The Night Sky in November
The planet Mercury will pass between Earth and the Sun on Nov 11, creating an event known as a transit of Mercury. Such alignments can only occur at specific times of the year, currently on dates near May 8 or Nov 10. The last took place on May 9 2016 and the one that follows this year’s event will happen on Nov 13 2032.
Before continuing, a word of warning. The Sun is the only natural object in the sky that can do you harm if observed incorrectly. Certified safety filters must be used to protect eyes and equipment. Failure to do so can result in serious damage and loss of sight. Seek advice from an astronomical stockist or a local astronomical society.
Mercury is the Solar System’s smallest main planet with a diameter of 4,880km. When positioned between us and the Sun on Nov 11 it presents a dark silhouetted circle around 10 arcseconds in diameter. The limit of resolution for the human eye is around 1 arcminute or 60 arcseconds. Viewing the event through, say, eclipse safety glasses won’t work because the planet will appear too small. Some form of magnification is required, typically achieved by using a suitably filtered telescope.
The transit starts at 12:35 GMT on Nov 11, ending at 18:04 GMT. The November Sun is low from the UK and sets around 16:20 GMT, 1 hour and 44 minutes before the transit ends. Mid-transit is at 15:20 GMT.
The spectacular constellations of winter are now beginning to appear in the night sky. Taurus the Bull heads the charge, a constellation that bridges the gap between autumn and winter. It represents the form of the magnificent white bull Zeus turned himself into to abduct the Phoenician princess, Europa.
The brightest star in Taurus is Aldebaran. It’s a red-giant star estimated to be 44 times larger than our own Sun and located 65 light years away. It is easy to find by virtue of the distinctive three-star-line formed by Orion’s Belt. Extend this line north-west (up and right from the UK) and this will point directly at Aldebaran.
The area of sky around this distinctly orange-hued star contains the sideways V-shaped pattern of the Hyades open cluster. This ancient family of stars is estimated to be 625 million years old and is the closest open cluster to our Sun at an estimated distance of 153 light years.
To the north-west of the Hyades lies another compact cluster of stars known as the Pleiades or Seven Sisters. This open cluster is 444 light years distant, roughly three times the distance of the Hyades. This is a much younger cluster, having formed within the last 100 million years. Its hot young stars appear blue-white while the older Hyades stars have colour closer to the cooler and redder end of the spectrum.
There are many hidden gems within Taurus including the famous supernova remnant known as the Crab Nebula (Messier 1). This object is the aftermath of a supernova explosion, which was witnessed on Earth in AD1054. Interestingly, as the nebula is around 6,500 light years from Earth, the explosion would have taken place in about 5,446BC, the light taking 6,500 years to reach our planet.
There’s another supernova remnant of note in Taurus which is much harder to see. Catalogued as Simeis 147, this object is roughly circular with a three-degree diameter. Full of delicate filaments resulting from the original explosion, it lies 3,000 light years from Earth, the explosion that caused it having occurred 40,000 years ago.