Partial Solar Eclipse – 2015
We are rapidly approaching what is undoubtedly one of the celestial highlights of the year, the spring equinox, which falls on March 20.
What, the spring equinox? Yes but, this year’s spring equinox will not be the anonymous affair it normally is, but will be marked with something rather more fitting, and for a lucky few, very much more memorable.
For a start, the moon turns new only 14 hours after reaching lunar perigee – the moon’s closest point to Earth in its orbit, so this moon is a super moon, actually a New super moon, normally not visible in our sky.
However, this one will be as it swings in front of the Sun, causing a total solar eclipse to herald the return of spring....at least it will should you lie directly under the path of totality (much joy and anticipation in the Faroe Islands and Svalbard). Few phenomena rival this wondrous spectacle, a magnificent and coincidental outcome of planetary orbital mechanics, manifest all too briefly in action as our nearest star is occulted by the moon causing its shadow to cut a swath across a part of our globe. It’s a case of ‘near and yet so far’ for us in the UK, as this shadow sweeps up across the north east Atlantic between Iceland and Britain missing Scotland by a few hundred miles.
But let’s not be downcast, for a very substantial partial eclipse will be witnessed from our neighbourhood which from Whitby will amount to around 90%, only 5% less than the 1999 eclipse- as seen from Whitby. The eclipse is a morning event, with mid-eclipse occurring around 9.37am. The eclipse starts just over an hour before this, and ends around an hour after at 10.42am.
Members of the WDAS will be hosting an eclipse event on the morning of the 20th, from the bandstand on pier road. Weather permitting we shall be there from 8.15am until 10.30am.
The next major solar eclipse will not be until Aug 2026, which will be similar to the March 20 event, after that we have to wait until 2090 for one of similar magnitude.
Observing a solar eclipse or any phenomena involving the Sun, such as a transit, safety is always of paramount importance. Never directly look at the Sun through any optical instrument unless a suitable solar filter is used, failure to do so and you could permanently damage your eyesight; remember the Sun is 1,000,000 times brighter than the Moon.
The small ‘screw on eyepiece’ type sun filters sometimes supplied with cheaper small telescopes can shatter due to excess heat - do not use them on any account – please introduce them to the head of a hammer - forcefully.
Home-made filters such as smoked glass, exposed film negative and extra dark sun glasses do not stop harmful rays from penetrating your eyes. Do not be tempted to use them.
Use only authorised solar filters such as Mylar and Baader solar film which are 99.99% safe to use at the objective end of a telescope, do not use them across an eyepiece, You can also utilise solar spectacles or a No14 or above welders glass (hand held) for short periods of observation, but never wear solar glasses and look through an eyepiece at the Sun (yes I have seen people about to attempt this).
Unless you have the correct type of solar filter, the safest way to view is by projection.
Items of equipment required: - Telescope, a refractor or reflector - aperture size does not matter; in fact a smaller aperture size is more preferable as it cuts down heat transmission on lenses or mirrors.
Binoculars can also be used, preferably tripod mounted, but be sure to the lens and eyepiece on one half are capped. (Obvious to astronomers, but apparently not so for everyone) You will also require a sheet of white card and ideally, a cardboard box.
Projection is a simple technique for viewing the Sun, but care must still be exercised. Obtain a cardboard box and insert a piece of white card in the bottom of it (roughly A4 or A3 size or cut to the appropriate dimension of your box).
Taking another piece of card approx 30-50cm square cut a hole in the middle of it just large enough for it slide snugly over the telescope or binocular tube. If using a star diagonal with your scope this second piece of card is not required.
Position the box around 1 metre behind the telescope or binoculars allowing the Suns image to fall onto it.
To accomplish this: - Semi-lock the telescope tube so that it can still be moved and aim in the direction of the Sun by sighting along it.
Make sure that end caps, including any finder scope caps are firmly in place. As an indication of how close you are, look for the smallest shadow cast by the tube onto the card in the box.
The telescope should then be aligned. Insert a low powered eyepiece and remove the telescope end cap, but not the finder scope ones. A bright circular disk should be visible on the card, this is the suns image.
