# Luminosity of Neowise

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So, I have been trying to figure out the bolometric luminosity of the comet C/2020 F3 (Neowise) on the 22nd of June, 2020. At that time, Neowise was $$1.4$$ AU away from Earth and had an apparent magnitude of $$m=3$$. By using the formula $$m=-2.5logBigl(frac{F}{F_O}Bigl)$$ and $$F=frac{L}{4pi D^2}$$ where $$F_0$$ is the flux of Vega, $$F$$ is the flux of the comet, $$D$$ is the distance from Earth to the comet. I found that the bolometric luminosity, $$L$$ ,of the comet Neowise was around $$7.45cdot10^{14}$$ watts when it was $$1.4$$ AU away from Earth. However, on the 22nd of June, Neowise was also $$0.4$$ AU away from the Sun. I have tried to use the flux from the Sun at this distance to determine the luminosity of Neowise again. I have found the flux from the Sun at that distance to be $$8488.26$$ $$Wm^{-2}$$ using the above formula for flux, but now using $$D=0.4 AU$$. After that I thought of calculating the luminosity by using flux from the sun times the area of Neowise. Assuming the nucleus of Neowise has a diameter of $$5 km$$, and assuming that the comet is fully illuminated,

should I assume that the nucleus of Neowise is spherical or circular? And why should the 2 luminosities be different?

I think I get it - you are trying to calculate a luminosity based on some assumption about how much light is reflected/scattered from the Sun towards the Earth - hence the relevance of the flux from the Sun at the comet.

I think it's very hard to adopt this approach. There is uncertainty about what is the appropriate geometry to use for the comet and how the reflection/scattering should be treated. It is doubtful that assuming a comet diameter of 5 km will be appropriate because I would have thought most of the light we see is scattered from a coma around the comet, not from the surface of the comet itself.

## Comet NEOWISE could be last comet visible to Earth, warn researchers

### Comet NEOWISE can be seen with 'naked eye' says the RAS

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Comet NEOWISE is currently visible in the night's sky and will continue to be for the coming weeks as it voyages through the solar system. But it could be the last one many of us will be able to see, according to a dire warning from scientists. Light pollution is increasingly making it difficult for astronomers and amateur stargazers alike, as artificial lighting is constantly on the increase, a team of researchers say.

### Related articles

According to the Natural History museum, light pollution caused by artificial lighting is increasing by an average of six percent a year.

And as things get lighter here on Earth, the sky at night seemingly gets darker.

Gareth Dorrian, post doctoral research fellow in Space Science at the University of Birmingham, and Ian Whittaker, senior lecturer in physics from Nottingham Trent University, said everyone should take advantage of the current comet, the first to be visible from Earth since the 90s, as it could be our last.

The pair wrote in The Conversation: "So comet NEOWISE will only be seen for a few weeks near Earth while it is near perihelion (its closest approach to the Sun).

Comet NEOWISE could be last comet visible to Earth, warn researchers (Image: GETTY)

Spot Comet NEOWSISE among the light pollution (Image: GETTY)

"It will then spend thousands of years moving slowly near the other end of its orbit.

"It&rsquos aphelion (farthest point) is estimated at 630 astronomical units (AU), with one AU being the distance between the Earth and the Sun.

"With the constant increase of light pollution in the night sky the observation of comets with the naked eye is becoming much rarer.

"For now, though, NEOWISE presents a fantastic opportunity for millions of people to see a night sky phenomenon which typically only presents itself perhaps once in a decade or more. Enjoy the view!"

Light pollution is on the rise (Image: GETTY)

### Related articles

The comet will reach peak luminosity from Earth's perspective on July 22, before it voyages nearer to the Sun and swings back round - by which time Earth will be far away from its orbit.

To view it now, Mr Dorrian and Mr Whittaker said: "Even though NEOWISE is very distant from Earth, with its closest approach on July 22 being almost as far away as Mars, it is still visible in the night sky to the naked eye &ndash hovering near the northern horizon.

"The comet is estimated to currently be at magnitude 1.4 &ndash a measure of brightness astronomers use, with smaller numbers denoting brighter objects.

"Venus, which is the brightest planetary object in the sky, is about -4.

Comets, asteroids and meteors (Image: EXPRESS)

### Trending

"Comet Hale-Bopp reached a maximum magnitude of 0 in 1997 due to its exceptionally large size, while comet McNaught was visible from the southern hemisphere with a maximum magnitude of -5.5.

"NEOWISE may get brighter over the next week, but which level of brightness it reaches will depend primarily on how much material erupts from its surface rather than the distance from the Earth.

