[Lvas] Neglected Galaxy and Cepheid Variables

Fri Jun 19 11:54:40 PDT 2009

All,

Re: NGC-6822 in Sagittarius

It has certainly given me a problem from my backyard...but again I was losing the necessary contrast required to see this object.

Remember, Skiff has observed it with a 60mm refractor...and Hubble could see it just a well thru a 4-inch finder than the 100-inch.

A small aperture scope using low magnification, dark skies, seems to be the way to go on this object. 

I am not going to work on N-6822 until July, as I will include with Messier, M-2 which is the "OC" object for August. I will attempt both objects with my 4-inch from a darker site than my backyard. 

At current I am still working on M-13 and the propeller. 

Potential for N-6822:

I am going to use my 4-inch with a 24mm Konig at 42x. 

65° Apparent Field/42x = 1.5° or 90 arc minutes (true FOV) ... this is the ticket on this object (I think). 

I have never seen or heard of anyone personally that has observed this galaxy. Pretty strange since it is so close to use and is a member of the local group of galaxies. This is going to be my year....I hope. 

NGC-6822 has a dimension of 10 arc minutes x 9.5. The galaxy should appear almost round in apperance. 

roger

    The moon and stars to govern the night....    Psalm 136:9

From: rayworth1969 at hotmail.com
To: lvas at lvlug.org
Date: Fri, 19 Jun 2009 12:34:15 -0500
Subject: Re: [Lvas] Neglected Galaxy and Cepheid Variables

All,

I only tried for it once in 1990 and couldn't find it. I was using my home-built 16" f/6.4 and it was in Eurovillas, Spain, with an altitude of about 3500 feet. According to my notes, it was at least the second try for it. At that time, I was not near as good finding stuff as I am now, so this will be a nice object.

Fred

From: drivester at hotmail.com
To: lvas at lvlug.org; trenglish at gtcc.edu
Date: Wed, 17 Jun 2009 13:12:36 +0000
Subject: [Lvas] Neglected Galaxy and Cepheid Variables

All,

I mentioned in an earlier e-mail that NGC-6822 also known as "Barnard's Galaxy" was discovered by E.E. Barnard in the 1880's. He was working at Vanderbilt University in Nashville Tennessee and used a 6-inch refractor for the discovery. This galaxy has been named in his honor as "Barnard's Galaxy" by the astronomical community. Again Herschel missed this large, LSB galaxy, and of course is not listed in the H-400 or H-II list.   

In the 20's Edwin Hubble discovered 15 variable stars, 11 were cepheid variables in this galaxy. The Galaxy was calculated at a distance of between 1.6 or 1.8 million light years. 

This galaxy is relatively close, as M-31 is 2.4 million light years away...almost next door, so to speak. 

I have never discussed this galaxy or compared notes with an amateur that has personally  observed this galaxy. I have been unable to see this galaxy from my backyard due to my poor southerly sky, and have never attempted from a dark site. Weather permitting I may try this weekend with my 4-inch refractor. I have attempted many times from my backyard, but a "pesky" streetlight reduces the contrast too much. The LSB (low surface brightness) of this galaxy requires a dark sky and low magnification. 

Skiff and Luginbuhl "Observing Handbook and Catalogue of Deep-Sky Objects" observing with a 60 mm refractor from Arizona.  "A weak but definite glow in 6 cm, where it appears elongated N-S and shows a very slight central concentration". 

A Cepheid is a type of star whose brightness varies periodically at the beginning of a period, it's brightness increases very rapidly, for as long as several hours. That is followed by a gradual dimming which may continue for several days. The cycle is then repeated. 

Cepheid's variables are named for the prototype Delta Cephei (F-5 -G-2) with a period of 5.366341 days. If you have never attempted variable star observing, this is the perfect star as it is visible most of the year due to it's northerly position. Delta Cephei has a maximum magnitude of 3.48 and a minimum of 4.37.

It's variation was discovered by the gifted deaf astronomer, John Goodricke in 1784. 

Tom English allowed me to participate in many of his class activities when he was at GWU. I learned much about variables from Tom's many projects. As a learning experience, Tom, myself and his class plotted this star over a period of more than a month. Since this learning experince in variable star observing in December of 1998 I have followed and plotted quite a few others.    

These relatively rare variable stars are very important as the length of their pulsation or period is directly related to their absolute magnitude. The longer their period of variation the brighter the star. By observing the period of variation, astronomers can determine a Cepheid's absolute magnitude. By comparing the star's absolute magnitude to it's apparent magnitude, the distance can be easily calculated. 

It was in 1923 that Edwin Hubble found several cepheid variables in the Andromeda galaxy using the 100-inch at Mount Wilson. From these variables he was able to determine the true nature of the this object as an external galaxy and not a nebula within the Milky Way by calculating the distance. The period-luminosity relationship of Cepheid Variables was discovered by American Astronomer, Henrietta Leavitt in 1912.  

The best way to locate this galaxy is to find the relatively bright planetary nebula NGC-6818 as "Barnard's Galaxy" is only 45 arc minutes to the SSE. 

Sources: "Burnham's Celestial Handbooks" by Robert Burnham, Jr., "Observing Variable Star's" by David Levy, "Glossary of Astronomy and Astrophysics", and "Astronomy made Simple". 

Hope some of you are able to observe NGC-6822 this weekend. 

Roger

    The moon and stars to govern the night....   Psalm 136:9

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