Thursday, March 14, 2013

A Little More About Comet PanSTARRS

As I sit down to type this, it is 5 pm Chicago time, Thursday, 3/14/13.

I didn’t see Comet PanSTARRS yesterday—About Not Seeing Comet PanSTARRS—but that kind of thing happens a lot in astronomy. You try to find a difficult object, sometimes you make it, sometimes you don’t.

But often, maybe even usually, if you don’t find something the effort of trying can familiarize you with an area of the sky and that makes things easier the next time you try.

Yesterday may have been a great example of that. I’ll find out the next clear sky. As I type this, the heavy overcast is clearing up a bit. The next clear night might be tonight. So I’m going to do this post about what I learned from yesterday’s attempt to see Comet PanSTARRS and how I’ve applied that to trying a better search tonight (or the next clear night).

Fair warning, this post is going to include a bit of technical stuff, some numbers. But please bear with me, the technical stuff is reasonably clear technical stuff and it all resolves down to some very simple stuff in the end.


First of all, that photo I posted yesterday was taken around 8 pm Chicago time. Almost certainly I was underestimating the general description “about ten degrees below the Moon.” In fact Comet PanSTARRS sets at around 8:15 pm Chicago time, but by 8 pm the comet probably was already lost in ground clutter at the horizon.

However, my attempts yesterday did give me a useful clue.

Earlier yesterday, about half an hour or more before I took that picture—that is, I mean just as the sky was becoming a dark twilight after sunset but before actual nightfall—I checked out the western sky with binoculars. I was concentrating on what I regarded as “about ten degrees below the crescent Moon” (that is, about a clinched fist width in the sky), but I also checked much further down. You just never know.

In the course of checking much further down, I noticed Mars very low in the west. In fact, soon enough the only way I could see Mars was through the winter branches of trees along the horizon.

That was a clue I should have followed up immediately. The position of Mars, I mean. But I didn’t. I’m getting old. I don’t think as quickly as I used to think. (And believe me I’m not happy about that.)

At any rate, almost all the finder charts I’d seen used the Moon as a point of reference for 3/12 and 3/13 because the Moon is such a visible object. The trouble is that the Moon travels many degrees every day. On 3/12 the comet was next to the Moon. On 3/13 the Moon was some distance above the comet. On 3/14 the Moon will be much higher in the sky.

Mars, on the other hand, travels much less quickly than the Moon against the backdrop of the sky. Last night, when I was flipping around the internet, I saw a finder chart that included Mars low in the west. I didn’t save the page, and for a long time I didn’t pay much attention to having seen it. (Again, I’m getting old. And believe me I’m not happy about that.)

But at some point this morning I realized that I now had a very good “landmark” in the sky in the planet Mars. Mars would be roughly in the same place every night, unlike the Moon. And although Mars is difficult to find right now, it is a manageable kind of difficulty. It is not very difficult.

Mars is very low in the sky, but Mars is a point-source. It is bright enough to stand-out against even a light sky. And the ruddy, almost-pumpkin color makes for an even better contrast against a bluish sky.

So, using Mars as a landmark, it may be much easier to sky-hop over to Comet PanSTARRS. I couldn’t find again the chart on the internet that showed the comet and Mars in the same diagram. That’s too bad. I looked, but I couldn’t remember where I saw it or what search words I used to flip over to it.

But with Mars as a landmark, it is comparatively easy to learn the details we need to know to find Comet PanSTARRS.

This post will be me describing how to find out such things. It’s a little technical, but trust me, the technical bits are very straightforward and this is the kind of thing that can help in many, many astronomical situations.

Now here is some technical stuff.

Since we can find Mars (comparatively) easily because Mars is (again, comparatively) easy to see, we will get some technical data on the position of Mars. Then we will get the same kind of technical data on the position of Comet PanSTARRS.

