The Night Sky in August 2007

Sunrise and Sunset Times for the UK

	Edinburgh Sunrise Sunset		Manchester Sunrise Sunset		London Sunrise Sunset
August 01	05:15	21:23	05:22	21:08	05:22	20:52
August 15	05:42	20:53	05:46	20:41	05:43	20:27
August 30	06:11	20:16	06:12	20:07	06:07	19:55

To find out today's sunrise and sunset times for where you are, click here

Phases of the Moon (August 2007)


Last quarter Sunday 5th	New Moon Sunday 12th	First quarter Monday 20th	Full Moon Tuesday 28th

Click HERE to see the phase of the Moon on each day of the month.

What's happening in the August night sky?

As the wettest summer on record squelches onward we will start to see the nights drawing in, such that between the beginning and end of August the amount of daylight will decrease by a whole 2 hours. The consolation is that these extra hours of darkness will give us more chance of seeing the night sky and perhaps catching one of the monthly highlights mentioned below.

Maps of the current night sky can be seen by clicking HERE

August 13th - Perseid Meteor Shower

During the year, meteor showers provide us with a better chance of seeing a meteor or 'shooting star'. Meteors are usually small pieces of rock or dust that enter and burn up in the Earth's atmosphere, creating bright firey trails across the night sky. The peak in meteor numbers will take place in the early hours of August 13th in a dark, moonless night sky; although there will be more than the normal amount of meteors for a few days either side. Astronomers predict that at its peak, the shower should produce around one meteor per minute, which is up from the usual 5 or 6 an hour.

Stellarium image showing the radiant of the Perseid meteor shower

The origin or radiant of the meteor shower, as shown on the above skymap, marks the point where the meteors are expected to start from and then trail out from in all directions. The meteors will last no more than a few tenths of a second, so you have to concentrate .... blink and you'll miss them. The lines going across on the skymap tell us the angle above the horizon at which we are looking, and run from 0° (the horizon) to 90° (right above our heads). The vertical lines represent sectors of 15° around the 360° compass. If the idea of compass angles confuses you, try asking one of your teachers.

So what causes Meteor Showers?

At certain times of the year, Earth passes through a trail of dust and debris that is left by a passing comet. In the case of the Perseid meteor shower the culprit is Comet Swift-Tuttle, which was first spotted passing through Earth's orbital path back in 1862 - thankfully at a point in the year when the Earth was elsewhere. The comet is now known to orbit the Sun every 120 years and is predicted to make a very close fly-by of Earth in the year 2126 and potentially pose a collision risk in the year 3044. Something that future generations may have to worry about.

August - Month of many planetary conjunctions

It just so happens that this August will see an unusually high number of planetary conjunctions. The term conjunction is used to describe the joining together of two objects in the same part of the sky. This does not mean they are close in terms of physical distance, they just appear in the same region of our view. In planetary terms, we say that a planet reaches conjunction when it appears (to us) to line up with the Sun - i.e. the smallest angular separation between the planet and Sun.

As shown in the diagram above, planets that orbit inside Earth's orbit, namely Venus and Mercury, can have inferior (between us and the Sun) and superior (other side of the Sun to Earth) conjunctions, whereas all the other planets only achieve conjunction on the other side of the Sun. The three events this month are Mercury at superior conjunction on the 15th, Venus passing inferior conjunction on the 18th and finally Saturn reaching conjunction on the 21st.

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.

Mercury - starts August rising in the east-northeast around 80 minutes before sunrise. If you wanted to catch a glimpse of this elusive planet, then the beginning of the month would provide the ideal opportunity, although it would mean a very early rise. Mercury passes superior conjunction (other side of the Sun to Earth) on the 15th and slowly re-emerges as an evening object. However, it will then be lost in the glare of twilight until the first week in September.

Venus - is lost in the evening twilight at the start of the month, setting just 10 minutes after the Sun. It passes in front of the Sun (inferior conjunction) on the 18th and re-emerges as a morning object for the first time this year, after spending all of 2007, thus far, dominating the western sky after sunset. By the end of the month, we will be able to see Venus again towards the East, where it will rise around 80 minutes before the Sun.

Mars - is becoming a much better target as the months roll on. At the start of the month, it rises near to the Pleiades Star Cluster (Seven Sisters) in the east-notheast at around 0.30am. This time moves forward an hour by the end of August, at which point Mars can be found high above the south-southwest horizon around dawn. Why not see if you can bag an image of Mars this month using Go Observing.

Jupiter - can be found low in the southern sky shortly after sunset throughout the month, which makes it a difficult target for the Liverpool Telescope to observe. At the start of August it sets in the west-southwest around 1.00am, and this moves forward by 2 hours by the month's end as we continue to move away. Try using the Electric Orrery to see how Jupiter gets further away from Earth in the coming months.

Saturn - is the third of the visible planets to pass conjunction this month. It starts August setting in the west-northwest just 40 minutes after the Sun, it passes conjunction on the 21st and ends the month rising in the east-northeast 40 minutes before sunrise. Because it is far away on the other side of the Sun, it will be very dim and therefore hard to pick out of the glare of twilight throughout 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 Draco, the Dragon, the head of which starts close to the Summer Triangle stars of Vega, Altair and Deneb. Once you have identified the triangle, extend the line between Altair and Deneb until you are looking almost directly overhead. There you will find the head of the Dragon. With this constellation being right above you, and with it being dark at the time, be careful not to fall over backwards.

Draco is not the most noticeable of constellations, as it has very few bright stars, but it is the eighth largest in the sky. It is not commonly known that the star Thuban was the northern pole star around 2700 BC, during the time of the ancient Egyptians. Due to an effect known as precession, the direction of the Earth's rotation axis, which is currently pointing at the star Polaris, will move very slowly along a circular path (as shown below) and will once again point to Thuban around the year 21,000 AD.

Changing direction of Earth's rotation axis

Animations of the 26,000 year precession of the Earth's rotation axis - Credit: Scott Anderson

In other words, precession is a slow wobble of the Earth's spin axis that takes around 26,000 years to complete. The phenomenon was discovered by the Greek astronomer Eratosthenes when he compared his own circa 200 BC records with older charts. In this wobble motion, the tilt of the Earth to the Sun stays roughly the same at 23.4°, but the direction in which it points is slowly changing.

Mythology: Draco

There are numerous myths behind the constellation Draco, due to its resemblance to a dragon. In the most famous of these, Draco represents Ladon, the hundred-eyed dragon that guarded the golden apples of the Hesperides. The eleventh of The Twelve Labours of Heracles (or Hercules) was to steal the golden apples. Heracles killed Ladon with a poisoned arrow, allowing him to freely take the golden apples. According to the legend, Hera later placed the dragon in the sky as the constellation Draco.

In another legend, Draco represents the dragon killed by Cadmus before founding the city of Thebes, Greece. In a third legend, it represents the dragon that guarded the Golden Fleece and was killed by Jason. The fact that the stars of this circumpolar constellation never set plays an important part in its mythologies.