Friday, August 31

Four bright planets still await you in twilight this week, though the brightest is getting lower. From right to left, they are Venus very low in the west-southwest, Jupiter in the southwest upper left of Venus, Saturn higher in the south, and bright Mars in the south-southeast. Best overall view: about 40 minutes after sunset. Here's a wide-field image of the four taken August 17th over the skyline of Rome, courtesy of Gianluca Masi.

• Look for bright Vega passing the zenith as twilight fades out, if you live in the world's mid-northern latitudes. Vega goes right through your zenith if you're at latitude 39° north (near Baltimore, Kansas City, Lake Tahoe, Sendai, Beijing, Athens, Lisbon).

Then Deneb follows two hours behind. For Deneb to pass exactly through your zenith you need to be a little farther north, at latitude 45°: near Bangor, Montreal, Minneapolis, mid-Oregon, northernmost Japan, Bucharest, Milan.

Venus and Jupiter near stars in twilight, Sept. 1, 2018
Venus pairs with Spica, magnitude 1.0, while Jupiter remains paired with Alpha Librae, magnitude 2.6. (The blue 10° scale is about the width of your fist at arm's length.)

Saturday, September 1

• As twilight fades this evening, spot Venus very low in the west-southwest as shown here. Upper right of it by just 1.3° is Spica, a 1st-magnitude star but less than 1% as bright as Venus. They're about a finger-width at arm's length apart.

• After dark at this time of year, the Great Square of Pegasus looms up in the east, balancing on one corner. Its stars are only 2nd and 3rd magnitude. Extending leftward from the Square's left corner is the main line of the constellation Andromeda. It's made of three stars (including the corner) that are about as bright as the ones forming the Square.

This whole giant pattern was named "the Andromegasus Dipper" by the late Sky & Telescope columnist George Lovi. Shaped sort of like a giant Little Dipper with an extra-big bowl, it's currently lifting its contents upward.

Sunday, September 2

• Mars shines fire-color in the south-southeast after dark this week. High above it, by three or four fists at arm's length, sparkles white Altair.

And a finger width above Altair is fainter Tarazed, an orange giant that's actually more luminous than Altair but far in the background. The two are 17 and 390 light-years away.

• The last-quarter Moon tonight rises in the east around 11 or 11:30 p.m., depending on your location. It's in Taurus. As dawn begins to brighten on Monday the 3rd, the Moon shines high in the southeast with Aldebaran to its left and Orion below it.

Monday, September 3

• How soon after sunset can you see the big Summer Triangle? Face southeast and look high. There's Altair, currently the triangle's bottom point. Vega, the Triangle's brightest star, is nearly at the zenith (as seen from mid-northern latitudes). Deneb is a bit farther to Altair's upper left.

Then look down below Altair. Saturn and Mars form a big triangle with it that's almost a mirror image of the Summer Triangle above. Altair is the top point of this brighter, temporary "Summer of 2018 Triangle."

Mercury and Regulus at dawn, Sept. 5, 2018
Find Regulus just below Mercury on the morning of the 5th, then and closer to Mercury's right on the 6th.

Tuesday, September 4

• As dawn brightens tomorrow morning, use binoculars or a wide-field telescope to spot Regulus twinkling about 1.6° below brighter Mercury. Look very low above the east-northeast horizon, as shown here.

Then on Thursday morning the 6th they'll appear even closer, with Regulus 1.2° to Mercury's right.

Wednesday, September 5

• As dusk turns to night, Arcturus twinkles due west. It's getting lower every week. Off to its right in the northwest, the Big Dipper is scooping to the right.

Thursday, September 6

• With the evening sky moonless, this is a great week for observing the Milky Way under a dark sky. When Deneb crosses your zenith (around 10 or 11 p.m. now), the Milky Way does too — running straight up from the southwest horizon and straight down to the northeast horizon.

Friday, September 7

• With summer waning away, Scorpius lies down in the south-southwest as soon as night arrives. Its brightest star, orange Antares, appears about midway between Jupiter and Saturn. Jupiter shines well off to Antares's right, in Libra, and Saturn is well off to Antares's upper left, in Sagittarius.

Saturday, September 8

• The wide W pattern of Cassiopeia is tilting up in the northeast after dark. Look below the W's bottom segment, by a little farther than the segment's length, for an enhanced spot of the Milky Way's glow if you have a dark enough sky. Binoculars will show this to be the Perseus Double Cluster — even through a fair amount of light pollution.


Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Jumbo Pocket Sky Atlas cover
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Mars on Aug. 9, 2018
The dust on Mars is thinning, leaving a somewhat changed geography. South is up. When Damian Peach and colleagues took this image on August 9th, Sinus Sabaeus and Sinus Meridiani were extending in from the left limb and slightly downward — and not looking like their usual selves. Will such changes be permanent? Yellow dust clouds were still present just below the South Polar Cap and as a sinuous line filling Coprates Chasma right of center.
Jupiter on July 27 (UT), 2018
Jupiter about as it appears visually in a large amateur scope during excellent seeing. S&T's Sean Walker took this image on the evening of July 26th. Jupiter looks historically unusual. Not only is the Great Red Spot very prominent, the normally bright Equatorial Zone has turned dusky.
Saturn on July 27 (UT), 2018
Saturn as it appears in a medium-size amateur telescope during excellent seeing. North is up. Note the Cassini Division in the rings, the bright Equatorial Zone on the globe and the darker South Equatorial Belt just above it, the shadier South Polar Region, and the dim gray C ring just inside the bright A and B rings. The C ring is most easily visible where it's in front of the globe. The shadow of the globe on the rings is clearly visible just off the globe's upper-left edge. Sean Walker took this image on July 26th.

