M 55 (Alberto Tomatis)

Celestial hemisphere: Southern · Constellation: Sagittarius (Sgr) · Contains: M 55 · NGC 6809

M 55

M55 è un ammasso globulare abbastanza grande (misura circa 19', quasi 2/3 del diametro apparente della Luna) ma così povero da apparire, agli occhi del sottoscritto, un ammasso stellare persino in un binocolo 7X50, laddove la maggior parte dei globulari ha un aspetto nebuloso: questo invece appare assai sgranato. A circa 20.000 anni luce di distanza, questo diametro corrisponde ad una misura lineare di circa 110 anni luce. M55 contiene solo poche variabili conosciute: 5 o 6. Il valore della magnitudine, secondo le fonti, varia da 5 a 7 e la sua luminosità totale è approssimativamente 100.000 volte quella del Sole.

M55 venne originariamente scoperto da Lacaille nel 1751-1752 (e denominato Lac I.14), nel periodo in cui si trovava in Sud Africa. Messier lo scoprì nel 1778 ma probabilmente lo cercò invano sin dal 1764: ciò in conseguenza della declinazione meridionale dell'oggetto. L'autore del presente testo può confermare che M55 è molto difficile da osservare anche dalla Germania meridionale ma che, già da poco più a sud diventa splendido (per esempio dalla Grecia settentrionale).

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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.

Submitted The date and time when you submitted this image for IOTD/TP consideration.	...
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.
Promotions by Submitters When 3 distinct Submitters promote the image, it moves on to the next stage of the process: evaluation for Top Pick status. This requirement, in addition to anonymization of images and distribution to only a subset of them, prevents biases and ensures that the best images are selected.
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.

Status	Basic success
Started	...
Astrometry.net job	7340510
PixInsight job	n/a
PixInsight queue size	n/a
PixInsight stage	n/a

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M 55

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