epsilon Aurigae





AAVSO eps Aur page



     International eps Aur Campaign



  eps Aur Wiki page


      BAAVSS Chart

Notes on Spectroscopy


Epsilon Aurigae Eclipse: 2009 - 2011

AAVSO eps Aur poster


The epsilon Aurigae eclipse is intriguing because of the long period between eclipses ( 27 years ), the length of the eclipse ( 21 months ) and the nature of the eclipse. The length of the eclipse means that the drop in magnitude cannot be caused by an eclipse of another star. The star would be far too big- there is no known star that would be big enough to extend out to the orbit of Neptune if it was in the solar system. Epsilon Aurigae itself extends out to the orbit of the Earth. As a star is ruled out it is thought that the eclipse represents the covering of epsilon Aurigae by a large cloud of dust and gas. One of the purposes of calling for intensive observations over the next two years is confirm the existence of the cloud. Wikipedia now contains useful background information on the system.


The nature of the eclipse explains the importance of visual observations. Experts do not expect the cloud of dust and gas to be regularly shaped. It may not be one mass. It may be of uneven density. For these reasons the expected drop in magnitude from 3 to 3.7 may not be smooth. There could be fluctuations which will be of large enough dimensions for visual observers to pick up. There may be fluctuations before the eclipse as epsilon Aurigae is obscured by subsidiary clouds. Visual observations may be crucial in mapping these detailed changes as vagaries of the weather may prevent instrumental observations for days. Recently there were no instrumental observations of epsilon Aur in the USA for a week due to cloud. A fortunate visual observer may be in the right spot to provide the only estimates for some time.




New Chart


The BAAVSS has produced a new chart for observers (see link above).


It is suggested that between now and the middle of May observers practice on making estimations of epsilon Aurigae using the chart. The magnitude should be around 3.0. There are brightness fluctuations outside of eclipse due to pulsations of the primary star. It is therefore possible that estimates of between 2.9 and 3.1 may be recorded.


From the middle of May to the beginning of July observers in the UK will find it difficult to make reliable observations because the star will be too close to the sun. Reliable observations will not be possible when the star is within 20 degrees of the horizon. This is because atmospheric turbulence will cause rapid and confusing changes in brightness. In addition the magnitude differences between epsilon and its comparisons are not reliable when seen through the thick atmosphere below 20 degrees.


From the middle of July observations will be possible before dawn. We would urge observers to make a special effort to carry out early observations in the month up the expected start of the eclipse on 6th August. This is because the eclipse may start earlier than predicted and because there may be, as mentioned earlier, subsidiary clouds of dust and gas that cause brightness fluctuations detectable by visual observers.


The Fade to December 2009


Once the eclipse starts ( and it may be late ) there will be a fade until totality which is scheduled around December 21st. Actually totality is a misleading term in the context of the eclipse of this star. The star is not totally obscured. Its light is reduced by about 200% by the thick cloud.


 If the fade was smooth then it probably would only be necessary to observe once a week. If there are fluctuations, more frequent observations may be useful. In any case all observations will be welcomed so that there is the best possible record of the eclipse.


We hope to be able to create a monthly report of all observations.  All observations will be credited to individual observers.


“Totality” is predicted to last until March 12 2011. In the middle there is a possibility that there might be a mid eclipse brightening that could be picked up visually. It is thought that there may be a gap in the cloud which reveals another star, contained within the cloud, which is orbiting epsilon.


epsilon  Aurigae Powerpoint  with emphasis on DSLR photometry














epsilon Aur International Campaign Light Curve



YouTube Citizen Sky epsilon Aurigae movie











Image credit Nick Camargo.



































2009 Aug 6th -      predicted start of eclipse, rising with sun as a morning star

2009 Nov/Dec -    eps Aur transits at midnight --> evening star

2009 Dec 21 -        predicted start of totality, evening star

2010 May -             eps Aur setting with the sun, mid eclipse brightening?

2010 Aug 1st -      predicted time of mid-eclipse, early morning star

2010 autumn -     end of mid-eclipse brightening?

2010 Nov/Dec -   eps Aur transits at midnight --> evening star

2011 March 12 -  predicted end of totality, evening star

2011 May 15 -      predicted end of eclipse, next one starts in 2036.



















Instrumental estimates are welcomed as the increased accuracy will allow more detailed effects to be picked. CCD and DSLR will reveal the pulsations of epsilon Aurigae itself. These have an amplitude that seems to vary between 0.1 magnitude and 0.16 magnitude with a period of about a hundred days. Instrumental estimates may also provide more detail on the dimensions of the dust/ gas cloud.