Mercury (about magnitude –1.0) can be spotted very low above the east-northeast horizon about 45 minutes before sunrise. Don't confuse it with twinkly Procyon far off to its upper right, or Sirius farther to Procyon's right or lower right.

Binoculars will show fainter Regulus less than 3° from Mercury on the mornings of September 5th, 6th, and 7th.

Venus (magnitude –4.6) shines low in the west-southwest in twilight. Find it far lower right of Jupiter; their separation diminishes from 24° to 20° this week. In a telescope Venus is a fat crescent about 40% sunlit and 30 arcseconds tall. For the best telescopic seeing catch Venus as early as you can, preferably long before sunset while it is still high.

Mars fades from magnitude –2.1 to –1.9 this week, still brighter than Sirius. It shines in the south-southeast to south during the evening hours and is highest around 11 p.m. daylight-saving time. Mars in a telescope shrinks from 21 to 20 arcseconds wide this week; it's still unusually large and close.

The dust in the Martian atmosphere continues to settle, allowing better views of surface markings. For a Mars map that shows which side is facing Earth at your time and date, use our Mars Profiler.

Jupiter (magnitude –1.9, in Libra) shines in the southwest in twilight. It's upper left of low Venus; their separation diminishes from 24° to 20° this week. Find Mars-colored Antares a similar distance to Jupiter's left.

In a telescope, Jupiter has shrunk to 35 arcseconds wide.

Saturn (magnitude +0.4, above the spout-tip of the Sagittarius Teapot) glows yellow in the south at nightfall. It's between brighter Mars, off to its left, and Mars-colored Antares, nearly as far to Saturn's lower right.

Uranus (magnitude 5.7 at the Aries-Pisces border) and Neptune (magnitude 7.8 in Aquarius) are well up in the east and southeast, respectively, by 11 or midnight. Finder charts for Uranus and Neptune.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (also called UT, UTC, GMT, or Z time) minus 4 hours.


"Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious."
— Stephen Hawking, 1942–2018


"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
— Carl Sagan, 1996


"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not a liberal conspiracy. They are how we determine facts. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor


"Facts are stubborn things."
— John Adams, 1770


Image of Rod


August 31, 2018 at 9:56 pm

"Four bright planets still await you in twilight this week" Great fun viewing the planets this summer. I checked my stargazing log for Mars observations recorded since early January when Mars and Jupiter close alignment in Libra took place through 23-Aug observation with Mars retrograding near border of Capricornus and Sagittarius. Mars stopped retrograde 28-Aug and now is moving eastward again.

26 observations made and magnification power running 25x to 216x views using my 90-mm refractor and 10-inch telescope. It has been enjoyable tracking the observable changes in Mars brightness, angular size, surface areas visible, and position changes among the stars along the ecliptic, including retrograde motion and eastward motion. Simple telescope observations serve to check the accuracy of predictions made about Mars using the ephemeris tables published for use like Sky & Telescopes, monthly Planetary Almanac. These reports are very handy for planet viewing.

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mary beth

September 1, 2018 at 11:47 am

You’re right, it’s been a wonderful summer! Have you ever thought about setting up a permanent observatory so you don’t have to lug everything through the horse pasture? It sounds like you have very nice equipment so if you could build something climate controlled and secure, it might make it easier for you. All I have is my two, well actually four eyes , in light polluted, hazy Houston conditions, but I do still enjoy what I can see. When I get in darker areas, I actually have a bit of trouble finding my way around the sky initially, since I’m seeing stars I don’t normally see!

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September 1, 2018 at 2:07 pm

mary beth, I have no plans to setup a dome on the land or in the horse barn. Most of my observations of Mars this year was with the 90-mm refractor (light weight configuration), July and August with the 10-inch reflector that I purchased in latter June. I also use 10x50 binoculars, these are economical and can be very enjoyable. If you do not have binoculars, you may want to check out 7x50, 8x50 and 10x50 pairs. My daughter-in-law recently gave me her 40-mm Halleyscope. it has a small star diagonal with small tripod stand that sits atop a table. Power runs 8x to 32x, I was able to see Saturn and the rings with Titan as well as Jupiter and its moons, even M31 (images are not bright though). The Halleyscope is terrestrial view so I looked at the ground hog too in the fields 🙂 My plans for early September, view the comet passing in early morning skies now through Auriga and Gemini. Presently too cloudy where I am at for stargazing activity and last night, quite a few t-storms moving around the region.

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mary beth

September 2, 2018 at 9:10 am

Thanks Rod! I thought about binoculars but I have not thought about putting them on a tripod. I will look into that set up, since more portable and maneuverable than a telescope. Great that your family involved! Rain here next seven days or so but we need it. Can’t believe I’m saying that....the flood was one year hope you see the comet!

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September 4, 2018 at 8:12 am

mary beth, I did see the comet 🙂 A few quick notes from my stargazing log. I viewed 0400 EDT this morning. [Observed comet 21P/Giacobini-Zinner this morning using TeleVue 40-mm and 32-mm plossls. Good views, with hint of short tail. A meteor flashed by moving from Auriga towards ESE in the direction of Orion or where the Moon was about 0330 EDT. The meteor was brighter than Capella but not as bright as the Moon. The meteor left a train or trail as it flashed by.] A more detailed comment is in Bob King's report on 21P comet on this site.

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mary beth

September 5, 2018 at 10:58 pm

What good timing! I’m going to check out the detailed comments you left on Bin’s page! Thanks!

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