November's Night Sky

The sun is setting at around 5pm during November, so here is how to enjoy the long winter nights!

The highlight of the evening sky is the planet Jupiter, visible low in the south to south-west up until 10.30pm in the evening. Take a look at Jupiter with binoculars, or a small telescope, and see how many of Jupiter's Moons you can spot – just as Galileo did 400 years ago. You should be able to see up to four moons, and if you take another look just a few hours later, you may be able to notice that the moons have moved a bit in just that very short period of time.

The planets Uranus and Neptune are also visible in the evening sky, but they are just-too-faint to be seen with the unaided eye, which is why these two planets were not discovered until after the invention of the telescope.

Early in the evening, looking towards the west, you can still see the summer triangle of stars – Vega, Altair and Deneb – until about 9pm (see the chart to the right; click on it to see it full size). Within the triangle, you can see the remains of two dead stars using a telescope – the ring and dumbbell nebulae. There is also a beautiful double star called Albireo within the triangle.

This is also a great time of year to see the Andromeda galaxy – the most distant object that you can see with your own eyes! It may be 2.25 million light-years away, but it is quite easy to find. Just go somewhere dark, away from the light pollution and inefficient lighting of our towns and cities, and look for the square of Pegasus. The square can be found by looking towards the South, about half way up the sky. It’s quite a big square – just bigger than your hand at arms length. Look towards the star that makes the top-left corner of the square, then follow two bright-ish stars up towards the top left, and then follow two more slightly fainter stars towards the top right (as in the map, right), and just there is the Andromeda galaxy! The W-shaped constellation of Cassiopeia also usefully “points” towards the galaxy.

And it is huge! It is actually six times the diameter of the full Moon, but it appears faint because it is so far away, and so with our own eyes we can only see the bright centre of this massive city-of-stars. For the best view, take a look through binoculars (telescopes usually have too high a magnification for you to see this galaxy clearly).

Now look to the left of the square of Pegasus, about 4 times its size, and you will see a bright red giant star called Aldebaran. Just to the top-right of Aldebaran, you’ll be able to see the Pleiades star cluster, also know as the seven sisters because you can see up to seven stars with your own eyes (pictured left as a wide-angle view, and right as a close-up photograph). This cluster is a beautiful sight through binoculars, where you can see up to 50 stars. Again, don’t use a telescope, since you will only be able to see one or two stars at a time – low magnification is what you need for a cluster that appears bigger than the Moon in the night sky.

You can get some very easy-to-use and clear star maps from either skymaps.com, or by using the excellent (and free) Stellarium Planetarium software.

October's Night Sky

October is traditionally the month when you notice that the Earth is moving through space, as this is the time of year when the nights are rapidly drawing in. As the month begins, the Sun is rising at 7am and setting at 18:30. By the end of the month, the Sun is rising an hour later and setting an hour earlier. Plus, we change the clocks back to normal on the 25th to give us some daylight in the morning, and so the sunset occurs another hour earlier. By the month's end, the Sun will be setting over Sussex at 16:30!

This is all because the Earth is tilted as it orbits the Sun. In summer, our side of the Earth is tilted towards the Sun; in winter, it is tilted away – and there is a difference of 47° between the two.

All this tilting also means that the summer triangle of stars is still visible at this time of year. Look directly upwards as soon as it goes dark and the brightest three stars you can see, covering quite a large patch of sky, are the summer triangle stars.

There are some amazing sights that can be seen in the summer triangle when using even a small telescope, such as the ring and dumbbell nebulae – the glowing remains of exploded stars. The star close to the centre of the triangle is a beautiful double star called Albireo – but you will need a telescope to be able to see this star as a pair, since they are so close together in the night sky.

At this time of the year the Milky-way, the city of stars within which we live, can be clearly seen for the first-half of the night from anywhere away from light pollution. The photograph to the left was taken from the outskirts of Brighton. The lower you look at the milky-way, the closer you are looking at the bright centre of our galaxy.

During October, Jupiter (as also seen in the photograph to the left) is rising in the south-east at sunset, and setting in the west at 2am when Mars is rising. Jupiter is the brightest object in the night sky at the moment (after the Sun and Moon, of course!), and if you go somewhere that is beautifully dark, away from any light pollution, you will be able to see your own shadow cast by the light reflected from Jupiter. As a guide, the Moon will be to the top right of Jupiter on the 26th of October, and to the top left on the 27th.

Take a look through a small telescope or binoculars, and you will be able to see up to four dots in a line around Jupiter. Those four dots are the four biggest and so brightest Moons of Jupiter, so bright that there were easily seen by Galileo 400 years ago with one of the first (and so very primitive) telescopes. Sometimes, one of those moons are hidden behind or in front of Jupiter – so just take a look an hour or two later to see if another moon has reappeared into view.

The darkest nights of the month will be from the 15th to the 25th of the month, when the Moon is close to new (the new Moon, when the Moon is in line with the Sun, occurs on the 18th of October). Full moon occurs on the 4th of October, and the 2nd of November, and so the sky is awash with moon light at the start and end of the month.

We hope you enjoy October’s beautiful night-skies! And if you want to see the night sky as it will be at any time on your own computer, I recommend that you download the excellent and free Stellarium software.

Autumnal Equinox

The Earth is tilted by 23.5°, and at 21:18 GMT on September the 22nd, this tilt will be neither towards or away from the Sun. The north pole of the Earth is tilted in the same direction - towards the star Polaris - throughout the year (although this will change slightly over thousands of years). But bfore 21:18 GMT on September the 22nd, the north pole of the Earth was pointed slightly towards the Sun (which is why we had summer in the northern hemisphere), and after that moment, the north pole of the Earth will be tilted slightly away from the Sun, which is why we have autumn beginning in the northern hemisphere.

This means that on this day we have - to within minutes - an even length of day and night. The name "equinox" originates from Latin words for equal (aequus) and night (nox).

The date of the equinox varies each year because the Earth orbits the Sun in 365.2422 days, and not 365 days exactly! This is also why we have a leap-day every four years, allowing our calendars to catch up with the orbit of the Earth.

More information about the equinoxes can be found on the Wikipedia.