SKYMATTERS Blackrock Castle Observatory www.bco.ie Download monthly skymatters newsletters from www.bco.ie/skymatters August 2016
Things to watch out for
August 2 The Moon is new and so remains invisible throughout the night. As the sky starts to get darker that little bit earlier in August com- pared to June or July, it is becoming increasingly easier to take advantage of the moonless skies, including taking the opportunity to observe faint objects.
August 10 The Moon is First Quarter and nicely placed until around midnight when it sets.
August 12/13 The Perseid meteor shower is generally considered to be the best meteor shower of the year, not only because of the number of bright meteors, but also because the nights are still quite warm! Under dark skies, away from bright city lights, you can expect to see up to 60 meteors per hour. The best time to view Perseids is after midnight, but you can look out for them any time after dark. Incidentally, while the Perseids peak on 12/13th, the shower gradually builds up in the days before then. Further information on page 3.
August 18 The Moon is full, rising before 9pm. Keep an eye out for it looking either bigger (which is an optical illusion) or redder (which is due to the Earth’s atmosphere) or both.
August 27 The planets Venus and Jupiter appear within 0.06 degrees of each other just after sunset. Both planets will be bright and so even with the sun-glow they should be easy to spot. Venus will be the brighter of the two planets. With a telescope you can see that Ve- nus is 92% illuminated, which tells us that it must be almost directly on the far of the sun to the earth at this time. If using a tele- scope be careful not to point it at the setting sun by accident and the best approach is to wait until the sun has definitely set. The exact time of this will depend on your local horizon.
Skychart for August
The simplest way to use the skychart is to find the North Star (marked on the chart as Polaris and circled red) in the real sky and point the pole star on our sky- chart in that direction.
The skychart is most correct for about 11pm in the middle of the Au- gust 2016 (or 10pm at the end of the month or 12 midnight at the be- ginning of the month). The constellation of Perseus is outlined in green. It is on the hori- zon at sunset and con- tinues to rise throughout the night in August.
Planets in August Mercury at its greatest eastern distance, or elongation, from the Sun on 16th. At a separation of 27.4 degrees, Mercury is almost exactly one moon diameter away. As always, be very careful if looking for Mercury and make sure there is no chance the Sun will make an unexpected appearance from behind some horizon-skirting clouds.
Venus continues to move away from the Sun and its phase is almost full. On 27th the planet is extremely close to Jupiter and should make a spectacular sight just after sunset.
Mars is becoming more challenging to observe, but still visible after sunset . On 23rd it is only 2 degrees north of Antares. Antares is a red su- pergiant star which is nearing the end of its lifetime. When it finally dies it will do so as a supernova, quite literally blowing itself apart and burn- ing as brightly as the entire Milky Way galaxy.
Jupiter gained a new orbiting satellite from Earth on July 4th called Juno (as mentioned in the July edition of Skymatters). It is, however, fading from the view of the earth for the next while and August is not a good month to observe it (except for its close encounter with Venus on 23rd).
Uranus gains altitude throughout the night, rising almost due south. It is not visible without binoculars or a telescope, Neptune rises in the east about 11:30 pm and is in the constellation of Aquarius. It is fainter than Uranus and so is also a binocular or telescope object. Constellations to keep an eye on in August
Although not particularly well placed to observe, the constellation of Perseus is “prominent” be- cause of the Perseid meteor shower this month. It is also home to the variable star “Algol” which is a three-star system where one of the stars eclipses the main star in the system every 2.86 days. A careful observer can see this change in brightness even with the naked eye. To find Algol look north- east after sunset. It can be easy to confuse Algol with the nearby star Capella, so watch out for that. And note that Algol is not even the brightest star in Perseus, that honour going to Mirfak.
The Perseids appear to originate in the constellation of Perseus. The bright- est star in Perseus is Mirfak. Perseus can be found underneath the W-shaped constellation of Cassiopeia around 11pm.
The Perseid Meteors August is best known for the Perseid meteor shower. Meteors occur when particles in space collide with the earth’s atmos- phere and the heat generated causes them to burn up. Parti- cle sizes vary from around 1mm to 1cm. The best time to ob- serve meteors is usually after midnight, because the earth’s dark side is also its leading side and so the planet is literally ploughing head-on into the particles that become meteors. This makes them brighter, and faster. Even smaller particles may become bright enough to be visible, so the number of visible meteors generally increases too. A bright meteor may last only a fraction of a second, but it can rival the brightest of stars in its fleeting lifetime.
