Thursday, May 18, 2017

Messier 61 /NGC 4303

Messier 61 is a barred galaxy , part of the Virgo  Cluster.
To find M 61 we may start at Porrima /Gamma Virginis , itself a beautiful double star worth of close examination.
From Porrima we should navigate toward West to the next naked eyes bright star Zaniah or Eta Vir.
From Zaniah we should change course toward North to 16 Virginis a fifth magnitude star.
Once we get there ,we are close to Messier 61.

Insert a low power ocular , let say of  25mm focal length and look for the star asterism adnotated below as ''a-b1-b2-c-d1-d2''.
Choose the star raw at East , namely b1-c-d1.
Follow the direction from ''a'' to ''d1''.
Go twice this distance further North and you will find a pair of stars.
The brighter is bearing the code HIP 60224 and it have a dimmer star to the North-East.
Imagine a right angle triangle having the right angle corner in the dimmer star.
At about twice the distance between HIP 60224 and the ''corner star'' , toward East-South East it lie Messier 61.

The above screen-print from Aladin Lite is not rendering well  the brightness difference between HIP 60224 of  8.15 mv  and the ''corner star'' which at 10.35 mv  is much dimmer ,with more than two magnitudes.
The magnitudes quoted above are from Stellarium.

Stellarium is rendering better this brightness difference between the two ''guide stars''.
But of course ,the galaxy looked much , much fainter in the Revelation 9 mm Plossl ocular ,at 96x in my 125mm F/7 Dobsonian.
My first observation of M61 happened on May 14 and the second last night ,on May 17.
I saw just a dim ,hazy ,round patch of light , a very ,very dim one.
No structure , no shape , no central condensation.
For all this I will have to come back latter ,with a bigger telescope.
But I'm happy and grateful I was blessed with the view of this galaxy considered as big as our Milky Way and located at 53 million light-years.

Note :
The screen-prints are made from Aladin Lite and Stellarium and the notes were added with Paint.

Tuesday, May 16, 2017

Enigma din R Crateris / The R Crateris Riddle

The telescope I'm  using most often is pretty  old at 20 years  but not a ''classic'' because it is home made.
It is a Dobsonian with a 125mm F/7 very good primary mirror made by late Gavril Beches.
Currently the mounting is under refurbishment ,some parts gave up after two decades of stargazing.

The book where I got the target for the observation below  is a classic , ''Pleasures of the Telescope'' by Garrett Putnam Serviss.

For a long time my pet  targets were double stars.
But since more than one year I'm addicted to a Deep Sky craze.
The  second week of May being around Full Moon , there were not   chances to see many galaxies in my small telescope...
On 10 and 12 of May I was looking for another type of  targets.
Like trying  to see Messier 68 , a globular cluster but without success.

Serviss suggest , while being in that part of the firmamant , to have a look to Delta Corvi which is a double star and to R Crateris ,a variable red star.
I started my star hopping with Algorab or Delta Corvi , an old friend because is the starting point when searching for Messier 104 ''Sombrero Galaxy''.
This time ,thanks to Serviss , I looked a bit more careful and ... yes , Delta Corvi is a not so  easy double star of very unequal stars ,separated by 24''  , split at 35x , if you look carefuly.
The dim companion is better seen at 69x /University 12.5mm ortho.

From Delta Corvi , I navigated toward West to Gienah Corvi /Gamma Corvi.
And here my science ended , I was not able to manage alone on the bright Moon lit sky ,among those dim and rare stars.
The Toshimi Taki atlas helped me to notice a triangular asterism located to the West of Gienah , composed of 31 Crateris -Eta Crt-Zeta Crt  .
The lower  side of this triangle ,namely 31 Crt- Zeta Crt  is pointing toward Gamma Crt.
From Gamma Crt the next step is bringing us to Alpha Crateris  or Alkes.
R Crateris is in the same field at 69x with Alpha Crt.
Here is a finder chart made using Stellarium and Paint.

R Crateris is the middle star of a boomerang shaped asterism of three stars.
The  color of the star was  ruddy and R Crt was the brighter  in the asterism.
Serviss is not mentioning that R Crt is also a double star.
Stellarium is stating R Crt have a separation of 63'' and PA= 268 degree.
I haven't searched in big data bases but I believe the companion is the small star of 9.9 mv we see in this print screen from Aladin Lite.

Checking with Stellarium,the position angle of the small star fit very well : R Crt is to the East of Alpha Crt .

The 9.9 mv star is located  between R Crateris and Alkes which lie to the West of R Crt .
This  mean a   PA of  about 270 deg against 268 degrees listed by Stellarium.
The difference in RA between R Crateris and the supposed companion is of about four seconds of time which mean 60'' against the separation of 63'' listed by Stellarium.

Again ,data agree well.

According to Simbad , R Crateris is a ''Helium burning asymptotic giant branch star'' :

However ,there is something  that I don't understand.
Stellarium is stating R Crt to be of 8.95 mv.
According to  Vizier the maximum brightness of R Crt is of 9.8 mv.

Stellarium is also showing the  9.8 mv brightness  in the row about range of variability.
But visualy ,R Crt was the brightest in the trio of stars shown in the screen-print.
Much brighter I dare to say...

So ,the ''riddle'' I found in R Crateris is this : how can a star of 8.95mv have a range of variability from 9.8 to 11.2 ?
Is this due to the different photometric systems used ?

Well ,it was fun to take a look at this giant red star.
But in the stellar world the red giant stars  are pretty cool .
So ,should I say it was ?

Thursday, May 11, 2017

Observatii din primavara lui 2017/Observations Spring 2017-Part III

The Moon and Jupiter on the Eastern sky on March 30.

 Jupiter,the same evening ,  in the constellation Virgo at end of March,as  recorded by the Coolpix S3300 camera , between Spica and Theta Vir.

On 10 of April I was taking - at least I was trying - afocal pictures with my 90x600mm ''zoth'' RFT refracting telescope.

Here we see the 90mm RFT refractor on my DIY ''Penelopa'' pipe-mount with LV 30mm 2'' ocular.

 Mizar-Alcor-Sidus Ludoviciana in the 90mm RFT refractor.

Arcturus and the star 22 Boo.

Delta Boo and companion.

Dubhe -Alpha UMa and optical companion.

Mu Bootis- Alkalurops as a double star.
At 100x the dim star prove to be a tight double star itself.

The Moon and Jupiter on April 10 through the lens of Coolpix S3300 camera and SVBony ''Moon&Skyglow Filter''.

The Moon and Jupiter through the same camera and a green filter.

Life is not always smooth !
The broken arm of right hand ocular of the Sakura 9x60mm binocular.

But we are still looking confidently to the future !