Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,434
Occultation of 3.7 mag lambda Aquarii by Venus on April 17
Re-post of a post by David Dunham on SEML
The day after next month's lunar eclipse is a rarer event, the occultation of a 3.7-mag. star by a planet with a thick atmosphere. It will occur around 18h UT visible from the Tasman Sea region, New Zealand, eastern Australia, Fiji just before sunrise, Papua New Guinea, the Caroline Islands, and islands in Micronesia farther north. Probably the best place is New Caledonia, where the event will occur highest (alt. 25 deg.) in a dark sky close to the time of the start of astronomical dawn twilight; the southern South Island of New Zealand is almost as good, and is only a few hundred km north of the predicted southern limit. In Australia, the event will occur at rather low altitude above the horizon, the highest being about 15 deg. in the Gold Coast region of southeastern Queensland. Venus will be 45 deg. from the Sun; its 19.3” disk will be 61% sunlit and a central occultation is predicted to last 7.0 minutes. Only the dark-side reappearance will be observable; the star will become lost in Venus’ dazzlingly bright disk before the real disappearance occurs. The star lambda Aquarii (= ZC 3xxx = HIP 112961 = SAO 146362) is a red giant spectral type M0 star with a diameter of 8 mas, 24 times the diffraction fringe spacing, so Fresnel diffraction will be negligible for this event. The overview figure of the event generated by Occult, computed by Dave Herald, is at http://www.asteroidoccultation.com/observations/NA/2014_04_16%20Venus.jpg .
I believe that this is the brightest star occulted by Venus (and by any major planet) since Venus occulted 2.1-mag. Nunki (sigma Sagittarii) as seen from eastern Africa in November 1981. The next occultations of bright stars by Venus will be of pi Sagittarii in 2035 and of Regulus on 2044 October 1. Before the space age, astronomers would have flocked to the Tasman/Micronesia region to observe this event, to learn more about Venus’ atmosphere, but now that space probes have descended through the atmosphere, there is not nearly as much interest now, it is more a curious event. Nevertheless, observers in the region are encouraged to try to observe it.
Observers in a narrow strip of ocean just north of the equator will have a central occultation, and possibly a central flash, with a ring of light briefly forming around Venus’ whole disk. During night, this strip includes no land except for the island of Butaritari (and maybe its satellite island Makin) at lat. 3.0 deg. N., long. 172.9 deg. E. At that island, Venus’ altitude will be 34 deg. with the Sun 6 deg. below the horizon. Although the twilight will be strong, a telescope may possibly see the central flash phenomenon. Looking at the aerial view, Butaritari has over 100 buildings and an air field; Makin has its own separate air field. Maps showing the central zone, and an interactive Google map of it (including the southern limit as well, but ignore the part east of the International Date Line, where the event occurs after sunrise) can be found in a box on the upper right side of Brad Timerson’s North America page (although this event is visible from North America only in daylight; it might be observed with large telescopes in the infrared) at http://www.asteroidoccultation.com/observations/NA/ .
David Dunham
From South East Australia, the reappeance occurs around 4am EST on pril 17 (18:00UT April 16) Altitude is 14 degrees from Canberra - bit more from Sydney, bit less from Melbourne.
Nice work Joe, thanks! Here's what the occultation will look like from my place, generated in Starry Night.
With chronic bad 'valley' seeing, low altitude and poor horizons, it's going to be difficult to get anything from here even if the sky is clear. Looking forward to what others can do though, good luck to anyone trying!
EDIT: Just checked, there's a big bright just-past-full Moon in the sky too.
EDIT: Just checked, there's a big bright just-past-full Moon in the sky too.
Surprisingly, this probably wont have much of an effect. Unless the target star is only a degree or two away from the Moon and below mag 9 you should be able to see the star fairly easily. That's one of the fun things about occultations, the Moon phase isn't necessarily the limiting factor, not like it would be for imaging or visual observations.
Surprisingly, this probably wont have much of an effect. Unless the target star is only a degree or two away from the Moon and below mag 9 you should be able to see the star fairly easily. That's one of the fun things about occultations, the Moon phase isn't necessarily the limiting factor, not like it would be for imaging or visual observations.
