MONTHLY OBSERVING HIGHLIGHTS HANDOUT – MAY 2012

We begin this month at the centre of the solar system, not as some people still believe with the Earth, but with the Sun.  And we find that in terms of sunspots it has been a bit erratic recently.  By observing the Sun through white light filters or by projecting the solar disc on to a piece of white card, you’ll notice that some days the face of the Sun will be almost blank, with very little to see. But a few days later the scene can change, with many sunspots appearing.  Observing the sun is always interesting, as it changes all the time.  But a hydrogen alpha telescope always gives you a view worth savouring.   

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On to the planets and our round up begins as usual with Mercury.   Unfortunately Mercury is not well placed this month and it’s best to leave it until it moves much further away from the Sun and therefore easier and safer to see.  It currently lies amongst the early morning stars of Pisces, rapidly making its way around to the far side of the Sun, where it will be at Superior Conjunction on the 27th.

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Venus, on the other hand has been magnificent for weeks and weeks.  However May will be the end of this particular apparition, as our evil twin has a date with the Sun on the morning of the 6^th of June.  That is the day when it will cross the face of the solar disc, in what is known as a ‘Transit’. 

We are fortunate to be living at just the right time to be able to witness this, as these events are very rare. The last one was 8 years ago in 2004 and the next will not occur until 2117.  Then there will be another eight-year gap until 2125, before another 121.5-year wait for the next pair of transits.  The reason for this is because of the tilt of the orbit of Venus in relation to the Earth.  Venus has to be at conjunction with the Sun and pass through the Earths orbital plane, the ecliptic.  Because of the 3.4 degree inclination between the two orbits this rarely happens and that’s what makes a Transit of Venus special.

In 2004 we were lucky, as it was a long Transit and the UK had a few hours and some clear skies to observe it.  Anyone who witnessed the Transit of Venus in 2004 and all the hype that went with it will remember the day well. Unfortunately this time Venus will already be in transit when the Sun rises on the 6^th of June and this time we only have less than 18 minutes before Venus leaves the solar disc, so unless you plan to be alive in 2117, you need to position yourself, so that you have a clear horizon over the sea.  That will give you the maximum amount of time and then just hope for perfectly clear skies for an hour at sunrise on the 6^th of June.  Not much to ask for, is it?

Remember that the same safety precautions must be taken when observing the transit as with any solar observing.  Filters on your telescopes, Hydrogen alpha telescopes, solar binoculars, projection methods or you should be able to pick out Venus through eclipse viewers, although it may be a bit small.

After the transit, Venus will eventually reappear as the Morning Star but we have to make the most of it now as the magnificent Evening Star.  Make a point of looking at Venus through even a small scope and you will see a wonderful crescent; like a small moon. 

As Venus moves between the Earth and the Sun, the crescent gets thinner but the diameter increases and the best time to see this is on the 22^nd of May at about 10pm.   With the Sun safely below the horizon, compare the crescent Venus with a lovely Crescent moon close by.  From the 22^nd, Venus will speed up and get ever closer to the Sun, so this is the last good opportunity to observe it in a reasonable dark sky.  

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For a change this month we have included the Earth, because sometime in the next few days an historical event will take place silently above our heads. 

In 2008 NASA awarded a $1.6 billion contract to SpaceX,to develop their Falcon 9 launch vehicle and Dragon spacecraft to fly a minimum of 12 flights to resupply the International Space Station, after the Space Shuttle retired. There is an option to order additional missions with a total contract value of up to $3.1 billion.  Apart from resupplying the ISS the Dragon Capsule can be converted to carry up to 7 American astronauts, so NASA will no longer have to rely on the Russians!  So a new episode in American manned spaceflight has begun, with a commercial company providing the rockets and the spacecraft for the first time.  The SpaceX company was founded by PayPal entrepreneur Elon Musk so if you have ever used PayPal, in a small way you can say that you have contributed to resupplying the ISS. 

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Mars is still shining like a bright red ‘star’ high in the south but it is fading each day as it moves away from us. But you should have no trouble locating it as it can still easily be found between the legs of Leo.

Although it is bright and easy to find, Mars is small and a long way away and now it is getting further away, as the distance between Mars and the Earth rapidly increases.   This of course results in it getting slightly dimmer and the disc of Mars reducing in size, making it more difficult for us with small scopes to see much detail.  However that’s what makes astronomy interesting.  So see if your scope can pick up the north polar cap on Mars before - a) the planet moves too far away from us and b) before the Martian summer makes the northern polar cap shrinks too much to be seen anyway. 

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Jupiter has moved behind the Sun for now, it will actually be at superior conjunction on the 13^th, so images like the ones on the internet and in magazines are the best views we’ll get of it until it reappears in the morning sky later in the month.

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Saturn is the only gas giant in the night sky for us to observe this month.  It can easily be found in the constellation of Virgo, not far from magnitude +1.0 Spica, which is the brightest star in Virgo. 

How do find Spica?  We use our old friend The Plough. Follow the sweep of the handle down through the bright star Arcturus in Bootes and continue until you reach Spica in Virgo.  Saturn shines at +0.3 so it is brighter; also it is the left one of the pair.   Put even a small telescope on first Spica and you will see a lovely blue-white star.  Spica is actually two stars; separated by less than 11 million miles.  They can’t be seen as separate stars through even our biggest telescopes.  They orbit a common centre of gravity in only 4 days. The resulting forces on these stars are so great that they are probably distorted, more egg-shaped than spherical.   Both stars are far hotter than our Sun.

