Binocular Messiers

You may remember way back in 2014 I wrote about Charles Messier and his list of comet-like objects. I also mentioned that I’d started tracking them down with binoculars, and that was a while ago, so what’s happened since?

I’m still working to my usual leisurely pace, but I’ve collected good observations of 60 of them now. This year would be a great time to finish this project since it’s the 200th anniversary of Charles’ death. The BAA are encouraging observers to complete a Messier Marathon, or at least view all the objects this year. Perhaps I will.

I’m basing my work on the Astronomical League’s Binocular Messiers Program that rate 102 of the 110 to be observable with binoculars. I’ve set the additional challenge to observe as many as possible from my north-west facing back garden. This is one reason why it’s taking so long to complete the project: some objects have a very short window of opportunity. That said, I seem to have managed a couple they don’t think I should be able to see, but I stand by my observations ;-), and having observed 58 from their list have 44 left to go.

Unfortunately most of those are pretty low in the sky from the UK. For example, I snagged M41 in Canis Major a few nights ago as it briefly appeared from behind the row of houses before falling into the trees, and all whilst standing on top of a wall peering through the undergrowth. On the other hand I couldn’t have done that with a telescope! I’m very glad that M41 is big and bright or the Industrial Estate light pollution would have rendered it invisible.

Image Credit: M41 by Digitized Sky Survey (DSS)
Image Credit: M41 taken from the Digitized Sky Survey (DSS) using Aladin Sky Atlas.

The upcoming galaxies of Virgo and Coma Berenices may cause some problems. I’ve observed all the brighter ones and have the trickiest to collect on a night of really good transparency. I’ll have another go at M108 and M109 in Ursa Major on that night too.

Then I’m down to the horizon huggers of Scorpio and Sagittarius below 25° altitude. I can’t think of anywhere around my house that they’re possible. Not the street outside, our front bedroom window, they’d probably be difficult from the roof. So I’ll have to start being mobile to mop the rest up, and perhaps that’s the time for a marathon?

The Scale of Space

On Monday night I took part in one of my Society’s outreach events for local Cub Scouts. These are a challenge. The Cubs meet around 18:00 and go home to bed before most astronomers would be getting started. It’s a very small window for clear skies in the cloudy and damp UK climate.

We aim for around the first quarter Moon since it’s there in the very early evening, it can take light cloud and the kids love to look at the Moon. I’d observed it on each of the previous three nights, which is not a common occurrence in these parts, but on Monday it wasn’t just cloudy, it was pouring with rain.

So what do you do with a 25 Cubs Scouts on a rainy evening in February? Our normal fallback plan involves Stellarium and a talk about the constellations and planets, but it’s a good idea to get the natives moving occasionally or they get restless!

As the Secretary of the Society I’m kinda expected to take a lead in things. So after a quick sky tour of the constellations and how to find the pole star I decided to try something new to me, and I hoped the Cubs: modelling the solar system.

Collectively we marked out the location of each of the major planets in turn on the hall floor – with sticky labels that are easily removed – on a scale that placed Neptune 15 metres from the Sun. I would have liked to include the Kuiper Belt, but the hall wasn’t long enough, and a smaller scale would have seriously crushed the Cubs representing the inner planets!

These Rocky Inner Planets were all squeezed into the first metre with the Gas Giants in the next four and an awfully lot of space for the Ice Giants. I have to admit that I’ve never laid it all out like this before and the spacing was impressive.

The Sun, which Copernicus pointed out, is at the centre of it all and represents most of the mass in the Solar System. It’s about 109 times the diameter of the Earth, but what really fried a few noodles was the discovery that on this linear scale the Sun is only about 5mm in diameter, or the size of a modest peppercorn!

Sun in the palm of my hand
The Sun to scale in the palm of my hand

That makes the mighty Jupiter around 0.5mm in diameter. I couldn’t find a spice in my cupboard that was small enough for this, and the other planets will be virtually invisible, like fine dust.