"This material consists of highly reflective water ice particles from the nucleus of the comet erupting outwards, shining when they catch the sunlight."

## Contents

When not qualified, the term "luminosity" means bolometric luminosity, which is measured either in the SI units, watts, or in terms of solar luminosities ( L ). A bolometer is the instrument used to measure radiant energy over a wide band by absorption and measurement of heating. A star also radiates neutrinos, which carry off some energy (about 2% in the case of our Sun), contributing to the star's total luminosity. [5] The IAU has defined a nominal solar luminosity of 3.828 × 10 26 W to promote publication of consistent and comparable values in units of the solar luminosity. [6]

While bolometers do exist, they cannot be used to measure even the apparent brightness of a star because they are insufficiently sensitive across the electromagnetic spectrum and because most wavelengths do not reach the surface of the Earth. In practice bolometric magnitudes are measured by taking measurements at certain wavelengths and constructing a model of the total spectrum that is most likely to match those measurements. In some cases, the process of estimation is extreme, with luminosities being calculated when less than 1% of the energy output is observed, for example with a hot Wolf-Rayet star observed only in the infrared. Bolometric luminosities can also be calculated using a bolometric correction to a luminosity in a particular passband. [7] [8]

The term luminosity is also used in relation to particular passbands such as a visual luminosity of K-band luminosity. [9] These are not generally luminosities in the strict sense of an absolute measure of radiated power, but absolute magnitudes defined for a given filter in a photometric system. Several different photometric systems exist. Some such as the UBV or Johnson system are defined against photometric standard stars, while others such as the AB system are defined in terms of a spectral flux density. [10]

A star's luminosity can be determined from two stellar characteristics: size and effective temperature. [11] The former is typically represented in terms of solar radii, R, while the latter is represented in kelvins, but in most cases neither can be measured directly. To determine a star's radius, two other metrics are needed: the star's angular diameter and its distance from Earth. Both can be measured with great accuracy in certain cases, with cool supergiants often having large angular diameters, and some cool evolved stars having masers in their atmospheres that can be used to measure the parallax using VLBI. However, for most stars the angular diameter or parallax, or both, are far below our ability to measure with any certainty. Since the effective temperature is merely a number that represents the temperature of a black body that would reproduce the luminosity, it obviously cannot be measured directly, but it can be estimated from the spectrum.

An alternative way to measure stellar luminosity is to measure the star's apparent brightness and distance. A third component needed to derive the luminosity is the degree of interstellar extinction that is present, a condition that usually arises because of gas and dust present in the interstellar medium (ISM), the Earth's atmosphere, and circumstellar matter. Consequently, one of astronomy's central challenges in determining a star's luminosity is to derive accurate measurements for each of these components, without which an accurate luminosity figure remains elusive. [12] Extinction can only be measured directly if the actual and observed luminosities are both known, but it can be estimated from the observed colour of a star, using models of the expected level of reddening from the interstellar medium.

In the current system of stellar classification, stars are grouped according to temperature, with the massive, very young and energetic Class O stars boasting temperatures in excess of 30,000 K while the less massive, typically older Class M stars exhibit temperatures less than 3,500 K. Because luminosity is proportional to temperature to the fourth power, the large variation in stellar temperatures produces an even vaster variation in stellar luminosity. [13] Because the luminosity depends on a high power of the stellar mass, high mass luminous stars have much shorter lifetimes. The most luminous stars are always young stars, no more than a few million years for the most extreme. In the Hertzsprung–Russell diagram, the x-axis represents temperature or spectral type while the y-axis represents luminosity or magnitude. The vast majority of stars are found along the main sequence with blue Class O stars found at the top left of the chart while red Class M stars fall to the bottom right. Certain stars like Deneb and Betelgeuse are found above and to the right of the main sequence, more luminous or cooler than their equivalents on the main sequence. Increased luminosity at the same temperature, or alternatively cooler temperature at the same luminosity, indicates that these stars are larger than those on the main sequence and they are called giants or supergiants.

Blue and white supergiants are high luminosity stars somewhat cooler than the most luminous main sequence stars. A star like Deneb, for example, has a luminosity around 200,000 L, a spectral type of A2, and an effective temperature around 8,500 K, meaning it has a radius around 203 R (1.41 × 10 11 m). For comparison, the red supergiant Betelgeuse has a luminosity around 100,000 L, a spectral type of M2, and a temperature around 3,500 K, meaning its radius is about 1,000 R (7.0 × 10 11 m). Red supergiants are the largest type of star, but the most luminous are much smaller and hotter, with temperatures up to 50,000 K and more and luminosities of several million L, meaning their radii are just a few tens of R. For example, R136a1 has a temperature over 46,000 K and a luminosity of more than 6,100,000 L [14] (mostly in the UV), it is only 39 R (2.7 × 10 10 m).

