THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
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.
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.
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."
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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