It makes you appreciate why it takes so long to travel between the planets. Interplanetary exploration involves a lot of waiting.

My Variables Stars

As a follow up to the post on starting out observing variable stars I thought I’d talk about my journey.

I started variable star observing about four years ago with the naked eye and the 10-Star tutorial. I soon moved on to binocular variables, to which I’ve added a smattering of telescopic Mira variables now.

As you can see below, fuelled with enthusiasm soon clocked up 200, receiving a certificate from the AAVSO for my first 100, which was unexpected. Then the observation rate started to drop for various reasons including the appalling weather, British summer time (these two are often linked), and the pursuit of other astronomical interests. It stalled drastically after the first 600.

120 day binned cumulative variable star observations
My variable star observation count up to 19 January 2017.

Well at the end of 2016, I decided it was time to pick up the slack and at least push through the 1000 observations barrier, which I did on 5 October 2016. At the time I generated the chart for this post I was handful short of the 1100 observation mark, but another clear night has put me well over the top.

Choosing my variable stars

I’ve got a telescopic aperture limit of 6 inches and a relatively light polluted site so those exciting, but faint, cataclysmic variables are off the menu for me. Eclipsing binaries are fine, but the most valuable observations of these are CCD photometric these days: visual observers need not apply. Most of my efforts are aimed at Long Period Variables (LPVs) with a few other types thrown in for variety, and delta Cephei for nostalgia.

I choose variables to suit the magnitude range of my equipment and by constellation. The latter allows me to concentrate my effort in a smaller area of the sky: it’s an efficiency thing. I also have favourite constellations: it’s a personal thing, and possibly pragmatic too 😉

My back garden has a terrible horizon for an amateur astronomer. Houses block most of the lower 30 degrees of the sky to the south and east, there’s heavy light pollution to the west now from an industrial estate, but I’ve a much better northern horizon.

For that reason I tend to favour circumpolar constellations that are accessible all year round, providing an unbroken record of observations. I’m concentrating on Cassiopeia, Cepheus, Draco, Ursa Minor and Ursa Major.

There are currently 49 variable stars on my observing list of which I have to admit only 30 get regular attention at the moment, and all of those are in the constellations mentioned above.

Making observations

I use a combination of instruments depending on the brightness of the star and the sky conditions.

I can monitor variables with magnitude brighter than 5 with my naked eye (as long as I’ve got my glasses on!). A pair of 2.1x binoculars extends this to 7, but from around there down to magnitude 9 can be handled by a 10×50 binocular on a good night, and 15×70 binoculars for the fainter end on a night of poor transparency.

These can be pushed to magnitude 10, but around that I fall back on my first telescope: a Skywatcher 130P (130mm F5) newtonian. With the right eyepieces it provides good 1 and 2 degree field of view, which is plenty of room for the variable and comparison stars near the centre.

My final limit is about magnitude 12–13 depending mostly on altitude and transparency.

A good example is the recent CTA 102 quasar which reached around magnitude 11.5 and should have been possible. But by the time I had a clear sky – bad weather – CTA 102 was low in the western sky glow and had faded to magnitude 12.7. With the Moon right on its doorstep it proved just too faint for any of my telescopes. I suspected as much, but its not every day you get the chance to see something eight billion light years away with your own eyes, so I had to have a go! I found the field stars, but no quasar. I could have filed a “fainter than” observation, but it didn’t seem worth it when I was limited to 11.4.

I try to observe these rare opportunities – the Nova V339 Delphini and SN2014J in M82 spring to mind – as they’re not often within my range of magnitudes or a part of the sky I can see.

Making regular observations of selected stars really has its benefits though, quite apart from the fun of following their progress. Practice makes perfect and with the comparison stars fresh in my mind I can manage one observation every three minutes, which is quick by my meagre standards, and maintain this rate for a couple of hours.

I just noticed on the AAVSO website that I might get another award for the first 1000 observations. I also noticed that the next milestone is 5000!