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Skynotes for August 2012

  • 01-08-2012 9:26am
    #1
    jfSDAS
    Registered Users, Registered Users 2 Posts: 352 ✭✭


    hi all,

    just beat the tape on this one (in keeping with the Olympic theme)!

    clear skies!

    John


    All times are in Universal Time (UT), same as winter time. Add one hour to get the BST equivalent.

    Skylight for August 2012
    If the sky is clear on the night of August 11th/12th, then you are in for a treat with the Perseids, one of the most reliable meteor showers of the year, reaching maximum. The predicted peak is around on August 12th at 13h so that means both the night of Saturday, August 11th, and the following evening, are ideal to spot these celestial fireworks.

    Perseid meteors are bright and fast with a number leaving brief trains. The Perseids were the first shower to be positively linked to a comet when computations in the middle of the nineteenth century showed a similarity between the orbits of the Perseids and comet 109P/Swift-Tuttle.

    Meteor showers are named for the constellation in which the radiant, or point of origin of the meteors, lies. Perseus is above the north-eastern skyline as darkness falls and the radiant gains in altitude throughout the night. Typical Perseid rates are about a meteor a minute when observing the shower from a dark site, though numbers do vary due to factors such as the radiant height.

    Moonlight interferes a little this year with the waning crescent rising around local midnight on the 11th but almost an hour later the next night. However, only the fainter members of the display will probably not be seen and it will be easy enough to block the glare of the Moon by picking a suitable observing location. See the Out & About section below for details of a meteor watch planned by the newly formed Balbriggan Astronomy Club.

    See also ...
    · http://earthsky.org/astronomy-essentials/earthskys-meteor-shower-guide
    · http://earthsky.org/tonight/wheres-the-radiant-point-for-the-perseids
    · http://meteorshowersonline.com/perseids.html (history of the Perseids)
    · http://www.imo.net/node/1434 (continuous updates of shower activity)

    The Sun
    See http://www.sunrisesunset.com/predefined.asp to create a sunrise/sunset calendar for the month and http://www.suncalc.net for details of the current day's sunrise/sunset positions overlaid on a map.

    Something different this month in that I'd like to highlight a branch of the hobby which probably falls somewhere between astronomy and weather. The subject is meteorological optics, the wonderful range of phenomena that are painted across the sky through the interaction of sunlight (or moonlight) and water in various forms (ice or raindrops): Two simple ingredients that produce delightful dishes such as halos, rainbows, sundogs, and much rarer treats.

    The premier site on the subject is that run by Les Cowley at http://www.atoptics.co.uk/ where you will find photographs and descriptions of a riot of colour in the sky. Click through to the Resources section on the site and you will find other links along with a list of books on the subject. For a general read though I highly recommend Kaleidoscope Sky by Tim Herd, whose site http://www.kaleidoscopesky.com is well worth browsing too.

    The Moon
    Full Moon is on August 2nd, Last Quarter Moon on the 9th, New Moon on the 17th, First Quarter on August 24th, and Full Moon again on the 31st.

    The second Full Moon in a month is popularly called a Blue Moon. The Moon revolves around the Earth in 29·53059 days (known as the synodic month) and so we may see the same lunar phase repeat on occasion during a month. This occurs about every 2.5 years on average. The next Blue Moon month will be July 2015. See http://earthsky.org/tonight/how-often-do-two-full-moons-happen-in-the-same-month

    The Planets
    Mars and Saturn play out a celestial ballet low above the southwest horizon as evening twilight descends. Both planets are in Virgo and form a trio with the magnitude 1.0 star Spica during the month, with them closest around the 10th. Mars is magnitude 1.2 and Saturn magnitude 0.8 about this time so it will be interesting check the colour contrast between the three objects -- binocular will make it easier, and they will all fit within the same binocular field-of-view. Saturn, Mars and Spica then form a near straight line on the evening of August 14th and the waxing crescent Moon joins the scene on the 21st. Mars is a tiny 5 arc-second disk this month and show a 90% lit phase in a telescope.

