The Seven Sisters


There have been so few clear nights this past month, Astrophotography is becoming a challenging task! Hopefully as the temperatures continue to drop we’ll be treated to some very crisp clear, albeit cold, nights.

I didn’t have much time to capture this month’s image, and it’s another well-known object in the night sky. The Pleiades (Messier 45), also known as the Seven Sisters is an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. It is among the star clusters nearest to Earth, it is the nearest Messier object to Earth, and is the cluster most obvious to the naked eye in the night sky.

17th Century stargazing

The cluster is dominated by hot blue and luminous stars that have formed within the last 100 million years. Reflection nebulae around the brightest stars were once thought to be left over material from their formation, but are now considered likely to be an unrelated dust cloud in the interstellar medium through which the stars are currently passing.

Galileo Galilei was the first astronomer to view the Pleiades through a telescope. He discovered that the cluster contained many stars too dim to be seen with the naked eye. He published his observations, including a sketch of the Pleiades showing 36 stars, in his treatise (Pamphlet) Sidereus Nuncius in March 1610.

A marmite effect

This image was taken using a Skywatcher 200 PDS Newtonian Reflector Telescope and dedicated Cooled Astro Camera with 2 1⁄2 hours of total integration time during November.

The diffraction spikes (that ‘Christmas star’ effect) created by the brightest stars are the result of the design of a Newtonian reflector telescope. The secondary mirror of the telescope is mounted on the front of the scope with 4 spider veins. As light passes through the tube, the spider veins cause the diffraction spikes seen in the image.
A bit like marmite, some Astronomers love the effect of diffraction spikes, others not so much! If you don’t want to have diffraction spikes in your images, stick to Refractor telescopes!

The Night Sky, December – what to see this month:

As the year draws to an end, the planets of our solar system line up for a final parade, set to a backdrop of some brilliant winter constellations and a final meteor shower to top off proceedings.

The Hunter

Orion (The Hunter) is a personal favourite constellation of mine and is now in full view above
the horizon from around 9pm looking east and moving south as the night draws on. The stars that make up Orion’s Belt are some of the easiest to identify in the night sky.

The Goddess of Love

On the 6th, find the crescent moon and then look towards the upper right to spot brilliant Venus, often best viewed during twilight, just after sunset. Viewing Venus during twilight with a telescope may reveal the details of this extraordinary world, including dense clouds within its 98% carbon dioxide atmosphere. It is named after the Roman goddess of love and beauty, a fitting description for the brightest natural object in Earth’s night sky after the Moon. On the 7th December, Venus reaches the brightest it will be this year, look towards the south-west after sunset.
The planets Jupiter, Saturn and Venus hang around the moon over the course of the 8th and 9th.

Meteor shower

On the night of the 13/14, the Geminids meteor shower will put on a display, clouds permitting! The debris that causes this celestial event is in fact debris from the asteroid Phaethon, rather than from the traditional comets.
On the 17th of December, the star Aldebaran and the Hyades star cluster lie to the right of the moon. Although, they are actually unrelated with Aldebaran being 65 light years away and Hyades about 2 1⁄2 times further away, this is what’s known as ‘line-of-sight coincidence’.

The Winter Solstice shortest day and night greets us on the 21st December at 15:59 pm. On the 31st of December at 7am low in the south-east, catch a glimpse of Mars close to the narrow crescent Moon.

And that brings our Night Sky of 2021 to a close. I hope you’ve enjoyed the column and the images that I’ve shared this year!

All that remains is to wish everyone a very Merry Christmas and New Year, and I hope Santa brings you a telescope so that you can observe the night sky in all its glory from where you are. Until next year, clear skies!

by Rob Nolan RPN Photography


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