τ Orionis (tau Orionis)

Altitude: 0.7° Azimuth: 258.1° Direction: West-South-West

τ Orionis is a multiple giant star in the constellation of Orion.

τ Orionis visual magnitude is 3.6. Because of its moderate brightness, τ Orionis should be easily visible from locations with dark skyes, while it can be barely visible, or not visible at all, from skyes affected by light pollution.

The table below summarizes the key facts about τ Orionis:

Color of τ Orionis ⬤

Magnitude of τ Orionis 3.6

Class Giant

VISIBILITY RIGHT NOW

τ Orionis (tau Orionis) is above the horizon from Greenwich, United Kingdom edit_location_alt.

Altitude: 0.7°
Azimuth: 258.1°
Direction: West-South-West

Celestial coordinates and finder chart of τ Orionis

τ Orionis is situated close to the celestial equator, as such, it is at least partly visible from both hemispheres in certain times of the year. Celestial coordinates for the J2000 equinox as well as galactic coordinates of τ Orionis are provided in the following table:

Right Ascension J2000 05h 17m 36s

Declination J2000 -06° 50’ 39”

Galactic Longitude 208.28°

Galactic Latitude -23.96°

Constellation Orion

The simplified sky map below shows the position of τ Orionis in the sky:

Finder chart τ Orionis (tau Orionis) star

Simplified finder chart for τ Orionis (tau Orionis).

Visibility of τ Orionis 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 τ Orionis (tau Orionis) 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: 96.8° RISE 0:42

Max altitude: 31.7° TRANSIT 6:10

Azimuth: 263.2° SET 11:33

Digitized Sky Survey image of τ Orionis

The image below is a photograph of τ Orionis 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 τ Orionis is -0.015 arcsec per year in Right Ascension and -0.008 arcsec per year in Declination and the associated displacement for the next 10000 years is represented with the red arrow.

DSS2 image of τ Orionis. The red arrow shows the motion of τ Orionis during the next 10000 years (-2.50 arcmin in Right Ascension and -1.33 arcmin in declination);

Distance of τ Orionis from the Sun and relative movement

τ Orionis is distant 554.42 light years from the Sun and it is moving far from the Sun at the speed of 20 kilometers per second.

Distance (parsec) 170.07 pc

Distance (light year) 554.42 ly

Heliocentric radial velocity 20 km/s

Proper Motion RA -0.015 arcsec/year

Proper Motion Dec -0.008 arcsec/year

Spectral properties of τ Orionis

τ Orionis belongs to spectral class B5 and has a luminosity class of III corresponding to a giant star.

Absolute magnitude -2.55

Spectral Type B5III

Color Index (B-V) -0.11

Temperature of τ Orionis 11744K

The red dot in the diagram below shows where τ Orionis is situated in the Hertzsprung–Russell diagram.

H-R diagram showing the position of τ Orionis. Attribution: Richard Powell / CC BY-SA

τ Orionis star system properties

τ Orionis is a visual double star which can be observed only with the help of very large telescopes. The table below shows key information about the τ Orionis double sysyem:

Main star magnitude 3.6

Secondary star magnitude 10.8

Magnitude difference 7.2

Separation 36 arcsec

Alternative designations of τ Orionis

Bayer designation τ Orionis
(tau Orionis)

Flamsteed designation 20 Orionis

Henry Draper Catalogue HD34503

SAO Catalogue SAO131952

Hipparcos Catalogue HIP24674

Durchmusterung Catalogue BD-07 1028

FK5 Catalogue 195

Aitken Double Star Catalogue ADS3877

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In Evidence

Other stars in Orion