    Distant Neptune reaches opposition on August 24th in Aquarius where it can be spotted as a magnitude 7.8 "star". Don't expect to see any detail on the planet though as its bluish-tinted disk just measures a tiny 2.4 arc-seconds. A detailed finder chart (and one for Uranus too) can be downloaded at http://www.skyandtelescope.com/observing/highlights/Uranus-and-Neptune-in-2012-138059253.html

    Jupiter can be found in Taurus, close to the Hyades star cluster at the start of August, and slowly moves eastward during the month. The planet brightens slightly from magnitude -2.1 to -2.3 and appears earlier each night, rising around 01h at the beginning of the month and before local midnight by the 31st. Look for the Moon nearby on the night of August 11th/12th as Jupiter rises.

    Jupiter's disk measures 38 arc-seconds in diameter and a small telescope will show the main cloud belts as well as the Great Red Spot, a massive storm system two-and-a-half times the diameter of the Earth. A double transit of the shadows of Europa and Io on the Jovian cloud tops can be seen on the morning of August 8th. Europa's shadow moves across the disk from 02h 04m and Io's at 02h 34m.

    Venus dominates the hours before dawn and is rising nearly four hours before the Sun by the end of August. The brightness declines slightly from magnitude -4.6 to -4.3 as the phase changes from 41% lit on August 1st to 58% lit on the 31st. The thin crescent Moon lies to the lower left of Venus on the morning of August 14th.

    Venus is predicted to be at half-phase, or dichotomy, when at greatest western elongation (46°) on August 15th. However, due to a phenomenon known as the Schröter Effect, observers often report the date they notice this exact half-phase as earlier during evening apparitions and later in morning apparitions. The effect is generally believed to be a contrast phenomenon between the day side of Venus and the unlit portion because of its bright cloud layers.

    Mercury puts on its best morning show of the year during August and reaches greatest western elongation on the 16th (18.7°) when it rises about 45 minutes before the Sun and is magnitude 0.1. The planet lies 4° above left of the waning lunar crescent this morning low above the west-southwest skyline. Mercury brightens rapidly to magnitude -1.0 by the 25th and is highest above the horizon on the 19th when it reaches 7° altitude. The planet should remain visible up to about the 28th.

    Comets
    No bright comets are visible during August. However, details of fainter objects can be found on the BAA's Comet Section web site http://www.ast.cam.ac.uk/~jds/

    Meteors
    One of the most reliable meteor showers is the Perseids which peak on the night of August 11th/12th this year. The shower features as this month's skylight but it is worth pointing out that you may also see what are called sporadic meteors during the night too. These are meteors that have no known shower association and the second half of the year often sees increased numbers of sporadics noted. They can appear from any direction in the sky and some may also be remnants of a long defunct shower.

    Although an old article, the second part of http://science.nasa.gov/science-news/science-at-nasa/2000/ast28sep_1/ is worth reading to learn why sporadic rates are higher in the autumn. The September 2012 issue of Sky & Telescope magazine also has an interesting article by meteor expert Peter Jenniskens about recently discovered minor showers.

    Details of annual meteor showers can be found at http://www.imo.net/calendar/2012 or http://meteorshowersonline.com/calendar.html

    Asteroids
    No bright asteroids reach opposition this month but 4 Vesta and 1 Ceres can both be spotted in Taurus in the hours before dawn. Vesta (magnitude 8.3) creeps within 15 arc-minutes of Aldebaran, a magnitude 0.9 red giant star in Taurus, on the morning of August 6th. Ceres is a bit dimmer, hovering around magnitude 9.0 during the month.

    See http://www.skyandtelescope.com/observing/objects/asteroids/Ceres-and-Vesta-July-2013-148149915.html for an excellent article and finder chart about the motions of these two distant worlds over the next few months.

