Astro-Challenge: Watch the Moon Occult Venus in the Daytime

The Moon meets Venus on February 26th, 2014. Image credit and copyright: Konstantinos Spanos

The year 2015 saved one of the best astronomical events for last, as the waning crescent Moon occults (passes in front of) the planet Venus as seen from North America on Monday, December 7th.

This is the final of seven naked eye occultations of planets by the Moon in 2015, three of which involve Venus. It’s also the best of the year, well positioned for North America. Continue reading “Astro-Challenge: Watch the Moon Occult Venus in the Daytime”

Catch a Fine Lunar Planetary Grouping This Weekend

Phew! Our eyes and thoughts have been cast so far out into the outer reaches of the solar system following New Horizons and Pluto this week, that we’re just now getting to the astronomical action going on in our own backyard.

You’ll recall that Venus and Jupiter have made a fine pairing in the evening sky since their close approach on July 1st. Despite some of the incredulous ‘Star of Bethlehem’ claims that this was a conjunction that happens ‘once every two thousand years,’ this sort of pairing is actually quite common. In fact, Venus and Jupiter are set to meet up again in the dawn sky later this year on October 25th. Continue reading “Catch a Fine Lunar Planetary Grouping This Weekend”

Comet C/2013 US10 Catalina: A Preview for Act I

Live in (or planning on visiting) the southern hemisphere soon? A first time visitor to the inner solar system is ready to put on the first of a two part act starting this month, as Comet C/2013 US10 Catalina breaks +10th magnitude and crosses southern hemisphere skies.

Though we’ve overdue for a this generation’s ‘great comet,’ we’ve had a steady stream of fine binocular comets in 2015, including 2014 Q2 Lovejoy, 2014 Q1 PanSTARRS, and 2015 G2 MASTER. US10 Catalina looks to follow this trend, topping out at just above naked eye visibility in late 2015 going into early 2016.

Discovered by the Catalina Sky Survey on Halloween 2013, the comet received its unusual ‘US10’ designation as it was initially thought to be an asteroid early on in a periodic six year orbit, until a longer observation arc was completed. This is not an unusual situation, as new objects are often lost in the Sun’s glare before their orbit can be refined.

Recent images of US10 Catalina from may 18th, 2015. Image credit and copyright: Joseph Brimacombe
Recent images of US10 Catalina from May 18th, 2015. Image credit and copyright: Joseph Brimacombe

We now know that US10 Catalina is on a million year long journey from the distant Oort Cloud. Most likely, it was disturbed by an unrecorded close stellar passage long ago. We say that such comets are dynamically new, and this passage will eject US10 Catalina from the solar system. The comet also has a highly inclined orbit tilted almost 149 degrees relative to the ecliptic, and was at +19th magnitude and 7.7 AU from the Earth when it was discovered, suggesting an intrinsically bright comet.

Prospects for US10 Catalina currently favor latitude 35 degrees north southward in late June, though that’ll change radically as the comet makes the plunge south this summer. As of this writing, US10 Catalina was at +11 magnitude ‘with a bullet’ and currently sits in the constellation Sculptor at a declination -30 degrees in the southern sky.

Image credit:
The orbit of Comet US10 Catalina. Image credit: NASA/JPL

Binoculars are our favorite tools for observing comets, as they’ve easy to sweep the skies with on our cometary quest. As with nebulae and deep sky objects, keep in mind that quoted magnitude for a comet is spread out over its apparent surface area, causing them to appear fainter than a star of the same magnitude.

Here’s a blow-by-blow for Act I for Comet C/2013 US10 Catalina over the next few months:

(Unless otherwise noted, we documented stellar passages below that are within 2 degrees of stars brighter than +5th magnitude, and fine NGC deep sky objects brighter than +8th magnitude)

July 1st: May break binocular visibility, at +10th magnitude.

July 6th: Crosses into the constellation of Phoenix.

July 23rd: Crosses into the constellation Grus.

July 25th: Crosses into the constellation Tucana.

