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Observing >> Variable Star Observing and Radio Astronomy

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Adam S
scholastic sledgehammer
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Reged: 12/21/05

Loc: Gunnison, Colorado
What do you wish you'd been told about.. new
      #6291451 - 01/04/14 10:29 AM

I've been observing with refractors for about 35 years, I can find about half of the Messier list without an atlas, I take reasonable astronomical images so I've got a solid base for the next astronomical pursuit. In enjoy imaging but I'm finding it to be be a little impersonal for myself and astronomy. I miss being at the telescope under the stars.

Over the last several months the idea of estimating variables has grown and I'm going to pursue it.

I've navigated the AAVSO site and am good with making charts and finding the obvious candidates (will start with the 10 star tutorial).

I've got three questions:

As experienced variable observers (or someone who's new and developing) what advice do you wish you'd been given when at ground zero and never made an estimate?

Second question, I use either a four inch or five refractor for observing. The both have a focal length of 819mm. What magnifications do you recommend? I did a quick look at Betelgeuse the other night and felt like a 20mm at 40x with 1.8 deg matched AAVSO's Chart B nicely.

Lastly, is there a book you recommend? While the AAVSO site seems to have everything you'd need, I'd still be interested in a book with charts, magnitudes etc.

Thanks in advance,


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lee14
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Reged: 12/19/09

Re: What do you wish you'd been told about.. new [Re: Adam S]
      #6291511 - 01/04/14 10:49 AM

As far as eyepieces, I use the lowest power necessary, since that yields the widest fov and allows for more comparison stars. I use a 32mm Televue widefield to identify the field (63X) and make the estimate if the candidate is visible. If the variable is faint, I'll go to a 12mm Nagler. On occasion I use a 9mm Nagler if the variable is near the threshold of visibility. The higher powers increase contrast by darkening the sky background, and also spread the the light over a small area which makes for an easier comparison than two point sources. Likewise, it's often helpful to slightly defocus the field to make comparisons.

Lee


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brianb11213
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: What do you wish you'd been told about.. new [Re: lee14]
      #6291729 - 01/04/14 12:19 PM

1a. Never go to the scope expecting a star to be a particular brightness. Corollary, do not over observe stars which vary slowly.

1b. Double check identification of variable & comparisons before making an estimate.

1c. Choose stars suitable for your equipment. For scopes in the 4 - 5 inch range that probably means those in the mag 10 - 13 bracket. Too bright leads to errors, too faint leads to frustration. There are few "sexy" stars (dwarf novae etc) in this sort of brightness range but there are immense numbers of underobserved long period / semiregular stars which would suit just fine.

1d. Do take the trouble to read & understand the Variables chapter in Sidgwick's "Observational Astronomy for Amateurs". That's the whole of chapter 17 with the exception of 17.2 if using AAVSO estimation technique, and 17.11 which relates to obsolete photographic techniques. So far as visual estimation is concerned, nothing has changed since this book was written.

2. Low power: exit pupil around 5mm. Medium power: exit pupil around 2mm. High power (for faint variables): exit pupil around 1mm ... That's enough to get you started. You may find an intermediate 1.4mm exit pupil useful for nights when the seeing is poor.

Eyepieces should have good definition across the whole field; superwide EPs with fuzzy edges lead to errors. I strongly reccomend orthoscopics for observing variable stars. Plossls OK but not as good as orthos. The relatively cheap "planetary" eyepieces with long eye relief & apparent fields around 60 degrees can also work well in scopes with longer focal ratios.


3. Apart from the Sidgwick mentioned above:

David Levy's Guide to Variable Stars (2nd edition, Cambridge University Press, ISBN 0-521-60860-0) - basic but good

Observing Variable Stars, Novae and Supernovae by Gerald North (Cambridge University Press, ISBN 0-521-82047-2) - excellent but a little technical in parts. The section on instrumentation is technical but well worth ploughing through! Lots of charts on the included CD however I found this feature a bit underwhelming.

Webb Society Deep Sky Observer's Handbook: Vol 8, Variable Stars edited by Kenneth Glyn Jones (Enslow Publishers Inc, ISBN 0-89490-209-3) - this is BRILLIANT but unfortunately very hard to get hold of.


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lee14
super member


Reged: 12/19/09

Re: What do you wish you'd been told about.. new [Re: brianb11213]
      #6291776 - 01/04/14 12:42 PM

An addendum about wide field eyepieces. Yes, avoid those with poor definition towards the edges. These days though, high quality eyepieces are not difficult to find, though they tend to be pricey. The extended fov is invaluable though, especially when comparison stars are scarce. In any case, the variable and comp star should always be compared when they are at the same distance from the edge of the field. At higher powers both stars will often require moving the scope between them, just make sure they're both at similar locations in the fov.

For inspirational books, you can't beat Leslie Peltier's Starlight Nights. For data, The General Catalog of Variable Stars is the ticket in the unlikely event that the AAVSO site can't give you what you need.

