#yo twilight is a hot topic again

[astrogeoguy]

It’s Easy to See Ceres, the Full Strawberry Moon meets Mars after Saturn, and the Ringed Planet Peaks for 2018!

(Above: On Wednesday, June 27, Saturn reaches its closest and brightest point for this year. That same night, the full moon will sit just above it. Many spectacular deep sky objects sit around Saturn, and are better seen once the moon moves away. Look for the large, bright open cluster designated M24 sitting above Saturn all summer.)

Astronomy Skylights for this week (from June 24th, 2018) by Chris Vaughan. (Feel free to pass this along to friends and send me your comments, questions, and suggested topics.) I post these with photos at http://astrogeoguy.tumblr.com/ where the old editions are archived. You can also follow me on Twitter as @astrogeoguy! Unless otherwise noted, all times are Eastern Time. Please click this MailChimp link to subscribe to these emails. If you are a teacher or group leader interested joining me on a guided field trip to York University’s Allan I. Carswell Observatory, or another in your area, visit www.astrogeo.ca.

If you’d like me to bring my Digital Starlab inflatable planetarium to your school or other daytime or evening event, visit DiscoveryPlanetarium.com and request me. We’ll tour the Universe together! 

Public Events

On Monday evenings, York University’s Allan I. Carswell Observatory runs an online star party - broadcasting views from four telescopes/cameras, answering viewer questions, and taking requests! Details are here. On Wednesday evenings after dark, they offer free public viewing through their telescopes. If it’s cloudy, the astronomers give tours and presentations. Details are here. 

On Friday, June 29, starting at 7 pm, the U of T AstroTour will present their planetarium show entitled Grand Tour of the Cosmos. Tickets and details are here. 

The next RASC Family Night at the David Dunlap Observatory will be on Saturday, July 7. There will be sky tours in the Skylab planetarium room, space crafts, a tour of the giant 74” telescope, and viewing through lawn telescopes (weather permitting). The doors will open at 8:30 pm for a 9 pm start. Attendance is by tickets only, available here. If you are a RASC member and wish to help us at DDO in the future, please fill out the volunteer questionnaire here. And to join RASC, visit this page. 

The Moon and Planets

To begin this week, the moon will be shining brightly in the evening sky as a nearly full (waxing gibbous) globe. Remember to pull out your binoculars or small telescope and look along the boundary separating the lit and dark sides. That’s where the most dramatic moonscapes are. Because the moon reaches its full phase on Thursday at 12:53 am EDT, the moon will look full on Wednesday evening and slightly past full on Thursday night.

(Above: The full Strawberry moon is nick-named for the bounty of Mother Nature in June annually.) 

The June full moon, colloquially known as the Strawberry Moon, Mead Moon, Rose Moon, or Hot Moon, always shines in or near the stars of southern Ophiuchus (the Serpent-Bearer). Because the moon reaches full when it is opposite the sun in the sky, full moons always rise in the east as the sun sets, and set in the west at sunrise. Since vertically impinging sunlight casts no shadows on a full moon, all of the surface brightness variations are generated by differences in the reflectivity, or albedo, of the lunar surface rocks. 

In the southeastern sky after dusk on the Wednesday evening, the full moon will sit one finger’s width above bright, yellowish Saturn. The two objects will cross the sky together during the night and will easily fit within the field of a small telescope at low magnification. Meanwhile, the moon’s separation from Saturn will noticeably increase as the moon slides eastward in its orbit during the night. 

The large open star cluster called Messier 24 will sit a few finger widths above (to the northeast of) the moon and Saturn. The cluster, also known as the Small Sagittarius Star Cloud, is three times wider than the moon! Try to see it using binoculars, or wait for the moon to move away on the following nights and use Saturn to find it then. 

After mid-week, the moon will slide east, rise later, and begin to wane – with the dark region growing on the moon’s western (our right-hand) side. About 11 pm local time on Saturday night, bright red Mars will rise in the east with the waning gibbous moon shining 4 finger widths to the upper left (northeast) of it. Both objects will fit into the field of view of binoculars. By dawn, the pair will appear low in the southwestern sky.

(Above: The inner planets Mercury and Venus continue to put on a good show this week, as shown here for 9:30 pm local time on Sunday, June 24. Mercury will fade and descend next week, while Venus will continue to brighten.) 

Venus continues to catch our eye in the western evening sky this week while it continues to swing away from the sun - and it will still get brighter! The planet will be setting at about 11:30 pm local time all week because it is travelling east while the entire sky is shifting west, holding it in place. Venus is gradually growing larger as it moves towards Earth. In a small telescope, the planet’s disk will not look round. Instead, it will exhibit a gibbous (70% illuminated) phase. 

This is the best week to see elusive Mercury sitting low over the northwestern horizon for a brief period after sunset. It recently peaked in brightness and the best time to look is between 9:45 and 10:15 pm local time. You’ll need a low open horizon because the planet will be only a few finger widths above the horizon (or less). 

Jupiter is the bright object you will see shining brightly in the southern sky after dusk this week. Around that time, it will be at its highest elevation (about three fist diameters) above the southern horizon. Over the following five hours, it will move west and descend – setting in the west-southwest about 3 am local time. Once it’s dark enough, look for a bright star sitting just to the lower left of Jupiter. That’s Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars or a small telescope, it splits into a closely separated pair of stars.

(Above: On Monday, June 25, the shadow of Jupiter’s moon Ganymede will transit the northern zone of the planet, along with the Great Red Spot, as simulated here at 10 pm EDT.)  

