The Sky This Month, November
Under the umbrella of transient meteor showers
The nuances of the ink blue sky punctuated with shiny white scintillating crystals of stars and planets in the Northern Hemisphere await special sights for the Earthly spectators this November.
Taurid Meteor Shower - November 5, 2018:
The annual meteor showers occur when the Earth passes through streams of debris left behind by comets and asteroids. As pebble-sized pieces of debris collide with the Earth, they burn up at an altitude of around 70 to 100 km, appearing as shooting stars.
The Taurid meteor shower will reach its maximum rate of activity on November 5, 2018. Some shooting stars associated with the shower are expected to be visible each night throughout the month of November.
The parent body responsible for creating the Taurid shower is 2P/Encke.
The maximum rate of meteors expected to be visible is around 10 per hour (Zenithal Hourly Rate or ZHR). This assumes a perfectly dark sky and that the radiant of the meteor shower is directly overhead. In practice, the number of meteors you are likely to see is lower than this, and can be calculated from the ZHR formula.
From Tiruchirappalli, the radiant of the shower will appear 75° above your eastern horizon at midnight. This translates to a ZHR of about 9 meteors per hour, since the radiant will be high in the sky, maximising the chance of seeing meteors.
The Moon will be 27 days old at the time of peak activity, presenting minimal interference.
To see the most meteors, the best place to look is not directly at the radiant itself, but at any dark patch of sky which is around 30–40° away from it. It is at a distance of around this distance from the radiant that meteors will show reasonably long trails without being too spread out.
Mercury at greatest elongation east - November 6, 2018:
Mercury will be well placed for observation in the evening sky, shining brightly at mag -0.3.
From Tiruchirappalli, it will be difficult to observe as it will appear no higher than 14° above the horizon. It will become visible at around 18:09 (IST) as the dusk sky fades, 14° above your south-western horizon. It will then sink towards the horizon, setting 1 hour and 25 minutes after the Sun at 19:14.
Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time.
It is observable only for a few days, that is, each time it reaches greatest separation from the Sun – moments referred to as greatest elongation.
These apparitions take place alternately in the morning and evening skies, depending on whether Mercury lies to the east of the Sun or to the west.
When it lies to the east, it rises and sets a short time after the Sun and is visible in early evening twilight. When it lies to the west of the Sun, it rises and sets a short time before the Sun and is visible shortly before sunrise.
On this occasion, it lies 23° to the Sun's east.
The key moments in this apparition of Mercury are as follows:
06 Nov 2018 20:29 IST – Mercury at greatest elongation east
11 Nov 2018 21:52 IST – Mercury at dichotomy
27 Nov 2018 14:39 IST – Mercury at inferior solar conjunction
After greatest elongation, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare.
A graph of the angular separation of Mercury from the Sun around the time of greatest elongation is
When Mercury remains in the sky for a few hours after the Sun has set, its altitude above the horizon depends on two factors.
One is its angular separation from the Sun. But equally important is how steeply the line of the ecliptic is inclined to the horizon.
If Mercury is widely separated from the Sun along the ecliptic, this may not translate into a high altitude if the ecliptic meets the horizon at a very shallow angle, running almost parallel to it.
Conversely, if the ecliptic is almost perpendicular to the horizon, a much smaller separation from the Sun may place Mercury higher in the sky.
The inclination of the ecliptic plane to the horizon at Tiruchirappalli varies between 77° and 55° On November 6, the ecliptic is inclined at 61° to the western sunset horizon, as shown by the yellow line in the planetarium view above, meaning that on this occasion Mercury is not ideally placed for viewing from Tiruchirappalli.
New Moon - November 7, 2018:
The Moon will pass close to the Sun and become lost in the Sun's glare for a few days.
The Moon's orbital motion carries it around the Earth once every four weeks, and as a result its phases cycle from new moon, through first quarter, full moon and last quarter, back to new moon once every 29.5 days.
This motion also means that the Moon travels more than 12° across the sky from one night to the next, causing it to rise and set nearly an hour later each day.
Over coming days, the Moon will rise and set an hour later each day, becoming visible in the late afternoon and dusk sky as a waxing crescent which sets soon after the Sun. By first quarter, in a week's time, it will be visible until around midnight.
At the moment of closest approach, it will pass within 4°50'of the Sun, in the constellation Libra.
Leonids Meteor Shower - November 18, 2018:
The Leonids are a prolific meteor shower associated with the comet Tempel–Tuttle.
The Leonids get their name from the location of their radiant in the constellation Leo - the meteors appear to radiate from that point in the sky. They peak in the month of November.
Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough – typically closer than Jupiter's orbit. The Leonids are a fast moving stream which encounter the path of Earth and impact at 72 km/s. Larger Leonids which are about 10 mm across have a mass of half a gram and are known for generating bright (apparent magnitude −1.5) meteors. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet.
The meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter and to a lesser extent by radiation pressure from the sun, the Poynting–Robertson effect, and the Yarkovsky effect. These trails of meteoroids cause meteor showers when Earth encounters them. Old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around November 18, but some are spread through several days on either side and the specific peak changes every year. Conversely, young trails are spatially very dense and the cause of meteor outbursts when the Earth enters one. Meteor storms (large outbursts) exceed 1000 meteors per hour, to be compared to the sporadic background (5 to 8 ZHR) and the shower background (several per hour).
Full Moon - November 23, 2018:
The Full Moon in November is named after beavers who build their winter dams at this time of year. It is also called Frost Moon and Mourning Moon, depending on the winter solstice.
According to some sources, the Full Moon for November is named after beavers because this is the time they become particularly active building their winter dams in preparation for the cold season. The beaver is mainly nocturnal, so they keep working under the light of the Full Moon. Beavers make dams of wood and mud. In the middle, they build dome/shaped homes called lodges with underwater entrances. There used to be more than 60 million North American beavers. However, because people have hunted them for fur and their glands for medicine, among other reasons, the beaver population has declined to around 12 million.
As the astronomical seasons do not match up with the lunar months, the month of the Mourning Moon varies. In some years, the Mourning Moon is in November, while in other years, it is in December.
