Posted on

This Weekend: The Moon Photobombs ‘Planet-palooza’ at Dawn

September planets
The planetary lineup at dawn (minus the Moon) from September 12th. Image credit and copyright: Alan Dyer (AmazingSky.com).

Following the Moon and wondering where are the fleeting inner solar system planets are this month?

While Jupiter and Saturn sink into the dusk on the far side of the Sun this month, the real action transpires in the dawn sky in mid-September, with a complex set of early morning conjunctions, groupings and occultations.

First, let’s set the stage for the planetary drama. Mercury just passed greatest elongation 18 degrees west of the Sun on September 12th.

The action warms up with a great pre-show on the morning of Saturday, September 16th, when the closest conjunction of two naked eye planets for 2017 occurs, as Mercury passes just 3′ north of Mars. The conjunction occurs at 16:00 UT, favoring the western Pacific region in the dawn hours. The pair is just 17 degrees from the Sun. As mentioned previously, this is the closest conjunction of two naked eye planets in 2017, so close the two will seem to merge to the naked eye and make a nice split with binoculars. This is also one of the first good chances to spy Mars for this apparition, fresh off of its solar conjunction on July 27th, 2017. Mars is now headed towards a favorable opposition next summer on July 27th, 2018, one that’s very nearly as favorable as the historic grand opposition of 2003.

Mars shines at magnitude +1.8 on Saturday morning with a disk 3.6” across, while Mercury shines at magnitude +0.05 with a 64% illuminated disk 6.4” across. Mars is actually 389 million km (2.6 AU) from the Earth this weekend, while Mercury is 158 million km (1.058 AU) distant.

The view looking east on the morning of September 17th. Stellarium

Follow that planet, as Mars also makes a close (12′) pass near Venus on October 5th. At the eyepiece, Venus will look like it has a large moon, just like the Earth!

Think this pass is close? Stick around until August 10th, 2079 and you can actually see Mercury occult (pass in front of) Mars… our cyborg body should be ready to download our consciousness into by then.

Mark your calendars: Mercury occults Mars in 2079. Stellarium

The waning crescent Moon joins the view on Monday, September 18th, making a spectacular series of passes worldwide as it threads its way through the stellar-planetary lineup. Occultations involving the waning Moon are never as spectacular as those involving the waxing Moon, as the bright limb of the Moon leads the way for ingress instead of the dark edge. The best sight to behold will be the sudden reappearance of the planet of star (egress) from behind the waning crescent Moon’s dark limb.

The Moon on Sept 18th
The sky looking east on the morning of September 18th. Stellarium

First up is an occultation of Venus on September 18th centered on 00:55 UT. Unfortunately, this favors the eastern Indian Ocean at dawn, though viewers in Australia and New Zealand can watch the occultation under post dawn daytime skies. The pair is 22 degrees west of the Sun, and the Moon is two days from New during the event. Shining at magnitude -4, it’s actually pretty easy to pick out Venus near the crescent Moon in the daytime. Observers worldwide should give this a try on the 18th as well… folks are always amazed when I show them Venus in the daytime. The last time the Moon occulted Venus was September 3rd, 2016 and the two won’t cross paths again until February 16th, 2018.

The footprint of the occultation of Venus by the Moon. Occult 4.2

Next up, the Moon occults the +1.4 magnitude star Regulus on the 18th at 4:56 UT. Observers across north-central Africa are best placed to observe this event. This is the 11th occultation of Regulus by the Moon in a series of 19, spanning December 2016 to April 2018.

The occultation of Regulus by the Moon. Occult 4.2

The brightest star in the constellation Leo, Regulus is actually 79 light years distant.

Next up, the dwindling waning crescent Moon meets the Red Planet Mars and occults it for the western Pacific at 19:42 UT. Shining at magnitude +1.8 low in the dawn sky, Mars is currently only 3.6” in size, a far cry from its magnificent apparition next summer when it will appear 24.3” in size… very nearly the largest it can appear from the Earth.

The occultation of Mars by the Moon. Occult 4.2

And finally, the slim 2% illuminated Moon will occult the planet Mercury on September 18th centered on 23:21 UT.

The occultation of Mercury by the Moon. Occult 4.2

Mercury occultations are tough, as the planet never strays very far from the Sun. The only known capture I’ve seen was out of Japan back in 2013:

This week’s occultation favors southeast Asia at dawn, and the pair is only 16 degrees west of the Sun. Mercury is gibbous 74% illuminated and 6” in size during the difficult occultation.

We just miss having a simultaneous “multiple occultation” this week. The Moon moves at the span of its half a degree size about once every hour with respect to the starry background, meaning an occultation must occur about 60 minutes apart for the Moon to cover two planets or a planet and a bright star at the same time, a rare once in a lifetime event indeed. The last time this transpired, the Moon covered Venus and Jupiter simultaneously for observers on Ascension Island on the morning of April 23rd 1998.

