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A Complete Guide to the Solar System and the Night Sky
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public Observing fromLocation: Greenwich, United Kingdom edit_location_alt
north SunriseRise: 7:40  
clear_day Transit: 11:47  
SunsetSet: 15:53 south
sunny DaytimeWhat's Visible Now?
All Constellations » Perseus » 

21 Persei

Altitude: 7.8°   Azimuth: 46.7°   Direction: North-East

21 Persei is a variable star in the constellation of Perseus.

21 Persei visual magnitude is 5.11. Because of its reltive faintness, 21 Persei should be visible only from locations with dark skyes, while it is not visible at all from skyes affected by light pollution.

The table below summarizes the key facts about 21 Persei:


21 Persei is above the horizon from Greenwich, United Kingdom edit_location_alt.

Altitude: 7.8°
Azimuth: 46.7°
Direction: North-East

Celestial coordinates and finder chart of 21 Persei

21 Persei is situated north of the celestial equator, as such, it is more easily visible from the northern hemisphere. Celestial coordinates for the J2000 equinox as well as galactic coordinates of 21 Persei are provided in the following table:

02h 57m 17s
+31° 56’ 03”

The simplified sky map below shows the position of 21 Persei in the sky:

Finder chart 21 Persei star
Simplified finder chart for 21 Persei.

Visibility of 21 Persei from your location

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

Today's 21 Persei rise, transit and set times from Greenwich, United Kingdom edit_location_alt are the following (all times relative to the local timezone Europe/London):

Azimuth: 58.1°
Max altitude: 70.5°
Azimuth: 301.9°

Digitized Sky Survey image of 21 Persei

The image below is a photograph of 21 Persei 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 0.5x0.5 degrees (30x30 arcmins). The proper motion of 21 Persei is 0.003 arcsec per year in Right Ascension and -0.031 arcsec per year in Declination and the associated displacement for the next 10000 years is represented with the red arrow.

Image of 21 Persei star
DSS2 image of 21 Persei. The red arrow shows the motion of 21 Persei during the next 10000 years (0.50 arcmin in Right Ascension and -5.17 arcmin in declination);

Distance of 21 Persei from the Sun and relative movement

21 Persei is distant 386.71 light years from the Sun and it is moving far from the Sun at the speed of 8 kilometers per second.

118.62 pc
386.71 ly
8 km/s
0.003 arcsec/year
-0.031 arcsec/year

Spectral properties of 21 Persei

21 Persei belongs to spectral class B9 21 Persei is also a Si chemically peculiar star.


The red dot in the diagram below shows where 21 Persei is situated in the Hertzsprung–Russell diagram.

HR Diagram
H-R diagram showing the position of 21 Persei. Attribution: Richard Powell / CC BY-SA

Alternative designations of 21 Persei