Download Skymatters Newsletter Sept 2016

SKYMATTERS
Blackrock Castle Observatory www.bco.ie
Download monthly skymatters newsletters from www.bco.ie/skymatters
Sept 2016
Things to watch out for
September 1
The Moon is new and so remains invisible throughout the night. This is a good time to get away from any city lights and see the sky
in all its glory, weather permitting of course!
September 1
There is an annular eclipse which unfortunately is not visible from Ireland as the moon and sun miss each other by about a moon’s
width for observers here. If you’re travelling to Africa then you’re in luck! An annular eclipse happens when the moon is slightly
farther away from the earth than during a total eclipse and so it appears too small to totally cover the disk of the sun. The fact that
total solar eclipses occur at all is a remarkable coincidence in any case—the moon is just big enough and just far enough away to
exactly cover the sun’s disk.
September 3
One of the outer gas giant planets, Neptune, is at its closest to the earth this year. It is visible all night long and it is also the
brightest it will be. A reasonable telescope is needed to pick Neptune out from the background stars due to its immense distance,
around 4.4 billion km. This distance changes because the two planets are travelling at different speeds around the sun and both of
their orbits are slightly elliptical.
September 16
The Moon is full and is called the Harvest Moon, being the full moon closest to the autumn equinox.
September 22
The autumn equinox occurs today. The sun is directly over the equator and the days and nights are of nearly equal length,
especially at our latitude in Ireland. The autumn equinox is mirrored by the spring equinox on the same day in the southern
hemisphere. Psychologically, the autumn equinox heralds the coming of the colder and darker months in the northern hemisphere.
Planets with a smaller tilt of their axis (earth’s is 23.5 degrees) undergo little change from one season to the next (for example, the
tilt of Venus is only 3 degrees and you would hardly notice any seasonal changes) while others undergo bigger changes than on
earth (for example, Uranus, where the tilt is 82 degrees, resulting in massive seasonal changes).
September 28
Mercury can be glimpsed, with great care, almost 18 degrees to the west of the sun in the morning sky and is best viewed before
sunrise.
Skychart for
September
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 skychart in that direction.
The skychart is most
correct for about 11pm
in the middle of the
September 2016 (or
10pm at the end of the
month or 12 midnight at
the beginning of the
month). The Great
Square of Pegasus is
outlined in green and
there are remarkably
few bright stars within
its bounds, making it
quite distinctive. The
Andromeda galaxy is
highlighted as a red
“star”, though of course
in reality it’s a galaxy!
Planets in September
Mercury at its greatest western distance, or elongation, from the Sun on 28th, at a separation of 17.9 degrees. Keep an eye out for the planet
low in the eastern sky before sunrise. 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, especially if you are using binoculars or a telescope.
Venus is an evening object and is 3 degrees away from the Moon on 3rd September, but it will not be so easy to spot due to the glare of the
setting sun. However, the waxing crescent moon is worth looking out for and Venus, if visible to you, will be a lovely accompanying bonus.
Mars remains somewhat more challenging to observe, but still visible after sunset. Look low in the west after the sun sets for a red object.
Jupiter is not visible this month, but the Juno satellite that went into orbit in July continues to function well in engineering tests.
Saturn is challenging as it is very low as night falls, so depending on your local horizon you may not get a chance to see it for a while from now.
Being low also means it does not generally appear so crisp in a telescope.
Uranus and Neptune are both well placed and visible throughout the night. Both require a telescope to view them as they are faint targets.
Constellations to keep an
eye on in September
The constellation of Andromeda is
mostly unremarkable except for the fact
that it houses the Andromeda Galaxy.
This is a challenging object and probably
best viewed with binoculars. Unlike a
star it appears extended and was labelled by Charles Messier, the great
comet hunter, as M31 (Messier 31) in
1764. As this isn’t a comet it was of little
interest to Messier and at the time (and
for over 150 years) there was no definitive way to know whether the galaxy is
close and small, or large and far away. It
turns out the latter is the case, relative to
the other stars we see in the sky, being
some 2.5 million light years away.
The Andromeda galaxy is shown as a red ellipse. The easiest way to find it is to find the
Great Square of Pegasus and after that it’s a matter of looking out for a smudge of light
that looks rather non-descript at first, until you realise what you’re looking at!
