October Night Skies Over Tanzania
Would you believe it if someone told you there are better worlds than our own that are far far away orbiting around other stars? It is true!! From among more than 2,000 exoplanets that have been discovered so far, scientist have categorised more than 100 of them in terms of their habitability for life by looking at factors such as how hot they are, which also determines if water can be in liquid form. In particular this new habitability index also looks at whether the exoplanet is rocky and how close to circular its orbits, which determines the energy it receives from its star. From the 100 or so exoplanets that have been categorized upto now, two of them are assessed as more liveable than Earth!! There is a place where we can go to after all, if we manage to destroy our home. But how we will get there and how long it will take to get there is another story.
Saturn is the only naked eye planet visible in the evening night skies. It lies low near the west horizon, close to the mouth of Scorpio. It shines with a steady sharpness near one of Scorpio’s tentacle stars. A crescent Moon will come close to within 3 degrees besides Saturn on 16th near the claw of Scorpio.
However the dawn skies in the east, just before sunrise, offers a conjunction (coming together) of four planets: Venus, Jupiter, Mars and Mercury. They change positions noticeably in the sky day by day and hence will present an amazing spectacle for the whole of this month.
Any early morning riser cannot have missed seeing an extremely brilliant star in the east since end of August. This is none other than the morning star, Venus. This brilliant beacon has been going up in the sky steadily since then and is now shining 40 degrees above the east horizon.
The three other planets, Mars, Jupiter and Mercury appear in a diagonal, with Venus at the top left of the diagonal and Mercury lower right, 15 degrees above the horizon. Jupiter and Mars are close, about 30 degrees above the eastern horizon. Jupiter is moving up in the sky and will be closest to Mars on 18 October width of a Moon apart less than half a degree.
October 26 is a date to mark in your calendar when Jupiter will have moved close to Venus within one and a half degrees and these two brightest objects will form a spectacular planet pair. They will also be a part of a trio with Mars which will be about five degrees below the pair. By the end of October, Jupiter will have moved further up from Venus but Mar will have come closest by November 3.
The remarkable brilliance of Venus is rated at magnitude negative 4, while Jupiter shines less brightly with a magnitude negative 1.5. Mars though dim, at magnitude positive 2 it shines unmistakably red. (Note that brilliant objects have negative magnitude, while for dim objects the magnitude becomes positive. The limit of visibility with naked eyes is around magnitude 6). Mercury also shines brightly at magnitude negative half but you can still make it out in the the brightness of the sky due to the rising Sun.
Through a telescope, Venus is seen in half shape since it is an inner planet and hence changes its phase from crescent to half to gibbous to full and back again as it catches up with Earth and passes it in its orbit.
October 26 is also useful to note for observation of planet Uranus when it will be close to and 4 degrees west of the almost full Moon. This distant planet, next after Saturn in distance from the Sun, is just outside our naked eye limit of viewing, so you will need a telescope to catch it. More details for viewing the planets can be found at the Astronomy In Tanzania website: http://www.AstronomyInTanzania.or.tz
There are numerous scare emails and social media messages flying around the internet scaring people of 15 days of darkness because of the coming together of so many planets. The information is allegedly attributed to NASA but that is absolutely false so you should ignore them all since it is impossible to get any such effects when planets come together in the sky.
This month the midday Sun is overhead over Tanzania which results in no shadows at midday. Over the four week period from end of September to end of October, the Sun will be overhead progressively for northern parts of our country up to the south most parts by 22nd October with it being overhead in Dar es Salaam on October 10. Even if the zero shadow day has passed for your place, the Sun is still very nearly overhead. So go out and get that impression of no or very small shadows so that you can compare them to the much longer shadows in December and June even at midday.
The Milky Way runs from southwest to northeast is a as a band of numerous stars can be recognized even in brightly lit city skies. It stretches from the tail of Scorpio in the south, through Sagittarius to Cygnus constellation in the north. The Milky Way is our own galaxy within which we live. Our Solar System is located in one of the arms of the flat spiral shape of our galaxy, one third of the way from its edge. While looking at the Sagittarius constellation you are actually looking towards the centre of our glaxay.
This month we can see two other galaxies with our naked eyes, though you will need to be well away from city lights. With a pair of binoculars the shape of the cloudy patch identified. The Andromeda galaxy, marked T near the north and close to the Square of Pegasus marked S, has the same flat spiral shape as our own Milky Way galaxy. It is nearly 2 million light years away from us (i.e. light travelling at 300 thousand kilometers per second takes 2 million years to reach us!). So the Andromeda galaxy is the farthest object visible with our naked eyes. A sight worth going out to look for! The other galaxy is our satellite galaxy, the Small Megallenic Cloud, closest to us at 500 thousand light years away. It is marked U towards the south in the sky map.
The bright stars in the early evening sky this month are marked in the sky map and can be identified as follows: A is Fomalhaut in the overhead sky towards the south, while towards the north the star marked B is Altair. C, which is close to the north is Deneb in Cygnus constellation while E is Antares, a red giant star in Scorpio. The star marked H, rising in the south east, is Achernar.
October 4 to 10 is a United Nations declared world space week so many astronomy events have been held during this time all over the world. Humans first went to space on October 4 1957 while the first space treaty was signed on October 10, 1957. Hence these dates are commemorated around the world with space related activities and events.