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public  Greenwich, UK Greenwich, UK  ⓘ
Timezone: Europe/London
Sunrise: 5:06 
Transit: 12:56 
Sunset: 20:47
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In Evidence

New Comet C/2025 J1 (Borisov) Discovered in May 2025
Detailed information about the discovery of Comet C/2025 J1 (Borisov) and pointers to useful resources to track and observe it. Read more...

Other deep sky objects in Sagittarius
All Constellations »  Sagittarius »  Deep Sky Objects » 

IC 4991 - Lenticular Galaxy in Sagittarius

Below the horizon.  Never rises today
Alt: -70.30°   Az: 292.67°   Direction: West-North-West

IC 4991 is a Lenticular Galaxy in the Sagittarius constellation. IC 4991 is situated south of the celestial equator and, as such, it is more easily visible from the southern hemisphere. Given its B magnitude of 12.33, IC 4991 is visible with the help of a telescope having an aperture of 8 inches (200mm) or more.

The image below is a photograph of IC 4991 from the Digitized Sky Survey 2 (DSS2 - see the credits section) taken in the red channel. The area of sky represented in the image is 0.5000x0.5000 degrees (30.00x30.00 arcmins).

Image of IC 4991 - Lenticular Galaxy in Sagittarius star
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DSS2 image of IC 4991 in the Red band. The green region on the image is a representation of the major (2.91 arcmin) and minor (2.13 arcmin) axes of the object's apparent size.

Celestial Coordinates

Apparent

20h 20m 05s
-40° 58’ 10”
10h 22m 41s
06h 42m 46s

J2000

20h 18m 23s
-41° 03’ 01”

Finder Chart

The simplified sky charts below show the position of IC 4991 in the sky. The first chart has a field of view of 60° while the second one has a field of view of 10°.

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Finder chart for IC 4991 - Lenticular Galaxy in Sagittarius.

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Finder chart for IC 4991 - Lenticular Galaxy in Sagittarius.

Photometric Information

The following table lists the magnitude of IC 4991 in different bands of the electomagnetic spectrum (when available), from the B band (445nm wavelength, corresponding to the Blue color), to the V band ( 551nm wavelength, corresponding to Green/Yellow color), to the J, H, K bands (corresponding to 1220nm, 1630nm, 2190nm wavelengths respectively, which are colors not visible to the human eye).

12.33
9.45
8.8
8.49

For more information about photometry in astronomy, check the photometric system article on Wikipedia.

The surface brightess reported below is an indication of the brightness per unit of angular area of IC 4991.

23.73 mag/arcsec2

Apparent Size

The following table reports IC 4991 apparent angular size. The green area displayed on top of the DSS2 image of IC 4991 is a visual representation of it.
2.91 arcmin
2.13 arcmin
129°

Morphological Classification

IC 4991 - Lenticular Galaxy in Sagittarius is classified as Lenticular (S0) according to the Hubble and de Vaucouleurs galaxy morphological classification. The diagram below shows a visual representation of the position of IC 4991 - Lenticular Galaxy in Sagittarius in the Hubble de Vaucouleurs sequence.

IC 4991 - Lenticular Galaxy in Sagittarius
Visualization of the morphological classification of IC 4991 - Lenticular Galaxy in Sagittarius, Lenticular (S0).
Credits for the background image: Antonio Ciccolella / M. De Leo / CC BY

Rise and Set Times

Location: Greenwich, UK
Latitude: 51° 28’ 47” N
Longitude: 0° 00’ 00” E
Timezone: Europe/London

IC 4991 - Lenticular Galaxy in Sagittarius is currently not visible from Greenwich, UK