New answers tagged comets
29
The comet sheds material each time it get close to the sun. The sun heats this dirty snow ball, the ice evaporates and tears dust and smaller rocks with it.
These dust particles then follow a similar orbit around the sun as the comet. But as they are ejected with some velocity and react differently to the solar wind & radiation, their orbit is slightly ...
10
The comet releases lots of dust particles. The sunlight pushes these particles into orbits not quite the same as the comet Some particles will be pushed into faster orbits, some will be pushed into slower orbits. Over time the dust particles get spread out in a band that goes all the way around the sun. So we don't just see meteors in the years that the ...
2
Not yet, as far as I can tell. The comet looks very different from Mars and while I haven't done the math, I don't think it has an apparent size from the rovers' perspectives to make it look like anything more than a dot. Since Neowise is moving away from the Sun, the length and brightness of its tail is diminishing rapidly.
3
What your calculations don't account for is the dynamics of the meterological system. An atmosphere with $10^{18}$kg of water vapour would be a powerful greenhouse, but at the temperatures on Earth, there is no way that the atmosphere could hold so much water vapour, it would rapidly condense.
Instead, in the case of a major impact into the oceans, a lot of ...
1
A recent paper, Way & Del Genio (2020) suggests that a Venus-like planet could have been habitable until the present day thanks to its slow rotation: on slowly-rotating planets, the buildup of reflective clouds over the daylight side of the planet could result in the planet remaining in a habitable state at higher insolations than fast-rotating planets (...
1
Mass extinctions have been linked with the Solar System's oscillations up and down through the galactic plane (the Galactic Cycle). You could also take a look at this question.
2
I suspect that that is simply a statement about where you would have the best visibility of each meteor shower. The name of each shower tells you where the radiant is, the point in the sky from which the trails of the meteors appear to originate. Perseus in the northern sky (with the specific radiant point of the Perseids at +58 degrees declination), ...
0
The verbal description in the NYT article is correct but not precise enough to locate the comet in practice.
Here is a finder chart generated by Stellarium for 90 minutes after sunset at New York City and similar latitudes.
The Big Dipper is at the top, just to the right of center.
The cyan dots indicate the comet's position at 21:50 EDT from July 22 to 31.
...
4
The comet's position changes from night to night.
It was in Auriga earlier this month but is now in Ursa Major.
Here is a finder chart generated by Stellarium, with cyan dots indicating the position of C/2020 F3 at 01:10 GMT+2 from July 22 to 31.
5
Horizon
The horizon is Earth's horizon ... absent any obstructions such as buildings, trees, etc. Or another way to think of it is the horizon you would observe looking out across the ocean while standing on a beach.
The notion that it is "10° above the horizon" means that from the horizon line, it would be 10° up. You closed fist (as if you are ...
2
I've seen it a few times over the last six nights.
The Comet of 2020? No problem.
Great? Not unless something very unexpected happens to it in the next few days.
It's a sight well worth the effort of looking and one you will remember if you get a good view of it.
1
I've been watching the comet for the last few nights from 50+ deg North, around midnight. A simple way to find it is to imagine the comet has been poured out of the end of the Big Dipper and is falling headfirst toward the horizon. It wouldn't hurt to imagine a strong wind has blown from behind the Dipper's handle and over cup to push the comet a little ...
1
The comet will be roughly 10 degrees above the Earth's horizon. But the horizon is a pretty vague indication as to where to look. To know what direction on the horizon to look towards, find the big dipper. The comet will be between the horizon and the big dipper.
3
I'm inclined to say a hard no using the casual definition of a "great comet"
A great comet is a comet that becomes exceptionally bright. There is
no official definition; often the term is attached to comets such as
Halley's Comet, which during certain appearances are bright enough to
be noticed by casual observers who are not looking for them, and
...
1
The article just refers to the earth's horizon. Neowise can be seen about 10 degrees above where the sky meets the earth.
6
Simply because we can see the sun.
The comet will be swinging around the sun, getting closer to it than the Earth does by a large factor. This path cannot always be in-line with the sun or other body orbiting the Earth or the Sun, so there isn't a way for our view to be blocked.
It is plausible that its approach could be mostly co-linear with the sun, or ...
9
It is important to appreciate the scale of the comet's orbit compared to the Earth's orbit. The Earth goes round the Sun in a nearly circular path. The average distance is one Astronomical Unit (AU).
C/2020 F3 (Neowise) has an incredibly skinny elliptical orbit. It's closest approach to the Sun (perihelion) is at 0.3 AU, which is inside the orbit of Mercury. ...
13
The time of the orbit is not well known but the inclination can't change as much (small changes in velocity due to outgassing can significantly change the orbital period, but can't change the inclination much. So, while we have a good idea of it's orbital track close to perihelion, we just don't know when it will be there.
We don't know where the Earth will ...
3
Supplementary answer:
"Near-parabolic" means almost or nearly parabolic, but not quite. Another term would be "highly elliptical". Technically speaking, no realistic orbit can really be exactly parabolic since that means eccentricity is exactly 1.00000000000.... and most of Physics (solar photon pressure, relativity, gravitational ...
4
Comet naming conventions limit "periodic comets" to those comets whose orbital period is less than 200 years. Comets in elliptical orbits with a period of greater than 200 years are classified as non-periodic. Comets in parabolic or hyperbolic trajectories are also classified as non-periodic (and they will never again approach the primary).
2
From that location, the easiest time in the morning to see the comet is between 4:50 and 5:10 AM EDT.
I've seen it at similar times relative to nautical dawn at my location.
Much earlier than that, the comet may be too low, especially if nearby trees obscure the horizon.
Some software mishandles daylight saving time.
As the comet shifts eastward, nautical ...
11
Close, but not quite right - the blue light is indeed emission from CO$^+$, but it's from the CO$^+$ ions themselves, with no need for recombination to CO; that (ionized) molecule has a strong set of energy transitions around 425 nm (4250 Angstroms), which is in the blue part of the visible spectrum:
Spectrum of Comet C/2016 R2 (Pan-STARRS), Figure 2 from ...
2
Nothing is more helpful to an aspiring astronomer than a good planetarium program.
Download and install Stellarium
https://stellarium.org/
It will show you the sky from your doorstep at any time of the day. No need to speculate the comets position. It will be displayed exactly where it is in relation to the rest of the sky.
3
I don't know if this is helpful but using the Python package Skyfield one can calculate the positions of things including comet C/2020 F3 (NEOWISE) and the times that they rise and set for the month of July:
Here are the rise and set times of the Sun and the comet for reference for the next week
sunset: 2020-07-12T03:06:17Z
sunrise: 2020-07-12T12:51:20Z
...
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