THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
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70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2459173.16
2020-2021: XLVIII
THE DAILY ASTRONOMER
Thursday, November 19, 2020
Remote Planetarium 127: Night Sky Revisited
Today we return to Earth.
Next week -which will be quite short-we will go as far afield as it is
possible to travel while still remaining within the physical Universe.
We've already traveled quite a distance already in our cosmic odyssey.
Now, we'll come home and recline in our backyard so as to admire the night
sky and review some of what we've covered since the Remote Planetarium
started in late March. (Our apologies to those who attend just for the
mythological excursions. Being on terra firma, we are far removed from
the ethereal realm where we tend to encounter those chimerical beings.)
The sun sets (in Portland at 4:12 p.m. today). As the planet is enshrouded
in an atmosphere, darkness won't descend instantly. Instead, we will
progress through three twilight phases
- *Civil *(when the Sun is between 0 to 6 degrees below the horizon)
ends at 4:43 p.m.
- *Nautical *(when the Sun is between 6 - 12 degrees below the horizon)
ends at 5:18 p.m.
- *Astronomical *(when the Sun is between 12 - 18 degrees below the
horizon. ends at 5:52 p.m.
While civil twilight conceals most celestial objects, tonight you will want
to see Jupiter, Saturn and the *waxing crescent* moon together in the
western sky. As the moon traverses the sky at a rate of half a degree an
hour (equal to its angular diameter), one might notice its position shift
slightly relative to the two planets during the time between their first
appearance and their setting about three hours later.
[image: waxing-crescent-moon.jpg]
See the waxing crescent moon "close" to Jupiter and Saturn tonight in the
western evening sky.
At magnitude -1.9, Jupiter will be ten times brighter than Saturn
(magnitude 0.6). Astronomers use the magnitude system to measure the
brightness of celestial objects. The lower the magnitude, the brighter
the object. As the scale is logarithmic, a magnitude 1 star will be 2.5
times brighter than a magnitude 2 star, which will be 2.5 times brighter
than a star of magnitude 3.
One will also find Mars high in the eastern sky tonight. Though
slightly dimmer than Jupiter at magnitude -1.5, Mars is quite distinctive
by virtue of its reddish color. Notice also that one can describe an
arc connecting Jupiter, Saturn and Mars. Their alignment with this
imaginary arc is no coincidence as the planets and the Moon all appear to
travel along an undulating curve called the *ecliptic. * The ecliptic is
the plane described by Earth's orbital motion around the Sun. Because
the solar system is disc-shaped, the planets will always be near this plane.
[image: SS2648245.jpg]
Although we're now in mid November, the famous Summer Triangle remains
visible high in the western sky tonight. The three stars comprising
this triangle, Vega, Deneb and Altair, are each part of different
constellations. Vega, the brightest of the three, marks the northern tip
of Lyra the Harp. Altair, the southern star in the triangle, represents
the eye in Aquila the Eagle. Deneb is the tail star within Cygnus the
Swan, better known as the Great Northern Cross. The longer axis of this
cross runs along the spine of the Milky Way, a luminescent band extending
between the eastern and western horizons. (As the image above is time
lapse, the Milky Way's luminescence is exaggerated.)
Although the Leonid Meteor Shower peaked earlier this week, one can still
expect to see 10 - 30 Leonids meteors an hour tonight. Meteor showers are
best observed after midnight, when our part of the world turns into the
densest part of the meteoroid stream. The radiant -the point from
which the meteors appear to emanate- is located within the constellation
Leo the Lion, hence the name "Leonids."
[image:
5f37349b-af82-4af9-89a5-d16d11b6b2b3-111318-leonids-meteor-shower_Online.png]
The meteoroids responsible for producing the Leonid meteors are fragments
cast off by Comet Tempel-Tuttle. This comet requires 33 years to revolve
around the Sun. Its last close approach to the Sun (perihelion) occurred
on Feb 28, 1998. It will next reach perihelion on May 20, 2031.
We regret that we cannot include the hundreds of other interesting night
sky sights one can observe this evening. We encourage you to venture
outside and simply observe our small region of the Universe high above you.
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