Melotte 20 / Collinder 39, alpha Persei open cluster (BrettWaller)

Celestial hemisphere: Northern · Constellation: Perseus (Per) · Contains: NGC 1245 · Part of the constellation Perseus (Per) · The star 29Per · The star 31Per · The star 34Per · The star Mirfak (αPer) · The star γPer · The star δPer · The star ιPer · The star σPer · The star τPer · The star ψPer

Melotte 20 / Collinder 39, alpha Persei open cluster, BrettWaller

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Melotte 20 / Collinder 39, alpha Persei open cluster

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Melotte 20 / Collinder 39, alpha Persei open cluster

Melotte 20 / Collinder 39 is an S-shaped, Trumpler Type III 3 m open cluster around it's most luminous member, the whitish-yellow supergiant star alpha Persei, or Mirfak. The bright cluster has a visual magnitude of 1.2 and spans nearly 3 degrees. All of the stars share a common proper motion toward the SE, and lies at a distance of 601 light years from Earth as measured by ESA's Hipparcos satellite; the true span of the alpha Persei moving group is approximately 33 light years. Over 100 member stars have been identified, with 40 or so visible with binoculars. This collection of stars is also known as the Perseus OB3 association.

All of the constituent members are bluish stars of spectral class B, and the prominent yellowish-orange sigma Persei is not a member, but rather lies along the line of sight.

Mirfak, like all of the cluster's members, is a young and bright B-type star. It is less than 50 million years old, and is a supergiant over 60 times the diameter of our Sun. It is extremely luminous, over 5000 times brighter than our sun.

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Distribution of astrophotographers

This table shows the number of distinct astrophotographers who have been assigned and IOTD/TP award compared to the total number of images awarded.
	Distinct awarded users	Total awarded images
Image of the day
Top picks
Top pick nominations

Distribution of subject types

This table shows the distribution of awards per subject type, compared to the popularity of images of that subject type.
	Image of the day	Top pick	Top pick nominations	Total submitted
Deep sky
Solar system
Extremely wide field
Star trails
Northern lights
Noctilucent clouds
Landscape

Distribution of data sources

This table shows the distribution of awards per data source, compared to the popularity of images acquired from that data source.
	Image of the day	Top pick	Top pick nominations	Total submitted
Backyard
Traveller
Own remote observatory
Amateur hosting facility
Public amaeteur data
Professional, scientific grade data
Mix of multiple sources
Other
Unknown

The “AstroBin Image of the Day and Top Picks”, or IOTD/TP, is a long-running system to promote beautiful, interesting, peculiar, or otherwise amazing astrophotographs, with a focus on technical excellence. Learn more.

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Views by Submitters (available since September 19th, 2023) Every image is assigned to 50% of available Submitters. In the event that at least 80% of them don't view the image before its time in the IOTD/TP process expires, it's assigned to the other 50% of Submitters and the process begins anew.
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Promotions by Reviewers When 3 distinct Reviewers promote the image, it moves on to the next stage of the process: evaluation for IOTD status.
Early dismissal Staff members have a lot of images to inspect on a daily basis, and they can dismiss images if they believe they don't meet the requirements for IOTD/TP selection. If an image is dismissed 5 times, it's removed from the process. This streamlines the process and ensures that any bias present in promotions could be overruled by other staff members.

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Melotte 20 / Collinder 39, alpha Persei open cluster

Melotte 20 / Collinder 39, alpha Persei open cluster

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Melotte 20 / Collinder 39, alpha Persei open cluster

Melotte 20 / Collinder 39, alpha Persei open cluster

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