July 2010 Night Skies over Tanzania
JULY NIGHT SKIES OVER TANZANIA
By Dr N T Jiwaji
ntjiwaji@yahoo.com
JULY NIGHT SKIES OVER TANZANIA
By Dr N T Jiwaji
ntjiwaji@yahoo.com
I have started receiving requests to confirm whether Mars will be seen as big as the Moon this coming August 27th. It will not! I have received this same request numerous times in the past seven years, since 2003. What is the problem? The culprit is how we use the World Wide Web (i.e. the Internet).
The actual event took place in 2003, and even in that year Mars did not (and can never) look as big as the Moon. It came closest to Earth that year (seven years ago), but even then it was 55 million kilometers away – too far for it to be seen as anything but a red star! Information on the web does not die because it is impossible to remove all traces of it. And even if it is left in only one of the billions of places on the web it will be found by a simple Google search.
Our curiosity gets the better of us when we are working with mysterious stuff, and astronomy is indeed as mysterious as it comes. The closest approach of Mars to Earth was a sensational event in 2003, since such an event had not happened for the past 60,000 years and will not be repeated next until nearly 300 years later in 2287. So it was an event of a lifetime worth witnessing in 2003. However, those who missed it are fascinated when they come across any such story on the web, and we hardly bother to look for the date that the information was first posted on the Internet. Knowledge gained from the internet can easily be outdated, interpreted wrongly or can even be false! You should always use your judgment when reading information on the web and always compare it with other sources of information.
Mars is currently seen as a not-so-bright red star, and is interesting to locate because it is quite close to Saturn, extremely bright Venus and faint Mercury. Indeed it is fascinating to watch these planets over the next couple of months as they shift their positions relative to each other and to the fixed stars in the background. It is this wandering characteristic of planets across the skies is what made the Greeks to name them “planets” since it means “wanderers” in their language.
Beginning Saturday July 10th, Mercury will come into view in the western skies near the setting sun at 10 degrees altitude at sunset; though it will be challenging to make out against the brightness of the sky in that area. Take it as a test of your observing power, and perhaps as a measure of your age since you may not have noticed yet that slight weakening of your eyes. Have a couple of young budding astronomer with you to use his/her sharp eyes to point it out. It can be fun to see who can locate it first and such an activity will definitely cement their interest in astronomy. CAUTION: DO NOT LOOK AT THE SUN DIRECTLY if you start your watch before sunset.
Still in the west, Venus is hard to miss since it is so bright. It is seen above Mercury at a height of about 40 degrees, almost at its highest height of 45 degrees that it will reach in early August. Above Venus, you will see Mars at 56 degrees elevation and above that is Saturn three quarters of the way up at 64 degrees altitude at sunset. You will notice that this makes them form a clear straight line, as they are all along the ecliptic, the line in the sky showing the path of all solar system objects since the orbits of all planets and the moon are all confined in one plane with the sun.
The Moon joins this group of planets that are aligned in a vertical line on Monday July 12th when it will be a New Moon at an elevation of 10 degrees at sunset. Make it a double challenge to make out the very thin crescent of the Moon a palm-width (5 degrees) below Mercury at sunset and be careful not to get the Sun directly into your eyes.
You can now begin to watch the “wandering” of the solar system objects, starting with the Moon. On Tuesday, July 13th it will have shifted its position and be seen between Mercury and Venus, that is, four palm-widths (20 degrees) below Venus and its thicker and brighter crescent will be much easier to see. The following day July 14th (Wednesday), the crescent Moon will be very close to and below and to the left of Venus, 4 degrees, less than a palm-width, apart. It will indeed be a beautiful sight, with the two cusps or end points of the crescent pointing upwards. The next day, Thursday, July 15, the Moon, with a thick crescent shape, will be between Venus and Mars, and on Friday July 16 the thick crescent Moon will be close to and to the left of Saturn, two palm-widths away. Over the next few days the Moon will have shifted above Saturn keeping faithfully close to the ecliptic line and by July 25th it will be rising at sunset as a Full Moon.
Meantime, Venus and Mars will be edging closer to Saturn, with Mars zeroing in faster, and will reach very close to Saturn by the end of the Month about three degrees (a fist-width) away. Venus will be close, about a palm-width below. By August 6th, Venus, Mars and Saturn will have bunched up together and shifting position daily to form a variety of triangles. Venus will then be at its maximum height of 45 degrees above the horizon at sunset. Mercury will also not be too far behind and will be at an altitude of 27 degrees which will make it very easy to locate this elusive planet.
Notice the planets are all shifting towards the east from their western positions. This is the normal movement of the planets in their orbits, though contrary to our intuition, since we are used to seeing the apparent motion of object in the sky as being from east to west.
Through a telescope Venus will be seen as a half disk while Saturn’s rings will be spread out more so will be make a beautiful sight. For those with telescopes, Venus will at a crescent shape and increase in it apparent size by September, when it will be edging closer to earth. Make the most of the cool clear skies to follow these planets in the coming days and the next couple of months.
The southern skies are filled with very bright stars that would be hard to hide! The north and south direction pointers, that is the Big Dipper and the Southern Cross, are still high enough in the evening skies and can be used to mark the north-south direction very well. Scorpius in the dominant constellation this month and occupies the overhead(zenith) skies in the evenings. Its three stars form the tentacles and the red star Antares its neck. The long winding tail ends in a close pair forming the “sting” of the scorpion. Scorpius is the only constellation that does full justice to its namesake, since the scorpion shape is unmistakable to even a casual stargazer. Use this opportunity to start (or continue) your stargazing hobby by independently identifying at least that one constellation and hopefully a few more also.
Below Scorpius, try to identify Sagittarius (the archer). This constellation marks the direction of the center of our Milky Way galaxy and you will notice dense concentration of stars here. The band marking the Milky Way contains numerous stars and dust patches and stretches from the southwest, passing through the Southern Cross and Sagittarius and upto Cygnus (the swan) in the northeast. Leo (the lion) with its distinctive inverted question mark head is low in the western horizon and will be lost after this month.
Among the brightest stars noticeable in the July skies are: Alpha and Beta Centauri in the south form the pair that points continuously towards the Southern Cross; the fourth brightest star Arcturus is overhead towards the north and the fifth brightest star Vega rises in the northeast. Other bright stars you will easily notice are Altair which rises in the east and Spica, the brightest star in the Virgo constellation can be seen almost overhead towards the west.
The International Space Station (ISS) makes bright passes that are interesting to watch on July 23rd and 25th. On July 23rd it will rise from the north western horizon at 19:40 and will reach high in the sky to an elevation of 58 degrees three minutes later. At that time, it will suddenly disappear in the middle of the sky when it enters the earth’s shadow and the sun’s rays no longer strike the football pitch sized station. On July 25th it will rise again in the northwest at 18:57 but will cross the whole sky over the next six minutes, in the western sky, passing very close to Venus, a sight not worth missing.
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