November 24, 2017

AstroEvent(s): Of Occultations & Daytime Stars.

Mekbuda Occultation from Tampa, Florida. (Created by Author in Starry Night). 

This week brings with it an interesting double-double header. First up is a challenge that comes to us via the Royal Astronomical Society of Canada … sure, you’ve seen Venus near the daytime Moon, and perhaps you’ve caught Jupiter low at opposition just prior to the setting of the Sun… but did you know that it’s possible to catch some of the brightest stars while the Sun is still above the horizon? Right around the first full week of April is a good time to give this a try; your assigned quarry is Sirius in the pre-dusk, and Vega in the post-dawn. Both of these stars are in the negative magnitude range and might just be visible from a pristine site with good seeing. In the case of Vega, a fun project would be to acquire it before sunrise and follow it into the daytime skies either visually or with an equatorial tracking telescope. Sirius, although brighter at magnitude -1.5 may be tougher; in this instance, finding the star in relation to a nearby landmark a day prior at dusk and then trying to acquire it before local sunset may work. I once successfully caught Jupiter in the daytime in this fashion, near opposition from the arming-end of runaway in Kuwait back in 1998. Good luck, and we’ll be attempting this feat of visual athletics right along with you!

But wait, there’s more… this week also sees the waxing crescent Moon pass through some interesting star fields in the constellations Taurus and Gemini. The result is a series of interesting stellar occultations; 1st, on the evening of April 7th, the Moon skims the Hyades cluster and occults Upsilon and Kappa Tauri for viewers in western North America. Kappa is of particular interest as it is a very close (0.1”) double. Even if you aren’t in the target zone, the crescent Moon+Hyades= a good photo op. Three days later, we US east coasters get a shot with an occultation of Zeta Geminorum, otherwise known as Mekbuda. This is another bright star around magnitude +4.0. Mekbuda is also a Cepheid variable with a period of 10.2 days, one of the brightest in the sky. Watching this star wink out and then reappear should be a good replay of last month’s Mu Geminorum occultation… the action for the US East Coast centers around ingress at 9:21 PM EDT and an egress of 10:35PM. The occultation extends up to a graze line cutting across the Canadian Maritimes… good luck, and watch this space for a video after-action clip if successful!      

The astro-term for this week is Transparency. In terms of astronomy, transparency is the ability for light to pass unhindered through the atmosphere. Pollution, dust, and aerosols all act to scatter light and dim objects. You can have clear skies, but poor, washed out transparency. Generally, the higher and drier you are, the better transparency will be, as evidenced by a deep blue daytime sky and an inky black nighttime sky. This is also an all important factor in success in daytime star-spotting as discussed above.  Transparency is rated 1 to 10, with 10 being the absolute best, and is closely tied with seeing, or the resolution ability based on atmospheric turbulence. I’ve had clear skies and decent transparency after a storm front, only to have poor seeing as the convective cells rolled before my eyepiece!   

Event: Mars passes the Beehive.


The path of Mars over the coming week. (Created in Starry Night & Paint).

The path of Mars over the coming week. (Created in Starry Night & Paint).


    This week offers a two-fer, an easy to spot naked eye conjunction of two very different objects and a difficult to observe occultation. 1st up is a close pairing of the planet Mars and M44, the Beehive Cluster. From the 13th of April until the 20th, both will be grouped in a visual circle less than 2° arc degrees in diameter, an easy target for both camera lens or binocs. Mars will be at closest apparent approach on the evening of the 16th. Both ride high near the zenith in the dusk skies for northern hemisphere viewers, making for an easy photo op. Of course, Mars is a scant 3 odd light minutes away; M44 is at an estimated distance of 577 light years. Also known as Praesepe, the Manger, this cluster in the heart of the constellation Cancer has been known since ancient times. Proper motion studies suggest that this open cluster may share its origins with the V-shaped Hyades in the constellation Taurus; about 1010 members of this group have been identified, including 11 white dwarfs.

Up for a challenge? On the evening of the 15th, the 3 day old crescent Moon will occult the close spectroscopic binary star Mu (µ) Arietis.  The action occurs around 3:00 UT (on the 16th) and favors viewers on the North American west coast. Unfortunately, the event does not occur under the most favorable circumstances; the Moon will be a thin crescent, the star is +6 magnitude, and the entire event will be low in the dusk skies. Still, we’d love to hear from anyone who successfully witnessed this difficult to observe event!      

The astro-word for the week is Messier Object. Back in 1771, French astronomer Charles Messier got tired of misidentifying faint little fuzzies he came across in the night sky in his quest for comets and decided to compose a catalog of these objects. The original published list contained 45 objects and Messier later expanded it to 103. The current tally stands at 110, although the list contains a few dubious entries. The catalog was the first list of deep sky objects, and has since spurred countless “Messier Marathons” common in spring. Morphologically, the catalog contains open & globular clusters, planetary nebulae, emission nebulae and galaxies. Of course, Messier had no inkling what these objects truly were when he cataloged them. It’s somewhat odd that such un-comet like objects as M44 and the Pleiades made this list, but say, the Double Cluster on the Perseus-Cassiopeia border did not. And of course, there was a whole menagerie southern sky objects yet to be categorized. That would have to wait for the Herschel dynasty of astronomers, and their expanded New General Catalog!