Sadly this one will be below the horizon for me.
Thanks Jacquie. Certainly no effect if you're considering timing or eye-balling it through a telescope but if you're looking for subtle effects caused by Venus' atmosphere it could have a big impact. And with the low altitude and illuminated air mass it will be difficult to see a mag 3.7 star visually so it probably won't be a naked-eye occultation.
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,434
The fullish moon is 15 deg above the west horizon. Opposite side of the sky to the event so if you have to have a full moon, it couldn't be better placed! Unfortunately I'm just recovering from a serious illness and am unlikely to be well enough in 2 weeks time to go out in the cold for the eclipse or the occultation.
Such fantastic information, thank you so much Joe. And thank you also to to RobK & Jacqui for the pic & tips. I'm only sorry you may not be well enough to observe it, Joe, I hope you feel better very soon.
Here's some more great information by Astroblogger (& fellow forum member), Ian Musgrave. He lists the times for your cites when it'll be viewable.
Occultation of 3.7 mag lambda Aquarii by Venus on April 17
Good seeing in Qld for this event. The reappearance on the dark side of venus, I thought, wasnt as instananeous as with lunar occultations or graze events.
Interested to hear others reports.
Very good seeing and transparency for this event south of Hobart, but of course some turbulence due to the low elevation. Despite the turbulence there were regular excellent moments of very clear seeing that gave excellent views. Best viewing was with a 7mm eyepiece (113X) through my Vixen ED103S.
I think I detected some dimming of Lambda Aquarii just before ingress on the bright limb of Venus. This might have been illusory given the very bright limb.
At egress on the dark limb, a clearly fainter Lambda Aquarii emerged almost, but not, quite instantaneously and proceeded to brighten over a period of several seconds (I was not counting) to reach it's full brightness. Certainly very different to the lunar occultations of stars that I have viewed.
It was an interesting and enjoyable session. Just a pity they are so rare.
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,434
Like Jonathon, I had rubbish seeing plus heat rising off local buildings as I was observing from the balcony of my apartment.
Using a 4" f12.5 Mak with 11mm eyepiece on a Vixen Polarie, I lost lamda Aquarii in the glare much earlier than the predicted time.
Equipment : Manfrotto 475, Vixen Polarie, 4" Maksutov f12.5, 11mm ES eyepiece
Seeing: very poor + heat from nearby buildings. Major turbulence, multiple images visible on occasions. Images reasonably still at times.
Disappearance :
Predicted: 17:59:40 (Starry Night Pro)
Observed : 17:56:15UT [lost in glare of Venus and turbulence/poor seeing]
Reappearance :
Predicted: 18:04:45 (Starry Night Pro)
Observed : 18:05:16UT [ no gradual brightening observed ]
Occultation of 3.7 mag lambda Aquarii by Venus on April 17
Stev,
You had the good foresight to use a 7mm eyepiece, I lost lambda Aquarii in the glare using a 12 mm eyepiece and in the 4 minute break turned on the tracking and changed to a 6mm eyepiece.
The reward was evident straight away with a great view of the reappearance
Location - Western Sydney (Penrith)
Equipment:- LX90-10", Point Grey Flea 3 03S3 @ 30fps, ADVS digital video recording system.
Conditions:- Planet / star were just 14 degrees above the horizon and the seeing was very poor. The air was bouncing around and I can say it's the worst seeing where I have ever attempted an occultation recording.
Time of disappearance:- 17:58:20 UT (this is an average of five replays of the video), accuracy is to the nearest second. Very hard to decide on the disappearance.
Time of reappearance:- 18:05:03.1 UT, accuracy is much better for reappearance. Good to 0.1 sec.
Note the frame numbers have a correspondence to UT, but the index is not shown to keep the video size to a reasonable limit. The false colour image is Tangra's HueIntensity function (thanks Hristo !) and the black and white is the raw video. The reappearance was recorded at 30fps.
Regards,
Tony Barry
WSAAG
Last edited by tonybarry; 20-04-2014 at 11:51 AM.
Reason: added movie link.
