Leonid Elenin spent a great deal of time searching for a comet and finally found one! That is quite an exciting achievement these days when there are so many eyes looking for comets every night, including robotic eyes! And then even more exiting, to learn that your comet could end up being what's known as a great comet. Great comets are comets that get bright enough that it is plainly visible without even trying to look for it. Comet Hale Bopp was an example of a great comet. But, the excitement faded somewhat as software for predicting the brightness of comets was showing that we might not be able to see it at all with the unaided eye. Well that just changed! The latest calculations are now predicting a brightness of magnitude 4, which means that it will easily be visible to the unaided eye. The scale of brightness used in astronomy is a logarithmic scale from magnitude -27 for the sun to magnitude 32 for an object so dim that not even the Hubble space telescope can image it. So magnitude 4 is great considering that magnitude 6 is just barely bright enough for the unaided eye to see in optimal conditions, a moonless night and in a location far away from city lights for example. And around the 27th of September we would normally not be able to see it because it will be between the earth and the sun, so if you looked in the direction that it is supposed to be in you would also be looking in the direction of the sun and the sun of course is so bright that only the sun can be seen. However, comet Elenin MAY get bright enough at this time that we might be able to see it in the day time in addition to the sun. A conservative estimate is that it may get to magnitude zero at this time. Magnitude zero is very bright for a night time object, but not bright enough to see in the day. Yet if it can get up to several magnitudes brighter at this time, say magnitude -13 for example, the brightness of the moon, you would be able to see it the same way you can see the moon in the day time. Also, depending on how active it gets, it MAY even appear for a few days as though there are two suns in the sky! It would need to approach magnitude -20 or more for this to occur. This is a very exaggerated suggestion, but not completely improbable. This jump in brightness is because all of the reflected sunlight of the tail will be concentrated in one spot as we will be looking down the tail, which will be very nearly pointed in the direction of the earth. To learn more, go to Leonid's article announcing the news on his web site at the following link. Comet Elenin may be brighter than expected
Well I certainly hope to see a comet in the day time, I've found & seen Venus & Jupiter in the daytime, not twilight. And I've personally seen a 7.1 magnitude star in Andromeda with my naked eye at Ft. Union, New Mexico, in 2009 (when 57) and have seen a record for the dimmest 'capture' at 8th magnitude.
ReplyDeleteBefore WWII, Japanese Zero pilots had to be able to spot Venus in the daytime."a book by Japanese Zero pilot Subaro Sakai that mentioned Japanese pilots being required to spot the planet Venus naked eye and other “stars” (as he called them) in the daytime as part of their training."
That is very interesting! I never tried it before, but I'll try it out as soon as clouds clear from my area. I might not have much luck though being that, when I was in my teens, I used to arc weld from time to time without protection. Also, I remember not being able to see comet Hyakutake without using averted vision. But I'll see what I can see! =D
ReplyDelete-20 IMPROBABLE? Very improbable, but perhaps not quite IMPOSSIBLE.
ReplyDeleteThere is no possibility of the comet reaching -13 or -20, even with the "forward scattering" that may take place around September 27 is taken into account. This effect enhances the brightness of dust-rich comets and is why some people are predicting that Elenin will increase greatly in brightness at that time, possibly to magnitude zero or thereabouts. However, recent indications are that Elinin is rather poor in dust - consistent with other indications that this is a small and intrinsically dim comet - and, if that holds true, there will be little forward scattering effect. The central condensation may become a little sharper, but the total brightness will increase little over its "base" value. Taking the most recent observations into account, the predicted brightness in late September (excluding forward scattering, i.e. the "base" value) is around magnitude 6. Unfortunately, the comet will then be within 3 degrees of the Sun, so if it is seen at all, it will only be on the SOHO webpage! If it is dust rich, forward scattering might brighten it to magnitude zero, but otherwise 6 is about the best we can expect. The comet might be a nice object in large binoculars in the western sky early September, probably looking like a small and condensed disk with a faint tail. It should again be visible before dawn prior to full moon in October, when it might be smoewhat larger and more diffuse (by being closer to Earth). The tail will likely be faint visually, but could be fairly long on photographs. Present prospects do not look good for naked-eye visibility at any time.
ReplyDeleteThanks for your reply.
ReplyDeleteYou mention the dust of comet Elenin. Have there been any infrared studies that you may know of that you could direct me to? If so, I would be highly interested in this. I did write to the WISE team requesting any data they had on comet Elenin the day after the initial data release, but they indicated that they're not interested in fulfilling any kind of special request.
As for your statement of "not possible." Isn't it true that comets are notoriously variable when it comes to predicting their behavior? =)
No IR studies of which I am aware, but photometry in March indicated quite a contribution from dust, which in April seemed to fall dramatically. Two possibilities were raised (1) Activity decreased (possibly due to a layer of very volatile materials boiling off the nucleus) or (2) the March readings were artifactual and caused by the strong back-scattering effect which enhanced the contribution from sunlight reflected off dust particles and made the comet seem more dust-rich than it really was (the comet was almost directly opposite the Sun in March, so back-scattering would have been about as strong as it could possibly be). There is also a third possibility, viz. that a large portion of the "dust" component was really comprised of ice grains and as the comet came closer to the Sun, these began to evaporate soon after being released from the nucleus. My guess is that all three effects were probably responsible to a greater or lesser degree. If the comet remains dust-poor, we cannot expect much brightening from the forward-scatter effect in late September and October, but if it gets an injection of fine dust near perihelion (from splitting for instance - although the probability of this is not great) the effect could brighten it by a few magnitudes. Still, even on the most optimistic prediction, I doubt that it will be more than marginally visible with the naked eye. More likely it will be a binocular comet only.
ReplyDeleteExcellent explanation! I'll keep this in mind.
ReplyDeleteI tend to be very optimistic in everything I do, even when I know the odds are against being so. Nevertheless, I do have an excellent pair of binoculars at the ready. =)