The Andromeda Galaxy
Galaxies are important. They provide the
conditions in which stars and planets form
and they are very common in the universe.
The Andromeda Galaxy is currently
approaching our home galaxy of the Milky
Way at 300 kilometres per second and the
two will eventually collide in about 3.5 billion
years time. The result will likely be a new
galaxy (see page 4).
Andromeda and the Milky Way make up the
two heavyweights of a group of galaxies
called, rather uninspiringly, the Local
Group. There are about 100 galaxies in
total in this group, including M110 and M32.
This long-exposure image of the Andromeda Galaxy (M31) would cover a diameter of about six
times that of the full moon! Another galaxy, M110 can be seen just beneath M31 and M32 just
above and slightly to the left of the nucleus of M31.
It seems likely that M32 has already passed through M31 at least once, and while it is not easy to spot in the image above, the result
appears to have been the triggering of a wave of star formation in two rings. At the center of the Andromeda Galaxy is a supermassive
black hole that weighs as much as 100 million suns—compare this to our own galaxy which has a central black hole of a mere 4.2 million
suns. The ultimate fate for ourselves and Andromeda is for these black holes to collide and generate an object called a quasar. As
matter falls into the centre of the quasar and becomes superheated in the process, this will make the new galaxy one of the brightest objects in this part of the universe.
Galactic Collisions
You don’t have to wait 3.5 billion years to observe galaxies already colliding. NGC 4676
is a beautiful example of what happens when two galaxies rather like the Andromeda
and Milky Way collide (below, left). Stars are ripped from their parent galaxy and flung
out into space. Many return—some do not and they live out the remainder of their lives in
the isolated depths between galaxies. The new galaxy will eventually settle down into
some form of elliptical shape (below, right). Sometimes these new, and often larger
galaxies, cannibalize other galaxies and grow bigger and bigger. Not surprisingly, some
of the largest galaxies are elliptical. By the time Andromeda and the Milky Way have
coalesced our sun will have reached the latter stages of its lifetime, so our ancestors will
hopefully be viewing this from a safe distance!
Website of the month
There is a lot of bad science and
bad astronomy on the internet.
Lots of unfounded speculation
which makes apparently solid
conclusions. The “bad
astronomy” website presents
really exciting and thoughtprovoking blogs, but all anchored
in good astronomy and good
science!
URL: http://www.slate.com/blogs/
bad_astronomy.html
Quote of the month
“The dinosaurs became extinct
because they didn’t have a space
program. And if we become
extinct because we don’t have a
space program it’ll serve us right.”
After the Milky Way and Andromeda collide they will likely form an “elliptical” galaxy. An
elliptical galaxy has the shape of a soccer or rugby ball, depending on the way the collision
occurs. The many elliptical galaxies we already see in the universe are evidence of many past
mergers.
Larry Niven, science fiction writer
Some Upcoming Events at CIT Blackrock Castle Observatory
Culture Night | September 16 | 18:00 – 21:30
A free night of science in our exhibition space and courtyard. Enjoy hands-on science activities and weather permitting
stargazing at nightfall (rain or clouds mean it will NOT take place). No booking required
Junior Space Camp | October 2 | 12:00 – 13:30
Space Week special! Explore the Moon and its craters in our fun hands-on workshop. How big is the Moon compared to
Earth – use balloons to figure out the size! Suited to 5 – 7 year old’s. €10 each (one parent is required to stay). Booking advised.
Space Week | October 3 - 8 |
Space Week is Ireland’s newest STEM (Science, Technology, Engineering and Maths) week. From October 3- 8, people around
the country can get involved. Check for space themed events in your area on www.spaceweek.ie. Discover YOUR Universe!
Spooky Space Camp | October 30 | 12:00 – 13:30
Our Junior Space Camp with a Halloween twist. Make Monster Volcano’s and Lava Lamps as well as the usual Mag-net Painting
and Mentos Rocket! Suited to 5 – 7 year old’s. €10 each (one parent is required to stay). Booking advised.
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. Be one of the first to experience our new “Journey’s of Exploration” exhibit.
PUBLIC OPENING Hours: 10:00 – 17:00 (Mon- Sun) Phone: 021-4326120 / Email: [email protected]
Blackrock Castle Observatory is operated by Cork Institute of Technology in partnership with Cork City Council