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Tau Librae — Star in Libra

Magnitude 3.7m Star Libra (Lib) Visible
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1Physical Properties

Magnitude 3.66
Spectral Type B2.5 V
Star Color Blue (B-V -0.17)
Distance 367 ly

2Position & Identifiers

RA 15h 38m 39.4s
Dec -29° 46' 40.0"
Constellation Libra (Lib)
HR 5812
HIP 76600
HD 139365
SAO 183649
Bayer Tau
Flamsteed 40 Lib
SIMBAD

3How easy to spot?

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Equipment Bortle 3 Bortle 4 Bortle 5
Naked eye Easy Medium+ Medium+
50mm finder Easy Easy Easy
150mm scope Easy Easy Easy
Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Apr – Jun (peak: May)

5Survey Image

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7

Size Comparison

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8

Compare Stars

9

Spectral Classification

10

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map
11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

14

Stellar Fusion

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15Stellar Notes

Sco OB2; Sco-Cen assoc.; probable member of Sco-Cen cluster; upper Sco region.
A Perkins Obs. spectrogram May 8, 1962 showed two spectra, sep. 200k/s, B3V, vsini 149k/s and B5:, vsini 100:k/s.
16

Light Travel Time Machine

17

Relativistic Travel

Nearby in the Sky

Other targets within a few degrees — pan your scope a little and keep exploring.

Visibility scores assume a 150 mm Newton at Bortle 4.

2 Sco
Medium
Tight double — a rewarding split at 2.0″
Double Star mag 4.59 5.5° Scorpius
NGC 5903
Medium+
Elliptical galaxy
Galaxy mag 11.5 7.3° Libra
NGC 5824
Easy
Globular cluster — dense ball of ancient stars
Globular Cluster mag 9.0 8.1° Lupus
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