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Planet viewing September/October 2021: Venus, Mercury and Mars

Venus, Mercury and Mars

Venus is the pre-eminent evening star shining brightly above the western horizon all summer and right through to the end of 2021. Mars is too close to the Sun this autumn to be easily visible; it emerges into the morning sky in a few months. Mercury makes a quick appearance on the east side of the Sun in the evening sky and reaches its farthest point from the Sun on September 14, but unfortunately both Mercury and Venus tend to ride low above the horizon and disappear fairly quickly after sunset. That being said, Venus is definitely up there playing its role as evening star, even if it is for a brief hour or so.

If you do spot Venus after sunset, it is an interesting sight in a telescope showing phases as it circles the Sun. It is currently gibbous and will stay this way until October when it becomes a quarter phase. Venus does not change in brightness much during the same time, staying around magnitude -4 for the duration. Look for it near Antares in mid-October but both will be only a few degrees above the SW horizon.

Mars is now in bright twilight as it gets closer to the Sun this fall and sets less than 30 minutes after the Sun does, so viewing it will be difficult. Spotting a 2nd magnitude planet under these conditions is next to impossible. Once it passes behind the Sun on October 8, it becomes a morning planet. There is an opportunity to see a thin Moon, Mercury and Mars on November 3. It is still a tiny 3.6° across, being on the opposite side of the solar system, but it has started to brighten and is magnitude 1.65 on November 3.

The next Mars close approach to Earth when it is large and bright in our sky (i.e., opposition) is on December 8/2022. It will not be quite as bright (magnitude -1.9), and will be a bit smaller (17.2" of arc) than it was in 2020, but that is because it is farther away (82 million km). On the upside, it will be 58° above the horizon, 8° higher in the sky than in 2020. Furthermore, also on December 8/2022, Mars will be occulted by the full Moon at 22:24 EST, an event which we will be able to see locally for a change.

More planets in the evening sky

The four gas giants Jupiter, Saturn, Uranus and Neptune are now rising by sunset and have become evening planets above our southern horizon. Even Neptune reaches opposition in September (Uranus follows with its opposition in November), and both are in the evening sky all night long. Charts are required to help locate Uranus and Neptune and are found on the Useful links page, but the other two are easy to spot.

September nights allow viewers to spot seven of the eight classical planets when Uranus finally rises in the east about 22:00. Strung out from Mercury eastwards are Venus, Saturn, Jupiter, Neptune and Uranus (Earth is #7). The FQ or waxing gibbous Moon passes the group as well in the middle of both September and October. The Saturn and Jupiter viewing guides for this season are here: S&T Saturn viewing guide and S&T Jupiter viewing guide.

August 1/2021, Canon 6D, 12 mm lens, ISO 6400, exp. =13 s - John Hlynialuk

The image above was taken from the ES Fox observatory and shows the two bright "stars" which are Jupiter and Saturn at lower left above the horizon. Both planets reached opposition in August, Saturn on August 2 and Jupiter on August 19, so they are prime targets for that first look as twilight deepens.


September 14: Mercury greatest elongation east (GEE) and Neptune opposition

These two planets are on the observing list tonight along with all the other planets except Mars which is too close to the Sun to see. Neptune will be easier to spot once it is dark than Mercury which sets within 45 minutes of the Sun. Neptune, though faint, is up all night long. The speedy Mercury transitions to the morning sky by the end of October (GEW on October 25). The diagram below shows how low Venus and Mercury are early in September; even 40 minutes after sunset, the two are only 7° and 1° in elevation, respectively, and are tough to see if the horizon is not absolutely clear.


October 13/14/15: The Moon passes Saturn and Jupiter

The Moon is FQ on October 12 and appears below Saturn and Jupiter on October 14 and 15 with a minimum 4° separation (during daylight) but 7° to 10° separation after dark on both nights. The two planets are both bright enough to see even in moonlight, so one can spend an interesting hour or two hopping from the craters of the moon to the clouds and rings of the gas giants.


October 16: Venus near Antares

Venus now sparkles at magnitude -4.3 and is cruising across Scorpius presently. On October 16, it is closest to Antares, the scorpion’s brightest star at magnitude 1 (the diagram above shows it 48 hours earlier), and the separation at minimum is 1° 26’. The sun sets at 17:37 EST on October 16, and there is a good 90 minutes or so before the horizon swallows Antares and Venus. The colour contrast as well as the brightness will be notable features of the view. Venus is at its best in late October, which is not saying much as far as elevation is concerned, but it is bright!


October 21: Orionid Meteors (20/h)

This is a minor shower and will be pretty much unobservable this year since the full Moon is in the sky all night long.


A note on observing meteor showers

There are an average of five or six random shooting stars ("sporadics") on any given night, and these will add to any meteors originating in a meteor shower. The particles (called meteoroids) that produce the streaks of incandescence (called meteors) appear to come from a point in a specific constellation (the radiant), but only because the Earth is moving into the stream of debris trailing behind the comet or asteroid that shed the particles.

Annual meteor showers are produced by sand grain sized particles with few larger pieces. Do not expect meteorites, the larger solid pieces of debris to drop down into a field near you; no meteor shower has been known to produce meteorites normally. Most meteorites found on the Earth’s surface are from larger, random pieces of space debris that encounter Earth.

Meteor observing requires no special equipment. Just relax on a recliner and keep warm with a blanket to ward off the chill and dew at night. Meteors appear all over the sky; the longer trails tend to appear farther from the radiant. More info is provided here: Sky&Telescope Meteors.

Observers in a dark location on meteor watch would like conditions to be perfect - no moonlight, radiant high in the sky and cooperative weather. The RASC handbook gives the zenithal hourly rate (ZHR) and assumes ideal conditions, so this is generally a maximum possible. Still, ZHR are predictions and outbursts do happen. Note that counts usually go up after midnight. If there is a group observing, useful information can be obtained about showers by simple counts over 20 minutes or so, logging every meteor seen all over the sky. A group of 3 to 4 observers is required to observe the entire sky but useful counts can also come from single observers facing the radiant.

Reports should be sent to the International Meteor Organization (IMO) or the American Meteor Society (AMS). Include the location, sky conditions, transparency, elevation of radiant along with the time and numbers. Useful report forms for showers as well as for reporting notable individual meteors (fireballs or bolides) are found on these websites.

Photography is also encouraged! This site provides hints on how: Imaging meteors. Another one from Sky&Telescope is here: S&T meteors imaging.


Content on this page created by John Hlynialuk except where otherwise noted