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astrogeoguy · 6 years

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The Perseids Peak over Sunday Night, the Moon Returns to Grace the Eve, Jupiter Sports Twin Spots, and the Demon Star Revives!

(Above: The path of Comet 21P/Giacobini-Zinner in the northeastern sky this week. It will be passing Casssiopeia heading downwards, shown here at 11 pm local time.)

Astronomy Skylights for this week (from August 12th, 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!

My latest column for Space.com is all about this week’s Mars opposition and closest approach. You can find it here.

My latest Mobile Astronomy column for Space.com is about the Perseid meteor shower. You can find it here.

Public Events

Taking advantage of the moon, Venus, Jupiter, Saturn, Mars, and other bright objects in the sky this week, the RASC Toronto Centre astronomers will hold their free monthly public City Sky Star Party in Bayview Village Park (steps from the Bayview subway station), around 8 pm on the first clear weeknight this week (except Wed and Fri). You don’t need to be an RASC member, or own any equipment, to join them. Check here for details, and check the banner on their website home page or Facebook page for the GO or NO-GO decision around 5 pm each day.

Every Monday evening, 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.

Teachers! The York University Astronomy department will hold Astro Workshop 2018, professional development for teachers, on August 14-16, 2018. Registration and details are here.

At 7:30 pm on Wednesday, August 15, the RASC Toronto Centre will hold their free monthly Recreational Astronomy Night Meeting at the Ontario Science Centre. The public are welcome. Talks include the Sky This Month, measuring double stars, and making your own Pluto images from free science mission data. Check here for details. Parking is free.

At 6:30 pm on Tuesday, August 14, the S Walter Stewart Library will host a free public lecture by Dr. Renée Hložek of the Dunlap Institute at U of T (she’s fantastic!). It’s entitled The Big, Dark and Beautiful Universe. Check here for details.

At 8:30 pm on Wednesday, August 15, the High Park Nature Centre will host a free public Urban Bat Walk followed by stargazing (weather permitting). Check here for details.

Eastern GTA sky watchers are invited to join the RASC Toronto Centre and Durham Skies for solar observing and stargazing at the edge of Lake Ontario in Millennium Square in Pickering on Friday evening, August 17, from 6 pm to 11 pm. Details are here. If it’s cloudy, they’ll try again on Saturday. Before heading out, check the RASCTC home page for a Go/No-Go call in case it's too cloudy to observe.

On Friday, August 17 at 8 pm, adults can enjoy some suds with their science at Astronomy on Tap T.O. at the Great Hall, a free event hosted by the U of T Astronomy Department. Talks, trivia, contest giveaways, and more! Details are here.

The next RASC Public Event at the David Dunlap Observatory will be on Saturday, August 18. 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 7:30 pm for an 8 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 Perseid Meteor Shower Peaks Tonight!

Overnight tonight (Sunday) the spectacular annual Perseid Meteor Shower will reach its peak, when the most meteors will be seen per hour. After tonight, the shower will taper off until it officially ends on August 26, so you should head out on Monday night if it’s clear, and continue to keep an eye out for bright meteors for the rest of this week, although the moon will increasingly affect seeing conditions. I wrote details about how meteor showers work here last week. Make an effort to see this show; next year the Full Moon will spoil the Perseid peak.

For best results, try to find a safe and very dark viewing location with as much open sky as possible. Even a 30 minute drive to a park or rural site away from big city light pollution will help a lot. You can start watching as soon as it is dark - to catch very long meteors produced by particles skimming the Earth’s upper atmosphere. These are rarer, but feature very long trains. Don’t worry about watching the radiant. Meteors from that position will be heading directly towards you and have very short trails.

Bring a blanket for warmth and a chaise to avoid neck strain, plus snacks and drinks. Try to keep watching the sky even when chatting with friends or family – they’ll understand. Call out when you see one; a bit of friendly competition is fun!

Don’t look at your phone or tablet – the bright screen will spoil your dark adaptation. If you can, minimize the brightness or cover the screen with red film. Disabling app notifications will reduce the chances of unexpected bright light, too. And remember that binoculars and telescopes will not help you see meteors because they have fields of view that are too narrow. I posted some diagrams here. Good hunting!

