"[6] The Galaxy Zoo concept was inspired by others such as Stardust@home, where the public was asked by NASA to search images obtained from a mission to a comet for interstellar dust impacts.

[7] Unlike earlier internet-based citizen science projects such as SETI@home, which used spare computer processing power to analyse data (also known as distributed or volunteer computing), Stardust@home involved the active participation of human volunteers to complete the research task.

[8] In August 2014, the Stardust team reported the discovery of first potential interstellar space particles after citizen scientists had looked through more than a million images.

[11] An online forum was later set up two weeks after the initial start, partially due to a large volume of emails being sent around, to the point that it was troublesome for those receiving them to process and respond to them.

This led volunteers to point out anomalies that on closer inspection have turned out to be new astronomical objects such as 'Hanny's Voorwerp' and 'the Green Pea galaxies'.

Its 'global moderator', volunteer communuity manager and UK astronomy enthusiast Alice Sheppard, said of it: "I don't quite know what it is, but Galaxy Zoo does something to people.

The contributions, both creative and academic, that people have made to the forum are as stunning as the sight of any spiral, and never fail to move me.

Roger Davies stated: "The community of Galaxy Zoo gives them the opportunity to participate that they're looking for.

As of July 2017, 60 scientific papers have been published as a direct result of Galaxy Zoo and hundreds of thousands of volunteers.

[17][18][19] However Chris Lintott says that crowdsourced results are reliable, as proven by the fact that they are being used and published in peer-reviewed science papers.

"[17] David Anderson, the founder of BOINC, stated: [For many sceptical scientists] "There's this idea that they're giving up control somehow, and that their importance would be diminished".

Chris Lintott stated: "Rather than letting anyone pitch for volunteers, we'd like to be a place where people can come and expect a certain level of commitment".

[3][21][22] Co-founder Chris Lintott stated: "What started as a small project has been completely transformed by the enthusiasm and efforts of the volunteers...

"[3] 125 million galaxy classifications resulting in 60 peer reviewed academic papers from at least 15 different projects have been made since July 2007.

[16] Karen Masters, an astrophysicist at Portsmouth University and project scientist for GZ stated: "We're genuinely asking for help with something we cannot do ourselves and the results have made a big contribution to the field.

"[3] As a result of GZ's success, the citizen science web portal Zooniverse was started, which has since hosted a 100 projects.

In these surveys, which involve many days of dedicated observing time, we can see light from galaxies which has taken billions of years to reach us.

[30] The abstract begins: "We present the data release paper for the Galaxy Zoo: Hubble project.

This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced visual classifications of colour composite images.

[32] Quoting: "We present quantified visual morphologies of approximately 48,000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic And Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and classified by participants in the Galaxy Zoo project.

[33] The CSIRO press release states that Radio Galaxy Zoo is a new citizen science project that lets anyone become a cosmic explorer.

Cosmologist Kate Land stated: "Some people have argued that galaxies are rotating all in agreement with each other, not randomly as we'd expect.

[49][50][51][52] The interstellar medium of spiral galaxies is filled by gas and small solid particles called dust grains.

Despite constituting only a minor fraction of the galactic mass (between 0.1% and 0.01% for the Milky Way), dust grains have a major role in shaping the appearance of a galaxy.

Because of their dimension (typically smaller than a few tenths of a micron), they are very effective in absorbing and scattering the radiation emitted by stars in the ultraviolet, optical and near-infrared.

The abstract states: 'Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light.

It's not yet clear whether the bars are some side effect of an external process that turns spiral galaxies red, or if they alone can cause this transformation.

[64] It is hypothesised that the black hole mass may be more tightly tied to the overall gravitational potential of a galaxy and therefore its dark matter halo, rather than to the dynamical bulge component.

[65] This was the first set of results from the Hubble Space Telescope CANDELS survey that was part of Galaxy Zoo 4.

The study reports "the discovery of strong barred structures in massive disk galaxies at z ≈1.5 in deep rest-frame optical images from CANDELS".