too far south to be seen.
It moves rapidly north in the constellation of Antlia, moving into Hydra and into Corvus where it’s brightness will rapidly fade and its apparent motion slows down.
I have generated this map to show the movement of the object over the next couple of days.
Comet 168P/Hergenrother brightens as it moves northwards through Pegasus.
It wasn’t expected to get above 15th magnitude, but it suddenly decided to erupted to about 10th magnitude.
Similar to Comet Holmes did a few years ago.
I took this animation on the 6th of October of it moving northwards.
This brings it easily in range of most amateur telescopes.
Easily visible in my 7.5 inch Mac Newt in my light polluted skies looking ever so slightly fan shaped.
I took this image on the evening of the 6th of October and show it has developed a small tail.
Following on from the news about two possible extremely bright comets in 2013.
See details here for details of their celestial paths over the coming months.
My Observers guide to Comet ISON for later this year and into 2014 has just been published. It is currently available on Amazon Kindle download:
Now no longer available, as ISON met its demise when it went too close to the Sun..
I have run Sky Safari to try and see what the comets MIGHT look like from the UK next year.
Please note that these are ONLY A REPRESENTATION and the comets will undoubtedly look much different to the images shown here
I have also produced some animations of their possible appearances here.
In all likelihood the tails will be curved due to the speed of the comet around the Sun, particularly with PANSTARRS.
Will they have a single ion tail, a separate dust tail, or multiple tails.
No-one can really tell at this stage?
Comet ISON C/2012 S1. Is currently very faint at magnitude 18 in Gemini.
Unfortunately for both comets, when they are at their brightest next year, they are quite low in the sky.
I have made these images to show them at their brightest at a reasonable height above the horizon.
These images are for central UK, but they can be used for any location in mid-northern latitudes.
Comet PANSTARR C/2011 L4
The comet is fairly close to M31, the great Andromeda Galaxy around this time.
COMET ISON C/2012 S1. This comet has now been downgraded a bit and may not be “quite” as bright as was initially hoped. But even with the downgrading of brightness it should still be a fabulous sight.
View Looking West on the evening of the 18th December 2013. 16.00h.
If these predictions are correct? WOW!!!
Let’s just keep those fingers crossed.