Once again, we’ll take a look at what to see in the sky over the coming month.
First of all, there will be an occultation of Saturn by the Moon, just after 5pm on Saturday 25 October. From Greenwich, Saturn starts to disappear behind the Moon at about 16:05 GMT (17:05 BST) and will reappear just over an hour later, emerging from the bright limb of the Moon at about 17:07 GMT (18:07 BST).
We do intend to run a Blackheath observing event to see the occultation. The problem that we will have is that, at the start of occultation, the Sun will not have set (it sets at about 5.45pm). At reappearance, though the Sun will have set, it will only be 4 degrees below the horizon, so the skies will still be relatively light. However, we will give it a go, if the weather looks favorable, using telescopes. The main problem may be finding the Moon – it’s only 3% illuminated! It will be a little over an outstretched hand width to the left and up from the Sun.
Looking south-west, the Moon will be about 20 degrees to the left of the Sun and about 6 degrees higher in the sky. It will pay to be ready to observe about 15 minutes before the occultation begins, to give yourself a chance of finding the Moon, so we will look to set up from 4.30pm. It goes without saying that you must be extremely careful with this observation, as the Sun has not set, if you value your eyesight… and, of course, your telescope’s optics!
The Orionids, which peak around the 21-24 October, should put on a good show this year. The Orionids result from the passage of Halley’s Comet through the solar system. When the comet passes through the solar system, the sun sublimates some of the ice which allows rock particles to break away from the comet. These particles continue on the comet’s trajectory and appear as they pass through Earth’s upper atmosphere. The Orionids this year coincide with the New Moon, so you may pick up a few. The zenith hourly rate is only around a third or a quarter that of the Perseids, but with the Moon out of the way, it’s quite likely that you will see quite a few.
The radiant of the Perseids is about two-thirds of the way between Betelgeuse and Gamma Geminorum (or Alhena), by the “club” of Orion. As usual, you could see meteors anywhere in the sky emanating from this radiant.
Ursa Major is climbing away from the horizon at this time of year, and contains a huge number of galaxies, most notably M81 and M82, which are only half-a-degree apart in the sky. M82, of course, was the site of a supernova earlier this year. M82 is a fainter “starburst” galaxy. A relatively recent encounter with M81 (i.e. 100 million years ago!) has caused star formation in its core to increase ten-fold in comparison to the Milky Way.
So, how to find them? Find the 4 stars that make up the “body” of the Plough. Draw a line running diagonally across the body of the Plough to Dubhe – if you take that as one step, take another step and you will be in the vicinity of M81 and M82. In the telescope, M81 is the more rounded galaxy and M82 is the thin one. M81 is a spiral galaxy, about 50,000 light years across, whereas M82 is an irregular galaxy.
The phases of the Moon during the coming month are shown below:
As regards the planets this month:
Finally, I wanted to highlight a couple of double stars in the constellation of Cygnus, which is high overhead in the west at about 10pm at the moment.
Those who went down to Herstmonceux on Saturday evening may have seen Albireo through the 30-inch Thompson reflector, which was quite a sight. Albireo (Beta Cygni) is the “beak” of the swan, and is a strongly coloured double star, consisting of a magnitude +3.1 “gold” star and a fainter +5.1 “blue” star. Albireo, by the way, is moving towards us. So, if you stick around for a few million years, it will be one of the brightest objects in the sky!
61 Cygni was named the “Flying Star” in 1792 by Giuseppe Piazzi for its large proper motion. It is a pair of orange stars, magnitude +5.2 / +6.0. Historically, 61 Cygni is one of the most important stars in the sky. 61 Cygni is only 11.4 light years away, making it the 4th closest naked eye star (after Alpha Centauri, Sirius and Eplison Eridani). Its motion reveals its nearness to Earth. As a result, 61 Cygni was the first star system to have its distance successfully calculated using trigonometric parallax, by Bessel in 1838. In fact, it’s also known as “Bessel’s Star”.
So, how to find them. For Albireo, find the Summer Triangle of Deneb, Vega and Altair, which is still well placed high in the west at about 10pm. The star at the “top” of the triangle is Deneb, which sits at the top of the Northern Cross (or the tail of the Swan, if you prefer). Albireo is the star at the foot of the cross.
For 61 Cygni, find Deneb at the top of the Northern Cross. Where the cross-piece meets the body is the star Sadr. The star of the left arm is Gienah. If you imagine a lopsided box, with Gienah, Sadr and Deneb making three of the corners, then the fourth corner of the box is where 61 Cygni can be found.
Check out a video of this presentation here.
Some recent astrophotography images taken by Flamsteed members can be seen in the video below, or click here.