If the cold is a deterrent to spending time under the night sky, see if you can use the coming summer months to give it a go. From 7th to 14th December should be a great introduction with the famous Geminid meteor shower sparkling the night sky. Meteor showers occur at well-defined times during the year, lasting from a few days to a couple of weeks.
Meteors, often called shooting stars, have nothing to do with stars at all. They start out as meteoroids which are essentially tiny ‘crumbs’ left behind by comets or, on occasion, asteroids. These fragments continue to orbit the Sun in the paths of their parent bodies and, if those orbital paths intersect with Earth’s orbit, Earth passes through those crumbs every year. The ones that strike Earth’s atmosphere are called ‘meteors,’ appearing as bright streaks in the sky, as they burn up due to air friction at high altitudes. Very rarely, larger fragments don’t fully burn up, and impact the ground, becoming known as ‘meteorites’.
Showers are best observed in the early hours of the morning – from about 1 or 2 a.m. through until dawn. This is because as Earth orbits the Sun, its ‘leading’ side (or bow if you think of Earth as a ship) is the morning side – i.e., from 12 am to 12 pm. Imagine Earth ploughing through a field of space dust with the bow collecting most of it and the stern seeing only a few, and you’ll get the idea.
Showers seem to emanate from particular directions in the sky. The direction is known as a shower’s radiant. The Geminids get their name from their radiant which is in the constellation of Gemini (the twins), just a degree or two below and left of Castor, the dimmer of Gemini’s two brightest stars. Remember that meteors do not appear at the radiant unless they are heading straight for you (what are the chances?), usually, they appear tens of degrees from it.
Globally, the Geminids are the most active shower peaking at around 100 meteors per hour. If the constellation Gemini was at our zenith (overhead), and we could observe the whole sky at once, we might observe 100 meteors in an hour. Sadly, for us in New Zealand, Gemini is low in our northern sky so we miss out on half of them, and of course we can’t observe the whole sky at once. Still, they are well worthwhile pursuing!
They will peak in the early hours of December 14th but should be worthwhile for a few days prior.
If possible get to a place where city lights won’t spoil your viewing, carry a blanket or a comfortable chair, along with some healthy dollops of patience. Be sure to check the weather and plan your viewing around moonrise timings (closer to the 14th the better).
Gemini will be approaching north, below and to the right of Orion. Look in the region of Orion, easily identified, and the area of sky to its right, and prepare to be amazed! Find out more here.
The ever-changing night sky is a fascinating vista best appreciated by patient and prepared eyes. By subscribing to our monthly ‘Space News,’ you’ll have access to our Sky Spotter column, which if read in conjunction with our Star Charts or a night sky app, will help you learn seasonal highlights of the night sky, spot the moon, planets, and spectacular conjunctions. Subscribe to Space News here.
Below: Looking north from Christchurch at 3 am December 14, 2017. Meteor trains will radiate outward across the sky from the radiant point.
Image at top: The Geminids shower as seen from Perth, Australia. Credit: Jacqui Hunt Unique Photography