The luminosity of a radio source is measured in W Hz −1 , to avoid having to specify a bandwidth over which it is measured. The observed strength, or flux density, of a radio source is measured in Jansky where 1 Jy = 10 −26 W m −2 Hz −1 .

For example, consider a 10 W transmitter at a distance of 1 million metres, radiating over a bandwidth of 1 MHz. By the time that power has reached the observer, the power is spread over the surface of a sphere with area 4 π r 2 or about 1.26×10 13 m 2 , so its flux density is 10 / 10 6 / 1.26×10 13 W m −2 Hz −1 = 10 8 Jy .

More generally, for sources at cosmological distances, a k-correction must be made for the spectral index α of the source, and a relativistic correction must be made for the fact that the frequency scale in the emitted rest frame is different from that in the observer's rest frame. So the full expression for radio luminosity, assuming isotropic emission, is

For example, consider a 1 Jy signal from a radio source at a redshift of 1, at a frequency of 1.4 GHz. Ned Wright's cosmology calculator calculates a luminosity distance for a redshift of 1 to be 6701 Mpc = 2×10 26 m giving a radio luminosity of 10 −26 × 4 π (2×10 26 ) 2 / (1 + 1) (1 + 2) = 6×10 26 W Hz −1 .

To calculate the total radio power, this luminosity must be integrated over the bandwidth of the emission. A common assumption is to set the bandwidth to the observing frequency, which effectively assumes the power radiated has uniform intensity from zero frequency up to the observing frequency. In the case above, the total power is 4×10 27 × 1.4×10 9 = 5.7×10 36 W . This is sometimes expressed in terms of the total (i.e. integrated over all wavelengths) luminosity of the Sun which is 3.86×10 26 W , giving a radio power of 1.5×10 10 L .

The Stefan–Boltzmann equation applied to a black body gives the value for luminosity for a black body, an idealized object which is perfectly opaque and non-reflecting: [11]

where A is the surface area, T is the temperature (in kelvins) and σ is the Stefan–Boltzmann constant, with a value of 5.670 374 419 . × 10 −8 W⋅m −2 ⋅K −4 . [16]

Imagine a point source of light of luminosity L that radiates equally in all directions. A hollow sphere centered on the point would have its entire interior surface illuminated. As the radius increases, the surface area will also increase, and the constant luminosity has more surface area to illuminate, leading to a decrease in observed brightness.

The surface area of a sphere with radius r is A = 4 π r 2 > , so for stars and other point sources of light:

For stars on the main sequence, luminosity is also related to mass approximately as below:

If we define M as the mass of the star in terms of solar masses, the above relationship can be simplified as follows:

Luminosity is an intrinsic measurable property of a star independent of distance. The concept of magnitude, on the other hand, incorporates distance. The apparent magnitude is a measure of the diminishing flux of light as a result of distance according to the inverse-square law. [17] The Pogson logarithmic scale is used to measure both apparent and absolute magnitudes, the latter corresponding to the brightness of a star or other celestial body as seen if it would be located at an interstellar distance of 10 parsecs (3.1 × 10 17 metres). In addition to this brightness decrease from increased distance, there is an extra decrease of brightness due to extinction from intervening interstellar dust. [18]

By measuring the width of certain absorption lines in the stellar spectrum, it is often possible to assign a certain luminosity class to a star without knowing its distance. Thus a fair measure of its absolute magnitude can be determined without knowing its distance nor the interstellar extinction.

In measuring star brightnesses, absolute magnitude, apparent magnitude, and distance are interrelated parameters—if two are known, the third can be determined. Since the Sun's luminosity is the standard, comparing these parameters with the Sun's apparent magnitude and distance is the easiest way to remember how to convert between them, although officially, zero point values are defined by the IAU.

The magnitude of a star, a unitless measure, is a logarithmic scale of observed visible brightness. The apparent magnitude is the observed visible brightness from Earth which depends on the distance of the object. The absolute magnitude is the apparent magnitude at a distance of 10 pc (3.1 × 10 17 m), therefore the bolometric absolute magnitude is a logarithmic measure of the bolometric luminosity.

