The Night Sky in September 2007
Sunrise and Sunset Times for the UK
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Edinburgh Sunrise Sunset |
Manchester Sunrise Sunset |
London Sunrise Sunset | ||||
| September 01 | 06:15 | 20:10 | 06:16 | 20:02 | 06:11 | 19:51 |
| September 15 | 06:43 | 19:33 | 06:41 | 19:28 | 06:33 | 19:19 |
| September 30 | 07:12 | 18:54 | 07:07 | 18:51 | 06:58 | 18:44 |
Phases of the Moon (September 2007)
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| Last quarter Tuesday 4th |
New Moon Tuesday 11th |
First quarter Wednesday 19th |
Full Moon Wednesday 26th |
Click HERE to see the phase of the Moon on each day of the month.
What's happening in the September night sky?
With the better weather we've had in the UK over the past month, there have been a number of nights where the heavens were clearly visible. As we move into September the nights continue to draw in, such that by the Autumnal Equinox on the 23rd (see below) there will be more darkness than light during each day.
Maps of the current night sky can be seen by clicking HERE
September 23rd - Autumnal Equinox
The autumnal equinox marks the mid-point between the summer solstice (longest day) and winter solstice (shortest day). In real terms, an equinox is the point during Earth's 365 day orbit, where the tilt of its rotation axis is at right-angles to the Sun. In other words, the earth's axis is not tilted toward the Sun, as in summer, or away from it, as in winter.
The changing tilt of the Earth
This all means that at equinox we have around 12 hours of daylight and 12 hours of nightime everywhere on Earth. There is another equinox in the spring (around March 21st), known as the Vernal or Spring equinox. This occurs when the Earth has moved around its orbit and the northern hemisphere is just about to start tilting towards the Sun again. The word equinox comes from a Latin word meaning "equal night".
If you find equinoxes a bit confusing or you wish to learn more about our seasons, then try following this link.
Harvest Moon
Keep an eye out for the Harvest Moon on the 26th. This is traditionally the name given to the full moon that is closest to the autumnal equinox. It was so named because it allowed the harvesting of summer crops to continue well on into the night. Around the equinox, we see the harvest moon rising just as darkness descends upon us, and because it never gets high above the horizon it seems to be bigger than at other times of the year.
If you are captivated by the beauty of the moon at different phases, then you may be interested in catching up on the two Moonsaic projects we ran recently. Essentially, the projects are aimed at Keystage 2/3 students and involve creating a large mosaic of the Moon using images taken by the Liverpool Telescope.
If you want to learn more then click on the following links: Moonsaic 1 Moonsaic 2
What are the planets up to?
Click HERE and start the Electric Orrery to see where all the planets are today in relation to each other.
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Mercury - can be found
low above the western horizon for around 30 minutes after sunset. As the month moves on
this linger-time remains fairly constant even though its angular separation from the Sun
continues to increase. Mercury will reach greatest elongation (separation from the Sun) on
the 29th September, before positioning itself to pass in front of the Sun next month. Because
it remains low above the horizon and sets during evening twilight, it will be very difficult
to spot Mercury this month.
Venus - passed inferior conjunction (between us and the Sun) in the middle of August and so starts the month rising in the eastern sky around 80 minutes before the Sun makes an appearance. This increases quite markedly during the month, such that by the end of September, Venus will rise a good 3.5 hours before the Sun and can be found high above the eastern horizon at sunrise. In essence, the brightest object in the eastern sky just before dawn this month will be Venus. Mars - starts of the month rising in the northeast around 11:30pm. Just before sunrise it can be found high above the south-southwest horizon. This time moves forward an hour by the end of September, such that Mars will be very high (almost above your head) to the South at dawn. Why not see if you can bag an image of Mars this month using Go Observing. Jupiter - can be found very low in the southern sky during the early part of the night, throughout September. Sadly it is too low for the Liverpool Telescope to observe safely. At the start of the month it sets in the southwest around 11.00pm, and this moves forward to 9.15pm by the month's end as we continue to move away. Try using the Electric Orrery to see how Jupiter gets further away from the Earth in the coming months. Saturn - remains relatively close to, but is outshined by, Venus during September. At the start of the month it can be found low above the eastern horizon for around 50 minutes before sunrise. This increases to nearly 3 hours over the course of four weeks, with Saturn reaching high above the east-southeast horizon by dawn. This means that Saturn will be observable again by the end of the month. |
Constellation of the month
Each month, a new constellation is highlighted for you to identify in the night sky.This month, we are going to look for the constellation of Cepheus, the King, which was named after King Cepheus in Greek mythology. Cepheus is not immediately obvious as a constellation, but we can once again use the more recognisable Summer Triangle to locate the crown-like grouping of stars high above our heads. With it being dark out there at 10 o'clock, be careful not to fall over backwards.
September Night Sky
The constellation is notable due to the presence of an unassuming star known as δ Cephei, which is very important to astronomers. On the face of it, it looks like a normal yellow star, but watch it for any length of time and you will notice that its brightness varies periodically. In other words, it gets brighter and then dimmer over a very regular timescale of a few to over a hundred days. Since the discovery of δ Cephei, other stars have been found that copy this behaviour. It was later noted (in 1908) that we can use the changes in such stars, known as Cepheid Variables, to find out the actual brightness of the star and from that its true distance.
Before Cepheid variables, it was hard to know whether we were looking at a very bright star that was far away from us or a dim star that was nearby - these could in fact appear the same brightness to our eyes due to the fact that lights get dimmer as they move away. However, knowing the true brightness reveals the star's distance, and allowed us to work out the first distances to nearby galaxies in which Cepheid variables were spotted.
Animation of a variable star
Cepheid variable are actually giant yellow stars in the latter stages of their lives and the variation in brightness is due to unstable layers of helium gas in the star's outer atmosphere, which make the star pulse both in size and brightness. As fuel continues to run out over the next few million years the star will move into the final phase of its lifetime.
Mythology: Cepheus
Cepheus, king of Ethiopia, was married to the beautiful Cassiopeia, and together they had a daughter, Andromeda. Although his name is most well-known in connection with his daughter, Cepheus was placed in the sky of his own right: He voyaged as an Argonaut with Jason on the quest for the Golden Fleece. All three members of the family may be found in the northern sky - Cepheus and Cassiopeia are quite close to the pole star (Polaris).
