May 2010 Night Skies over Tanzania

Cooled and scrubbed clean by regular downpours, the night skies this month offer some very choice viewing. Though you may be let down once in a while by overcast skies, the effort will pay off once the skies clear. You get a crisp view with minimum twinkling and, for urban viewers; there is less light pollution because the dust hanging in the atmosphere is regularly washed out by rains.

The parade of three planets and the Moon will hold your interest as they change their positions day by day, reaching a climax in July when several planets will be seen close together.

Venus is easiest to identify in the western skies as a brilliant star that is seen low in the horizon soon after sunset. Mars is higher up in the west and seen as a reddish dot once the sky becomes dark. It shifts noticeably close by the end of the month to Regulus, which is the brightest star in the constellation of Leo. It will be closest to this star on the 6th of next month. Saturn is almost overhead at 8 pm and shines as a tiny point with a piercing light that does not twinkle. With the ring system back into view it is a most stunning view when viewed through a telescope.

The more interesting formation to notice this month is that the three planets all lie in a line running from west to east (see dotted line on the map). The line becomes even more apparent after May 15^th, when the Moon enters the sky. It shifts between the planets, always lying along the same line that the planets make.

Why do the planets and the Moon stay close to this line, called the Ecliptic? To answer this question we get the opportunity to understand the power of astronomy to fire the imagination so that you can get a mental view of our Universe, though there is no chance of getting such a view directly. The ecliptic line can be explained by the fact that we are looking up at an arrangement of the planets that are all part of a flat system; meaning that the sun and all the planets and objects in the solar system are restricted to revolve around the sun in this flat plane only, extending outwards to the farthest reaches of the solar system, even beyond the dwarf planets Pluto and Eris. The Zodiacal constellations of Gemini, Leo Virgo, Scorpio, and Sagittarius are seen to lie on this ecliptic line also.

The Moon also revolves around the earth in this same plane within which the planets are restricted though of course, the Moon is closer to the Earth while the planets are much farther away. So the Moon is seen along the ecliptic line (dotted line on the map), but moves quickly along that line, shifting places between the planets. Go out at night from May 17^th, and watch how the Moon’s position changes day by day, always keeping along the ecliptic line. The Moon is just 2 degrees above Venus on May 16^th, and close to Mars and Saturn on the 20th and 22nd respectively. On May 24^th, with the Moon close to full, and in the eastern sky, the ecliptic line is very easy to make out by joining the line from Venus in the west through Mars and Saturn and ending at the Moon in the East.

Among the constellations and stars, this month, the most recognizable constellation, Orion bids us farewell and sets by 8 p.m. Leo dominates the overhead skies, though the full glory of this constellation with an inverted question mark forming the head of the lion, and its lounging body can easily be obscured by city lights.

The Pointers, the Southern Cross in the southern sky and the Big Dipper in the northern sky, are well positioned from early evening and are high in the sky so they can be used to locate the directions of south and north (see map). Scorpio pops its front claws early in the evening and by 10 p.m. the sweeping, curving tail with the sting at its end formed by a close pair of stars is easily made out. Sagittarius also rises early and can be recognized as shown on the map. The southern sky contains the Milky Way stretching from west to east with the Southern Cross, the Centaurs, the tail of Scorpio, and Sagittarius lying within the Milky Way.

From our unique geographic position close to the equator, we can see 16 of the top 21 brightest stars in the evening sky between 7 and 8 p.m. They are (in order of brightness, with their constellations in brackets) SIRIUS (the Dog), CANOPUS (Carina), ALPHA CENTAURI (Crux), ARCTURUS (Bootes), CAPELLA (in Auriga, just off the map, and sets at 7:30 in southeast), RIGEL (Orion), PROCYON (the Dog), BETELGEUSE (Orion), BETA CENTAURI (Crux), ALDEBARAN (in Taurus, just off the map, sets in the west at 7 p.m.), ACRUX (Southern Cross in Crux), ANTARES (Scorpio), SPICA (Virgo), POLLUX (Gemini), MIMOSA (Crux) and REGULUS (Leo). Identify the brightest stars using the map and you will understand better how to relate the sky to the star map, and the distortions of distances, especially close to the horizon.

The International Space Station (ISS) will be seen extremely brightly (magnitude -3.1) on May 26^th. It will rise in the northwest horizon at 7:15pm; will move gracefully towards the southeast. It will be high in the sky (65 degrees) by 7:18 and will suddenly disappear from view at 7:19pm near the Southern Cross, when it goes into the earth’s shadow about 40 degrees altitude in the southeast near the top star of the south pointing diagonal of the Southern Cross.

On May 28th, it will again take a similar path but will cross the sky fully from the northwest horizon at 6:30 pm to the southwest horizon at 6:37pm rising 60 degrees in the sky at its hightest and passing close to the brightest star of the Southern Cross which is at the bottom of its south-pointing diagonal.

ntjiwaji at yahoo dot com

END