Universe Guide

Megrez (Delta Ursae Majoris, 69 Ursae Majoris) Star Facts

Megrez Facts

Megrez's Alternative Names

Delta Ursae Majoris (Del Uma) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR4660. HIP59774 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD106591. The Gliese ID of the star is GL 459. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 69 Ursae Majoris with it shortened to 69 Uma.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD+57 1363.

More details on objects' alternative names can be found at Star Names .

Location of Megrez

The location of the main sequence star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Megrez, the location is 12h 15m 25.45 and +57° 01` 57.4 .

Radial Velocity and Proper Motion of Megrez

Proper Motion

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving 7.30 ± 0.11 milliarcseconds/year towards the north and 104.11 ± 0.15 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -15.30 km/s with an error of about 0.50 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Megrez Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 25.03 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Megrez

Megrez Colour and Temperature

Megrez has a spectral type of A3Vvar. This means the star is a blue - white main sequence star.

The star's effective temperature is 8,613 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Megrez Radius

Radius has been calculated as being 2.22 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,543,622.30.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.19. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is -0.35 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Megrez Apparent and Absolute Magnitudes

Megrez has an apparent magnitude of 3.32 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of 1.33 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.36. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to Megrez

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 40.05 which gave the calculated distance to Megrez as 81.44 light years away from Earth or 24.97 parsecs. If you want that in miles, it is 473,288,128,795,011.64.

In 2007, Hipparcos data was revised with a new parallax of 40.51 which put Megrez at a distance of 80.51 light years or 24.69 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

Using the 2007 distance, the star is roughly 5,092,642.58 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

The star's Galacto-Centric Distance is 7,409.00 Parsecs or 24,165.44 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Time to Travel to Megrez

A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

If you were to drive there at about 120 m.p.h. in a car with an infinity engine so you didn't have to pull over for petrol, it would take you 3,989,627,086,600.60 hours or 455,436,882.03 years.

At the time of writing, the fastest probe so far created is the New Horizon probe which is travelling at a speed of 33,000 m.p.h. If the probe was travelling to Megrez then it would take 14,507,734,860.37 hours / 1,656,134.12 years to get there. Speed Ref: N.A.S.A.

It would to take a spaceship journey travelling at the speed of light, 81.44 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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Additional Megrez Facts and Figures

Visual Facts

Primary / Proper / Traditional NameMegrez
Alternative NamesDelta Ursae Majoris, Del Uma, HD 106591, HIP 59774, HR 4660, 69 Ursae Majoris, 69 Uma, BD+57 1363, Gliese 459
Spectral TypeA3Vvar
Constellation's Main StarYes
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
GalaxyMilky Way
ConstellationUrsa Major
Absolute Magnitude 1.33 / 1.36
Visual / Apparent Magnitude3.32
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)12h 15m 25.45
Declination (Dec.)+57° 01` 57.4
Galactic Latitude59.42 degrees
Galactic Longitude132.57 degrees
1997 Distance from Earth40.05 Parallax (milliarcseconds)
 81.44 Light Years
 24.97 Parsecs
2007 Distance from Earth40.51 Parallax (milliarcseconds)
 80.51 Light Years
 24.69 Parsecs
 5,092,642.58 Astronomical Units
Galacto-Centric Distance24,165.44 Light Years / 7,409.00 Parsecs
Proper Motion Dec.7.30 ± 0.11 milliarcseconds/year
Proper Motion RA.104.11 ± 0.15 milliarcseconds/year
B-V Index0.07
Radial Velocity-15.30 ± 0.50 km/s
Iron Abundance-0.35 ± 9.99 Fe/H
Semi-Major Axis8751.00
Stellar Luminosity (Lsun)25.03

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Calculated Facts

Radius (x the Sun)2.19
Effective Temperature8,718 Kelvin

Sources and Links

SIMBAD SourceLink

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.

Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
106591+57 1363.0A3.40000101.000004.00000A2White

Location of Megrez in Ursa Major

Megrez Location in Ursa Major

The map was generated using Night Vision, an awesome free application by Brian Simpson.

Ursa Major Main Stars

Comments and Questions

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William CreedThursday, 2nd March 2017 5:58:14 AM
When I was a kid in around 1955 to 1969 that star was very visible in the night. Why has it seemed to fade over the 20 some years.
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