Russell Eberst's Sky View
May 2012
The duration of dark hours in Scotland rapidly diminishes as the month advances. Although many outdoor activities benefit from the increase in the light available in the evenings, it does mean that astronomers have to wait till 11 p.m. British Summer Time (or later) for any dark skies.
During the hours of daylight, it is possible to observe the Sun's disc, although a great deal of care is required when undertaking this type of observation. The intense heat and light of the Sun is so great, that immediate and irreversible blindness will be caused if the solar heat and light are focused on the human eye. It is therefore vital that eyes are kept well away from the eyepiece end of optical instruments such as binoculars or telescopes when attempting to monitor the activity on the Sun.
The correct method of making these solar observations is to focus the image of the Sun on a piece of white card located a metre or so beyond the eyepiece and to refocus the instrument so that a sharp image is obtained. The instrument should have a firm base or support such as that provided by a tripod. This mounting will give a steady view, and it will be far easier to locate the images of the sunspots that are visible on the solar disc at the time of observation.
Several areas of sunspots may be expected as we approach the next solar maximum. This signals the highest point in the Sun's cycle of activity that requires over a decade to complete. Since displays of the aurora borealis, or northern lights, depend on the Sun's emission of huge clouds of ionized gases and particles, it can be confidently predicted that more displays will be observable in the coming months, as solar activity continues to increase.
Although long-term predictions cannot be made of specific dates when aurora is expected, it is possible to monitor activity on the Sun, and when a large eruption (often referred to as a Coronal Mass Ejection or CME). occurs, then the arrival of solar material will cause the Earth's upper atmosphere to glow with the pulsating light of amazing auroral displays, usually 2-3 days after the original solar explosion.
During May the Moon will be experiencing considerable variations in its distance from the Earth. Its elliptical orbit means that when at its furthest (apogee), it is about 12% more distant than when at its closest (perigee). This month that difference increases to nearly 14%, due to gravitational attraction of the Sun, and (to a lesser extent) the planets. May 6 sees the Moon reach perigee at 03.34 U.T. within a minute or two of the time of Full Moon. The Earth-Moon distance (centre to centre) will be 356953 km. So the disc of the Moon will appear just about at large as it can possibly be. This type of event is often referred to as a "supermoon".
It is well known that the Moon causes tides in the seas and oceans, and the occurrence of past super moons have led to speculation that some of the watery disasters in past years have been caused by the unusual closeness of the Moon. The sinking of the Titanic in 1912 followed a supermoon on January 4 of that year, which might have led to a very high number of icebergs breaking away from the Arctic ice sheet. In 2011 a supermoon occurred on March 19. This was 8 days after the Japanese tsunami that caused the horrendous death and damage in widespread areas of the east coast of Japan.
You might ask how a devastating earthquake could be caused by a supermoon that happened 8 days later. At the time of the earthquake, the Moon was racing in from a distant apogee to its closest perigee, at around 5000 km. per day. The rapidly increasing strain that resulted may well have been sufficient to trigger disastrous seismological activity.
Circumstances will be similar this year at the end of April and beginning of May, so watch should be kept to see if any big earthquakes occur at this time. Following the supermoon, the next lunar apogee will again be very distant, and this will show clearly, since the solar eclipse on May 21/20 occurs just over a day after the apogee which is some 406450 km distant. The Moon's disc will be smaller than usual and insufficiently large enough to completely cover the Sun's disc. This provides us with an annular eclipse when a narrow circle of the Sun is still visible surrounding the silhouette of the Moon. The path of annularity this time starts from southern China.
It then crosses Japan, including Tokyo, to track across the Pacific Ocean. The maximum duration of annular eclipse occurs near the International Date Line lasting 5.77 minutes. As the date line is crossed, the local date of the eclipse slips back to May 20. The path leaves the Pacific on reaching the west coast of the United States. As sunset approaches, it passes through a number of states, before leaving the Earth's surface in Texas.
Although not nearly as amazing as a total eclipse, an annular eclipse is well worth observing, especially noting the vast drop in the local temperature due to most of the solar radiation being obstructed by the Moon.
The planets are now well past their best, but still nicely placed. Venus, which has dominated the western sky after dark, will draw in rapidly towards the solar glare. It starts May almost 40° from the Sun, passing less than 1° from Elnath, in Taurus, on May 6. By month's end, its elongation from the Sun is less than 8°. Furthermore, its path takes it directly across the Sun's disc in June, but more on that next month.
Jupiter is out of sight behind the Sun at superior conjunction in the middle of May, thereafter becoming a morning object. Mars moves steadily eastwards, through the constellation of Leo, the lion. It ends the month close to the star chi Leonis. As its distance increases, its size decreases as does its brightness. The start of May sees it at magnitude 0.0 (similar to Arcturus, Vega and Capella) but it ends the month at 0.5, slightly fainter than Procyon.
The other bright planet in the evening sky is Saturn, located in the equatorial constellation of Virgo. Although it is rather low in U.K. skies, and getting lower from year to year, it is still worth observing in binoculars or a telescope. Its ring system is fairly well open, allowing those with telescopes to spot the major Cassini division in the rings. The largest moon, Titan should also be on view. Saturn is less than 5° from Spica, the brightest star in Virgo. The pair are joined by the Moon on the evening of May 4. The chief meteor shower in May in the eta Aquarids, but this year the maximum activity occurs at time of Full (Super)Moon, and this will overwhelm all but the very brightest of the members of this meteor shower.
Moon phases:
- First Quarter: May 28th
- Full Moon: May 6th
- Last Quarter: May 12th
- New Moon: May 20th
