Algol in Perseus – an eclipsing binary star system

I had a great two nights of stargazing with guests at the Grant Arms Hotel in Grantown-on-Spey this weekend.  The Grant Arms is a 3 star gold hotel located on the main street of Grantown-on-Spey, and a superb base for adventure holidays within the Cairngorms National Park.  The Cairngorms also doubles as one of Scotland’s best stargazing locations due to the area’s superb dark skies and elevated position.

The Grant Arms Hotel in Grantown-on-Spey

After dinner on Friday I met my guests and we travelled out to the remote moors beside Lochindorb, where the skies were ablaze with stars and the Milky Way soared overhead.

Most of the main autumn constellations were on display with only the low western flank of the sky obscured by some distant weather fronts.  Some of my guests had never seen the Milky Way under really dark conditions before and were amazed at the clarity of the galactic disc soaring overhead.

We opted for naked eye and binocular observing and had stunning views of objects like the Pleiades, Hyades and the Andromeda galaxy, which was a clear naked eye target and resolved into a lovely oval haze in binoculars.  Most of the bright stars shone with stunning intensity under these conditions, allowing us to pick out clear colour differences in Orion’s main stars (just rising in the east), and within constellations like Aries and Andromeda.

During my tour I told the story of Algol, the ghoul star in Perseus, and how the ancients were mystified by its queer dimming every few days lasting several hours.  What I didn’t realise was that at that moment we were looking up at Algol during its lowest brightness, which only happens around 3% of the time you care to look at it.

How to find Algol

The reason for Algol’s periodic dimming is because it has a larger but dimmer companion star in a relatively tight orbit.  Every three days the larger companion occults Algol, reducing the intensity of light reaching an observer.  Algol is therefore classified as an eclipsing binary system.

We headed out into the darkness again on Saturday evening for more fleeting but equaly rewarding observing, with scattered cloud providing tantalising glimpses of clusters and constellations.   Afterwards we packed up and headed back to the Grant Arms for some hot chocolate, and I concluded the weekend with an astronomy presentation in the lecture theatre.

I’d like to thank my guests for being such great company and making it an enjoyable and memorable weekend.  I’ll be operating more Stargazing weekends out of the Grant Arms in the near future so keep a look out for new dates.

I met some lovely and interesting people during the weekend