Lee
AAVSO since 1991


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Adam S
scholastic sledgehammer
*****

Reged: 12/21/05

Loc: Gunnison, Colorado
Re: What do you wish you'd been told about.. new [Re: lee14]
      #6292072 - 01/04/14 02:42 PM

Thanks for the info so far. I have a 31mm Nagler and a bunch of Pentax XWs. The 20mm Pentax was a great fit for Chart B. I read Peltier's book years ago and loved it. I almost reread it several weeks ago; however, went for CNs own Thomas Watson's Olcott book (great read if you've been at this for awhile). I'll pick Starlight Nights up and read it again. David Levy's book looked interesting, thanks for the validation.

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brianb11213
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: What do you wish you'd been told about.. new [Re: Adam S]
      #6292127 - 01/04/14 03:09 PM

Quote:

I have a 31mm Nagler and a bunch of Pentax XWs. The 20mm Pentax was a great fit for Chart B.



Don't get me wrong, Pentax XWs are IMO excellent for general astronomy, but the quality of the view towards the edge of the field seems to vary a lot depending on which scope is used. Some people call it field curvature. Also you really don't want stars to be out on the edge of a 70 deg AFOV when making comparisons - they should be brought to the centre - the only purpose of a wide AFOV is to make locating the field easier.

The only Nag in my posession (20mm T5) has a noticeable "tint" & I avoid making VS estimates with it for this purpose. It also seems to have a low light transmission, losing ~0.2 mag in light grasp compared with a 20 mm plossl in the same scope. I've noticed the same characteristics with other Naglers, and TV Plossls ... nevertheless they're great general purpose EPs, especially for outreach with undriven scopes.

BTW you don't need to fit the AFOV to the chart. You soon learn to pick out "asterisms" in and around the area of the field & it's those that you make mental reference to after you've learned the field (which happens surprisingly quickly - two or three visits to the field is usually enough in my experience). The angles between the stars are much more important than the scale in recognising the field.

In any case the AAVSO lets you plot charts to any scale / field of view / orientation (this last is IMPORTANT as finding a field with an incorrectly oriented chart (diagonal!) can be challenging!)

Some variables happen to have lots of close companions - for SS Cyg a 15 arc min field is plenty - others don't - RV Tau is "difficult" for this reason, although it's easy to find and usually about 2 mags brighter than SS Cyg you need to use comparisons which are over 1 deg away. Obviously it's easier to start with the more convenient stars, moving on to the more difficult when you have more experience.


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Ed Wiley
scholastic sledgehammer


Reged: 05/18/05

Loc: Kansas, USA
Re: What do you wish you'd been told about.. new [Re: brianb11213]
      #6292507 - 01/04/14 06:41 PM

Re: Webb Society Deep Sky Observer's Handbook: Vol 8

Check Amazon, I bought a used copy for a very reasonable price (less than $20).

Ed


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Rich (RLTYS)Moderator
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Reged: 12/18/04

Loc: New York (Long Island)
Re: What do you wish you'd been told about.. new [Re: Adam S]
      #6295349 - 01/06/14 06:27 AM

Always make each VS Observation as if it was your first.

Rich (RLTYS)


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Philler
sage


Reged: 07/15/13

Loc: Kansas, USA
Re: What do you wish you'd been told about.. new [Re: Adam S]
      #6297320 - 01/07/14 01:34 AM

Some things I learned, mostly through experience VSOing.

I like using Uranometria copies for finder charts, but use whatever works for you. I would take the 2000 coordinates from the AAVSO charts. If the variable is too faint to be already plotted the atlas or finder charts I'll mark it on my atlas chart. I'll used RU Peg for example,(I don't have its AAVSO chart in front of me),and mark it as RU on the atlas chart. You don't have to be perfectly exact marking it.
Going out to observe, let's again use the "dwarf nova" RU Peg example. Start out with a low power ep and locate RU on whatever atlas chart you like, and find it in your FOV with your scope, then go to your your b or c AAVSO chart for RU Peg and identify RU in the pattern of background field and comparison stars. Find two comparison stars that are close but not too close to RU, one brighter and one fainter than RU. RU, according to chart, varies between about 9.0 to 13.3, so if necessary, go to a higher power ep and to d or even e chart if needed, if provided. Lets say RU looks fainter than an 11.5 comp star but brighter than a 12.3 comp star. Lets say that RU looks closer in brightness to the 11.5--about a third closer to it in brightness, you could then estimate RU at about 11.8, and record it as such. Remember, you don't have to exact: this is not rocket science, (you'll see the combined light curves from other observers that it can look like a swarm of bees riding a roller coaster). Try not to overdo an estimate, too much time spend straining to make an estimate and your eyes natural way of judging brightness will start to fool you. Also reddish stars can make estimates more difficult.
When you record your estimate, be sure to record your the local time of the estimate. You can convert it to UT or GMAT later if you are going to report it.
VSOing just takes practice, adaptability, tenaciousness, and most of all, desire. And if you regularly observe DSOs, you have the basic skills for VSOing. I've used just a 10" Dob star hopping, Telrad, and finderscope and 3 or 4 EPs and a Barlow, 44x to 170x, which have been adequate. BTW, not all of the comp stars on the AAVSO charts are perfectly accurate, but I have seen 15.5v comp stars (barely) with my 10 in. at high power. So, VSOing will allow you to go to the mag. limits of you scope. Good hunting and clear skies. Phil

