Wow, even after decades of observing Venus, I have to say that the old gal is still pretty impressive. The close approach with the moon last night had a less than auspicious beginning, as it was cloudy from late afternoon until nightfall here in Denver. But as the clouds cleared away, there they were, standing high and proud in the western sky. Boy, is Venus ever bright!
I had actually observed them in mid afternoon, about 3 p.m., through a bit of high haze. The moon was easy, but I admit that I could not see Venus without a small pair of binoculars. But in seeing it after sunset, it’s hard to imagine that I couldn’t see it with the unaided eye in daylight. Sometimes it is easy, sometimes it is hard.
This all got me to thinking of what it would be like if Jupiter, the undisputed king of the planets, were as close as Venus. How would it compare in brilliance? Well, it turns out that such a calculation is not really all that easy, due to many variables involved. But a first approximation is fairly simple, based on actual sizes of the two planets and their reflectivity, a measure called "albedo." The surface area of Jupiter is about 140 times that of Venus, so if they had the same albedos, Jupiter would be about 140 times brighter than Venus at the same distance. However, Jupiter is only about 80 percent as reflective as Venus, and so the actual brightness difference would be about 112 times as much. [Again, this is just a first approximation and does not take into account all factors.] That’s just a skosh more than 5 magnitudes. Last night Venus shone at about a minus four magnitude, so if Jupiter had been in its place, it would have been about a minus nine magnitude — that’s bright! [The smaller or more negative a magnitude, the brighter the object is.]
But what about apparent size? Jupiter is nearly 12 times the diameter of Venus, so at the same distance it would appear 12 times wider. Venus was roughly 19 seconds of arc across last night, as viewed from earth. So if Jupiter were there instead, it would be nearly 4 minutes or arc across, which is about one-eighth the diameter of a full moon. Instead of appearing as a bright pinpoint, it would have a distinct and easily discernible disk viewed with just the human eye! Now, that would be impressive.
But be thankful Jupiter isn’t there. If Jupiter somehow suddenly replaced Venus, its gravitational effects would be enormously disruptive, and it is likely that earth would soon find itself in an orbit either too far or too close to the Sun, or be ejected from the solar system altogether!
great article!
Very cool, Larry! Thanks for a great thought experiment …
I guess to see Jupiter as a brilliant -9 magnitude disk, we’ll have to rely on robot spacecraft for now …
Or … hmmmmm. Wonder how Jupiter would look from Mars … someday, some earthlings will see that!
Deborah
Sam & DB,
Thanks, I think that imagining other scenarios can stimulate thinking. Maybe that will be a topic in itself for a future blog!
“Why, sometimes I’ve believed as many as six impossible things before breakfast.”
The Red Queen, _Alice in Wonderland_
LS
I’ve been reading The Light of Other Days by Arthur C. Clarke and Stephen Baxter. Great science fiction! It’s set in the not-too-distant future when humanity learns to use wormholes to peer at others anywhere on Earth … now (where I am now in the book, about halfway through) they’re using them to peer at places out in space. They combine that with a type of holographic technology (I think) to give some characters the experience of standing on a planet orbiting Proxima Centauri. They describe, for example, the two larger suns seen in the sky of that triple system … and they describe viewing our sun as part of the constellation Cassiopeia.
There’s something about using your imagination to shift your perspective like that that’s truly fascinating!
And of course there are softwares that let you do that. In fact I am part of a NSF-funded program that uses software capable of that, and in projecting it onto the dome (this is not, however, a specific part of the research). It is just stunning to fly through the Galaxy and out into deep space — not something that is possible even in theory, but absolutely fascinating.
I think Starry Night also has a title that does something similar, but of course on a PC.
And as for Arthur Clarke, have you ever read 2061? I’m in it!
LS
if it is what i think it is. here is a photo i took last night of the moon, with the planet next to it.
i used a long exposure time to get the moon highlighted.
Joe, I couldn’t see your picture, but I’m sure it is nice. I bracketed my exposures from, as I recall, F2.8 to F7, and exposures from 2 to 5 seconds. I think the photo I posted is F2.8 and 2 seconds.
LS
Larry, I haven’t read 2061. What do you mean you’re in it? You’re a character? Which one??
Thanks for the speculating, Larry. Thinking about Jupiter so close and large is fun - it reminds me of those Mars hoax emails from a couple years back that said Mars would appear as large as the Moon. Ha! But it was fun to imagine.
As for 2061, let’s just say that I am mentioned by name.
And about the Mars email, it’s about time for that to start making its rounds again, isn’t it? I’ve gotten dozens of copies every year for 3 or 4 years now, and sometimes from folks who should know better!
Larry, have you met Arthur C. Clarke?
Ah, the Mars email! I miss it! I’m sure it’ll reappear soon. It’s a 15-year martian cycle, isn’t it? And the real closest approach was in 2003. Just think, if the hoax email keeps going around every summer for another decade or so, it’ll be almost true again! Though off in some details … like, er, well, the part about Mars appearing as large as the moon … also the best month to see it …
Deborah
In 1986 I was a staff astronomer on a cruise in the Indian Ocean (Society Expeditions) to see Halley’s Comet. We stopped off a day in Colombo, Sri Lanka and I spent the afternoon and evening with Dr. Clarke. He was working on 2061 at the time, as I recall. Several months later he contacted me for some information about the Comet, and gratiously acknowledged me in the book. We have corresponded occasionally since then, although not recently.
Larry, your scenarios are great! Thanks for that.
Gosh, Arthur C. Clarke!! I’ll have to get that book. I didn’t even know that he was still writing.
Since I work with geosynchronous satellites as part of my job, I know of him also as the one who conceived the idea of satellites that appear to stand still in space. The name, “Clarke Belt,” for this orbital altitude, immortalizes him. His only reward for the idea, I believe.
Ray
Hi, Ray. Dr. Clarke has not been terribly well for a while, and I don’t think he is still writing, or certainly not much. “2061″ was 20 years ago, and he has done some things since then, including some collaborative efforts, but I don’t think he is too active anymore. Too bad, because he truly is, in my opinion, the best science-oriented science fiction writer ever. Or may be I should add “at least for his time” because I frankly don’t read much science fiction, and I know there are some very good recent writers as well.
As as for communications satellites, you can find his original technical paper online somewhere, I think.
LS
This question is sort of unrelated, but I think you would know.
I live in Southern British Columbia, outside of Vancouver.
I can see a very bright “star” in the Northern part of my sky. Is it Venus? It’s much brighter than any stars I see.
PS I’m a science teacher and I love to tell my students things that they can go and look at outside.
jk,
To answer this fully, since the sky changes, I need to know when you are observing this star. However, I will make the obvious assumption that you mean in the early evening. I am as sure as I can be that it is Venus you are seeing. Technically, it is the in northwest sky, starting almost due west for the Vancouver area at sunset, and moving farther to the northwest as the night wears on. Right now, it should be setting at about 11:40 p.m., PDT. If you are seeing this at other times or in other places, it is something else, but I suspect highly that it is Venus. You also should be able to see Jupiter as a bright “star” in the southeaswt sky at this time. It is in a darker part of the sky, but in fact is not nearly so bright as Venus.
I hope this helps, and don’t hesitate to post other questions or email me directly (starman@starportal.net).
Larry Sessions
Denver