The Moon and Planets

After reaching its new phase on Saturday, the young crescent moon will return to grace the low western evening sky for a short time after sunset tonight (Sunday). For the rest of the week, it will wax and slide east, lingering longer after sunset each evening.

In the western sky on Tuesday evening, the moon will take up a position a palm’s width above bright Venus, making a lovely wide field photo opportunity. On Wednesday evening it will sit a similar distance above the bright white star Spica in Virgo (the Maiden). On Thursday and Friday, the moon will hop over Jupiter, moving from the planet’s upper right to its upper left. Using the moon as a starting point, you might be able to spot Jupiter in daylight using binoculars.

(Above: The moon and Jupiter in daylight at 7 pm EDT on August 16. The following day, the moon will hop to Jupiter’s upper left. The orange circle represents a binoculars field of view.)

This is the best week of the moon’s monthly orbit to view it in binoculars or a telescope. The moon waxes because the sun is slowly rising over its eastern horizon. The shallow angle of the sunlight casts deep black shadows all along the terminator line – the boundary between the lit and unlit hemispheres. New terrain will be showcased every night!

Extremely bright Venus will still blaze away in the western evening sky this week – and it’s still brightening! On Thursday, Venus will reach its widest angle east of the sun. After that, the planet will begin to swing back towards a meeting with the sun in October. The descending evening ecliptic is pulling Venus a bit lower each night, but we can observe it until about 10 pm local time. In a small telescope, the planet’s disk will resemble a first quarter moon, half-lit on the sunward side (although your telescope might flip the view).

(Above: Venus reaches greatest elongation east of the sun on August 16, after which it will start to swing back towards the sun. Meanwhile the moon will look upon Jupiter as it passes close above the bright double star Zubenelgenubi,as shown here for 9 pm local time.)

We only have a few more good weeks to enjoy Jupiter this year. This week, the very bright planet will be in the southwestern sky after dusk, and then set in the west-southwest at about 11:30 pm local time. Jupiter has been slowly shifting eastwards. In the middle of this week, it will pass close above a nearby bright star. Afterwards it will start to pull away. The star is Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars, you’ll plainly see that Zubenelgenubi is a pair of stars. While you have the binoculars handy, see if you can see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) flanking the planet.

From time to time, the small round black shadows cast by Jupiter’s four Galilean moons become visible in backyard telescopes as they cross (or transit) the planet’s disk. On Thursday, August 16, Europa’s shadow will begin to transit at 7:56 pm EDT (in evening twilight). At 8:05 pm EDT, Io’s shadow will join Europa’s and the duo will transit Jupiter until they both move off the planet at 10:10 pm. 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, including some double shadow ones.

(Above: A double shadow transit caused by Europa and Io will occur on Jupiter on Thursday, August 16, as shown here at 9:15 pm EDT.)

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. Try to look within an hour before or after the following times: Sunday, August 12 at 8:57 pm, Tuesday, August 14 at 10:36 pm, Friday, August 17 at 8:07 (in twilight), and Sunday, August 19 at 9:46 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.

Around 9 pm local time, when the first bright stars appear overhead, medium-bright Saturn will appear not too high up the darkening southern sky. The yellow-tinted planet will reach its highest elevation of about 2 fist diameters above the southern horizon at around 9:30 pm, and then descend to set in the west at about 2:30 am. This summer, the ringed planet has been on the eastern (left-hand) outskirts of the Milky Way, and situated just above the “lid” star of the Teapot-shaped constellation of Sagittarius (the Archer). As the sky darkens, even a small telescope should be able to show you some of Saturn’s larger moons, especially Titan. Using a clock’s dial analogy, Titan will move counter-clockwise this week from a position at 12 o’clock (above the planet) to 7 o’clock (to the lower left of it). (Remember that your small telescope might flip and/or invert the view. Use the moon to find out how your telescope changes things.)