This is important: The specific numbers in the data aren’t all that important. It may appear daunting to see numbers that look like surveyor jargon about “altitude” and “azimuth” but we don’t really have to worry about the specific numbers themselves. All we need to look at are the differences between the numbers describing Mars and the numbers describing Comet PanSTARRS.

And all we really need to focus on are the general differences between the numbers.

For instance, if the “altitude” of one object is a larger number, then, obviously, the object with the higher number will be higher in the sky. If the difference is small, then the objects will be close.

Binoculars typically show a field of about five degrees. So if one object is, say, ten degrees higher than another, that would be two binocular fields apart. You can measure the sky, approximately, by moving binoculars one field-of-view at a time.

The same kind of things are true for the “azimuth.” With “north” as zero, an azimuth direction just moves around a circle with 90 degrees as east, 180 degrees as south and 270 degrees as west.

We don’t need to worry much about the particulars of two azimuth readings, but rather we can simply look at the difference. If Comet PanSTARRS has an azimuth reading larger than Mars, the comet will be to the right. If Comet PanSTARRS has an azimuth reading less than Mars, the comet will be to the left. And, again, we can expect binoculars to show about five degrees of sky in one field at a time.

It’s really that easy. Or, well, you know, it can be that easy.

So we can find Mars easily enough. I saw Mars yesterday. It is almost directly west, very low, but easily visible in binoculars immediately after sundown.

So: Where do we get “altitude” and “azimuth” numbers?

The easiest place nowadays is at Wolfram|Alpha.

Wolfram|Alpha sometimes can be very frustrating, but it can also deliver amazingly deep datasets if you can figure out the right search terms.

For Mars, it can be as simple as: “planet mars position from Chicago at 7 pm

For Comet PanSTARRS it can be as simple as: “comet C/2011 L4 panstarrs position from Chicago at 7 pm

If you type in those searches or click on those links, Wolfram|Alpha will think for a minute and then give you a lot of information. (It defaults to the current date. When I created those searches, it returned information for 3/14. As they get clicked on in the future, Wolfram|Alpha will default to whatever the current date is.)

It will draw charts that are interesting but not very helpful. It will deliver a lot of facts and figures that are interesting but not very helpful.

And near the bottom of the results it will give the information that is very helpful indeed, the “altitude” and the “azimuth” as seen from that particular location at that particular time.

And that’s all we need.

The info boxes look like this. Mars results are first, then Comet PanSTARRS:

So we’ve learned that Mars—which we know about and can see—is at azimuth 254 degrees and at altitude 16 degrees.

At that same time Comet PanSTARRS will be at azimuth 255 degrees and at altitude 26 degrees.

The numbers and what we know about them are as good as a diagram.

Since the comet’s azimuth is about one degree higher than Mars, that means the comet will be just a little further “north” than Mars and, in the sky toward the west, that means the comet will be just a little to the right of Mars.

The comet’s altitude is almost exactly ten degrees higher than Mars, so the comet will be higher in the sky than Mars. The comet will be about two binocular fields above Mars. (Or about one if you use wide-angle binoculars.)

And that’s really all we need to know to go out and start a good search!

Those numbers will change a little every day, but the procedure will work every night.

And the general procedure works for finding any astronomical object any night.

Nowadays, of course, many amateur astronomers will use telescopes that have computerized mounts which find and track objects by computers—Limits Of A Gadget: A Love Story—using what are called equatorial coordinates of right ascension and declination. And that’s wonderful if you have those tools.

But for casual astronomers, getting the altitude and azimuth numbers and then star-hopping from a known location to a new, unknown object can be a lot of fun.

And that’s one way it’s done.

This is what I’ll be doing later tonight, or the next clear night.

(It looks like it is clouding up again, so if I can’t see anything tonight, I will get myself updated numbers tomorrow or the day after, whenever the sky clears up. If I see anything, I’ll post again.)

Good luck, if anyone else gives it a try.

The sky is waiting for us! And so is Comet PanSTARRS!

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