July 26th: Passes the +4th magnitude star Gamma Tucanae.

Image credit: Created using Starry Night Education software
The path of Comet US10 Catalina as seen from 30 degrees south.  Image credit: Created using Starry Night Education software

August 1st: Reaches opposition.

August 2nd: Passes the +4.5th magnitude star Delta Tucanae.

August 4th: Crosses into the constellation Indus.

August 6th: Photo op: Passes 12 degrees from 47 Tucanae and the Small Magellanic Cloud.

August 8th: Crosses into the constellation Pavo.

August 12th: Passes the +4th magnitude star Epsilon Pavonis.

August 14th: Reaches its greatest declination south at almost -74 degrees.

August 15th: Sits at 1.1 AU from the Earth.

August 17th: Crosses into the constellation Apus.

August 19th: Passes 5 degrees from the +7.7 magnitude globular cluster NGC 6362.

August 22nd: Crosses into the constellation Triangulum Australe and passes the +1.9 magnitude star Atria.

August 28th: Passes the +2.8 magnitude star Beta Trianguli Australis.

August 29th: Passes 3 degrees from the +5th magnitude open cluster NGC 6025.

September 1st: Crosses into the constellation Circinus

Image credit: Starry Night Education software
The passage of Comet US10 Catalina through the southern sky from mid-June through September 1st. Image credit: Starry Night Education software

From there, Comet US10 Catalina heads towards perihelion 0.8229 astronomical units from the Sun on November 15th, before vaulting up into the northern hemisphere sky in the early dawn.  Like Comet Q2 Lovejoy last winter, US10 Catalina should top out at around +4th magnitude or so as it glides across the constellation Ursa Major just after New Years.

And like many comets, the discriminating factor between a ‘great’ and ‘binocular comet’ this time around is simply a matter of orbital geometry. Had C/2013 US10 Catalina arrived at perihelion in the May time frame, it would’ve passed less than 0.2 AU (30 million kilometres) from the Earth!

Image credit:
The projected light curve for Comet US10 Catalina. The black dots denote actual observations, and the purple vertical line marks the perihelion passage for the comet. Image credit: Seiichi Yoshida’s Weekly Information about Bright Comets

But that’s cosmic irony for you. Keep in mind, with Comet US10 Catalina being a dynamically new first time visitor to the inner solar system, it may well up brighten ahead of expectations.

And there’s more to come… watch for Act II as we follow the continuing adventures of Comet C/2013 US10 Catalina this coming September!

Luna vs. the Hyades! The 1st of 13 Occultations of Aldebaran Set For January 29th

The cosmos is continually in motion.

Be it atoms, stars or snowflakes from the latest nor’easter pounding the New England seaboard, anything worth studying involves movement. And as skies and snowbound roads clear, this Wednesday and Thursday evening will give us a reason to brave the January cold, as the waxing gibbous Moon pierces the Hyades star cluster to graze past the bright star Aldebaran.

During Thursday night’s passage, the Moon will be 78% illuminated. In a sort ‘cosmos mimics controversy’ irony, the gibbous Moon is doing its best to mimic a sky bound ‘deflategate’ football just in time for Superbowl XLIX this weekend.

Stellarium
The motion of the Moon this week across the Hyades. Credit: Stellarium.

But the January 29th event also marks the first occultation of Aldebaran for 2015.

Fun fact: At magnitude +0.8, Aldebaran is the only star brighter than +1st magnitude north of the celestial equator that the Moon can currently occult. Regulus, the runner up, shines at magnitude +1.4.  Two other second magnitude stars — Antares and Spica — lie along the Moon’s path on occasion, and up until the 2nd century BC, it was possible for the Moon to occult Pollux in the constellation Gemini as well.

There are 13 occultations of Aldebaran in 2015, and the Moon occults the star 49 times overall until the last event in the current cycle on September 3rd, 2018. Aldebaran is also occulted by the Moon more often in the current 2010-2020 decade than any other bright star. You can even spy Aldebaran near the daytime Moon with binoculars, as we did back in 1996 from North Pole, Alaska.

