Lancaster and Morecambe Astronomical Society

Epsilon (e) Aurigae observations 2009

Epsilon (e) Aurigae is a naked eye star in the constellation of Auriga, the Charioteer.

Every 27.1 years, this F0 super giant star is eclipsed by a mysterious object. At the beginning of the eclipse, which lasts for 18 months, the star’s brightness drops from ~3.0 to ~3.8. The Society has been monitoring the brightness of (e) Aurigae for several months and has generated a light curve, clearly showing the gradual dimming of the star by the eclipsing object. No one is quite sure what this object is, but it must be very large to produce an 18month long eclipse. Current theories include a large dusty disk surrounding a hidden secondary star which itself orbits (e) Aurigae.

The eclipse is almost total (at the time of writing) and the brightness of the star is expected to remain ~3.8 during the whole of 2010, before starting to rise again to ~3.0 in late spring 2011.

(e) Aurigae can be observed with the naked eye, or binoculars. Below is a beginner’s guide to estimating the magnitude of (e) Aurigae, using binoculars

Estimating Epsilon (e) Aurigae (with binoculars)

· Identify the three comparison stars.

· Eta (h) = mag. 3.2

Zeta (z) = mag. 3.8

58 Persei = mag. 4.3

· Look at e Aurigae – its apparent brightness should be either between h & z or between z & 58 Persei.

· You now have a brighter comparison star a fainter comparison star and the variable.

· Look at each of the three stars separately by placing them in the centre of your field of view and obtain an impression of their brightness by using the same part of your retina.

· Use these three separate observations to place the brightness of the variable somewhere on the magnitude interval between the two comparison stars.

· This is your magnitude estimate of e Aurigae.

· DO NOT place all three stars in your field of view and allow your eyes to roll around from one to the other.

· DO NOT make several estimates and take an average – this will introduce bias.

· Make a written note of the date & time together with your magnitude estimate.

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This page was last updated on 26th February 2008