HAA Skywatch

ASTEROID TO ASSAULT ESKIMO CLOWN, Oct 7-8

It happens even here in the cold northern wastes. If you are out in the morning before sunrise to image Orion high above the trees, have a look at Gemini.

Imagers like taking pictures of 10th magnitude NGC 2392, called the Clown or Eskimo Nebula. It's a rather bright and compact planetary nebula just 2.3 degrees SW of 3rd magnitude Wasat (Delta Geminorum). On 7-8 October the 10th magnitude asteroid Harmonia will pass within 8' of arc N of the bluish ball of the nebula - a great imaging opportunity. Below is a chart roughly 1 degree wide with RA and Dec for the nebula, stars down to magnitude 11.5 and arrows showing the direction of the asteroid.

I wasn't quite sure which heading to put this under since it's more of an observing tip than a target but, anyway, here is something I've noticed the past couple of nights.

Fall nights seem to cool rapidly and this not only makes it difficult for your scope to acclimatize but can also result in early, and heavy, dew. Most astronomers combat this with dew shields and other dew busting equipment.

Although my 12" reflector has a small fan attached to the rear of the primary, which does an adequate job of keeping the mirror near the ambient temperature, I feel it lacks the horsepower to quickly rid the mirror of the "stored" daytime temperature. My solution has been to place a 10" room fan behind the mirror on a medium fast setting. The resulting breeze can be felt coming out of the top of the OTA which is a good sign that the tube is also being cleared of the pesky tube currents.

The last time I did this I noticed that the coating of dew, that had already formed on the OTA, dried up while the big fan was doing its thing - which got me to thinking.

A light breeze will generally keep dew at bay, so when I was ready to observe I put the big fan on a stand and had it oscillate to get some air movement within the confines of the observatory. Although reflectors are easier to protect from dew than other scope configurations I did notice that dew did not reform on the OTA while the fan was operating. Dew did eventually form on the finder objective but I still feel this was at least delayed somewhat.

On the down side, the fan also cools down the observer somewhat, but it is nice not to have everything you touch soaking wet :)

SEPTEMBER NOVA IN SCORPIUS

If you have been observing Jupiter in the evening, you'll know the familiar Teapot shape of Sagittarius, just to the right of the planet above the horizon in the SW.

There is a Nova just E of Gamma Sagittarii, the bright star at the tip of the Teapot's spout. Finding Gamma in binoculars, your field of view will take in a number of globular clusters (the NGC numbers marked) and HIP 88060, a 5th magnitude star marked on the two charts below:

Nova Scorpii 2008 is (as of Sept 2nd) a 9th magnitude star located just S of HIP 88060 at the cross marked on the following AAVSO chart:

Use the comparison stars (marked with the decimal point missing from their magnitude, so 98 = mag 9.8) to estimate the brightness of this "new star", designated V1309 Sco by AAVSO.

JUPITER'S RETROGRADING STOPS, GAINS 2 MORE MOONS

Before our September HAA meeting Jupiter will have ceased its retrograde motion (ie: moving W toward M22) and will again start moving E.

On the evening of September 25th, have a look at Jupiter. In addition to Io, Europa, Ganymede and Callisto the planet will seem to have picked up 2 more bright moons as it passes through that part of the sky. As dark descends, Jupiter will be sitting directly to the S, on the meridian. Here's the view through a small telescope at 8 pm (dark descends earlier as summer gives way to fall):

The two extra "moons" just SE and SW of Jupiter are really two distant, bright red giant stars. Mag 7.5 star HIP92980 SE of Jupiter is 340 light years away and mag 5.9 HIP 92931 at almost 900 light years, is 400 times more luminous than our sun.

During August and September, Jupiter is moving just S of the bright and widely-separated stellar pair called Nu Sagittarii - you can see them shining at mag 4.8 and 5.0 in the same low-power field 1/2 degree N of the planet. Between Jupiter and the 5th magnitude star Nu1 is a faint globular cluster, NGC 6717 - an easy imaging target but only 4' in diameter. It's not M22 by any means! In fact, if you go to my gallery and open the image of M22 from last summer, there's a faint globular in the upper right-hand corner of that picture that's ver much like NGC 6717.

CATACLYSMIC VARIABLE SS CYGNI IS IN OUTBURST!

Overhead in the evenings, have a look at the dwarf nova SS Cygni. From Astronomy Magazine:

"... August 21, I observed SS Cygni and recorded its magnitude at 11.7. The next night, SS Cygni had jumped a nearly full magnitude to 10.8. The outburst had begun! For the past three evenings, I've watched SS Cygni continue to slowly brighten to magnitude 9.0 on Monday, August 25. I expect it to be even brighter tonight. [Mike: it has reached mag 8.0 as of Aug 28th] The current outburst differs from typical SS Cygni flare-ups, which usually exhibit a rise from 12th magnitude to around 8th in less than a day. Occasionally, SS Cygni takes its time, requiring several days to reach maximum. If you missed this outburst, you can still catch SS Cygni in its "up" state [Mike: I think he means "at maximum". "Up" can mean a lot in astronomy]. SS Cygni usually remains at peak brightness for a week or two before fading back to 12th magnitude...outbursts occur every 50 to 60 days."

The AAVSO light curve below shows SS Cygni's visual brightness for 365 days ending 28 August. Each hatch mark along the top edge marks off approx. 2 weeks. Note the irregularity of SS's period and the speed with which it has brightened and faded 6 times in the last year:

SS Cygni (RA 21h 43m Dec +43.6 degrees) is easy to find using the AAVSO chart below (which I have severely edited). The 4th magnitude star Rho Cygni marked on the chart is nine degrees due W of first magnitude star Deneb (Alpha Cygni).

If you prefer to start from open cluster M39 marked on the chart, SS is a few degrees S of M39 and just NE of a 5.1 magnitude star (75 Cygni but I did not add the Flamsteed number to the chart, as it would have confused the AAVSO magnitude nomenclature marked on the chart):

What do I mean by "AAVSO magnitude nomenclature"? The chart is cluttered with numbers noting the brightness of comparison stars, with the decimal point removed (so "65" means magnitude 6.5 for example).

Here's a chance to see a bona fide exploding star at maximum brightness!

What makes SS explode from time to time? It's a white dwarf star with a close companion. The dwarf strips gas from its companion star, creating an accretion disk. As this new fuel accumulates on the small hot star and reaches a "flash point", the star becomes about 60x brighter until the fuel has been exhausted.

Get out binoculars and have a look while SS is bright! What a great hobby!