In the case of the Perseids, the meteors come from particles thrown off by comet Swift-Tuttle which was discovered in 1862. This comet has an orbital period of 133 years and its next return is due in 2126! As it heats up in the vicinity of the Sun it leaves a trail of debris in its wake, and it is this trail that provides the particles for the Perseid meteor shower. The rate at which material is thrown off the comet varies from orbit to orbit and the exact location along the debris that the earth encounters also varies from year-to-year, meaning we never quite know what the meteor shower will be like from one year to the next.
For first-time observers, there is an easy way to distinguish meteors from satellites. Meteors are fast-moving and cover maybe 30-50 de- grees of sky, whereas satellites take several minutes to travel across the entire sky. If you do go outside just after sunset, when the sky is still a bit light, you might see an “earthgrazer”. These rare meteors are a real joy to capture. They come from particles of dust that are quite literally grazing the top of the atmosphere and they make long, slow trails (though not as slow as satellites!).
Meteors and Meteorites Website of the month The best way to observe meteors is with your unaided eye. The darker the location, the The International Space Station higher the number of meteors you will see, but even if you are looking out from your back (ISS) is one of the technological garden in the suburbs you will very likely see some Perseids every 15 minutes or less. marvels of our time, currently The best place to look is overhead and slightly towards the north, but if you have no nor- home to five mail and one female therly view do not be discouraged as Perseids can appear anywhere in the sky. It can be astronaut. ISS is visible from time fun to see if you can identify any colours. For example, the colours blue, green and yel- to time from Ireland and if you low likely come from the metals in the meteor itself as it burns up, while red is likely to haven’t yet seen it then check out come from oxygen in our atmosphere as it is super-heated by the meteor. Large meteor this website for your location: events are sometimes called bolides, and there is some anecdotal evidence that they can cause a hissing sound. Really bright meteors are called fireballs and these have URL: https:// been known to generate a sonic boom and leave a trail which is visible for some time in spotthestation.nasa.gov/ the sky. They may result in meteors reaching the ground and becoming meteorites. The later in the night you look for Perseids the better, with the optimum time being 2-4am.
Famous meteorite events include the Chicxulub asteroid that caused the extinction of the Quote of the month dinosaurs 65 million years ago, the Barringer Crater in Arizona which is roughly 50,000 “Space is for everybody. It’s not years old and the Tunguska meteorite on 30th June, 1908 in Siberia. just for a few people in science or Photographing meteors is easy if you have a camera with a shutter than can be set to math, or for a select group of as- “open” for an extended period of time. Simply put the camera on a tripod, using the wid- tronauts. That’s our new frontier est angle setting you have, and leave the shutter open for twenty minutes or so. If you out there, and it’s everybody’s point your camera towards the north and are fortunate to capture a few meteor trails you business to know about it.” will see they all point towards a single point of origin in the constellation of Perseus. This point is called the radiant. Meteors which appear close to the radiant are shorter than Christa McAuliffe, Challenger those which appear further away. And while we may say that the number of meteors is astronaut and teacher 60-100 per hour, meteors are unpredictable and the rates will rise and fall.
Some Upcoming Events at CIT Blackrock Castle Observatory
Space Camp | July 11-15 or 25 – 29 for 7-9 year old’s or July 18 – 22 for 10 – 12 year old’s | 09:30 – 12:30 Booking is now open for our Summer Camp. Discover the Universe and the secrets of the Solar System, build and fire Rockets and explore Engineering and Telescopes! The cost for each Space Camper is €95 which includes 1 week of Space Camp, Space Camp t-shirt & all activity materials.
Cork Heritage Open Day | August 20 | 10:00 - 12:00 Free 30 minute tours for Cork Heritage Open Day. Take a journey back in time to learn about the colourful history of the inner harbour fort & the later expansions that created Blackrock Castle of today. Booking is essential and tickets will go live on bco.ie on July 29
Junior Space Camp | September 4 | 12:00 – 13:30 Only 6 places left. Our hugely popular Junior Space Camp is amazing science with an intergalactic twist! We’re go- ing to take a journey into Space and give our budding space enthusiasts a chance to explore and experiment with science. Suited to 5 – 7 year old’s. €10 each (one parent is required to stay). Booking advised (July & August are fully booked)
Planetarium Shows | Daily | 12:00, 14:00 16:00 Discover the wonders of the night sky in our live planetarium shows. Shows are included in your admission ticket.
Castle Tower Top & Gunnery Tours | Daily | 11:30, 13:30 15:30 Blackrock Castle is the oldest surviving structure still in use in the city of Cork; a 16th century fort turned robotic observatory and science centre with panoramic views of Cork Harbour. Your tour guide will bring the past, present and future together and take you on a trip back through the colourful history of Blackrock exploring over 400 years of Cork Harbour stories. Tours are included in your admission ticket