Astronomy events in Tanzania for 2015 

August Night Skies Over Tanzania - Pluto and Perseids



Pluto has recently been in the news following remarkable discoveries by the New Horizons spacecraft launched in January 2006, a few months before it was declared a dwarf planet by the International Astronomical Union.  The spacecraft flew by Pluto last month and sent back the first extremely detailed pictures and measurements ever made.  Pluto, the farthest former planet, is on average, about six billion kilometers away, 40 times more than our distance to the Sun so, its light and radio signals take five hours to reach us.  Remember that light goes 300,000 km in one second, which gives you some way of imagining how far Pluto is. The dwarf planet takes 250 years to go around the Sun so it has only traveled only a third of its orbit since its discovery by Tombaugh in 1930.

 

All the planets had been studied from close up during the Voyager 1 and 2 missions launched in 1970s.  However they could not include Pluto in these flyby missions due to its positon.  New Horizons was specifically launched to fulfil the aim of studying all the planets at close range. After nearly ten years of travel, with gravitational catapult assist from Jupiter, New Horizons approached and flew by Pluto on 14 July just 12,000 kilometers away.  Such a close successful flyby is equivalent to firing a gun so that you miss an object placed at the other end of a football ground, by just one tenth of a millimeter.  The spacecraft will now fly on, sending back more images and measurements it has collected from Pluto and go on deeper into the solar system to flyby other distant objects and eventually out of the Solar System.  Incidentally, the two Voyager space crafts have now crossed out of the Solar System and are in interstellar space, still regularly sending information back to Earth.

New Horizons found that Pluto has more moons than those around the inner planets, and has a million times the amount of atmosphere that Mercury has. Its surface has distinct features with water-ice mountains bigger than many large mountain ranges here on Earth. Its frozen plains are surrounded with ridges that suggest there is geological activity that causes changes to its surface.  This extreme activity on Pluto has now given support to those who were in disagreement about the decision to make Pluto a dwarf planet. New Horizons came just in time to provide detailed information that Pluto is not a quiet dwarf planet so this debate will continue in the years to come.  

 

The early days this month, from 10 to 15 August are prime times to observe the Perseid meteor shower which produces around 20 meteors per hour at our latitudes.  When the Earth moves in its orbit around the Sun, it is rushing through space at a speed of more than 100,000 kilometers per hour.   When the orbit of the Earth crosses the orbit of past comets it strikes concentrations of dust particles left behind by the comets. During the Perseid shower which peaks on the night of Wednesday August 12, Earth will hit material left behind by comet Swift-Tuttle whose dusty-ice ball is softened and releases material during its close approach to the Sun (and Earth) in elongated orbits every 133 years, the last of which was in 1992.  When such dust particle strike the atmosphere they are heated by friction as it speeds through the air and glows brightly, showing up as lines in the sky which we call meteors or shooting stars since it looks as though a star has fallen from the sky.

 

The Perseid meteors are often persistent and visible for longer time even after the meteor has passed.  This light is produced by ionization of the air through which the meteor has passed.

 

Maximum meteor shower occurs when the Earth hits the comet dust head on, which is at sunrise and in overhead sky, hence the best time to see the most meteors is when it is still dark just before dawn.  Earth will be in the most concentrated dust region on the night of 12 dawn of 13 August and at that time the Moon will be in a waning (decreasing) crescent phase so there will be minimum disturbance from moonlight. The following day, August 14 is a New Moon so there will be no moonlight so it is also worth going out to watch the meteors.

 

From around 10 pm onwards there can be a few earth grazing meteors that strike the atmosphere not head-on, but at a glancing angle.  These produce long slow trails that pass across the sky overhead.

 

The position in the sky from which the dust strikes the atmosphere is called the radiant, and meteors trail lines when extended back, will meet at the radiant which shows that the meteors are radiating or originating from space around that position.  The radiant of the Perseid meteors is in the Perseus constellation from which the shower takes its name.  The Perseus constellation is towards the north and does not rise more than 30 degrees at maximum hence northern hemisphere observers will enjoy this shower even more.

