The Astrogators' Guide to

Epsilon Eridani

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    One of the nearest stars most like our own sun, Epsilon Eridani beckons as an early destination for an interstellar expedition.

Location in Space

Radial Distance:

    Parallax = 0.31074 ± 0.00085 arc-seconds, which leads to;

        10.5 lightyears ± 0.03 lightyear

        663,786 AU ± 1897 AU

Equatorial Coordinates:

    Right Ascension; 3 hr, 32 min, 55.846 sec - 0.438t sec

    Declination; -9 deg, 27 min, 29.72 sec + 2.1t arcsec

        [t measured in centuries, Jan 2000 is t = 0]

Imagine standing on the north side of the plane in which Earth's equator lies. The celestial north pole floats directly overhead and you look toward the First Point of Aries (now in Pisces just southeast of the Circlet). Look eastward (to your left) by a little less than 53-1/4 degrees and then look south a little less than 9-1/2 degrees. You will see Epsilon Eridani slightly more than 26 degrees and a trifle south of due west of Rigel in Orion.

Ecliptic Coordinates:

    Ecliptic Latitude; -21 deg 42 min 56.71332 sec + 24.19812t arcsec.

    Ecliptic Longitude; 48 deg 10 min 3.9906 sec - 106.3454t arcsec.

        [t measured in centuries, Jan 2000 is t = 0]

Look toward the First Point of Aries, shift your gaze eastward along the Ecliptic (the line that the sun traces through the Zodiac in the course of one year) by 48 degrees plus a little over ten minutes of arc and then shift your gaze south by almost 21-3/4 degrees.

Galactic Coordinates:

    Galactic Latitude; -48.04 degrees.

    Galactic Longitude; + 195.86 degrees.

Look toward the radio source Sagittarius-A, move your gaze in an easterly direction along the plane of the Milky Way by 195.86 degrees and then tilt your gaze in a direction perpendicular to the plane of the Milky Way in a southerly direction by 48.04 degrees.

Annual Proper Motion

    in Right Ascension = -0.97636 arcsec/yr (3.142 AU per yr)

    in Declination = + 0.01798 arcsec/yr (0.0579 AU per yr)

        Total proper motion = 0.98 arcsecond per year in a direction 271.1 degrees counterclockwise from due celestial north. This corresponds to 3.1538 AU per year or 14.95 km/sec.

    in Parallax = 15 km/sec (3.164 AU per yr)

        Total motion = 4.46746 AU per year = 21.1779 km/sec.

From the present Epsilon Eridani reached its perihelion 7.4122 lightyears from Sol 105,280 years ago on the southern edge of what is now Monoceros about six degrees north of the current location of Sirius.

Orientation in Space

    Because Epsilon Eridani has only one stellar component, we have no information on the orientation of its spin axis or presumed planetary plane in space. Therefore this section is irrelevant.

The Star Itself

    Rotation Period; 11.1 days

    Diameter; 1,204,000 km (0.865 Sol)

    Harvard Class; K2 V (5073 K ± 42 K)

    Age; 850 million years

    Mass; 0.85 Sol

    Brightness; 0.292 Sol

    Habitable zone: 0.51 AU B 0.74 AU (0.54 AU, 0.447 yr= 163.31 days)

    Surface composition: hydrogen 74.4%, helium 25.8%, other 1.07% (Sol = hydrogen 73.7%, helium 24.5%, other 1.81%)

Planetary system properties:

    The system has a Jupiter-like planet revolving around it and hints of a Saturn-analogue planet as well. Using the Jupiter-analogue as a basis we calculate the orbits of the other assumed planets analogous to those in our solar system in the same proportions they have in this system. This presumed Epsilon Eridani system also follows its own version of the Bode-Titius rule, include a gap corresponding to the Neptune-analogue. The Epsilon Eridani B-T rule says that the radius of the orbit (in AU) equals 0.25 plus 0.20 multiplied by the powers of two in sequence.

1. The Mercury-analogue:

    Orbit semi-major axis by analogy; 0.26152 AU

    Orbit semi-major axis by Bode-Titius; 0.25 AU

    Period; 0.15069 year = 55.04 days.

2. The Venus-analogue:

    Orbit semi-major axis by analogy; 0.4577 AU

    Orbit semi-major axis by Bode-Titius; 0.45 AU

    Period; 0.3489 year = 127.44 days.

3. The Earth-analogue:

    Orbit semi-major axis by analogy; 0.6538 AU

    Orbit semi-major axis by Bode-Titius; 0.65 AU

    Period; 0.5957 year = 217.58 days.

4. The Mars-analogue:

    Orbit semi-major axis by analogy; 1.046 AU

    Orbit semi-major axis by Bode-Titius; 1.05 AU

    Period; 1.2054 year = 440.27 days.

5. The Asteroid Belt-analogue:

    Orbit semi-major axis by analogy; 1.83 AU

    Orbit semi-major axis by Bode-Titius; 1.85 AU

    Period; 2.789 years.

    Comment; some astronomers infer an asteroid belt at 3 AU.

6. The Jupiter-analogue:

    Orbit semi-major axis by analogy; 3.39 ± 0.36 AU (inferred from measurements of the period).

    Orbit semi-major axis by Bode-Titius; 3.45 AU

    Period; 7.064 years.

    Orbital Inclination; 25 - 35 degrees.

    Mass; 1.55 ± 0.24 times Jupiter.

7. The Saturn-analogue:

    Orbit semi-major axis by analogy; 7.7 AU

    Orbit semi-major axis by Bode-Titius; 6.65 AU

    Period; 25 years by measurement, 24.075 years calculated from orbit radius.

8. The Uranus-analogue:

    Orbit semi-major axis by analogy; 12.81 AU

    Orbit semi-major axis by Bode-Titius; 13.05 AU

    Period; 51.66 years.

9. The Neptune-analogue:

    Orbit semi-major axis by analogy; 19.67 AU

    Orbit semi-major axis by Bode-Titius; none.

    Period; 98.30 years.

    Comment; some astronomers infer an asteroid belt at 20 AU.

10. The Pluto-analogue:

    Orbit semi-major axis by analogy; 25.367 AU

    Orbit semi-major axis by Bode-Titius; 25.85 AU

    Period; 143.96 years.

11. A planet of 0.1 times the mass of Jupiter may revolve 40 AU from Epsilon Eridani in a 280 yr orbit. The next B-T orbit after the Pluto-analogue has a semi-major axis of 51.45 AU. Astronomers have also detected a disk of dust of radii from 35 AU to 100 AU, perhaps indicative of the system's analogue of the Oort cloud of our own solar system.

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