    Spaceflight
    NASA's Year of the Solar System, running since October 2010, comes to a close in August. YSS featured a different Solar System exploration theme each month over a period that was actually equivalent to a Martian year in length. But what a way to end YSS though, with the Mars Science Laboratory mission scheduled to land on Mars on the morning of August 6th at 05:31UT (06:31BST).

    The mission will deploy the Curiosity rover, the largest and most sophisticated ever launched, to a landing site near the 5km high mountain Aeolis Mons in 160km wide Gale Crater, just to the south of the Martian equator. Curiosity has a mass of 900 kg, is designed to explore Mars for at least a year and will cover a minimum range of between 5 and 20 km.

    Mission home page is http://marsprogram.jpl.nasa.gov/msl/
    The DAWN spacecraft is due to depart 4 Vesta on August 26th and cruise towards an encounter with 1 Ceres in February 2015. DAWN has spent more than a year orbiting 525km wide Vesta and has carried out a detailed mapping of the asteroid along with measuring its composition and other characteristics. The mission page is http://dawn.jpl.nasa.gov/

    See http://en.wikipedia.org/wiki/2012_in_spaceflight and also the Planetary Society blog at http://www.planetary.org/blogs/emily-lakdawalla/ after the start of each month for updates on the status of unmanned missions across the solar system.

    Out and about
    · August 11th -- Balbriggan Astronomy Club meteor watch. Contact carl at webtreatz dot com for more details. Please note, only confirmed attendees will be permitted access to the grounds of Ardgillan Castle for the watch.
    · August 13th -- Astronomy Ireland lecture "Ancient Astronomical Alignments" to be held in Trinity College Dublin. See http://www.astronomy.ie/lecture201208.php for details.
    · August 18th (to 26th) – A number of science events and lectures will be held during Heritage Week, including talks by science journalist Mary Mulvihill in Drumcondra, Raheny, and Dublin City Library about Dublin's scientific heritage. More details can be found at http://www.heritageweek.ie/index.php/whats-on/event-search (enter "Science" as the keyword for the search)

    Photo competitions
    · Clean Coasts Photography Competition 2012 (closing date is 17th August 2012). See http://www.cleancoastphoto.org/
    · National Heritage Week Photo Competition 2012 (closing date is 31st August 2012). See http://www.heritageweek.ie/whats-on/national-heritage-week-photography-competition
    · Irish Meteorological Society Photo Competition 2012 (closing date is 30th September 2012). See http://www.irishmetsociety.org/ims-photography-competition-2012/2/ckforms
    · Irish Rural Landscape Amateur Photography Competition 2012 (closing date is 28th September 2012). See http://www.icomos.ie/irish_rural_landscape_photo_competition_2012/irish_rural_landscape
    · ESAI Photography Competition 2012 (closing date is 28th December 2012). See http://www.esaiweb.org/photography-competition/

    Exploring further
    The following web sites are also a great resource for information about what’s on view in our skies during the month -- we also recommend downloading the free planetarium program Stellarium at http://www.stellarium.org/

    www.skymaps.com — superb charts you can download
    www.jb.man.ac.uk/astronomy/nightsky/
    www.guardian.co.uk/science/series/starwatch
    www.telegraph.co.uk/news/newstopics/nightsky/
    www.heavens-above.com — space station predictions
    http://dcford.org.uk/index.php -- the Digital Astrolabe
    http://earthsky.org/astronomy-essentials -- absolutely essential reading for what's up

    www.jodcast.net — monthly night sky tour for MP3 players

    www.spaceweather.com – details of transitory events during the month as well as aurora alerts

    http://spaceflightnow.com — mission launches and other news (click “Launch Schedule” too)

    www.skymania.com – astronomy and space news
    www.universetoday.com – more astronomy and space news
    www.nightskyobserver.com/the-sky-this-month.php -- Gary Nugent’s astronomy and space news


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