Wikipedia:Reference desk/Archives/Science/2022 January 13

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January 13

Which telescope has more magnification: Extremely Large Telescope or James Webb Space Telescope?

I heard JWST could likely detect a bumblebee on the moon. What about Extremely Large Telescope ? Our article on Extremely Large Telescope says it would provide images 16 times sharper than those from Hubble. Can it detect a bumblebee on the moon like JWST? Rizosome (talk) 06:42, 13 January 2022 (UTC)

Neither of the telescopes can "detect" (the correct word is "resolve") a bumblebee on the moon. The angular resolution of the ELT (the largest of the lot) is about 10 milliarcseconds (depends a bit on the wavelength), which is about 5·10⁻⁸ radians. At the distance of the moon (384000 km), this corresponds to about 20 meters. A bumblebee would be far too small to see. --Wrongfilter (talk) 07:23, 13 January 2022 (UTC)

The JWST sure can detect a bumblebee at the distance of the Moon cause the JWST team said that it could. I could see the Sun with my eyeballs till it is about 10⁵ times too small to resolve (at least 70 light years), the JWST can see blackbody radiation of the bumblebee in front of a ≤-200°F lunar night background. Sagittarian Milky Way (talk) 06:54, 14 January 2022 (UTC)

the largest of the lot means ELT beats JWST by a lot? Rizosome (talk) 07:29, 13 January 2022 (UTC)

The angular resolution of the JWST also depends on the wavelength, but ranges reportedly from 32 to 65 milliarcseconds^[1] if we equate the arc subtended by one pixel with resolution, which is optimistic. Detecting a bumblebee on the moon would mean a scientific revolution, regardless of the distance at which the observation is made. And if there is a Bumblebee on the moon, perhaps it is a giant one with size exceeding 20 meters.  --Lambiam 07:51, 13 January 2022 (UTC)

The JWST team literally says it can detect a bumblebee on the Moon. The eyeball can still see stars even though they're too small to see. And the JWST is just really damn good at seeing a bumblebee glow like an LED in midish-infrared (presumably at least one cold enough to not hyperthermia to death on Earth, and possibly as cold as 0°C below which it could become a bumblebee carcass). It might be impossible to see when the moon rocks are glowing 100°C though, keep the bee body 30-60°C by magic and put it on the trailing side of the dark side of the Moon which is like -200°F and it should be able to see a star, at least from 2 lunar distances from the Earth during a total lunar eclipse so that the Earth is still near enough to comfortably block out the worst twilight glare and nothing glances off the edge of the Moon. Photographs have been taken of the crescent Moon only about 4 degrees from the Sun, the Danjon's limit is not the thinnest possible crescent. I wonder which wavelength have the most contrast or be easiest for the telescope to see the bee with. Sagittarian Milky Way (talk) 06:54, 14 January 2022 (UTC)

I believe Lambiam meant "largest of the lot" to be understood as "the largest telescope among all the ones you have mentioned". --User:Khajidha (talk) (contributions) 17:57, 13 January 2022 (UTC)

@Lambiam: So ELT has more magnification? Rizosome (talk) 08:14, 13 January 2022 (UTC)

The concept of magnification is awkward when applied to digital imaging. If all goes according to plan, the ELT will have a better angular resolution than the JWST. However, unlike the JWST, it has to cope with atmospheric distortion.  --Lambiam 08:46, 13 January 2022 (UTC)

It can cope with that though, as it is equipped with adaptive optics. That's a prerequisite for it to reach the diffraction limit where the angular resolution is determined by the diameter of the primary mirror. @Rizosome: the largest of the lot means the largest of those three telescopes, entry 2 or 11 of wikt:lot#Noun. --Wrongfilter (talk) 08:58, 13 January 2022 (UTC)

This line solved my doubt: If all goes according to plan, the ELT will have a better angular resolution than the JWST. Rizosome (talk) 17:23, 14 January 2022 (UTC)

Resolved

any information about gravitational wave propagation

based on existing literature the GW gravitational Wave propagate without effecting of permittivity of vacuum ,why it occurs so?----Akbarmohammadzade (talk) 09:41, 13 January 2022 (UTC)217.219.154.2 (talk) 09:39, 13 January 2022 (UTC)

Vacuum permittivity is a constant, defined by the formula

$\varepsilon _{0}={\frac {\alpha e^{2}}{2hc}},$

where $\alpha$ is the fine-structure constant, $e$ the elementary charge, $h$ the Planck constant, and $c$ the speed of light in vacuum. For it not to be constant, at least one of the other constants also needs to be susceptible to change. Apart from $c$, which is fixed by definition, there is no a priori reason to think their constancy is a fundamental fact, but neither do we have a reason to think they will be affected by ripples in spacetime. The values of these constants are ultimately based on measurements, and spacetime curvature does have an influence on measuring instruments. It may be a challenge to define these constants in a curvature-independent way. But as the wave gets away from its source and propagates through space, the changes in curvature and therefore any possible transient effect on any of these constants – far too short for any hope of directly measuring it – is minute.  --Lambiam 17:12, 13 January 2022 (UTC)

The correct formula is

$\varepsilon _{0}={\frac {e^{2}}{2\alpha hc}}.$

Ruslik_Zero 20:34, 13 January 2022 (UTC)

Oops, yes, thanks for the correction. I've fallen victim to the curious convention of listing the numerical value of its reciprocal.  --Lambiam 19:26, 14 January 2022 (UTC)

Sodium peroxycarbonate and Sodium percarbonate are different or interchangeable terms?

In article of Sodium peroxycarbonate(Na₂CO₄) it is written "Sodium peroxycarbonate or Sodium percarbonate" which means Sodium peroxycarbonate and Sodium percarbonate are interchangeable terms but Sodium percarbonate has its own article with different formula Na
₂H
₃CO
₆, so if Sodium peroxycarbonate and Sodium percarbonate are not same then does that mean that line from Sodium peroxycarbonate about their interchangeability is wrong.ExclusiveEditor _{Notify Me!} 12:45, 13 January 2022 (UTC)

The term "sodium percarbonate" is ambiguous. It is used in the literature for Na₂CO₄,^[2] but also for Na₂H₃CO₆, or, more properly, Na₂CO₃·1.5H₂O₂.^[3]  --Lambiam 17:32, 13 January 2022 (UTC)

Whether these compounds could be considered the same depends on whether we are describing the isolated pure material or that substance dissolved in water. Starting from peroxycarbonate we can see that the chemical structure of sodium peroxycarbonate is Na^{+ -}O-O-C(O)-O^- Na⁺ and the single reference in the article sodium peroxycarbonate, namely this book gives its preparation (note that this has errors in the text!) as sodium peroxide + carbon dioxide or phosgene. So far so good. However, the same reference says that the compound is not stable in aqueous solution: in water it behaves as a mixture of sodium carbonate and hydrogen peroxide, and from the stoichiometry this must be 1:1. Now, sodium percarbonate is a very well-characterised and much-used substance. However, the stoichiometry, as the article makes clear, is Na₂CO₃·1.5H₂O₂, as Lambian said. So in terms of properties, sodium peroxycarbonate when dissolved in water will have relatively less peroxide than the more familiar sodium percarbonate. In my opinion, the sodium peroxycarbonate article is poor and probably could do to be WP:PRODed but that's a different issue. Mike Turnbull (talk) 18:00, 13 January 2022 (UTC)