Mars will still be very bright and close to Earth this week. Visually, it will appear pink or orangey. It will rise over the southeastern horizon at around 8 pm local time (give or take, depending on your latitude) and then climb higher until midnight local time, when it will reach an elevation of about 20° (or two outstretched fist diameters) above the southern horizon. (That will be the best hour to view the planet in a telescope because it will then be shining through the least amount of Earth’s distorting atmosphere.) Note that 20° is lower than many trees and buildings, so a clear southern vista is essential.

(Above: Mars and Saturn dominate the overnight southern sky, as shown here for 10 pm local time this week. Tiny Pluto sits near Sagittarius, between the two naked-eye planets.)

At visual magnitude 5.8, blue-green coloured Uranus is visible from late evening until dawn. You can see it without optical aid under very dark skies, or in binoculars and telescopes under moderately light-polluted skies. The ice giant planet is located in the eastern sky, about 4.5 finger widths to the left of the modestly bright star Torcular (Omega Piscium), which is above the “V” where the two starry cords of Pisces (the Fishes) meet.

(Above: The detailed positions of Uranus and Neptune in August, 2018.)

Using a decent quality telescope this week, you can see the distant and very blue planet Neptune among the dim stars of Aquarius (the Water-bearer). It will rise in the east shortly after 9 pm local time. Look for the magnitude 7.8 planet sitting 1.75 finger widths to the right of the modestly bright star Phi (φ) Aquarii and 4 finger widths to the left of the brighter star Hydor (Lambda Aquarii).

At 1:36 am EDT on Wednesday, August 15, distant dwarf planet Pluto will pass in front of, or occult, a dim distant star. The planet is positioned roughly midway between Mars and Saturn. Many serious astronomers will try to record the event to study how Pluto’s atmosphere dims the star.

A Binocular Comet

Comet 21P/Giacobini-Zinner has been gradually brightening for some time because it is approaching Earth’s orbit. This week, you should be able to see the faint fuzzy object in binoculars or a small telescope, if you can escape city lights. The comet will be heading downwards every night past the bright star Segin, which marks the bottom-most star in the “W” of Cassiopeia (the Queen).

(Above: This animation was assembled from a series of 55 images of Algol taken with the CHARA interferometer at Mount Wilson Observatory, using the infrared part of the spectrum (coloring the normally white star red). It shows the dimmer companion star orbiting Algol and passing in front of it - a classic eclipsing binary star system. The numerical labels range from 0.0 at the start of the orbit, to 0.868, near the end of the orbit.)

See the “Demon” Star Brighten

The “Demon Star”, more formally known as Algol, is a star that is easy to see using unaided eyes. In Perseus (the Hero), it is among the most accessible variable stars for beginner skywatchers. Despite the connotation of its nickname (it represents the severed head of Medusa the Gorgon being held by Perseus), the star is a hot white star located 92 light-years from Earth.

Algol’s brightness dims noticeably for about 10 hours once every 2 days, 20 hours, and 49 minutes because a dim companion star orbiting nearly edge-on to Earth crosses in front of the much brighter main star – an arrangement that is called an eclipsing binary star system. On Saturday, August 18 at 9:32 pm EDT, Algol will reach its minimum brightness of magnitude 3.4 and will sit just above the northeastern horizon. By 2:30 am EDT, it will be halfway up the eastern sky and will have brightened to its usual magnitude of 2.1. The dimming periods can fall at any time of the day or night. The timing of this particular event makes watching the return to brightness a convenient project for evening observers.

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

#space #astronomy #stars #planets #Algol #Jupiter Shadow Transits #perseid meteor shower #Comet 21p/Giacobini-Zinner

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astrogeoguy · 6 years

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The Moon moves into Morning and Mars moves Even Closer, while the Planet Parade Continues!

(Above: This image of Mars taken on July 27, 2018 by Christopher Go of Cebu, Philippines, shows surface features and the southern polar cap, despite the dust storm that has been enveloping the planet.)

Astronomy Skylights for this week (from July 29th, 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.

My latest column for Space.com is all about this week’s Mars opposition and closest approach. You can find it here.

Public Events

Today, July 29 at the Ontario Science Centre, kids are invited to participate in a fun activity to develop and deploy a Mars rover mission. Check here for details. This event is free with your admission to the science centre, on a first come-first served basis.

