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Enter the Ice Giants: The brighter planets begin to give way as Uranus and Neptune jostle for our attention this month.

The glorious evening bridge of four bright planets we've enjoyed through summer comes to an end this month. Venus falls and fades from sight into the Sun's afterglow, then leaves the evening sky altogether later in October. Jupiter is visible in the west-southwest at nightfall, lower and for less time, and near month's end is close to low and elusive Mercury. Saturn shines in the south-southwest at dusk, much higher than Jupiter, and remains visible into the second half of evening. Mars at nightfall burns in the south-southeast and, though it fades, still shines brighter than any star until after the midnight hour when it sets and Sirius rises.

The only bright planet visible at dawn this month is Venus, very low and late in morning twilight, at the end of October.


Venus starts October very low in the west after the Sun sets for viewers around latitude 40[degrees] north. It gets even lower and even more difficult to spot with each passing day. It's out of sight by the 7th. Venus reaches inferior conjunction on October 26th and is then 6[degrees] south of the Sun--after which it starts emerging before sunrise (see below).

Jupiter shines at magnitude -1.7 by late October and the interval between sunset and Jupiter-set decreases to only about 1 hour by month's end. Even Jupiter is less than 32" wide by the second half of October and presents a shaky image so low in the sky.

Mercury may be glimpsed very low in the west shortly after sunset toward the end of the month; optical aid will help.


Saturn is already past the meridian as night falls but doesn't set until after 11 p.m. October 1st and after 9 p.m. late in the month. Serene Saturn dims from magnitude +0.5 to +0.6 during October and its globe shrinks to less than 16" in equatorial diameter. But the rings, though now a year past their time of maximum tilt, are only slightly less tilted and remain a stirring sight. Saturn is slowly trekking eastward above the Teapot of Sagittarius.

Mars loses half its brightness yet again this month, dimming from magnitude -1.3 to -0.6--but even the latter figure is impressive. The Red Planet culminates around 9 p.m. in early October, and about an hour earlier by the end of the month. That's when it's highest and most likely to provide a steady sharp image in telescopes. The apparent diameter of Mars shrinks from 16" to 12" in October--only half as wide as it was in late August. Nevertheless, this is still large enough to get some fine views of Martian surface and atmospheric features with a good telescope on a good night. The northern hemisphere of Mars reaches its winter solstice on October 16th. For information about observing the Martian north polar hood clouds and north polar icecap, along with other features at this apparition, see p. 22 in the July issue.

Mars races eastward across most of the compact pattern of Capricornus this month. At the end of October the planet approaches the eastward end of the Sea Goat, marked by the magnitude-2.85 star Delta ([delta]) Capricorni, also known as Deneb Algedi (see p. 45 for more on the stars of Capricornus).


Uranus arrives at opposition on October 23rd so is highest in the middle of the night this month. It shines at magnitude 5.7 in southwestern Aries and thus is capable of being seen with the naked eye at dark locations. Telescopes show its blue or blue-green globe 3.7" wide.

Neptune, in Aquarius, is only magnitude 7.8 and 2.3" wide but is already on the meridian by late evening or mid-evening. Finder charts for Uranus and Neptune appear in the September issue.


Venus leaps back into view at the very end of October, rising less than 40 minutes before the Sun on the 31st. Venus is then about 61" wide and little more than 1% lit. Viewers around latitude 40[degrees] north can see it that dawn about 4[degrees] high and upper right of the Sun at sunrise.


The Moon is a thin waxing crescent some 3[degrees] upper right of Jupiter at dusk on October 11th and a thicker crescent 2[degrees] upper right of Saturn on October 14th. The waxing gibbous Moon is about 6[degrees] either side of Mars on October 17th and 18th. The waning gibbous Moon shines in the Hyades on October 27th at dawn.

To find out what's visible in the sky from your location, go to almanac.

* Contributing Editor FRED SCHAAF has been writing about the skies above us for more than 40 years.

Caption: These scenes are drawn for near the middle of North America (latitude 40[degrees] north, longitude 90[degrees] west); European observers should move each Moon symbol a quarter of the way toward the one for the previous date. In the Far East, move the Moon halfway. The blue 10[degrees] scale bar is about the width of your fist at arm's length. For clarity, the Moon is shown three times its actual apparent size.

Caption: ORBITS OF THE PLANETS The curved arrows show each planet's movement during October. The outer planets don't change position enough in a month to notice at this scale.
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Title Annotation:OCTOBER 2018 OBSERVING: Sun, Moon & Planets
Author:Schaaf, Fred
Publication:Sky & Telescope
Date:Oct 1, 2018
Previous Article:The Sea Goat in the Skies: The ancient constellation Capricornus bears an interesting history.
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