Skynotes for May 2012

jfSDAS

Skylight for May 2012
The Moon’s orbit about the Earth is not perfectly circular, resulting in its distance from us varying over the course of a month. This also leads to a change in the Moon’s angular diameter or apparent size in the sky. The closest Full Moon of 2012 falls during the early hours of May 6th when the disc will measure 33½ arc-minutes but the sight at moonrise the previous evening will be spectacular.

From a location giving a clear eastern horizon the Moon will loom large as it rises and the markings on its disc will appear more easily discernable than usual. But there are some other phenomena to look out for. The temperature gradient of the layers of our atmosphere often cause the Moon and Sun's disc to appear flattened as they rise and set. Some spectacular effects of this can be seen in the galleries at http://www.atoptics.co.uk and looking at the moonrise in binoculars this May 5th should show at least some distortion along the lunar limb -- in fact, you can see some of these effects at any Full moonrise depending on atmospheric conditions.

Make a note too of the Moon's colour as it rises and then watch it changing hue as it climbs higher in the sky. The initial orange tint will change to a pinkish-colour and then bronze-yellow to be later replaced by a lighter primrose hue. Finally, once the Moon gains altitude, we'll see the disc a brilliant glaring white. I recall one occasion in 2003 when the Moon appeared an unusual shade of purple. It’s normally attributable to our atmosphere thick with pollutants and aerosols but this time maybe it was caused something else because reports came from right across the country remarking on the unusual aspect.

See http://earthsky.org/tonight/high-tide-alert-closest-full-moon-of-2012-on-may-5 for more information or the perigee/apogee calculator at http://www.fourmilab.ch/earthview/pacalc.html

UPDATED: Two images of the Moon at perigee and apogee taken by Greek astrophotographer Anthony Ayiomamitis dramatically demonstrate the differences in angular size. See http://www.perseus.gr/Astro-Lunar-Scenes-Apo-Perigee.htm

UPDATED: Check out the image at http://apod.nasa.gov/apod/ap070607.html which shows the Moon's changing colour as it rises.


The Sun
April saw a large number of spot groups peppering the Sun's disk and an increase in solar activity towards the end of the month led to probably the best aurora display so far in 2012 from Ireland. A number of diligent sky watchers captured wonderful photographs of the event and it bodes well for some further dramatic displays over the next 12 months. Dave Gradwell's site at http://www.davegradwell.com/ streams live data from his solar flare monitor erected at Birr.

An annular solar eclipse sweeps across the US and China on May 20th and 21st -- the different dates are due to the track crossing the International Date Line. May's New Moon is the most distant of the year so its angular size in the sky isn't large enough to fully cover the Sun during mid-eclipse so observers will see an annulus, or ring of sunlight, surrounding the Moon's silhouette. Fred Espenak's page at http://eclipse.gsfc.nasa.gov/eclipse.html has more details of the event.

For the curious, the next total solar eclipse visible from Ireland is not until 2090. Dubliners have an even longer wait -- the next total solar eclipse to sweep over the City will not occur until the year 2600!


The Moon
Full Moon is on May 6th, Last Quarter Moon on the 12th, New Moon on the 20th, and First Quarter on May 28th.

New Moon on May 20th occurs at 23h 47m which means that the following night, May 21st, gifts the opportunity to try spot an especially young Moon that will be only 21 hours old. The catch is that the golden thread of the crescent will be only two degrees above the western skyline around twenty minutes after sunset so you'll need a perfectly clear view in that direction to have any chance of success. The bright twilight will make it an even greater challenge but there's some hope by using Venus as a guide. Drop an imaginary line straight down from Venus to the horizon at 21:45pm (Summer Time) and scan one-and-a-half binocular field-widths to the right. The Moon should now be centred in your instrument's field-of-view.

On the evening of May 26th the 6-day old Moon will occult (pass in front of) the ancient star cluster M67 in the constellation Cancer. The occultation occurs in deep twilight and with the brightest member of the group only magnitude 7.8 a small telescope is required to observe the event.


The Planets
Venus continues to catch the eye in the evening sky and does not set until after midnight at the beginning of May. However, that will rapidly change as the planet plunges towards the solar glare over the next few weeks and inferior conjunction on June 6th when Venus will transit the Sun. It is worth preparing for this historic event -- the next transit of Venus isn't until the year 2117 -- by reading the material at http://www.astrosociety.org/tov/ where you can also download the pdf extract from Mercury magazine for an excellent account of transits and their historical importance.

A small telescope will let you follow the changing phase of Venus during the month and steadily held binoculars are sufficient to reveal the slender crescent the latter part of May. The two-day old Moon will be near Venus on the 22nd and it will be interesting compare the phases both bodies exhibit at this time.

May 4th is when Venus reaches its greatest northerly declination on the celestial sphere until 2239 AD as it glides by the star beta Tauri during the first week of the month.

Mars is an orange ember under the belly of Leo the Lion this month. The planet's brightness declines from -0.0 at the beginning of May to +0.5 by the 31st as it recedes from Earth -- the gap between us and Mars is one astronomical unit (the mean Earth-Sun distance) on May 8th. The apparent size of the disc is now only two-thirds that when Mars was at opposition in March and shrinks from 10 arc-seconds to 8.5 arc-seconds during the month. A small telescope will let you see the planet's gibbous phase and some markings still as well as the polar caps.