The difference in bolometric magnitude between two objects is related to their luminosity ratio according to:

The zero point of the absolute magnitude scale is actually defined as a fixed luminosity of 3.0128 × 10 28 W . Therefore, the absolute magnitude can be calculated from a luminosity in watts:

where L0 is the zero point luminosity 3.0128 × 10 28 W

and the luminosity in watts can be calculated from an absolute magnitude (although absolute magnitudes are often not measured relative to an absolute flux):

## How To Find Clear Skies

The easiest way to make sure you aren’t “skunked” by clouds is, of course, to simply check the weather! Indeed, there are tons of apps available that can help you do this, but as a landscape and nightscape photographer, I have found a couple that are the most helpful for not just predicting perfectly clear skies, but also things like predicting the perfect sunset!

The first app I always check is called MeteoBlue, it is unique because it gathers forecasts from as many different actual meteorological (weather) stations as possible, and presents them all to you. In addition to that, it actually shows a very useful graphic of cloud cover and elevation, so, for example, you can predict if there will be low-lying fog, or high-altitude clouds. (The latter of which are what often make for epic sunsets and sunrises, by the way!)

## Is it possible to see the tail of neowise without binoculars/telescope?

Im looking up at the sky right now at the big dipper. All the bright dots pretty much look the same. I don't know if one of those dots is neowise. If it helps I'm in the bay area.

You’re looking for something that kind of looks like a smudge

Having seen it helps now its its dimmer. But like the other dude said you're looking for a faint smudge in the sky. Almost like a dim white line.

It's about midway between the big dipper and the horizon. But it has lost a lot of luminosity, so it's barely visible with the naked eye.

Maybe but doubtful. It's dimming quickly now. Use binoculars.

It was very clearly visible a few weeks ago. Right now (lat 48 deg N) it was just a tiny smudge with a faint streak above it. Possible to see if you knew where to look and what to look for but way dimmer than before.

## Comet NEOWISE

Great shot. Very nice work capturing the nucleus. Probably the best shot I've seen in that regard. Well done indeed.

Seeing it in person has been great. Went out the last two nights at 3:30 am.

What a sky. Jupiter, Saturn, Mars, Venus, a waning moon and a comet!

Yes, the past week has been amazing!

We can see all of that right now? Sorry I'm new to the community

I’m jealous! I’ve seen all the planets and moon and even Jupiter’s moons and saturns rings for the first time with my eye (telescope and not a picture in a book or online). Hoping to see the comet before it’s gone.

Nikon 70-200 lens at 135mm

Stacking: Deep Sky Stacker

Photoshop: Levels, Curves, Camera Raw

Follow my Instagram for more photos like these: hk.astro

I wish I could catch it but I think too low in horizon, living in suburbs sucks

Same here! I traveled to a park about 20-30 minutes away to get this (well not a park a soccer field inside a commercial space)

Look for a reservoir, a lake, a flood zone. I saw it at our local flood reservoir.

Same case here. My eyes are literally watering now as I've been awake for over an hour now by the time of writing this comment. It's too damn low and the sunrise is inbound in 33 minutes from now. I will try later this evening to get the best shot. Meanwhile please tell me whether I'll ever be able to view it with naked eyes or do I need a telescope ASAP from the data - screenshots I took from my Mob. Observatory Pro 3 app?

## Luminosity of Neowise - Astronomy

The comet C/2020 F3 (NEOWISE) was discovered in March 2020 by a space probe named NEOWISE. On 03 July 2020 Neowise passed the point of its orbit closest to the sun, the so-called perihelion. Since then it has been moving away from it again. On 23 July the comet came within 103 million kilometers of our Earth. Especially the first image of the comet shows that it has formed a second bluish tail in addition to the whitish comet tail. Before a tail can develop at all, the comet must come relatively close to the sun. Actually, a comet like NEOWISE spends most of its existence in the icy cold of a great distance from the sun beyond the orbit of Neptune. The C in its name refers to this circumstance. The C receive non-periodic comets with an orbital period of over 200 years. For comparison: The Neptune year lasts 165 earth years.

Comets are dirty snowballs. When a comet - for whatever reason - crashes towards the sun, its icy components sublimate: Ice suddenly turns into gas that carries away dust particles. At about the distance of Jupiter, a cloud of gas and dust - called a coma - forms around the comet nucleus, which is actually only a few kilometers in size. When the solar wind and solar radiation hit this coma, the particles are entrained. A tail is formed. By the way: Ice here means not only water ice, but also frozen ammonia, methane, carbon monoxide, carbon dioxide, methanol, ethane, hydrogen sulfide and other substances that are not solid substances at the distance of our earth from the sun. There are two different mechanisms for the formation of the tail: The pressure of solar radiation (light pressure) slowly sets the dust particles in motion and forms the dust tail. The inert mass of the dust particles also gives them an impulse in the direction of the original orbit of the comet. Therefore the dust tail is curved.

