Sky Notes for September 2012, with James Abbott #stargazing
The Autumnal Equinox takes place this year on 22nd September just before 3pm BST when day and night are broadly equal across the world. For UK astronomers, the darker autumn nights that follow can bring good observing conditions in reasonable temperatures before the frosts of winter set in.
Full Moon this month is in the early hours of the 30th at just after 3am BST. The waning gibbous Moon of early September is the Harvest Moon. Moonrise in the East only advances by about an hour and a half from the 1st to the 5th September, providing evening light across the landscape.
By the end of the month, Jupiter is becoming more dominant in the East during the late evenings, just to the left of Aldebaran in Taurus. The opposition of Jupiter this year is particularly good, with the planet steadily brightening to a peak of mag -2.8 in early December when it will reach an altitude of 60 degrees when due South.
For early risers, there will be a fairly close conjunction between the last quarter Moon and Jupiter high in the pre-dawn Eastern skies of the 8th September, when Venus will also be visible lower down.
By mid-month it is fully dark around 9pm and the night sky is taking on an autumnal appearance with the Square of Pegasus well up in the East followed by Perseus and the familiar W shape of Cassiopeia in the North East.
By late evening the summer constellations are over towards the West but still prominent. Almost overhead mid-month at 10pm BST is Deneb, the brightest star in Cygnus. Looking at the stars with the unaided eye it is impossible to tell how far away they are. Using astronomical techniques such as parallax, it is possible to estimate distances and it turns out that Deneb is very distant, possibly in excess of three thousand light years, although it could be half that due to uncertainties in the measurements. In any case, across this distance range it means Deneb must be a real celestial powerhouse to be seen as a bright star, with a luminosity of around 100,000 times that of our Sun.
Despite great advances in astronomy, distance measurements for stars beyond the solar neighbourhood remain uncertain – which in turn creates problems for defining scale across our galaxy. The European Space Agency Hipparcos mission delivered improved data with a catalogue published in 1997 listing over 100,000 stars, but this was still with limited accuracy for distant stars. The ESA Gaia mission due for launch in 2013 aims to greatly increase accurate distance measurements derived from parallax, which will help to improve our understanding of the true dimensions of our galaxy.
The Sun continues to become more active as it moves towards the maximum in its 11 year cycle. Maximum activity could arrive in 2013, with increasing occurances of solar flares which throw charged particles out into the solar system and can cause Aurora if the Earth’s magnetic field interacts strongly with the solar material. So the next few years offer the best chance of seeing the Northern Lights from Essex. Whilst very bright all sky displays are rare, such as the one in April 2000, modest displays can be seen more often and one such was seen and photographed from Heybridge in July (shown here):
James Abbott is an astronomer, NEAS member and CfDS Regional Information Officer.