Edited by Philler (01/07/14 05:58 PM)


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Michael Rapp
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Reged: 04/27/04

Loc: Dickinson, TX
Re: What do you wish you'd been told about.. new [Re: Philler]
      #6324779 - 01/20/14 06:51 PM

I've been off and on in variable star observing for the past year or so. It is important that you do it primarily because you enjoy it, not because you need to feel that you are contributing to science. (Note, I did not say because you would like to contribute to science.... need and like are two different notions.)

If you need to feel that you are contributing to science, you'll get sucked into the entire visual vs CCD discussion, which is demoralizing, and/or you'll start seeking out "hot research topic" stars that are ill-suited for your equipment and you'll get frustrated.

I started out that way and it burned me out in just three months. Now I make variable star estimates because I enjoy the process. I like star-hopping, verifying the field, and the process of deciding the brightness of my star.

If an astronomer uses AAVSO data to which I've contributed to further their research, I would be delighted, but I approach my observations with no expectation of that happening any time soon.


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Adam S
scholastic sledgehammer
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Reged: 12/21/05

Loc: Gunnison, Colorado
Re: What do you wish you'd been told about.. new [Re: Michael Rapp]
      #6324948 - 01/20/14 08:25 PM

Thanks for all of your responses. Michael, the interests stems from several areas. One, I love using my telescope and the night sky. I live in an area with atrocious seeing, planetary observing is a frustration even with premium optics. While it's a recent interest, I find variables in their many forms fascinating. Lastly learning to make proper estimates is personally challenging.

The entire project is new to me, I've never given two seconds thought to the actual magnitude of a star. I know the names of about 20 or so stars but until the other night didn't know the actual magnitude of a single one. A whole new world of challenges is open.

Speaking of challenges... I printed several AAVSO charts several nights ago. The first night was a disaster, I hadn't thought about where I was going to put charts, pencil, clipboard etc on a -5f night. When I wasn't looking for a place to put things I was was experiencing ZERO success of making sense of the charts at the ep. The second night I was better prepared, a place for everything. Still no success with the charts. I came inside after estimating three naked eye stars and have decided to use chart C (2.0 deg, same as my 24mm Pan) and change the chart to a lowest magnitude to 10 rather than 14.5 as generated by the AAVSO as the number of stars appears to be more in line with what I'm seeng in a four inch refractor.

Tonight's a new night with new charts, onward and upward.


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Michael Rapp
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Reged: 04/27/04

Loc: Dickinson, TX
Re: What do you wish you'd been told about.. new [Re: Adam S]
      #6325699 - 01/21/14 08:53 AM

Quote:

Speaking of challenges... I printed several AAVSO charts several nights ago. The first night was a disaster, I hadn't thought about where I was going to put charts, pencil, clipboard etc on a -5f night. When I wasn't looking for a place to put things I was was experiencing ZERO success of making sense of the charts at the ep.




My first nights were like that....light wind....charts blowing around....and nothing made sense at the eyepiece. I hadn't really paid attention to how I was going to match the chart with my field of view.


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Rich (RLTYS)Moderator
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Reged: 12/18/04

Loc: New York (Long Island)
Re: What do you wish you'd been told about.. [Re: Michael Rapp]
      #6327944 - 01/22/14 09:46 AM

Quote:

Quote:

Speaking of challenges... I printed several AAVSO charts several nights ago. The first night was a disaster, I hadn't thought about where I was going to put charts, pencil, clipboard etc on a -5f night. When I wasn't looking for a place to put things I was was experiencing ZERO success of making sense of the charts at the ep.




My first nights were like that....light wind....charts blowing around....and nothing made sense at the eyepiece. I hadn't really paid attention to how I was going to match the chart with my field of view.




It takes time to get know the charts as compared to your scopes field of view. Orientation is important.

Rich (RLTYS)


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Adam S
scholastic sledgehammer
*****

Reged: 12/21/05

Loc: Gunnison, Colorado
Re: What do you wish you'd been told about.. new [Re: Rich (RLTYS)]
      #6329292 - 01/22/14 08:16 PM

It helps that I'm using an altaz mount. Theoretically a N is up/W to the left map should be perfect for a refractor with diagonal. I made one for Betelgeuse knowing that it would be an easy star to find and fine tune the magnitude and orientation of the background stars.

Worked perfectly, used maps in the above orientation, 10th magnitude limit and two degree fov are perfect with a four inch Tak, 24 Pan, diagonal and altaz mount. Maps were dead on with Miu Cep, Eta Gem and R Lep. No luck with U Gem last night but I generally pack it in when it hits 10 below.

Edited by Adam S (01/22/14 10:17 PM)


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