Now move your telescope over to Saturn and you will see the wonderful ring system, which at the moment is tilted towards us so we get a really good view.  A medium sized scope, say a 6” reflector, may be needed to reveal the shadow of the rings on the planet, but small scopes will usually show you Titan, Saturn’s largest moon.  With an 8” telescope you will be able to pick out more of the fainter moons and the 20^th of May is the best time for that, when they are ideally placed in a nice grouping around Saturn.

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Both Uranus and Neptune are staying out of sight this month, hiding behind the Sun so they are unobservable.

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Moon   The phases of the moon are as follows and I’ve included the early part of June.

Full = 6^th May     Last Quarter = 12^th May      New Moon = 20^th May     1st Quarter = 28^th May   Full = 4^th June

This next bit I’ve taken virtually word for word from the Jodrell Bank website as I think it describes what is going to happens fairly well.

“At 1 am on the 6th May, the full Moon transits (lies due south), at which time its distance from the centre of the Earth will be 356,954 km.   This is the closest Full Moon to the Earth since January 1912.  (The same year the Titanic sunk).  It will thus appear larger in the sky than at any time since then.   This is because the Moon has an elliptical orbit and thus its distance from the Earth varies by about 12%.  When the Moon is closest, called "at Perigee" it can, of course, have any phase from new to full.   On the 5th/6th May Perigee corresponds very closely with Full Moon - hence its large apparent size.  

At transit, the UK (on the Earth's surface) will be somewhat closer and the diagram gives the distance - 354,600 km - from us.   Hopefully, we will be able to see the Moon as it rises at ~8:15 BST on the evening of the 5th when the "Moon Illusion" will make it appear very big.   The cause of this illusion is disputed, but many believe that it is due to the fact that we perceive the sky as forming a flattened, rather than a hemispherical, dome above us.   We thus believe that objects near the horizon are further away and our minds make them appear larger than when we "believe" that we are seeing them closer to us.

Occasions when the Full Moon is close to perigee occur about every 412 days, so are not that rare.   At this time the angular diameter of the Moon exceeds 33 arc minutes and its diameter is 12% larger than when at apogee.   This makes the apparent area around 30% greater than when we see the full Moon close to apogee.   Quite a difference” - so it’s well worth looking out for.  So that’s this Friday at about 20:15 for a nearly full moon and a little later on Saturday when the full moon rises.

Now, you may have noticed that the date of the new moon is in the 20^th of May.  Well this month the new moon will slip across the face of the Sun and there will be an Annular Eclipse of the Sun. 

Annular eclipses occur when the moon is a little too far away in its elliptical orbit and the disc does not properly cover the Sun.  It leaves a ring of light or annulus around the edge. 

Now don’t think too hard about this next bit as it could hurt your brains, but this particular eclipse is odd, not unusual, as we’ll find out in November but odd just the same.  The shadow of the Moon touches the surface of the Earth first in Hong Kong on the 21^st of May, then it crosses over the Eastern China Sea, Taiwan and Japan, before heading out across the Pacific to the USA.  The reason it will be the 21st when the eclipse starts is because it will begin when it is on the west of the International Date Line.   By the time it reaches the South Western USA in the afternoon, the Moons shadow will have travelled eastward and it will have crossed the International Date Line, meaning that it will be the 20^th of May when the USA get to see the eclipse. 

Monthly Challenge

For this month’s moon challenge we have chosen something different, one that can be observed with binoculars and with a small telescope.  On the 26^th of May the Moon will occult the open cluster M67 in the constellation of Cancer the Crab.

The Moon will be a waxing crescent and will be travelling upwards through the cluster towards the left. The first stars will disappear behind the dark limb of the Moon at around 9pm.  As it is likely to still be quite light when this happens we are unlikely to see this but at about 10:50pm they will start to reappear from behind the bright edge of the crescent.  The size of the M67 cluster is about the same size as the Moon so we should see lots of stars reappear one after the other.  Through a telescope this should be fascinating to watch. Even without a GOTO scope M67 is easy to find.  Unless it is really dark, it’s not that easy to pick out the shape of Cancer, but it does sit between Leo and Gemini, two big prominent constellations and of course we’ll have a bright crescent Moon to point the way on the 26^th.

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COMETS  Comet Garradd is still around but has now dimmed to magnitude +10.5.   This means it can be found with large binoculars and telescopes trekking southwards from southern Lynx into northern Cancer.  So that’s another target for us while we are waiting for M67 to reappear on the 26^th.

And while on the subject of comets, this gives me the opportunity to mention the much more famous Halley’s comet.  As you know this comet last visited us in 1986.  At the moment it is way out beyond the orbit of Neptune and will not return to the inner solar system until 2061.  But each time it swings by the sun, solar heat vaporizes approximately 6 metres of ice and rock from the nucleus. The debris particles, about the size of sand grains, spread along the comet’s orbit, filling it with tiny meteoroids.  And the Earth passes through this debris twice a year.  As these tiny particles fall through the atmosphere we see meteors.   In October we see the Orionids and in May we get the Eta Aquarid meteors.    These meteors are very bright and often fast, striking the Earth’s atmosphere at about 41 miles per second.  That’s 147,600 miles an hour.  It’s no wonder they vapourise!   

The maximum occurs before dawn on the morning of the 6^th.  So you need to have a good East-Southeast view with a low horizon and you should be able to see up to 25 meteors an hour.  The Eta Aquarids are active up to the 20^th May, so there’s a chance you see at least one any time up to then.

Unfortunately the UK is not the best location to observe this meteor shower, as the radiant point in Aquarius is fairly low and the best time to catch an Eta Aquarid is in the early hours of the morning, just before it starts to get light.  But if you do see some they will be worth it.  Remember that you are actually seeing a piece of Halley’s comet doing a kamikaze death dive into the atmosphere.

Sources :-          Sky at Night Magazine