York University’s Allan I. Carswell Observatory are still turning their telescopes on Mars this week, with free public viewing from Monday through Wednesday between 9 and 11:45 pm. Details about this Mars Extravaganza are here.

At 8:30 pm on Wednesday, August 1, the High Park Nature Centre will host a free public Urban Bat Walk followed by stargazing (weather permitting). Check here for details.

On Friday, August 3, starting at 7 pm, the U of T AstroTour will present their planetarium show entitled The Life and Death of Stars. Tickets and details are here.

On Thursday, August 2, starting at 9 pm, the U of T AstroTour will present a talk entitled Discovering new galaxies through the eyes of a Dragonfly. Details are here.

The next RASC Public Event at the David Dunlap Observatory will be on Saturday, August 11 – in celebration of the Perseid meteor shower peak on that weekend. 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.

Teachers! The York University Astronomy department will hold Astro Workshop 2018, professional development for teachers, on August 14-16, 2018. Registration and details are here.

The Moon and Planets

After this past weekend’s full moon and lunar eclipse, the moon will wane and rise later each night, while also lingering into the morning daytime sky. Our bright natural satellite will pass through the dim water constellations of Aquarius (the Water-Bearer), Pisces (the Fishes), and Cetus (the Whale), and then end the week on the outskirts of Taurus (the Bull).

If you are out after midnight this week, grab your binoculars or telescope and look along the terminator – the boundary line that separates the lit and dark hemispheres of the moon. All along it, the steeply slanted sunlight will generate spectacular vistas of bright ridges and deep black shadows. It’s the same shadowed terrain we see on evenings around First Quarter, but instead lit from the opposite direction.

The moon will officially reach its Last Quarter phase on Saturday afternoon, August 4. At that time, the 90° angle made by the moon, Earth, and sun will cause everyone on Earth to see the moon half illuminated – on its western side. And, an observer standing anywhere on the moon’s near side would see Earth half illuminated, too!

(Above: The western evening sky, shown here at 9:30 pm local time, features the two brightest planets, Venus and Mars. Venus will soon reach the outer rim of its orbit and begin to depart the evening sky. Jupiter will be carried into the western sunset over the next weeks.)

Extremely bright Venus continues to catch our eyes in the western evening sky this week – and it’s not even at its brightest yet! The descending evening ecliptic is now pulling Venus a bit lower each night, but we can observe it until almost 10:30 pm local time. In a small telescope, the planet’s disk will resemble a first quarter moon, lit on the sunward side (although your telescope might flip the view).

Our opportunities to enjoy Jupiter will soon be over for this year. This week, the bright planet will continue to shine very brightly in the southwestern sky after dusk, and then set in the west-southwest at just before midnight local time. The bright star sitting just to the left of Jupiter is Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars, you’ll plainly see that it is a pair of stars. While you have the binoculars handy, see if you can see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) flanking the planet.

On Tuesday, August 31, Io’s shadow will begin a crossing (transit) of Jupiter’s disk at 9:49 pm that ends at midnight. 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, including some double shadow ones.

(Above: Io and its black shadow will transit Jupiter on Tuesday evening, as shown her at 10:20 pm EDT.)

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. Try to look within an hour before or after the following times: Tuesday, August 21 at 9:02 pm and Thursday, August 2 at 10:41 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.

This week, medium-bright and yellowish-tinted Saturn will be visible from dusk, when it’s shining over the southern horizon, until it sets in the west at about 3:30 am local time. It will be the first star-like object to pop out of the southern twilight sky. The ringed planet is spending this summer just east (to the left of) the Milky Way, and just above the Teapot-shaped stars that form Sagittarius (the Archer). As the sky darkens, even a small telescope should be able to show you some of Saturn’s larger moons, especially Titan. Because Saturn’s axis of rotation is inclined about 27° from vertical (a bit more than Earth’s is), we can see the top surface of its rings, and its moons can appear above, below, or to either side of the planet. The tilted axis also gives Saturn seasons. But they last 7.5 years, as opposed to our “short” 3-month-long seasons.

(Above: The ice giant planets Uranus and Neptune are visible in the post-midnight eastern sky, as shown here at 12:30 am local time.)