 

At midnight, the radiant is at the horizon, hence before and around midnight, grazing meteors will appear to originate from the horizon and streak upto the overhead skies.   By dawn when maximum meteors appear, the radiant is overhead with meteors shooting out in all directions from a point overhead.

 

The best way to observe meteors on the night of 12/13 or 13/14 August is to pick a dark place where the north east horizon is not obstructed. Lay on an armchair or on a mat on the ground and scan the whole sky.  Meteors appear without any particular pattern so you have to be patient and keep your eyes relaxed and observant for long periods.  The satisfaction of seeing a steady streaks of light is immense since most people will have seen just one or two chance meteors only. If you can see a bolide, which is an even more dramatic event when a larger particle breaks up while you are watching it, your day will definitely be brighter since you would be among the extremely few people who have seen such an event.

 

Venus and Jupiter have bid us farewell at the end of last month.  Jupiter will be seen again in the early evening skies after about six months, while Venus, the evening star that was with us for the past eight months, will be hidden in the Sun’s glare for a couple of weeks, after which it will reappear in the dawn skies as a morning star at the end of this month.

 

Saturn is the only visible planet in the evening skies and shines almost overhead to mid skies close to the mouth of Scorpio.  Mercury makes a highest entrance in the western skies this month, rising to more than 20 degrees above the horizon at sunset by the end of August, and hence provides a very good opportunity to see this elusive planet. Visit www.astronomyintanzania.or.tz for updates and further information.

 

Among the evening constellations are the long, winding Scorpio, and Sagittarius the archer.  The Southern Cross lying on its side close to the southwestern horizon points south.  In the north you can make out Cygnus the swan as a cross with the bright Deneb (A) at its tip.  Among the bright stars you can try some with famous names.  These are, from west to east, Spica (B) in constellation Virgo, Arcturus (C), Alpha (D) and Beta Centauri (E) the two bright stars in the southern skies that point to the Southern Cross, the red star Antares (F) in the neck of Scorpio, Vega (G), Altair (H) and Deneb (A) all in the north and Fomalhaut (J) just rising in the east at 8 p.m

 

The best view of the International Space station will be on 31 August, when it will cross the sky starting from northwest horizon at 6:38pm and reaches nearly 70 degrees at 6:41pm shining extremely brightly.  Just before this, at 6:40pm it will pass close to Saturn in the sky. It will then drop towards the horizon and disappear after 6:44pm.

 

 

****** 


Planet string in JUNE NIGHT SKIES over Tanzania

MARCH VIEWS OF International Space Station (ISS)

GROUND PATHS OF ISS


FEBRUARY NIGHT SKY MAP


Eclipses, Meteors, Planets and Moon, 2015

The following is a summary of interesting astronomical events during this year 2015 that can be observed by the public without the need of a telescope.

The events are described for positions in the sky and the times for viewers in Tanzania, or East Africa.   You may read about some of these events in international media but some of these are not seen from Tanzania and the timings can be different.

The events are chronologically arranged by dates that they occur.

Eclipses:

Glossary:

Ø  Solar eclipses occur when our view of the Sun is blocked by the Moon during the daytime causing a small shadow of Moon to fall on Earth. The Moon is in between the Earth and the Sun.

Ø  Lunar eclipses occur when the large shadow of Earth falls on the Moon.  The Earth is in between the Sun and the Moon.

Ø  Total eclipses occur when the shadow is dark, called umbra.

Ø  Partial eclipses occur when the shadow is not completely dark (called penumbra) since some light falls in the shadow area.

Ø  Exciting Note: Next year 2016, an annular solar eclipse passes through a 100 kilometer path across southern Tanzania on Sept 1, 2016. The whole of Tanzania will experience nearly 90 percent of the Sun being covered.