When is the next time this will occur? We’re crunching the numbers as we speak… watch this space!

Looking into next week, the Moon reaches New phase on Wednesday, September 20th at 5:31 UT/1:31 AM EDT, marking the start of lunation 1172. Can you spy the razor thin Moon Wednesday evening low to the west? Sighting opportunities improve on Thursday night.

Don’t miss this weekend’s dance of the planets in the early dawn sky, a great reason to rise early.

Read about conjunctions, occultations, tales of astronomy and more in our free guide to the Top 101 Astronomical Events for 2017 from Universe Today.

Posted on

A Spectacular Set of Conjuctions on Tap for the Moon, Mars and Saturn this Weekend

Got clear skies this July 4th weekend? The Moon passes some interesting cosmic environs in the coming days, offering up some photogenic pairings worldwide and a spectacular trio of occultations for those well placed observers who find themselves along the footprint of these events.

Stellarium
The path of the Moon on July 5th, 6th and 7th. Credit: Stellarium

First, let’s look at our closest natural neighbor in space. The Moon reaches first quarter phase on Saturday, July 5th at 11:59 Universal Time (UT)/7:59 AM EDT. First Quarter is a great time to observe the Moon, as the craters along the jagged terminator where the Sun is just starting to rise stand out in stark profile. Watch for the Lunar Straight Wall and the alphabet soup of elusive features known as the Lunar X or Purbach Cross and Lunar V on evenings right around First Quarter phase.

Starry Night
Mars off of the limb of the Moon as seen from North America on the evening of July 5th. Credit: Starry Night.

Our first conjunction stop on this weekend’s lunar journey is the planet Mars. Although the Moon occults — that is, passes in front of a given planet from our Earthly perspective — exactly 16 naked eye planets in 2014 (24 if you add in Uranus events and 1 Ceres and 4 Vesta on September 28th), the Moon will only occult Mars once in 2014, on the night of July 5th/6th. Northern South America and southern Central America will have a front row seat, while the rest of North America will see a close pass less than one degree from the lunar limb. This will still present a fine photographic opportunity, as it’ll be possible to snag Mars and the limb of the Moon in the same field of view. The Moon will be 56% illuminated during the conjunction, and Mars will present an 88% illuminated disk 9.2” across shining at magnitude +0.3.

Occult 4.0
The occultation path for Mars. Graphics created using Occult 4.0.

Both will be 96 degrees east of the Sun during geocentric (Earth-centered) conjunction, which occurs around 1:00 UT on July 6th or 9:00 PM EDT on the evening of the 5th. For those positioned to catch the occultation, it’ll take about a minute for “Mars set” to occur on the lunar limb. The last occultation of Mars occurred on May 9th, 2013 and the next won’t happen ‘til March 21st, 2015.

Virginis
The footprint of Lambda Virginis…

Next up, the Moon occults the +4.5th magnitude star Lambda Virginis on July 7th centered on 8:26 UT. This event is well placed for observers in Hawaii on the evening of July 6th. Located 187 light years distant, the light that you’re seeing departed the far-flung star on 1827, only to be interrupted by the pesky limb of our Moon a second prior to arrival on Earth. This star is also of note as it’s a spectroscopic binary, and while you won’t be able to resolve the pair at a tiny separation of just 0.0002” apart, you just might be able to see the pair “wink out” in a step wise fashion that betrays its binary nature. The Moon misses the brightest star in Virgo (Spica) this month, as it’s wrapped up a series of occultations of the star in early 2014 and won’t resume until 2024. Aldebaran, Antares and Regulus also lie along the Moon’s path on occasion, and the next cycle of bright star occultations resume with Aldebaran in January 2015. You can check out a list of fainter naked eye stars occulted by the Moon this year here courtesy of the International Occultation Timing Association.

Saturn
… and the occultation footprint  for Saturn.

And finally, the Moon visits Saturn, now residing just over the border in the astronomical constellation of Libra. This occultation occurs just 49 hours after the Mars event at 2:00 UT on July 8th (10:00 PM EDT on the evening of July 7th) and favors observers in the southernmost tip of South America. As with Mars, North America will see a close miss, although it will also be possible to squeeze Saturn in the same field of view as the Moon at low power, though it’ll sit about a degree of off its limb. We’re in a cycle of occultations of Saturn this year, with 11 occurring in 2014 and the next on August 4th. The reason for this is that Saturn moves much more slowly across the sky than Mars from our perspective, making for a relatively sluggish moving target for the Moon. Saturn shines at +0.6 magnitude as the 75% illuminated Moon passes by and subtends 42” with rings and will take about five minutes to pass fully behind the Moon.

These events will make for some great pics and animation sequences for sure… can you spot Saturn or Mars near the lunar limb with binoculars or a telescope before sunset? Or catch ‘em in the frame during a local fireworks show? Let us know, if enough pics surface on Universe Today’s Flickr page, we may do a post weekend roundup!