Saturn is a magnitude +0.5 object outshining the brighter stars of the constellation Virgo in the southeastern sky as soon as darkness falls. The northern aspect of its magnificent ring system is tipped towards us at the moment and recent data from the Cassini spacecraft orbiting Saturn has shown some intriguing and unexpected features within the disc of material. The brighter moons can be seen in a moderate-sized telescope and a number of online utilities let you calculate their positions. One such utility is that offered by Sky & Telescope magazine at http://www.skyandtelescope.com/observing/objects/planets/3308506.html

Jupiter passes through solar conjunction on May 13th and so is not visible. Mercury is very, very low before sunrise and probably will not be seen this month. Uranus and Neptune are returning to the morning sky.


Comets
Comet C/2009 P1 (Garradd) is now receding from Earth and is predicted to be magnitude 8.2 at the start of May, fading to magnitude 9.3 at the end of the month. The object is now just being mostly tracked by dedicated comet observers. Garradd passes from southern Lynx into Cancer during May and is visible as soon as darkness falls. More details can be found at http://www.ast.cam.ac.uk/~jds/


Meteors
The Eta Aquarids reach a peak on May 5th/6th but the radiant (point of origin of the meteors) is low from here and only at a useful altitude in the pre-dawn hours. With maximum this year falling on the day of Full Moon you’ll be hard pressed to catch more than a handful of the brighter Eta Aquarids. The shower is associated with Comet 1P/Halley. On occasions Venus fords the meteoroid stream at the same time as we do and at these times we can imagine a tenuous bridge of particles connecting the two worlds. Details of meteor showers during the year can be found at http://meteorshowersonline.com/calendar.html or http://www.imo.net/calendar/2012


Asteroids
The 200km diameter Main Belt asteroid 7 Iris is at opposition in Libra on May 4th when it reaches magnitude 9.5. A small telescope or giant binoculars are a prerequisite to spotting the object. Iris crosses into Virgo the last week of the month but will have faded to magnitude 10 by this time. The asteroid was discovered in 1847 by John Russell Hind -- more details are in the ubiquitous Wikipedia entry at http://en.wikipedia.org/wiki/7_Iris

3 Juno will be even fainter when it reaches opposition on May 20th in the constellation Serpens. This is one of the more distant oppositions possible for Juno and consequently it will only be magnitude 10.2 at this time.


Spaceflight
Delayed from April, the first launch to the International Space Station of SpaceX's unmanned Dragon spacecraft on May 7th will be closely watched. Engineers put the mission back a number of times to allow critical tests to be completed but other missions queued at Cape Canaveral then took priority as the Dragon launch date slipped. Lift-off also had to be fitted into a rather busy series of arrivals and departures at the ISS. Dragon is an ISS resupply craft built by the commercial outfit SpaceX which was founded by former PayPal entrepreneur Elon Musk. The spacecraft will not dock automatically with the ISS but instead make a close approach after which it will be grabbed by one of the station's robotic arms and manoeuvred into place.

The Cassini spacecraft currently orbiting Saturn makes a flyby of its enigmatic moon Enceladus at a distance of only 74km on May 2nd. This icy moon was discovered to have geysers of water ice and vapour erupting high above the moon's surface from a number of fissures at its south pole. Enceladus is now high on the list of targets for future exploration to determine whether the moon harbours a liquid ocean and conditions for exotic life-forms. Cassini will also pass 955km above Titan, Saturn's largest moon, on May 22nd. Although Titan will be targeted for other flybys this year, no other moon will see a close pass until March 2013 because the current path followed by Cassini on its complicated looping orbit about Saturn doesn't suit.

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

• May 2nd and 3rd -- talks by wildlife expert Eanna Ni Lamhna in Walkinstown Library and Ballymun Library. See the Events page on http://www.science.ie for more details
• May 3rd – Science Gallery talk “Antarctica” by Gabrielle Walker. More details at http://www.sciencegallery.com
• May 4th – Invasion Dublin “Star Wars” event. More details at http://www.invasiondublin.com/
• May 5th -- Physics High Flyers, a chance to hear talks by a Nobel Laureate and scientists at the forefront of physics research. See the Institute of Physics in Ireland web site at http://www.iopireland.org/
• May 15th – Astronomy Ireland lecture “The Science of Armageddon”. More details at http://www.astronomy.ie/lecture201205.php
• May 15th – UCD/RDS Distinguished Speaker Series talk “Lasers in the Fast Lane”. More details at http://ssmr.ucd.ie/speakerseries2012/speaker_series2012.html
• May 17th – IAS/SDAS members night/short talks in Gonzaga College, Ranelagh at 8pm. This is the last meeting before the summer break
• May 28th and 30th -- talks by artist and astronomer Deirdre Kelleghan in Rathmines Library (28th) and Ballymun Library (30th). See the Events page on http://www.science.ie for more details

Exploring further

The following web sites are also a great resource for information about what’s on view in our skies during the month;

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


Clear skies!

John

jfSDAS

hi all,

I've added two links under the piece about May 5th's super-sized Moon that show the different angular size of the lunar disk at perigee/apogee and the varying colours as the Moon rises.

john

HilltopViewer

Hi,HilltopViewer here from Dublin.I want to find out did anyone see the asteroid 2004 BL86 near Jupiter and Procyon tonight,26th January 2015?I was checking for it in the backyard when the clouds rolled over.I couldn't see a thing!

coylemj

There's already a thread on the topic.