Welcome to the October night sky. This is the month when the clocks go back and we really know that we are in the autumn season and summer is long gone. Our clocks in Portugal are set to the same time as in the UK, this means that, for time-keeping purposes, our prime meridian is at Greenwich (0º). Now, Portugal is approximately 8º west of Greenwich and the earth turns one degree every four minutes. This implies that we are normally 32 minutes ahead of the sun. If this sounds confusing, think about when the sun is at its highest in the sky.
In the summer, when we are one hour ahead of Greenwich mean time (GMT), the sun is at its highest at 1.32pm and now, when we go back to GMT, the sun is at its highest at 12.32pm. This is one of the reasons why the hottest part of the day here is in the mid-afternoon.
Looking overhead, in the late evening sky, the grand constellation of Pegasus is visible. This constellation represents the mythical winged horse of ancient Greece. Next to Pegasus in the sky, we have the constellation of Andromeda. The main claim to fame of this constellation is the Great Galaxy whose catalogue number is M31. This galaxy is the furthest object visible with the unaided eye and just appears as a faint smudge against the black night-time sky.
In reality, this faint ‘smudge’ is a giant galaxy of more than 300 billion stars and is two and a half million light years away. Just think, as you catch sight of this ‘smudge’ that the photons of light that are entering your eyes left M31 before humans existed on the planet earth!
Finally, in the early morning of October 28, the full moon enters into total eclipse. This event will start around 2.30am and finish at 3.45am. This is when the moon enters into the shadow of the earth. The moon is at last quarter on October 6, there is a new moon on October 14, first quarter on October 20 and the full moon is on October 28.
• Clive Jackson is the director of the Astronomical Observatory and the Camera Obscura of Tavira, specialising in education and public outreach. Tel: 281 321 754, Fax: 281 324 688, email: [email protected] or visit www.cdepa.pt