At visual magnitude 5.8, blue-green coloured Uranus is visible between midnight and dawn without optical aid under very dark skies, or in binoculars and telescopes under moderately light-polluted skies. The ice giant planet is located in the eastern sky, about five finger widths to the left of the modestly bright star Torcular (Omega Piscium), which is above the “V” where the two starry cords of Pisces (the Fishes) meet. The major asteroid Juno is in the same region of sky, about a fist’s diameter to the lower left of Uranus.

Distant, blue Neptune, among the dim stars of Aquarius (the Water-bearer), will be observable in telescopes in the eastern sky after it rises after 10 pm local time. This week, look for the magnitude 7.8 planet sitting 1.5 finger widths to the right of the naked eye star Phi (φ) Aquarii and about 4 finger widths to the left of the brighter star Hydor (Lambda Aquarii).

I’ll post sky charts for the observable planets here.

Mars at Closest Approach

Last Friday, Earth passed Mars on the “inside track”, a term astronomers call opposition. On that day, Mars rose in the east as the sun set in the west. And because we were so much closer to Mars, it appeared brighter and looked larger in binoculars or a telescope.

(Above: On July 27, 2018 (left panel), Mars will reach opposition for 2018, when Earth will pass between the Red Planet and the sun. A year from now (right panel), Earth will return to the same position, but Mars will be on the far side of the sun from Earth, having only completed half of an orbit. Mars will reach opposition again on October 13, 2020.)

But our minimum distance from Mars will occur this Tuesday, July 31. At that time, the Red Planet will be 57.6 million km or 0.385 astronomical units (the mean sun-Earth separation) from Earth. That translates to only 3 minutes and 18 seconds for radio signals to reach the planet, or vice versa. It will continue to look spectacular, so keep your telescope handy!

Here’s how to find and see Mars this week. Tonight (Sunday) Mars will rise at about 9 pm local time (depending on your latitude). It will climb until 1:15 am local time, when it will reach an elevation of about 20° (or two outstretched fist diameters) above the southern horizon. This is the best time to view the planet in a telescope because it will then be shining through the least amount of Earth’s distorting atmosphere. Note that 20° is lower than many trees and buildings, so a clear southern vista is essential.

Because Mars is still close to opposition, it will descend into the west in the wee hours and set around dawn. Mars will be rising about 5 minutes earlier every night, so on Tuesday it will rise just before 9 pm.

(Above: Saturn and Mars parade through the southern overnight sky this week, as shown here at 10:30 pm local time on Sunday, July 29.)

If we have clear skies, the planet will be impossible to miss. It will be brighter than anything nearby, except the late-rising moon. The planet’s red coloration will be obvious - as opposed to Saturn’s mere tint of yellow. The planet will not rapidly move location, or flash or blink. Anything doing that is a plane �� keep hunting.

The farther south you live, the higher Mars will climb. An observer in Florida will see Mars nearly halfway up the sky after midnight. And someone at the latitude of Sydney, Australia will see Mars directly overhead at midnight!

Wherever you are, even with a small telescope on a night of good seeing (i.e., with clear, steady air), you should be able to see Mars’ southern polar cap of frozen CO2 and water ice, and also some darker and lighter regions on the planet. Because Mars’ rotational period (its day) is about 38 minutes longer than Earth’s, by viewing the planet over many nights you can see different parts of its surface. In fact, it would take you 41 nights of observing to see the entire globe of Mars. But since we have about 7 hours of darkness during nights in late July, you could also observe Mars from about 10 pm local time, soon after it rises, until 4:30 am just before it sets, and see about one-quarter of the globe in a single night.

A global dust storm has recently enveloped the planet – hiding its surface. But skilled planetary imagers like Damian Peach have reported that the storm is abating. Fingers crossed!

Don’t worry if your Mars viewing is clouded out this week. After Tuesday, Earth will slowly begin to pull away from Mars, but Mars will decrease in apparent size more slowly than it has been increasing. In fact, it will look 90% as large for the next month! Its visual brightness will also remain intense for weeks to come. I posted some Mars sky charts and diagrams here.

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

#planets #stars #astronomy #Jupiter #mars opposition #Venus #Saturn #space #Universe

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