 

·         Total Solar Eclipse, 20 Mar, North Pole, None visible in Tanzania

·         Total Lunar Eclipse, 04 Apr, Pacific Ocean, None visible in Tanzania

·         Partial Solar Eclipse, 13 Sep, South Pole, None visible in Tanzania

·         Total Lunar Eclipse, 28 Sep, Atlantic Ocean, Partial eclipse visible in Tanzania

 

Meteor Showers:

Glossary:

Ø  Meteors are light streaks in the night sky that look like a shooting star.  The light is emitted by burning in the atmosphere of tiny dust grains from coming from space. Sometimes larger particles can strike the atmosphere and the light glows much more brightly or even explodes known as bolides.

Ø  Meteor showers are formed when high concentrations of dust from past comets trails and asteroids strike Earth at the same time causing many meteors in a short period.

 

·         Quadrantid, Weak, North, Jan 3-4, Big Dipper, Moon too bright

·         Lyrids, Weak, North, Apr 22-23, Cygnus, Vega(Alpha Lyrae) Moon too bright

·         Eta Aquarids, Strong-60 met/hr, Equator, May 5-6, Aquarius, no Moon so meteors can be detected

·         Delta Aquarids, Weak, near Equator, Jul 28-29, Fomalhaut-pegasus square, Moon too bright

·         Perseids, Strong- 60 met/hr, North, Aug 12-13, Perseus, No Moon so meteors can be detected

·         Draconids, Weak North Oct 8-9, Little Dipper, Moon too bright

·         Orinids, Weak, Equator, Oct 21-22, Orion, Moon sets early so meteors can be detected, (additional - Venus-Jupiter-Mars in morning sky)

·         Taurids, Weak, Equator, Nov 5-6, Taurus, Quarter Moon too bright in morning sky

·         Leonids, Ok, Equator, Nov 17-18, Leo, Quarter Moon sets early so meteors can be detected

·         Geminids, VeryStrong-120 met/hr, Equator, Dec 13-14, Gemini, Crescent Moon sets early so meteors can be detected

·         Ursida, Weak, North, Dec 22-23, Little Dipper, Moon too bright

 

Planets:

Glossary:

Ø  Planet opposition occurs when the full face of the planet is lit by sunlight with the planet on one side (east side) of Earth while the Sun is on the opposite side (west). So a brightly shining planet rises from the east at sunset.

Ø  Close approach of planets in the night sky occurs when their lines of sight as viewed from Earth are separated by very small angles.  Hence though they appear to be close to each other in the night sky, it does not mean that they are actually close to each other in space.  All planets are separated by millions of kilometers of space in their orbits around the Sun.

 

·         VENUS and MERCURY close, Jan 10, they will be seen close together 20 degrees above the west horizon just after sunset. Start watching from now up to mid-January as Mercury approaches Venus from below and comes closest on Jan 10 within one degree and then moves down again away from Venus.  Mercury is a faint point and can be a challenge to detect, while Venus will be bright. Venus will continue to rise in the sky in the following months rising to 40 degrees in June and then quickly coming down to the horizon by August.

·         JUPITER at opposition, Feb 7, brilliantly bright Jupiter will be seen rising in the east just as the sun sets in the west. It will remain in the evening night sky for the next six months moving gradually westwards.

·         VENUS and MARS close, Feb 21, they will be seen close together 20 degrees above the west horizon just after sunset. Start watching from mid-February up to the end of February as first Venus approaches Mars from below and comes closest on Feb 21 within half a degree and then moves up away from Mars.  Mars is a tiny red point while Venus will be very bright yellow.

·         Uranus and VENUS close, Mar 4, though Uranus cannot be seen easily since it is very faint, it can be seen with naked eyes only in darkest skies since it is just at the limit of naked eye visibility.  However this is an excellent opportunity for telescope observation of the planet (even through small telescopes) since it can be located within a tenth of a degree from Venus on Mar 4 so it can be easy to catch even in a small telescope. The pair will be 30 degrees above the horizon at sunset with Uranus approaching Venus from above coming closest to Venus within a tenth of a degree on Mar 4 and passing below on following days.