On Monday, June 25, and visible between 9 pm (in twilight) and 10:42 pm EDT, the little, round, black shadow of Jupiter’s moon Ganymede will cross (or transit) near the north pole of Jupiter’s disk. On Saturday, June 30 starting at 1:14 am and visible until Jupiter sets, the shadow of Jupiter’s moon Io will transit. A reasonable backyard telescope will show the black shadows, but a very good telescope is needed to see the moons themselves. More shadow transits are available in other time zones around the world. 

The Great Red Spot (or GRS, for short) takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2-3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air – when the stars are not twinkling too much. The best times to try this week are: Monday, June 25 at 1:18 am and again at 9:09 pm (in twilight, with a Ganymede shadow bonus), Wednesday, June 27 at 10:48 pm, and Saturday, June 30 at 12:27 am. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone. Try to look within an hour before or after the times I’ve given.

(Above: Look for Saturn above the Teapot-shape of Sagittarius all summer. On opposition night, June 27, the full moon will join the party, as shown here at 11 pm local time.)

On Wednesday, the Earth’s orbit will carry us between Saturn and the sun. Sitting opposite the sun in the sky (a term that astronomers call opposition), Saturn will be visible all night long, and the planet’s disk will be the brightest and largest (18 arc-seconds) for the year. Planets don’t emit their own light. We see them because the sun’s light has travelled all the way out to them and reflected off their surfaces. At opposition, the reflected light from Saturn will travel for 75 minutes to reach Earth – and our human eyes. 

Yellow-tinted Saturn will rise in the southeastern sky at about 9 pm local time this week, just as the sun sets. The ringed planet will be spending the summer of 2018 just to the left of the Milky Way, and just above the Teapot-shaped stars that form Sagittarius (the Archer). Saturn moves over the southern horizon, its highest point in the sky at 1:30 am local time. It will remain visible until about 5 am local time, when it will sit more than a fist’s width above the southwestern horizon. Scientists have recently determined that Saturn’s reflective icy rings formed only a few hundred million years ago – during Earth’s Carboniferous Period, when early dinosaurs roamed our planet! 

(Above: Mars rises well after Saturn, but still before midnight, as shown here on June 27 at 11 pm local time.)

Mars is getting good now! The Red Planet will be rising in the east just after 11 pm local time this week. Mars will continue to steadily brighten and increase in apparent size (when viewed through a telescope) as the Earth’s faster orbit brings us closer to the red planet until July 31. Mars will reach its highest position, over the southern horizon, around 3:30 am local time, and then remain visible until just after 5 am. 

Distant blue Neptune, among the modest stars of Aquarius (the Water-bearer), is observable in telescopes in the eastern sky after it rises around 13:30 am local time. This week, look for the magnitude 7.9 planet sitting one finger width to the right of the naked eye star Phi (φ) Aquarii and about five finger widths to the left of brighter Hydor (Lambda Aquarii). 

Blue-green coloured Uranus is visible in binoculars, if you know where to look. It, too, is in the eastern pre-dawn sky, located about four finger widths to the left of the modestly bright star Torcular, which is down toward the “V” where the two cords of Pisces (the Fishes) meet. I posted sky charts for Uranus and Neptune here. 

It’s Easy to See Asteroids - Sometimes

Here’s a very easy way to see an asteroid with your own eyes. After dusk on the evening of Wednesday, June 27, the large dwarf planet (formerly asteroid) Ceres will sit only 9 arc-minutes (or less than one third of the moon’s apparent diameter) above the bright, visible double star Algieba in Leo (the Lion). Algieba marks the throat of the lion, midway along the backwards question-mark that forms the front of the constellation. After dusk, the lion will be positioned over the western horizon and tipped with his face downward to the right. I’ll post a sky chart here. 

(Above: Thursday, June 27 brings the perfect chance to see the dwarf planet Ceres when it passes very closely above the naked-eye double star Algieba in Leo the lion. Use binoculars and small telescopes on the double star and look for a small object just above it. The sky is shown for 10:30 pm local time.)

Use binoculars to look for Ceres as a little, star-like object just a short distance above Algieba. A small telescope at medium-high magnification will show Ceres and Algieba’s close-together pair of distant stars together in the same field of view.

(Above: A detailed view of the region around Algieba and Ceres on June 27. The yellow circle represents the field of view of a medium power telescope.) 

After a determined search by many astronomers who were looking for a theorized missing planet, Ceres was the first asteroid ever discovered, by Giuseppe Piazzi in Palermo, Sicily, on January 1, 1801. It was named after the Roman Goddess of Agriculture. (The same name gave us the word “cereal”!) Ceres was originally given planet status, orbiting as it does between Mars and Jupiter. But calculations of its 950 km diameter, and later discoveries of countless additional bodies in the asteroid belt, led to its demotion to queen of the asteroid belt. But in 2006, the same rules that demoted Pluto to dwarf planet status promoted Ceres to the same class of objects. Good luck! 

(Above: The path of the large asteroid Vesta (red line) over the month surrounding June 19, when it reached peak brightness, within range of binoculars. The sky is shown at 10:30 pm local time.)

As I mentioned last week, another asteroid, the minor planet (4) Vesta, is now visible all night long, and appearing about its brightest (magnitude 5.33) for the year - within reach of binoculars and small telescopes. Look for the object above the Teapot-shaped constellation Sagittarius (the Archer), about a fist’s diameter to the upper right of Saturn.

Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.