HAA Skywatch

It's been well phrased, so here it is again...

It would appear that there will be observers on the hill tonight also.
As per last night - get there early (before 8:30pm) if you don't know the combination (or come with someone who does ;)

Well I can see a ton of forest fire smoke on the satellite imagery over the southern Prairies from the fires out in Northern Sask and Alberta. Looks like after the cold front goes through tomorrow night/Thursday morning we may be seeing the effects from it high up in the atmosphere. So even though the forecasts/CSC may show clear skies on the days/nights following... the atmosphere could have smoke particles posing some challenges when it comes to astrophotography and faint fuzzy hunting. Depending on how thick it is it could make for excellent planetary viewing and beautiful sunsets/sunrises.

GOT BINOCULARS? CHECK OUT CORONA BOREALIS

Every amateur astronomer will recognize Arcturus high in the evening summer sky. The orange beauty is the sixth brightest star in the heavens and the major star in the constellation Bootes.

To the E of Bootes is the pretty little constellation Corona Borealis, the Northern Crown. CrB has no bright deep space objects, but it does have some interesting double and variable stars. HAA members will have read about the variable star R CrB in past editions of our club newsletter, the Event Horizon.

R CrB is usually a 6th magnitude star, visible in binoculars and easily located in the Northern Crown as it forms a triangle with the bright stars delta and epsilon CrB. Here is a chart:

In September 2007, R fell quickly to magnitude 14 and has stayed there since - an extremely long minimum for this star. Here is the light curve:

If you're out observing this summer, check the Northern Crown for R CrB. It could quickly brighten to magnitude 6 again any day now!

8th MAG CYBELE PASSES BY GLOBULAR CLUSTER M9 JULY 7TH

This is the time of year when observers take advantage of the balmy weather to observe objects in or near the Milky Way. Those with SCTs especially like to observe the many dozens of bright globular clusters in and around Ophiuchus, a large but faint constellation N of Scorpius. Here's a chart of the general location, centred on the globular cluster M9:

The 8th magnitude asteroid Cybele will be passing through the area in the 1 degree wide chart below (I marked its daily motion with pink dots, June 29th to July 7th), passing just 1/3 degree S of 8th magnitude globular NGC 6356 at the end of June and then on July 6-7th, Cybele passes just a few minutes of arc N of 7th magnitude globular M9.

What a great imaging opportunity!

DOUBLE ECLIPSE OF IO AND EUROPA, 28 JUNE

Now that Jupiter rises before midnight, the casual observer can catch the Jovian moons in transit and eclipse. Early on 28 June the bright moons Io and Europa will be eclipsed by Jupiter's disk... but wait, it gets better! It's 10 days before Jupiter is at opposition, so the immense cone of shadow behind the planet is offset slightly to the W of the disk and the moons will enter the shadow before the disk appears to cover them.

You will see the moon suddenly dim to 1/60th of its usual brightness while it is still visible just off the limb of Jupiter. Io will dim from magnitude 5 to magnitude 9 at 3:46 a.m. while Jupiter is still 21 degrees above the horizon in the SW sky. Here's a diagram of the relative positions and brightnesses of the moons at 3:47 a.m. (after it has entered the shadow cone and dimmed)-

Just before dawn at 4:58 a.m., after Io has been eclipsed by Jupiter, Europa will enter the "cone of darkness" behind Jupiter and dim from magnitude 5.3 to 9.3 while still visible off the planet's disk (9" or arc from the disk, actually).

After July 8th, you won't be able to see this pre-eclipse dimming. The planet's shadow will switch sides - appear on the E side of the disk; moons will then re-appear from eclipse while dimmed and suddenly brighten 60x as you watch them emerge from the planet's shadow.

Here's a challenge for imagers with a webcam or CMOS video recorder: make a brief video of the moon as it dims. On playback, analyze the image and let us know how instantaneous the dimming is - after all, (a) Jupiter has a vast atmosphere and (b) the Jovian moons are small disks, not pinpoint stars. Does Jupiter's shadow cut off Io's light as sharply as the limb of the Earth's airless Moon stops starlight during an occultation?