Variable Star Photometry

Back in the 90's I recorded the apparent magnitude of a number of stars known to change their brightness, sending off the information to the British Astronomical Association (BAA). To record the magnitude, I used a pair of binoculars to find the star via a chart provided by the Variable Star Section of the BAA. I then compared the brightness of the target star with stars of known brightness that did not change. All this ended when I broke my binoculars and , at that time, I was not able to afford a new pair.

Zoom to present day.

Two things, one being I have thought I would resume taking some variable star measurements, plus, we are going on holiday to Aquitaine where there should be really dark skies. I toyed with the idea of buying a pair of Celestron 20 x 80 binoculars, but in the end decided the steadier platform of a small Dobsonian would be more pleasurable to use. So, I bought a second hand Sky-Watcher Heritage 130P FlexTube Dobsonian Telescope. It looks like a toy, but has a 1300 mm parabolic mirror that is really good quality. Marrying this to y Televue 25 mm Plossl or BST 25 mm Starguider  and optically, I have a very nice telescope indeed. It is very portable, easy to use for star hopping, has a field of view of just under 3 degrees (with the BST 25 mm Starguider eyepiece) and the only electronics are the red dot finder.

I did a few mods, one ot add some thick grease to the helical focusser, to remove the slop, to add a couple of velcro patches to make the telescope tube cover  more likely to stay on and to  add a little extension piece and a bigger red dot finder to make it more usable, especially for targets close to the zenith.

I have used it to take a few readings of X Herculis and AC Herculis.

I have also tried doing some DSLR Photometry, with the Skywatcher 80 ED Pro. That involves finding the traget variable star (via  Carte Du Ciel), defocussing, then taking images  but making sure the stars are not saturated. I have had one attempt so far, but I think I defocussed too much ( 1 1/2 turns of the fine focus). When I tried using IRIS (from AAVSO), it had problems identifying stars at the registration stage.

So, next time, I shall be trying iso 400, 30 s exposures and  3/4 turn fine focus to defocus.

Solar Astronomy

So, the telescope is sitting htere, it is the time of year when there is no astroniical night, what can I do?

Look at the Sun! So, after buying a pack of Baader Solar film and following the instructions to make a solar filter that fits over the dew cap of the Skywatcher ED 80 Pro, I am no able to take images and video if the Sun in white light. The colour cast in the photo is because I am not bothering to remove the  Light Pollution filter from the camera. So far, because the Sun is at solar minimum, there have't been any faculae or sunspots.

What can be seen (just) is the limb darkening and a hint of the granulation.
Limb darkening is an optical effect seen in stars (including the Sun), where the center part of the disk appears brighter than the edge or limb of the image.

Granules on the photosphere of the Sun are caused by convection currents (thermal columns, Bénard cells) of plasma within the Sun's convective zone. The grainy appearance of the solar photosphere is produced by the tops of these convective cells and is called granulation.

Telescopes come and go

Scope changes......

Even though I really liked the Celestron XLT 6, with my current mount, it wouldn't have been practical to have set up a guider on it, so I decided to reinstate the Skywatcher 80ED Pro and said bye bye to the Celestron.

After a couple of sessions where the tracking was AWFUL, I was contemplating paying the £300 to have the Celestron CG5 GT mount hypertuned.  However, after re calibrating the mount for PHD2 and now using 2 alignment and 2 calibration stars, plus polar alignment (Celestron software via Nexstar +), the tracking has been really good.

Owl Planetary Nebula in Ursa Major

North America Nebula in Cygnus

Ring Nebula in Lyra

Iris Nebula in Cepheus

It's been a while....

1. Not really mentioned it before but since the end of January 2019 I have had an observatory shed ! It is now on Shed 1.1, the main changes being making some of the cabling positions more permanent. The opening roof isn't causing any problems and has been completely water tight . The main issue overall was the adhesive I used for sticking foam seals along the edge of the opening roof hardened and then disintegrated. So, this was replaced with silicone, which hopefully will be more durable and remain flexible.

BBC Sky at Night Magazine Deep Sky Tour

A change from my usual way of doing things. Tonight I followed the March 2019 edition of the Sky at Night Magazine Deep Sky tour, in Canes Venatici and Coma Berenices. I looked at the following object by taking a 120 s  exposure, no stacking. Having found the most interesting looking one, I then took 240s exposures (around 2 hours worth) and processed that in the usual way.

NGC 4565 The Needle Galaxy

NGC 4559

NGC 4274

NGC 4656 The Hockey Stick or Crow bar Galaxy and NGC 4631 The Whale

NGC 4244

The next is 240s x 24 :

NGC 4274 and friends

Via Astrometry.net, this can be solved as follows:

Leo Triplet

This is the first image taken with the Skywatcher ED80 in a while. Had a few problems getting the  Celestron CG5 GT mount to track anything like accurately, so that I could use guiding. The problem seems to be the cabling was too tight, the mount wasn't  'East heavy' (so the gears are in constant mesh) and maybe other things since  the tracking is still not as good as other people get. I need to save the pennies and get a NEQ 6 Pro I think!

Anyway, this pic is based on 170 x 60s lights, and the usual flats, darks and bias. I think the gradient is caused by some ambient lighting (I have a red light on in the 'shed' (= Observatory!). Mental note to self - turn it off!

Triplet of Galaxies in Leo

The Leo Triplet (also known as the M66 Group) is a small group of galaxies about 35 million light-years away in the constellation Leo. This galaxy group consists of the spiral galaxies M65, M66, and NGC 3628.

While I was waiting for the Triplet to cross the meridian, I also took a few exposures of the Whirlpool Galaxy:

Whirlpool Galaxy 

The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. Its distance is estimated to be between 15 and 35 million light-years.

Celestron XLT 6 as imaging telescope

Owing to changes at home, it was going to be really difficult to get the tripod plus ED80 outside easily and safely, so I thought that I would get myself a smaller more portable telescope. I came across a Celestron XLT 6, which seemed to fit the bill. I  have spent a few very interesting nights just observing, anything and everything from asterisms to double stars, nebulae etc. The Celestron is a beautiful piece of optical machinery! My only complaint has been that it is not a 11 or 14 inch! When I compared it with the ED80, even thought the ED80 is acknowledged to be a great telescope for a beginner to do wide field deep sky astrophotography, it is definitely lacking in resolution compared with the Celestron.  Last night, I tried taking some images with the Celestron, which was made more difficult by having  to set up the finder, camera and then find out how to focus it accurately (software was being difficult!). Anyway, in the end I managed to get 3 useable 30 second frames and the photo below shows the result. Compare this with the one If did last year using the ED80. Some way to go I think !!

Orion Nebula seen via Celestron  XLT 6 (but only 3  30s frames, no calibration frames at all)

Orion Nebula via a Skywatcher ED80 (45 x 45s with calibration frames)

Even though the image is rubbish, it does hold some promise for what I might get with a good series of frames , plus a full set of calibration frames. The field of view is narrower and the resolution higher.