## Comet NEOWISE could be last comet visible to Earth, warn researchers

### Comet NEOWISE can be seen with 'naked eye' says the RAS

When you subscribe we will use the information you provide to send you these newsletters. Sometimes they'll include recommendations for other related newsletters or services we offer. Our Privacy Notice explains more about how we use your data, and your rights. You can unsubscribe at any time.

Comet NEOWISE is currently visible in the night's sky and will continue to be for the coming weeks as it voyages through the solar system. But it could be the last one many of us will be able to see, according to a dire warning from scientists. Light pollution is increasingly making it difficult for astronomers and amateur stargazers alike, as artificial lighting is constantly on the increase, a team of researchers say.

### Related articles

According to the Natural History museum, light pollution caused by artificial lighting is increasing by an average of six percent a year.

And as things get lighter here on Earth, the sky at night seemingly gets darker.

Gareth Dorrian, post doctoral research fellow in Space Science at the University of Birmingham, and Ian Whittaker, senior lecturer in physics from Nottingham Trent University, said everyone should take advantage of the current comet, the first to be visible from Earth since the 90s, as it could be our last.

The pair wrote in The Conversation: "So comet NEOWISE will only be seen for a few weeks near Earth while it is near perihelion (its closest approach to the Sun).

Comet NEOWISE could be last comet visible to Earth, warn researchers (Image: GETTY)

Spot Comet NEOWSISE among the light pollution (Image: GETTY)

"It will then spend thousands of years moving slowly near the other end of its orbit.

"It&rsquos aphelion (farthest point) is estimated at 630 astronomical units (AU), with one AU being the distance between the Earth and the Sun.

"With the constant increase of light pollution in the night sky the observation of comets with the naked eye is becoming much rarer.

"For now, though, NEOWISE presents a fantastic opportunity for millions of people to see a night sky phenomenon which typically only presents itself perhaps once in a decade or more. Enjoy the view!"

Light pollution is on the rise (Image: GETTY)

### Related articles

The comet will reach peak luminosity from Earth's perspective on July 22, before it voyages nearer to the Sun and swings back round - by which time Earth will be far away from its orbit.

To view it now, Mr Dorrian and Mr Whittaker said: "Even though NEOWISE is very distant from Earth, with its closest approach on July 22 being almost as far away as Mars, it is still visible in the night sky to the naked eye &ndash hovering near the northern horizon.

"The comet is estimated to currently be at magnitude 1.4 &ndash a measure of brightness astronomers use, with smaller numbers denoting brighter objects.

"Venus, which is the brightest planetary object in the sky, is about -4.

Comets, asteroids and meteors (Image: EXPRESS)

### Trending

"Comet Hale-Bopp reached a maximum magnitude of 0 in 1997 due to its exceptionally large size, while comet McNaught was visible from the southern hemisphere with a maximum magnitude of -5.5.

"NEOWISE may get brighter over the next week, but which level of brightness it reaches will depend primarily on how much material erupts from its surface rather than the distance from the Earth.

"This material consists of highly reflective water ice particles from the nucleus of the comet erupting outwards, shining when they catch the sunlight."

## Enjoy the view on the comet Neowise from the ISS

I believe your social media timeline is covered in photos of the comet Neowise. Perhaps you’ve taken some photos yourself, too. But here’s something a little bit different. The astronauts on board the International Space Station (ISS) have captured photos of the comet from some 254 miles above the Earth. And then, Seán Doran turned them into this beautiful 7-minute video.

Seán is a visual artist and he’s interested in science and astronomy. We have seen painting-like photos of Jupiter he has processed, as well as an animation of Jupiter that he created. To make the video of Neowise from the ISS, he used NASA’s timelapse photography from 5 July 2020. He repaired and processed the material, and converted it to the real-time video you can see above.

I tried finding the comet this weekend in the countryside. I was without my camera and without luck – because I couldn’t see it with the naked eye. I plan to try my luck again tomorrow night. I came back to my flat for the camera, I’m traveling again tomorrow, and this video has made even more determined to find it and add one more photo of Neowise to people’s timeline. :)

## NEOWISE from Arizona

This was taken on Wednesday night (7/22) from Dateland, AZ.

That was the closest clear skies I could find that night..

Amazing capture. Imagine a time lapse from the front of the comet, all the things it would see, all the distance it travels. Would be mind blowing!

Still no views here in North India :(

Nice picture! Great capture of the ion tail.

Thanks! This was on 7/24 around 10pm..

bro imagine not having light pollution

When is a good time to see it

Last week. It's all but invisible to the naked eye now.

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