Adjust the focus accordingly until the image becomes clear and sharp revealing any features visible on or against its disc.
In the case of a solar eclipse the dark silhouette of the lunar limb will be apparent.
This procedure can take a little time if you are unfamiliar with the movement of a scope, so don’t get frustrated and be tempted to look through the eyepiece, this is how accidents happen.
If you do not have a telescope or pair of binoculars you can use the pinhole method of projection ie; make a very small hole (1mm) in a sheet of card and then hold another sheet of card 1m or so away to gather the image, however it will be a small image.
Another method worth trying is to fill a bucket with water to within 5cm of the top and view the reflection of the sun and eclipse in action. Again the image will be small but quite acceptable.
Whatever method you employ please do be careful.
Brilliant Venus passes the green gas giant on the 4th, with both in the same field of view at low power magnification. Venus lies upper right of Uranus. Mars encounters Uranus on the 11th, which will lie to the lower left of the red planet. Venus will of course be obvious to spot, dominating that part of the sky.
Mars, at mag 1.5, should also be visible to the naked eye, but you will require binoculars (preferably a telescope) to spot Uranus. The crescent moon lies below Mars on the 21st and below Venus the following evening.
Anyone who ventures out into the evening twilight cannot fail to notice the two planetary beacons of Venus and Jupiter facing each other on opposite sides of the sky. As Venus slides down into the west, Jupiter rises into the east arcing across the sky as the night progresses.
When conditions allow you should never miss an opportunity to observe Jupiter, even if it is with just binoculars. The quicker than expected rotation (around 10 hours) of this huge gas world, mean visible cloud features may be seen to change over an observing session.
The dance of the Galilean moons also has its fascination.
Saturn is visible in the dawn sky to the SE and S not that far above Antares in Scorpius. The moon lies nearby on the 12th.
The comet should still be visible through binoculars and telescopes as it heads into Cassiopeia high to the NW. The comet is now circumpolar so you have all night to spot it.
The date of the Vernal Equinox and officially the start spring in the northern hemisphere falls on March 20 this year. This is when the Sun’s path - the ecliptic, first crosses the celestial equator on its apparent journey northwards into the sky.
The orientation of the Earth at the spring or autumnal equinox is such that neither of the poles are inclined towards the Sun and all locations experience equal hours of daylight and darkness - hence the term equinox.
The Vernal Equinox is also known as the ‘First point of Aries’, as the Sun used to stand before the constellation of the Ram when it first crossed the celestial equator.
Although still called the ‘first point of Aries’, today its location now resides in Pisces, a consequence of the effect known as precession - the Earth’s slow wobble.
Over thousands of years our ancestors noted that certain star patterns rose just before the Sun at specific times and were considered significant for this very reason. Subsequently they were able to build a picture of the apparent path of the Sun against these constellations. The narrow path upon which occasionally the Sun and Moon would meet giving rise to an eclipse, became known as the Ecliptic.
The broader belt along which the ‘wandering stars’ or planets travelled was known as the Zodiac, so called because all 12 constellations located on it were associated with living creatures.
Zodiac literally means ‘Band of Animals’. Libra used to be considered being part of Scopius, the claws to be precise. Ophiuchus, the serpent bearer immediately following Scorpius was instead regarded as a zodiac group. Ever since the stars of Libra were elevated in status, Ophiuchus, being surplus to requirements, was ditched, much to the relief of astrologers. If you find it difficult to remember the order of the zodiac constellations, then the following rhyme may be of use.
The Ram, the Bull, the Heavenly twins and next the Crab the Lion shines, the Virgin, and the Scales. Scorpion, Archer and Sea goat, the man who pours the water out and Fish with glittering tails.
Next Whitby and District Astronomical Society open nights at the Bruce observatory, Caedmon College, are March 8 and 15 from 7.30pm.
The spring equinox (and solar eclipse) occur on March 20 and BST begins at 1am on March 29 - clocks go forward one hour. Visit www.whitby-astronomers.com