Credit: Occult
Maps for the 13 occultations of Aldebaran  by the Moon in 2015, click to enlarge. solid lines denote regions were the occultation occurs under dark skies. Credit: Occult 4.0.

Of course, the January 29th event is an occultation only for the high Arctic, with only a scattering of villages and distant early warning stations along the northern Nunavut coast welcoming the sequence of 2015 occultations of the bright star.

The rest of us will see a close photogenic pass, as the Moon makes an end run through the Hyades star cluster every 27.3 day sidereal lunar month in 2015. The Moon will thus occult several members of the Hyades on each pass. Our best bet for North America is the occultation of Aldebaran on November 26th, though the Moon will be just 13 hours past Full.

68 Tauri. Credit: Occult 4.0
The occultation of 68 Tauri (a member of the Hyades) for January 29th. Credit: Occult 4.0.

Why doesn’t the path of the Moon just stay put with respect to the sky? Because the orbit of our Moon is fixed at an inclination of 5.1 degrees not with respect to our equator, but to the plane of the ecliptic. This means that the Moon’s orbit is in motion as well, and can wander anywhere from declination 28.6 degrees north to south as it cycles from a shallow to steep path every 18.6 years. We’re actually in a shallow year in 2015 (known as a minor lunar standstill) after which the apparent path of the Moon through the sky begins to widen again until April 2025.

An occultation is celestial motion that you can see in real time as a star or planet is photobomb’d by the onrushing Moon like a January snowplow… but those background stars are in motion as well.

The Hyades themselves — along with our own solar system — are moving around the galactic center. The nearest open cluster to us at 153 light years distant, the Hyades provided a unique object of study for 19th century astronomers. Astronomer Lewis Boss of the Dudley observatory spent several decades studying the proper motion — the apparent motion that a star seems to be moving across the sky from our solar system-bound perspective, measured in arc seconds — of the Hyades, and found the entire group was converging on a point in the constellation Orion near 6 hours 7’ right ascension and +7 degrees declination.

Starry Night
The imaginary convergent point of the Hyades in the night sky. Credit: Starry Night Education software.

Of course, this motion is relative and demonstrates a changing perspective, as the Hyades recedes from our solar system like a defensive line rushing to sack a quarterback.

OK, enough with the sports similes. The Hyades are so close that the actual Hyades Stream — often referred to as the Hyades Moving Group — is actually strewn across the constellations Orion, Taurus and Aries and more.

Some stars, such as 20 Arietis in the adjacent constellation Aries and Iota Horologii in the southern hemisphere may actually members as well. There’s always a bit of ongoing controversy when it comes to actual moving group membership, which is usually pegged by determining proper motion, coupled with the age and metallicity of prospective stars. Growing up in the Milky Way galaxy, our Sun was once a member of some unnamed ancient open cluster that has since long dispersed, like the Hyades are in the process of doing now.

Photo by author
The asterism of the Hyades and the ‘eye of the Bull.’ Photo by author.

The Hyades contains hundreds of stars and ironically, Aldebaran is not a member of the cluster, but is merely 65 light years away from us in the foreground. The V-shaped asterism of the Hyades gives the Head of Taurus the Bull its distinctive shape. The Hyades are named after the rain nymph daughters of Atlas from Greek mythology, whose half daughters the Pleiades also adorn the nearby sky.

And as an added bonus, don’t miss comet C/2014 Q2 Lovejoy crossing the constellation Triangulum, also nearby. Q2 Lovejoy reaches perihelion this week on January 30th, and although it’s completing with the evening Moon, it’s still holding out at a respectable magnitude +4.5.

Credit:
Comet Q2 Lovejoy skirts by  the Hyades and the Pleiades. Credit and Copyright: John Chumack.

All reasons to get out these chilly January evenings and ponder a hurried universe continually in motion, both fast and slow.

-Check out Q2 Lovejoy on January 30th courtesy of the Virtual Telescope project.