Good estimates can be made with a DSLR. The settings with Canon 350D DSLR and 85 mm lens are ISO 200, f4.5 and an exposure of 5 seconds. 20 images form one set to be analysed with AIP4WIN.


The international instrumental campaign started in October 2008. Most of the time epsilon Aurigae has been around 2.99V but has dipped to minima at 3.06V and 3.14V in March 2009








June 1st 2009,  Des Loughney


Following its March/ April fade epsilon brightened to around 2.87V at the beginning of May.

Observations have been difficult in May, particularly after the middle of May, because the system is so low down ( under 20 degrees).

From the observations of the members of the International Campaign it seems that epsilon slowly declined during May to its usual
brightness around magnitude 3 by the end of the month.

Despite the difficulties we will continue to monitor the system ( which is circumpolar at the latitude of Edinburgh ) throughout June.





Observational updates (earliest first)









September 12th, 2009


It seems that the eclipse has started as the magnitude is now below the normal out of eclipse variation.   If it is the eclipse fade then the shape of the recent light curve suggests that the fade started around the middle of August which is only about a week later than predicted. The prediction was quite accurate given the long period ( 27.1 years ) of the system.  For visual observers it should soon become apparent that epsilon has  dropped from its usual magnitude of around 3.






August 23rd 2009

The eclipse was predicted to start on 8th August. At the time of writing there has been no indication that the eclipse has started in visible wavelengths. Over the last five weeks epsilon has hovered around magnitude 3.01. There have been occasional brightenings. For example it brightened to around 2.93 on 22/7/09.

A late start to the eclipse was always a possibility given the nature of the eclipsing body which is thought to be a cloud of dust and gas. It is always difficult to precisely predict the start of an eclipse with a 27 year period.

Epsilon is, at the time of writing, in a good position for observation at around 2 am BST.'

































Des Loughney

EB Secretary

desloughney [at] blueyonder.co.uk



November 15th 2009

Broadly speaking epsilon Aurigae has continued to fade as the updated light curve illustrates at the top of the page. There has been however some sort of shoulder in the light curve or change in the rate of decline. This is mirrored in the spectroscopic data. It is not known what is the cause of this change. It may be variations in the density of the cloud of gas and dust that is eclipsing epsilon or the variations of epsilon itself. The change in the light curve may mean that ' totality' occurs later than the predicted third week in December. It may not now occur until the New Year.'


October 18th 2009


The eclipse is now well underway. Epsilon is about half way to minimum which should be reached in late December. There has been some discussion regarding the start of the eclipse. It has been difficult to establish the exact start because epsilon is a variable star itself. The predicted start was the 6th August. Some experts consider that the eclipse started on 19th August and others on 27th August. Either way the start was a bit late. By start of eclipse we mean the start visually or relative to V filters.

Robin Leadbeater detected the spectroscopic start at around the 20th July when a spectroscopic signature of the eclipsing cloud developed.

January 9th 2010

Epsilon Aurigae has continued to fade from the middle of November 2009. By the 23rd December it had reached about 3.67V. It had been predicted that it would continue to fade until the system reached a magnitude of perhaps 3.83. Since the 23rd December it has hovered between 3.66 and 3.69.  It may have reached totality. A further fade is possible so observations are still welcome. Variations in the obscuring dust and gas cloud are of interest so observations should continue  so that these can be picked up. Have a look at the Astronomy Picture of the Day for 8/1/10 at http://apod.nasa.gov/apod/ap100108.html


February 22nd 2010

It is now thought that Epsilon reached ' totality' on 16/1/10 at around 3.7 V magnitude. This signifies that epsilon is obscured to the maximum extent by the cloud of dust and gas ( see the artists impressions of the system at the top of the page).

Epsilon continues to slowly fade over the past month. At the time of writing it is around 3.75V and still apparently dropping. The further fade is probably due the intrinsic variability of the star itself - it can vary through up to  0.15 magnitude.


25th April 2010

Epsilon Aurigae has continued in its ' totality' phase with a magnitude of around 3.77. There was an increase to 3.71 in March followed by a fade back to 3.77 which it is at currently. The brightening in March is thought to be part of the intrinsic variation of epsilon itself. The accepted model of the system predict a brightening around the centre of the eclipse to about 3.60 magnitude. Picking up this increase is the next target in the campaign. However, observations will be difficult from the middle of May until the middle of July as epsilon will be low down and in the twilight ( from the UK) Corrections for atmospheric extinction can be made so it is hoped that instrumental observations will continue over the summer.