December 7, 2015: Dark Adaption Really Does Take Awhile . . . So Observe During the Day!

One thing I missed discussing in terms of “What I did last summer” in the previous two blog posts was going out to see the Perseid meteor shower.  The last time I had gone out to see a meteor shower was the Leonids, about 17 years ago, in 1998.  The Leonids occur in November, but generally don’t put on much of a show at only about 15 meteors per hour.  However, that year they were supposed to hit a big peak, which they do about every 33 years due to the stream being refreshed by a new passing of their parent comet, Temple-Tuttle.  The 1998 display was supposed to be a good one with extra meteors – over 100 per hour, and maybe thousands like in 1966!

The best displays for just about any meteor shower actually occur in the morning hours, because at that time, that side of earth is actually travelling directly forward along earth’s orbit into the meteor stream in space, resulting in more meteors.  It’s also because the radiant point – the point in the sky, in the constellation that the shower is named after, from which the meteors appear to come from – is higher in the sky at that time, so there is less atmosphere between you and the meteor to absorb the light, so you can see dimmer meteors, and therefore more of them.

I can’t quite recall how it was 17 years ago, but I’m sure I saw a couple over the course of an hour or so.  Y’know, light pollution.   After a 17-year-layoff, I decided to give meteor showers another go this summer.  My SLT mount was still in the shop, and I hadn’t seen a shower in many years, so what the hey, right?  The Perseid shower occurs in August, and this was supposed to be a particularly good one due to the complete lack of the moon.

I left my well-lit apartment and went up to the roof of my apartment building at 11pm.  I settled myself in on a lounge chair, and started staring in the area of the radiant, which was pretty much Northeast, but still fairly low in the sky.  After a very short time, it gets boring to just stare at one spot continuously, so whaddaya do?  You start looking around.

Well, there was the summer triangle, right overhead.  No sign of Albireo, though.  It just wasn’t there.  3rd magnitude is about my zenith limiting visual magnitude here in Manhattan.  Some nights, like this one, I have difficulty picking out Albireo, which was pretty much overhead, and is magnitude 3.05.

After 10 minutes or so of doing nothing but staring at the sky, I could just see Albireo with averted vision.  After another 10 minutes, I could just see it directly.  After another 10 minutes, it was practically staring me in the face.

The Perseid meteor shower was another bust, unfortunately.  It seems that most meteors peak at only about 4th or 3rd magnitude as they streak across the sky, so I just can’t see them from my apartment roof.  I stayed out for an hour until midnight, and I only saw one meteor the whole hour.  That one looked like it was heading right for me, though.  It stayed in one spot, got brighter, maybe 2nd magnitude, and then dimmed back out.

But I did learn something important.  It really, truly does take a good half hour for your eyes to fully dark-adapt.   Good to know, especially if you’re planning on doing some heavy-duty observing.  One way to prepare for it is to wear an eyepatch (arrr, matey!) tightly over your observing eye for a good half hour before going out.  To preserve that eye’s dark-adaption, you can put a dark t-shirt over your head, like old-timey photographers from the 19th century, and only remove the eyepatch while observing under that dark hood.

As I’ve mentioned before, the easiest way to beat light pollution is to observe during the day.  “How?” you might ask.  Well, obviously, you can observe the sun.  Frankly, I find the sun pretty boring in white light – just a few random sunspots moving along the surface, and by moving, I mean the motion is only visible across the face of the sun over the course of a couple of days.  It’s not even like the sunspots are old friends, like the craters and features on the moon.  The sunspots change constantly, so all you’re looking at is a Rorschach test, and not even an interesting one at that.

Now, observing the sun in H-alpha is something entirely different, what with the flares and prominences dancing around, and the faculae oozing.  That’s something to see – a star actually being a star.  But there are other things to see during the day.  Not very many, mind you, but a couple.  Like today.

Today, the moon occulted Venus just past high noon.  The moon was just about 4 days before new, so it was just a little sliver in the sky.  The prediction was that the occultation would occur at 12:41, so I went up at 11:30 to give the scope a chance to cool down.  Man, it was hard to even pick out the moon, what with the sun being so blindingly bright and only 40 degrees away to the left/east.  From my apartment building’s roof I had to use the elevator tower to block out the sun to even be able to find it.

But there it was.  And there was Venus, right next to it.   Even though the moon is at negative 8th magnitude, and Venus was “only” negative 4th, Venus is much, much “brighter” than the moon through the scope.  Obviously this would be the case because the moon’s brightness is spread out over a much, much larger area.  But she “wasn’t” as bright with the naked eye.  In other words, I didn’t see Venus with my naked eye until I looked for it next to the moon, while through the scope, the moon is barely there, just a ghostly sliver, while Venus is very bright.  Seeing Venus during the day!  Pretty neat.

It was a very good thing I had gone up that hour early.  When I went back up at 12:30, some high, light, thin clouds had appeared on the southern horizon, and the setting moon, at first just ghostly, turned a whiter shade of pale.  It was barely even visible in the scope, and I couldn’t find it in the sky for the life of me.  Another good thing was that the scope has such good tracking!   Interestingly, even though I set it to track the moon, it seemed to track Venus better, as Venus was just about where I left it an hour later, but the moon had moved a bit off center.  Maybe it doesn’t have specifically lunar rate tracking?

The occultation occurred just about as exactly on schedule as it is possible to predict, I think.  Curt at Cloudy Nights predicted that for roughly my location, Venus would be in mid-occultation at 12:41:42.  That’s just about dead-on balls accurate, (an industry term).  Unfortunately, the vibrating roof returned, or else I would have tried to take pictures.  It was bad – Venus was bouncing around and just would not sit still.  I wonder what goes on with the building’s mechanical systems that the amount of vibrations changes like that from time-to-time.

It was hard to tell when first contact was, between the paleness of the moon and the roof vibrations, but I estimate that it was roughly at 12:41:25, with complete extinction at 12:42:07.  That puts mid-occultation just a couple of seconds past Curt’s prediction.  Pretty cool stuff!  Since I couldn’t get pictures myself,  I nicked this off of someone who posted it at Cloudy Nights:

venus occultation

Nice shots, Steve OK!

Unfortunately, by the time Venus was due to reappear on the dark side of the moon, the moon was already setting behind some buildings.  Still, it’s always nice to see an an “unusual” astronomical event.  Well, unusual for me, that is, anyway.


5 thoughts on “December 7, 2015: Dark Adaption Really Does Take Awhile . . . So Observe During the Day!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s