Why are the winter stars so brilliant?
It’s nearly winter within the Northern Hemisphere (summer season within the Southern Hemisphere), and if you happen to look exterior within the night you’ll see you’ll see many brilliant stars. Starting round now, the night sky as seen from all over the world will look clearer and sharper than it did 6 months in the past, assuming no clouds are in the way in which.
On December, January and February evenings our night sky faces away from the center of our Milky Way galaxy. As an alternative, we glance towards our galaxy’s outskirts right now of the 12 months. There are fewer stars between us and extragalactic area now. We’re additionally trying towards the spiral arm of the galaxy wherein our solar resides – the Orion Arm – and towards some gigantic stars. These enormous stars are comparatively near us, inside our personal galactic neighborhood and native spiral arm, so they appear brilliant.
Evaluating the winter and summer season sky
Take into account the sky on the reverse time of the 12 months. In June, July and August, the night sky seen from all the Earth is going through towards the middle of the Milky Means galaxy.
The galaxy is about 100,000 light-years throughout. Its middle is a few 25,000 to twenty-eight,000 light-years away from us right here on Earth. We don’t see into the precise middle of the Milky Means, as a result of it’s obscured by galactic mud.
However throughout these Northern Hemisphere summer season months (Southern Hemisphere winter months), as we peer edgewise into the galaxy’s disk, we’re gazing throughout some 75,000 light-years of star-packed area. (75,000 light-years is the gap between us and the middle, plus the gap past the middle to the opposite facet of the galaxy.)
Thus – on June, July and August evenings – we’re trying towards the mixed gentle of billions upon billions of stars. The mixed gentle of so many distant stars offers the sky a hazy high quality.
The Orion Arm
Our spiral arm of the galaxy is the Orion Arm. It additionally goes by the identify of the Orion Spur, Native Arm, Orion-Cygnus Arm or the Native Spur. It’s not one of many major spiral arms of the Milky Means, only a “minor” spiral arm. And our native Orion Arm is a few 3,500 light-years throughout. It’s roughly 10,000 light-years in size. So our complete photo voltaic system resides inside this Orion Arm. We’re situated near the internal rim of this spiral arm, about midway alongside its size.
Maybe you realize the brilliant stars of the outstanding constellation Orion the Hunter? This constellation is seen within the night throughout Northern Hemisphere winter (Southern Hemisphere summer season). The celebs of mighty Orion additionally reside inside the Orion Arm of the Milky Means. In actual fact, scientists named our arm of the galaxy for this constellation.
Backside line: In December, January and February, we’re trying away from the thick stars and clouds of the Milky Means’s core towards the Orion spiral arm, the place brilliant stars reside.