·         Uranus and MARS close, Mar 11, presents another opportunity to locate the faint Uranus through even a small telescope when it comes closest to Mars to within half a degree.  Mars is a faint red star and can be identified among the other stars.

·         SATURN at opposition, May 24, sharply shining Saturn will be seen rising in the east just as the sun sets in the west. It will remain in the evening night sky for the next six months moving gradually westwards.

·         JUPITER and VENUS close, Jun 30, two brilliant planets will shine as bright stars in the evening sky close together 40 degrees above the in the west soon after sunset. Start watching from mid-June to mid-July as Jupiter approaches Venus from above and comes closest on June 30 within half a degree and then moves down away from Venus. This will be an extremely noticeable event since many people will see two extremely bright objects close in the sky for more than a month.

·         JUPITER and MERCURY close, Aug 7, seen 15 degrees above the western horizon at sunset, with Venus 10 degrees to the left below the Jupiter-Mercury pair.

·         JUPITER and MARS close, Oct 18 they will be seen close together 30 degrees above the east horizon just before sunrise. Start watching from beginning of October to mid-October Jupiter first approaches Mars from below and comes closest on Oct 18 within quarter of a degree and then moves up away from Mars.  Mars is a tiny red point while Jupiter will be very bright white.

·         JUPITER and VENUS close, Oct 26, two extremely brilliant stars, Venus and Jupiter will be seen close together 40 degrees above the east horizon just before sunrise. Before sunrise they will be seen closer to the east horizon.  Start watching from mid-October up to the end of October as first Jupiter approaches Venus from below and comes closest on Oct 26 within half a degree and then moves up away from Venus. This will be an extremely noticeable event especially for early rises since they will be seeing two extremely bright objects in the sky for almost the whole of October.

·         VENUS and MARS close, Nov 3, they will be seen close together 45 degrees above the east horizon just before sunrise.  They will come closest to within half a degree as Mars approaches Venus from below and then moves up away from Venus.

·         VENUS and SATURN close, Jan 9 2016.  They will be seen 35 degrees above the western horizon at sunset and will come closest to each other within a tenth of a degree.

 

Moon:

Glossary:

Ø  Full Moon occurs when Moon is on one side (east) of Earth while Sun is on the opposite (west) side. Hence sunlight is striking the Moon full face and the full bright circle of Moon is seen in the east from sunset onwards.

Ø  New Moon occurs when Moon is viewed with Sun directly behind it hence dark (night) side of Moon is facing us and dark face is in the west horizon at sunset.

Ø  Crescent Moon occurs immediately after New Moon once some sunlight is able to strike the Moon but we see only a thin part of the lower side of the Moon. Crescent Moon are seen low in the west horizon at sunset or low in the east horizon at sunrise.

Ø  Half Moon occurs when we see the Moon as a half circle and is .  It is actually called First Quarter or Last Quarter since it occurs during first or last quarter of the Moon’s cycle around Earth.

Ø  Gibbous Moon is shaped like an oval and occurs between half Moon and Full Moon.

 

·         Full Moon, Jan 5

·         New Moon, Jan 20

·         Crescent Moon close to MERCURY Jan 21, will be seen 12 degrees above the western horizon at sunset with Moon 2 degrees below Mercury.

·         Crescent Moon close to VENUS and MARS Jan 22, will be seen 25 degrees above the western horizon at sunset with Moon in between Mars above and Venus below 10 degrees apart.

·         Crescent Moon close to MARS Jan 23, will be seen 40 degrees above the western horizon at sunset with Moon 2 degrees above Mars.

