SUMMERSIDE, P.E.I. – Hi Sky Watchers.
It's time to discuss the night sky again. What shall we choose this month? I think we'll make it star time again and choose a star to talk about.
This month I'll choose a star that struck terror into the ancients - a true demon star - Algol. It was also called the Demon's Head, or Satan's Head, or Mischief Maker. Because it occurs in the constellation Perseus, and in antiquity Perseus carried Medusa “The Gorgon's Head,” this was further associated with Putrefaction.
But enough of unpleasantness. Let us look at ways Algol is truly interesting. Algol is a binary star, or two stars rotating around each other. Further, they rotate along our line of sight, and thus, to our eyes, pass in front of each other. In the case of Algol, this occurs every 2.87 days causing the light from the further star to be blocked, and the light from the two to dim significantly. This blockage lasts for approximately 10 hours and you can watch this change with your naked eye. Several internet sites will give you the times to watch.
I have always considered this the demon star twinkling its evil eye at me.
I should mention that Algol is 100 light years distant, and remember – each light year is 6 trillion miles or 9.6 trillion kilometres. Wow!
To find Perseus and Algol, you need start with the Big Dipper. Use the star where the handle joins the pot, draw a line through Polaris, the North Star, go the same distance again and you will come to Cassiopeia, a large "M" in the sky at this time of year. Follow the inside line of the "M" upwards almost to the top of the sky and you will come to Perseus, a rather large "Y" shape. Algol is out in the left arm of this “Y.” Good hunting to see it winking,
So, what’s in our sky this month of January, 2018.
Firstly, I must admit you will miss some objects as this article it will not make it to you for the first of the month. My apologies. But I will list them any way - for your knowledge.
This is one of those unusual months with two full moons – Jan. 1 and Jan. 31. You will perhaps remember that when we have two full moons in a month, we call the second one – a Blue Moon. But because this is January, I’m going to look ahead a little.
Because February is a short month, there will be no full moon in February, but there will again be two full moons in March, and thus another Blue Moon. Interestingly, if this February had been a leap year with 29 days, the 29th would have been a full moon, and not March 1, and thus – no Blue Moon in March. This set of circumstances can only occur in January, February or March, and then only rarely when Jan. 1 is a full moon.
So, what else did we likely miss. Well, the night of Jan. 3 into the morning of Jan. 4 was the night of the Quadrantid Meteor Shower – usually the most prolific Meteor shower of the year, but spoiled this year as it was only a couple of days after the full moon.
At the end of January – the 31st, there is a Lunar Eclipse, visible throughout much of North America, but unfortunately, not for us in Atlantic Canada, as day will have begun. I guess this is another example of the old adage – “Go west young man!” The West Coast will have a terrific view of the whole eclipse.
So that’s what we will have missed or won’t see. What can or will we see.
As far as visible planets go, it’s all about the mornings before dawn.
Let’s start with Mercury – our “going away” planet. For this month, Mercury orbits around the sun very quickly – in 88 days versus our approximately 365 days, thus it shifts relatively rapidly from being a morning to an evening planet, and back again. Right now, it’s a morning planet, and will be for the first three weeks of the month. But, it will get closer and closer to sunrise, and thus harder to see as the days pass.
Next, Saturn. It had been an evening planet for months, and has just finished passing behind the sun, which we call a Superior Conjunction. So now, in just the opposite of Mercury, Saturn shouts “Look at me, I’m coming into view” in the morning sky. It can be spotted as early as Jan. 3, but is difficult to see. It slowly rises higher, or earlier before sunrise. By month’s end, it will be 10 degrees above the horizon, one hour before sunrise.
A special treat occurs this month. From Jan. 11 to 13, Mercury and Saturn will dance with each other, low in the east-southeast sky, one hour before sunrise.
Venus is not visible this month. It is passing behind the sun.
What about Jupiter and Mars? Well we’ve already discussed Mercury and Saturn, Mars and Jupiter are much higher in the predawn sky – about 45 degrees to the upper right of the other two. More to come about Mars in the months ahead.
There are no significant naked eye objects up there this month, except as always, to watch the march of the constellations across the sky.
See you next month.
Your Sky Guy