·         Full Moon, Feb 4

·         Full Moon close to JUPITER Feb 4, will be seen rising in the east horizon soon after sunset and will be visible throughout the night, slowly shifting westwards through the night

·         New Moon, Feb 19

·         Crescent Moon close to VENUS-MARS pair, Feb 20, will be seen 20 degrees above the western horizon at sunset with the planet pair 5 degrees above crescent Venus. The trio will slowly drop lower through the night and set after about an hour.

·         Almost full Moon close to JUPITER, Mar 3, will be seen rising above the east horizon at sunset and the pair will be seen slowly shifting westwards through the night.

·         Full Moon, Mar 5

·         New Moon, Mar 20

·         Crescent Moon between Venus and Mars, Mar 22, seen at 25 degrees above the western horizon at sunset, with Venus 5 degrees above and Mars 10 degrees below the crescent Moon. The trio will slowly drop lower through the night and set after a couple of hours.

·         Half Moon close to JUPITER, Mar 30, will be seen near the zenith from sunset, shifting westwards through the night.

·         Full Moon, Apr 4

·         New Moon, Apr 18

·         Crescent Moon close to VENUS, Apr 21, will be seen 35 degrees above the western horizon at sunset with Venus 10 degrees to the right of crescent Moon. The pair will slowly drop lower through the night and set after a few hours.

·         Half Moon close to JUPITER, Apr 26, will be seen near zenith 5 degrees apart with the pair shifting westwards through the night and set below the western horizon soon after midnight.

·         Full Moon, May 4

·         New Moon, May 18

·         Crescent Moon close to VENUS, May 21, seen 40 degrees above the western horizon at sunset.  The pair will slowly drop lower through the night and set after a few hours.

·         Half Moon close to JUPITER, May 23, 24 seen close to zenith overhead about 10 degrees apart.  They will shift slowly westwards and set before midnight.

·         Full Moon close to SATURN, Jun 1, with the pair rising above the eastern horizon at sunset. They are 2 degrees apart and shift westwards throughout the night.

·         Full Moon, Jun 2

·         New Moon, Jun 16

·         Crescent Moon between JUPITER-VENUS pair, Jun 20, seen 45 degrees above western horizon at sunset, with Moon 5 degrees apart from the planet pair. The trio will slowly drop lower through the night and set after a few hours.

·         Almost full Moon and SATURN close, Jun 28, seen half way up the eastern sky at sunset with the pair 5 degrees apart and shifting slowly westwards through the night.

·         Crescent Moon close to VENUS-JUPITER pair, Jul 18, seen 30 degrees above the western horizon at sunset forming a triangle 5 degrees apart.  The trio drops slowly, and sets below the horizon after a couple of hours.

·         Gibbous (oval) Moon close to SATURN, July 26, near zenith 65 degrees above eastern horizon at sunset.  The pair shifts slowly westwards and sets after midnight.

·         Full Moon, Jul 31

·         New Moon, Aug 14

·         Half Moon and SATURN close, Aug 22, seen close to zenith overhead two degrees apart.  The pair shifts slowly westwards through the night setting close to midnight.

·         Full Moon, Aug 29

·         New Moon, Sep 13

·         Half Moon and SATURN close, Sep 19, seen close to zenith overhead two degrees apart.  The pair shifts slowly westwards through the night setting close to midnight.

·         Full Moon, Sep 28

·         New Moon, Oct 13

·         Crescent Moon and SATURN close, Oct 16, seen 40 degrees above western horizon at sunset 2 degrees apart.  The pair sets slowly below the western horizon after a few hours.

·         Full Moon, Oct 27

·         New Moon, Nov 11

·         Crescent Moon and SATURN close, Nov 13, seen 20 degrees above western horizon at sunset with crescent 5 degrees above Saturn.  The pair sets after an hour.

·         Full Moon, Nov 26

·         New Moon, Dec 11

·         Full Moon, Dec 25

·         New Moon, Jan 10 2016

 

==xx==





 
 

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